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1/98 WM“

COMPARISON OF THE COOLING EFFECTIVENESS OF
SUPERHEATED STEAM AND HOT AIR IN
INTERNAL TURBINE BLADE COOLING
By

Ramakrishnan Pudupatty

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

1998

ABSTRACT
COMPARISON OF THE COOLING EFFECTIVENESS OF

SUPERHEATED STEAM AND HOT AIR IN
INTERNAL TURBINE BLADE COOLING

By

Ramakrishnan Pudupatty

Turbine inlet temperatures continue to increase, and this increase in temperature has led
to an unfavorable combination of thermal stresses, oxidation and creep in the hot sections
of the turbine engine components, particularly in the turbine blades section. The reduction
of the blade temperature to an appropriate level in order to maintain the material integrity
and decomposition of temperature gradients in the blade proﬁle sections becomes a
principal concern. Combination of various cooling methods and cooling agents are used
to address this problem and the current discussion concentrates on comparing the heat
transfer characteristics of compressed air and super heated steam in a single pass internal
cooling conﬁguration, both experimentally and numerically. The experiments establish a
base line data for the internal coolant capabilities of steam and air on the basis of heating
tests on a simple ﬂat blade geometry. Once the base line data have been established, the
coolant properties of air and steam are compared and an evaluation of the experimental
technique for conduction and convective heat transfer for this geometry is performed
using analytical tools to compare the experimental results with the analytical predictions.
The experimental surface temperatures are measured using precisely calibrated liquid
crystals, and the temperature gradients above the blade are determined using specially
designed thermocouple probe and the numerical validation is done using AN SYSS3

package.

ACKNOWLEDGEMENTS

I would like to express my gratitude for the thoughtful and patient guidance of my
advisor, Dr. John R. Lloyd, throughout my graduate program. The assistance of my
master’s committee members, Dr. Mei Zhuang and especially Dr. Abraham Engeda, for
his patience and conﬁdence in me, are gratefully acknowledged. Their insightful

comments were particularly helpful in placing my work in perspective.

Special thanks are due to Roy Bailiff, for his extensive assistance in building the test rig.
Thanks are due to Gloria Elliott, Ramez Abdulnour and Paul Hoke for their thoughtful
comments. Thanks are also given to my dear friends who have listened and Offered

support.

This research was funded by the US. Department of Energy.

Finally, a special thank you to my parents, brother and sisters, for their patience,

encouragement and conﬁdence.

iii

TABLE OF CONTENTS

LIST OF FIGURES ................................................................................. v
NOMENCLATURE ............................................................................... vii
INTRODUCTION ................................................................................... 1
LITERATURE REVIEW .......................................................................... 10
EXPERIMENTAL APPARATUS ................................................................ 21
RESULTS AND DISCUSSION .................................................................. 30
CONCLUSIONS .................................................................................... 47
APPENDICES ....................................................................................... 48
REFERENCES ...................................................................................... 92

iv

LIST OF FIGURES

Figure 1. Illustration of various cooling modes ................................................ 3
Figure 2. Schematic of Internal Turbine blade cooling in a

modern turbine blade cross section ............................................ 7
Figure 3. Photograph of the Experimental Setup ............................................. 22
Figure 4. Experimental Setup for the Hot air conﬁguration ................................. 23
Figure 5. Experimental Setup for Super Heated Steam Conﬁguration ..................... 24
Figure 6. Schematic of the One pass test blade ................................................ 25
Figure 7. Calibration Facility of Liquid Crystals ............................................... 27
Figure 8. Typical HSI signals used for calibration of Liquid Crystals ...................... 31
Figure 9. Polynomial ﬁt for the calibration data of Liquid crystals ......................... 32
Figure 10. Corrected Conﬁguration of the blade .............................................. 34
Figure 11. A typical velocity proﬁle on the electrically heated ﬂat blade

(At the location x/L = 0.72 from the leading edge) ........................ 35
Figure 12. A typical temperature proﬁle over the electrically heated blade

surface (At the location x/L= 0.72 from the leading edge) ................. 36
Figure 13. Local N usselt Number versus Local Reynolds Number for

an Electrically heated plate .................................................... 36
Figure 14. Illustration of the electrical analogy model set up to compute 'hin‘ ............ 37
Figure 15. Dimensionless Temperature Proﬁle at 4.194cm from the leading

edge with hot air being circulated internally .................................. 39
Figure 16. Dimensionless Temperature Proﬁle at 4.194cm from the leading

edge with super heated steam being circulated internally ................... 39
Figure 17. Average Internal N usselt Number versus Average Internal

Reynolds Number ................................................................ 40
Figure 18. Local Nusselt Number versus dimensional distance in the

direction of internal ﬂow ........................................................ 41
Figure 19. AN SYS 3D Numerical Model that was built to verify

the experimental assumptions .................................................. 42
Figure 20. Computed velocity proﬁle of the internal ﬂuid at the center

cross section in the external ﬂow direction ................................... 44
Figure 21. Temperature Proﬁle of the internal ﬂuid across the middle

along the external ﬂow direction ............................................... 45
Figure 22. Temperature Proﬁle of the internal ﬂuid from inlet to exit ...................... 46
Figure A1. Velocity proﬁle of the air ﬂow across the width Of the

test section for an entrance length of 0.9m ................................... 50
Figure A2. Velocity proﬁle of the air ﬂow across the width of the

test section for an entrance length of 1.2m ................................... 50
Figure A3. Velocity proﬁle of the air ﬂow across the width of the

test section for an entrance length of 2.1m ................................... 51

Figure A4. Velocity proﬁle of the air ﬂow from top to bottom of the

test section for an entrance length of 0.9m .................................... 52
Figure A5. Velocity proﬁle of the air from top to bottom of the

test section for an entrance length of 1.2m .................................... 52
Figure A6. Velocity proﬁle of the air ﬂow from top to bottom of

the test section for an entrance length of 2.1m ................................ 53
Figure B 1. Calibration Facility of Liquid Crystals .............................................. 64
Figure BZ. Comparison of 8 bit versus 24 bit values ........................................... 66
Figure C1. Overall System Design ................................................................ 70
Figure C2. Flowchart of the control algorithm .................................................. 71
Figure C3. Second Order Polynomial Fit for Hue versus Temperature ...................... 75

vi

RGB

HSI

kext

(dT/dY)ext

NOMENCLATURE

Temperature of the hot gas, K
Temperature of the coolant ﬂuid, K
Velocity of the hot gas, m/s
Velocity of the coolant ﬂuid, m/s
Red, Green and Blue
Hue, Saturation and Intensity
distance along the external ﬂow direction from the leading edge of the
blade, m
distance normal to the ﬂat blade surface, In
distance along the internal ﬂow direction, In
total length of the blade from the leading edge along the external ﬂow
direction, In
total internal ﬂow opening in the blade in the ‘y’ direction, In
total length of the blade along the internal ﬂow direction, In
hydraulic diameter, m
external convective heat transfer coefﬁcient (of air), W/mzK
internal convective heat transfer coefﬁcient (of hot air, super heated
steam), W/mzK
thermal conductivity of air close to the wall, W/mK
temperature gradient of the external ﬂow(air) in a direction normal to the

ﬂow, near the wall, K/m

vii

Nux(or)Nux,cxt local external nusselt number, based on the local distance from the leading

Nu, NuDh

Rex(0r)Rex,ext

Re, Reph
Pr

Tamb. Text
Tw. Tm:

Tin

t

kcu

Acu

ACXbAin

edge of the blade

internal Nusselt number based on the hydraulic diameter
local external reynolds number, based on the local distance from the
leading edge of the blade

internal reynolds number based on the hydraulic diameter
prandtl Number of gas

external ﬂow (air) temperature, K

external surface (copper) temperature, K

internal ﬂow (hot air or super heated steam) temperature, K
thickness of the copper surface, In

thermal conductivity of copper, W/mK

cross sectional area of the copper surface, In2

cross sectional area in the direction of heat transfer, In2

viii

INTRODUCTION

In the development of aircraft and land based power plants serious difﬁculties are
encountered in the effort to cool certain structural elements - combustion chamber walls,
nozzles, or gas turbine blades - against the inﬂuence of the hot gases. The maximum
cycle temperature at which gas turbines are designed to operate is increasing as rapidly as
the technology of high temperature materials and cooling methods will allow. All modern
aircraft as well as industrial power producing gas turbines, operate at cycle temperatures
which require turbine vane and blade cooling, as well as Special cooling conﬁgurations
for other hot section components such as combustors etc. In conjunction with blade
cooling, special considerations in materials and coating selections are required to insure
the reliable operation of these advanced engines. New cooling methods have been

proposed and are being developed to meet this requirement.

High gas temperatures of 1600 to 1800 K require sophisticated cooling mechanisms. The

cooling has the same functions for both the rotor as well as the stator blade namely:

(1) reduction of the blade temperature to a level which is appropriate to maintain material
integrity, and

(2) decomposition of temperature gradients in the blade proﬁle sections, to avoid steep

temperature gradients and thus avoid thermal stress.

Turbine inlet temperatures continue to increase, but the rate of increase is slowing down

because most of the malfunctions that occur during the Operation of these engines

originate in its hot sections, thereby reducing the overall efﬁciency. The reduction of
fuel consumption, which is necessary for improving the overall cooling efﬁciency of
turbine blades, can be achieved not only by improving the component efﬁciencies but by
also increasing the turbine inlet temperature and the pressure ratio. These improvements
require active cooling of the hot turbine components in order to avoid a reduction of
operating life due to an unfavorable combination Of oxidation, creep, and thermal
stresses. However, the coolant mass ﬂow rate can become so large that the excess
compressor (in the gas turbine power cycle) power for cooling can offset the power gains
associated with an incremental increase in turbine inlet conditions. Low grade fuels
introduce corrosive agents into the hot stream and the metal temperature of hot
components may have to be reduced to avoid corrosion. This reduction in metal
temperatures results in increased demand of cooling drawn from the compressor and,
hence in performance penalty. In order to optimize the above factors there is a need to not
only improve the existing cooling conﬁgurations but also to look for new alternative

cooling agents.

Prior to a detailed study about the heat transfer aspects of the coolants, in particular
steam, a brief introduction about the various modes of the cooling methods that are
currently being used in the hot sections of turbine blades is discussed. Figurel shows a
Sketch of the different blade cooling conﬁgurations. Figure 1(a) shows the standard
internal convection cooling method. Figure 1(b) is the ﬁlm cooling process in which a
stream of coolant is blown through a series of slots in a direction that is inclined at an

angle to the surface. In this way a layer which insulates the wall from the hot gases is

created . The coolant ﬁlm is gradually destroyed by mixing with the hot gases so that its
effectiveness decreases in the downstream direction. This disadvantage can be avoided by
the process indicated in figure 1(c) called transpiration cooling. In this method the wall is
manufactured from a porous material and the coolant is blown through the pores. The
coolant ﬁlm on the hot gas side is, therefore, continuously renewed and the cooling
effectiveness can be made to stay constant along the surface. A principal disadvantage of

this mode of cooling is the low strength of the blades.

When the hot medium is hot gas, the cooling effectiveness obtained in both transpiration
and ﬁlm cooling can be substantially increased by using a liquid as a coolant. In this case,
which corresponds to Figure 1(d), a liquid ﬁlm is created on the hot gas side. The liquid

is evaporated on its surface, and the energy

 

 

 

 

 

 

 

CONVECTION FILM COOLING
Hot Fluid Tg, Vg—-> Hot Fluid ;‘ g, V? I
Coolant Tc, Vc —’ Coolant Tc, Vc '—"’
(a) (b)
TRANSPIRATION FILM EVAPORATION
Hot ﬂuid Tg, Vg —> Hot Gas Tg, Vg -—->
Coolant Tc, Vc "—’ Coolant Tc, Vc ’
(C) ((1)

Figure 1. Illustration of various cooling modes

absorbed by the evaporation process substantially increases the effectiveness of this
method. This method is known as evaporative ﬁlm cooling or evaporative transpiration
cooling, depending on whether the coolant is discharged through slots or through a
porous wall. This method is seldom used in cooling turbine blades, and hence is not

discussed in detail in this report.

Air is a good cooling medium for the processes mentioned above because of the fact it
can be continuously provided at places where engines are used. At higher speeds the
temperature of the air increases, and so it is often useless as a coolant unless its
temperature is decreased by some cooling cycle. The cooling process consumes power
and weight and necessitates reducing the amount of coolant air required to a minimum. In
this respect a coolant with a better heat carrying capacity can be used as a substitute for
air. This is the focus of current research where the cooling potential of Steam which has a
better heat carrying capacity than air is evaluated. Steam also has an advantage over
water, in that its much lighter than water, and thus when it is used as a coolant it can

avoid the excess cost incurred in carrying a heavier coolant.

To Obtain a fundamental understanding of the different types of cooling methods that
have just been introduced, a uniform set of operating conditions as described below is
maintained while comparing the three common conﬁgurations namely internal convection
cooling, ﬁlm cooling and transpiration cooling. Here a hot gas stream of temperature Tg

ﬂows adjacent to the a wall. The bulk temperature of the ﬂuid, Tg, does not change in the

ﬂow direction. The velocity Vg in the gas ﬂow outside the boundary layer is also assumed
constant along the wall. Under normal conditions, the thickness of the boundary layer is
so small such that the curvature effects due to the blade geometry do not play a signiﬁcant
role. Consequently for this present work a ﬂat plate subjected to hot gas ﬂow on either
Side with uniform temperature Tg and Uniform velocity Vg is considered (Figure 1). The
temperature drop through the wall is assumed to be negligible compared with that of the

coolant and hot gas side.

In an internal convection cooling arrangement, the cooling stream ﬂows along the
coolant side of the blade wall as shown in Figure 1(a). The coolant ﬂow has to be limited
for reasons stated earlier, and hence the coolant medium gets heated up considerably on
its passage through the blade. Optimum conditions for convection cooling are obtained by
increasing the surface area on the coolant side of the wall by adding ﬁns. The strength
characteristics of the wall material prescribe a certain wall temperature that can be
tolerated. Optimum conditions are attained when the entire surface is kept at that
temperature. Overcooling of certain sections consume more coolant. This constant wall
temperature can be obtained either by varying the ﬁn surface area along the cooling path
in order to compensate for smaller temperature differences between the wall and the
coolant medium, by increasing the coolant medium velocity toward the downstream end

of the surface, or by a combination of both.

In the internal cooling method, the coolant from the compressor is introduced through the
hub section into the blade interior, and then discharged out of the blade trailing edge.

Radially aligned coolant channels of basically rectangular cross section are used

extensively to cool the mid chord regions of turbine blades; these channels are connected
by 90 and 180 degree turns to form serpentine cooling passages as shown in Figure 2.
Frequently these passage surfaces are roughened with ribs to enhance the convective heat
transfer. It is well known that both the nature of the ﬂow and the associated convection
heat transfer are usually signiﬁcantly altered in and around the turn. In general, the
centrifugal forces present in a turning ﬂow induce secondary ﬂows which have the effect

of augmenting heat transfer in the streamwise direction.

Film cooling, shown in Figure 1(b), is comprised of introducing a secondary ﬂuid, at one
or more discrete locations along the airfoil surfaces or endwalls, which are exposed to a
high temperature environment. The objective is to protect the surfaces, not only in the
immediate region of the injection sites, but also in the downstream region. The
introduction of cooler ﬂuid into the boundary layer produces an insulating layer between
the wall to be protected and the gas stream ﬂowing over it. Additionally, the injected ﬂuid
mixes with the mainstream can be considered as a heat sink, that effectively lowers the
mean temperature in the boundary layer. Another beneﬁt of ﬁlm cooling is that it not
only protects the surface downstream of injection, but it also provides convective heat
transfer cooling on the surfaces of the ﬁlm injection holes. Usually spent coolant from

internal cooling can be further used for ﬁlm cooling.

The coolant is ejected through slots in a direction parallel to the surface. A cool ﬁlm is

built up, but it is gradually destroyed by turbulent mixing and heat conduction from the

hot gas ﬂow. The cooling ﬁlm can be renewed by arrangements of addition slots arranged
at certain distances downstream. No uniform wall temperature is possible for ﬁlm

cooling.

Promotersl

Turbulence shaped Internal
1 Passages

 

   
 

Turbulence
Promoter:

Pin fins

Cooling
Air

Figure 2. Schematic of Internal Turbine blade cooling in a
modern turbine blade cross section (Han J .C.(1986))

The wall is coolest near a slot and increases in temperature downstream of the slot
hole.The temperature of the wall which would eventually attain the gas temperature at

sufﬁcient distance from the slot can be decreased by increasing the number of slots.

The arrangement for transpiration cooling is shown in Figure 1(c). For this cooling
method, the wall is fabricated from porous material, and the coolant medium passes
through the wall in the gas ﬂow. A protective ﬁlm builds up on the gas side of the wall
and insulates it from the hot gas stream. The cooling air is directed away from the surface
as it leaves the wall. In this way, a counterﬂow condition is created between the heat
carried away from the surface with the coolant stream and heat transferred from the hot
gas toward the wall. This counterﬂow reduces the overall heat transfer between the gas
and the wall surface. Another advantage of this cooling method is based on the fact that
the area of contact between the coolant medium on its way through the wall and the wall
material is very large. As a consequence the coolant medium will be heated up almost to
the wall temperature. A constant wall temperature can be Obtained over the entire surface

by proper adjustment of the local coolant ﬂow through the porous wall.

The comparison of the different modes of cooling can be made with respect to the highest
wall temperature. This basis somewhat underestimates ﬁlm cooling because the average
wall temperature for this method is lower than that for the previously described
transpiration and convection cooling method. when the maximum temperatures are
adjusted equal for all three methods. Therefore, parts of ﬁlm cooled wall will have lower

temperatures and better strength, and to a certain extent , these parts can support the hot

portions of the wall. Consequently, under the same strength limitations, the maximum
temperature of the ﬁlm cooled wall could be somewhat higher than the temperatures for
comparable transpiration and convection cooled walls. But convection cooling normally
requires more coolant ﬂow compared to the other two modes of cooling, while the
strength of blades becomes relatively low when transpiration cooling is used extensively.
Considering the above advantages and disadvantages, the combination of internal cooling
with ﬁlm cooling becomes a highly attractive scheme, and this is what is being currently

used in cooling turbine blades.

LITERATURE SURVEY

Chyu (1991) has actively investigated turning ﬂow and heat transfer in different channel
cross-sectional geometry’s. These studies investigated the turning induced secondary
ﬂow ﬁelds and their effects on heat transfer and head loss. Metzger et.al (1968, 1973,
1985) have published a series of studies on ﬂow visualizations, pressure measurements,
and heat transfer characteristics for a large family of smooth and rough channels. Boyle
(1984) reported the distribution of heat transfer coefﬁcient along the centerline of
channel span for both smooth and rough surfaces. Murthy and Chyu (1987) numerically
modelled the laminar ﬂow and heat transfer with passage rotation. Wagner eta] (1986)
experimentally investigated the rotational effects on regional heat transfer. Chyu (1991)
investigated the regional heat transfer in two and three pass passages with 180 degree
sharp turns. Russell et. a1 (1993) generated a set of experimental data in order to validate
the computer codes that existed for internal cooling systems and found major
inconsistencies suggesting the need for further computational studies on complicated
geometry’s. Zhang eta] (1991) performed experiments to determine the local heat transfer
performance in a rotating serpentine passage with rib roughened surfaces. They found that
the there was a signiﬁcant heat transfer enhancement in both stationary and rotating cases

resulting from an installation of the ribs.

Recent activity in internal ﬂow heat transfer related to blade cooling has been centered

around rotation effects, impingement cooling and pin ﬁns. Abe et. al (1984) describe

10

11

turbine blade cooling which incorporates convection cooling with different pin ﬁns in the
mid chord and trailing edge regions, impingement cooling on the inside of the leading

edge, and ﬁlm cooling on the leading edge (showerhead) and pressure surface.

Mori et. al (1971) reported effects of rotation on heat transfer from a rotating circular
tube, and Johnson et.al showed that the effect of rotation was to change the effect of
turbulence near the leading and trailing walls of a rectangular passage in a fully
developed ﬂow. Wang’s (1993, 1994) studies of impingement cooling have been
concerned with the effects of crossﬂow of spent ﬂuid and the geometry of the jet array,
and the inﬂuence of heat transfer around holes in the target plate . Hollworth et.al (1983)
conducted a detailed study of heat transfer to a target plate equipped with vent holes. The
authors concluded that the high performance came, not from the increased heat transfer
around the vent holes, but because of reduced entrainment of heated air into the

impinging jets.

Convection cooling in almost capillary passages is used in several structures. In general,
these are laminated, diffusion bonded, multilayer assemblies with high heat transfer area
per unit volume inside a sheet of material which appears to be perforated. This laminated
structure is used as a non load bearing aerodynamic shell attached to a load bearing spar,
which is well protected from the gas stream. Effusion of the coolant through the holes can
be described either as transpiration or as diffusion hole injection, depending on the

spacing and size of the holes and on the ejection velocity.

12

One of the earliest works in transpiration cooling was done by Eckert and Livinghood
(1954). Transpiration cooling is one of the most effective methods for protecting a
surface exposed to a hot gas stream. The coolant penetrates into the bottom of a porous
plate and exchanges heat with the porous medium, and blows Off from the other surface
of the test porous plate. Kikkawa et. al.,(199l) found that because of a high heat exchange
between the coolant and the porous medium, one can expect a much higher cooling
effectiveness by transpiration than by ﬁlm cooling, in Spite of a low consumption of

coolant.

There have been many experiments on heat transfer with transpiration, beginning in the
early 19608 and covering many situations. The earliest studies done by Torii (1966) were
on smooth, ﬂat plates with uniform transpiration and uniform free stream velocity.
Similar studies were performed by Moffat et.al (1966). Next came studies of accelerating
ﬂows and decelerating ﬂows which were done by Thielbhar (1970, 1972). Rough surfaces
with transpiration were covered by Healzer and Pimeta (1978) and rough walls with
transpiration and acceleration by Coleman (1977). Moffat (1987) reports that most
investigators have not focussed on the cooling effectiveness, but only on the decrease of
the heat transfer coefﬁcient with gas injection. In particular, very few papers have been
published on the investigations of transpiration cooling. In Kikkawa’s (1991) work on
transpiration cooling, the experimental results were compared with a one dimensional

theoretical analysis.

13

Due to limitations for developing heat transfer coefﬁcients associated with internal
cooling and the amount of coolant consumption, internal convective cooling alone cannot
meet the cooling requirements at turbine inlet temperature above a certain value. Film
cooling is a means for meeting more difﬁcult cooling requirements and provision Of

better cooling effectiveness.

There has been considerable research over the past 30 years to increase our understanding
of coolant ﬁlm behavior and its interaction with free stream ﬂow. The ﬁlm cooling
literature is extensive, and references [Goldstein(l97l), Metzger(l968,l973),
Sasaki(l979), Ito(1978), Dring(1980)] provide a reasonable sampling of many of the
early works. Many of these earlier works looked at only the adiabatic effectiveness and
the factors which affected it. They rely on the assumption that the heat transfer coefﬁcient
could be taken from data. With the prospect of full coverage ﬁlm cooling it became
necessary to document both the heat transfer and the effectiveness to have a complete

description of the situation.

Kasagi et.al(198l) and Kumada et. A1. (1981) looked at both the ﬁlm cooling
effectiveness and the heat transfer properties on a ﬁlm cooled surface and also the heat
transfer properties of the impingement cooled back face of that surface. The combination
of impingement with ﬁlm cooling employing the spent coolant has been used in several

designs.

14

Work on ﬁlm cooling has examined the interaction of curvature with other effects and the
structure of turbulence in the full coverage, ﬁlm cooled boundary layer on a convex wall,
as done by Hay(1985). Goldstein et. al (1971) showed that surface roughness affects the
average effectiveness for single and double rows of holes. They also showed that the
secondary ﬂows can strip the coolant away from the suction surface of a vane over a

signiﬁcantly large region near the hub

Remarkably little has reached the Open literature about the losses incurred with ﬁlm
cooling. Favorskii and Kopelov(1981) estimated that each 1% of cooling air discharged
through the blades dropped turbine efﬁciency by 1%. They also documented the
increased vibration resulting from leading edge injection. Louis(198l) pointed out that
proﬁle losses for ﬁlm cooling are linearly proportional to the thickness of the injected
ﬂow, though the effectiveness is not. Kawaike et.al.(l994) concluded that there are
signiﬁcant performance advantages to be gained by passing cooling air completely
through the vanes, thence to an intercooler, and using the same air to cool the associated
rotor blades. This treatment avoids more than half the thermodynamic penalty associated

with the mixing of low temperature coolant with the mainstream.

Dunn and Hause (1981), reported an increase in stator vane heat transfer associated with
the presence of an active rotor, and cautioned against the use of stator only data to
characterize full stage behavior. Dring (1982) measured the heat transfer on rotor blades

and stator vanes. Further evidence of the inﬂuence of the rotor on heat transfer to the

15

stator was reported by Dunn(l984). Hay et.al (1985) investigated the effects of cooling
ﬁlms on the heat transfer coefﬁcient on a ﬂat plate with zero mainstream pressure
gradient, by injecting the coolant at different angles. They found that the heat transfer
coefﬁcient values increased near the injection holes, but still called for basing realistic
design of ﬁlm cooled components on heat transfer coefﬁcient with injection. Ekkad et.al
(1995) investigated the effect of the coolant blowing ratio on the ﬁlm cooling
performance. Hempel et.al (1980) investigated the performance of full coverage ﬁlm
cooled blades and found that under certain speciﬁc conditions full coverage ﬁlm cooling
approaches the cooling effectiveness of transpiration cooling. Shen et.al (1994)
investigated the heat transfer enhancement within a turbine blade cooling passage using
ribs and combinations of ribs with ﬁlm cooling holes. Gillespie et.al (1994) did some
local heat transfer measurements in the entrance to normal and inclined ﬁlm cooling

holes.

Improvements in air cooling techniques are actively being pursued for aircraft engines,
but other cooling technologies using water and superheated steam are being considered
for ground based power plants. Although air will always be the primary choice as the
coolant for aero engines, there very likely will be situations where the use of other ﬂuids
like water and superheated steam will be appropriate. Eckert (1954) was farsighted
enough to understand this 40 years ago, and the application of this method of cooling to

Stationary gas turbines is now being studied.

l6

Rice(1980) proposed steam as a cooling agent for cooling gas turbine blades and vanes in
a combined cycle for ground based power generation. Also, cooling of the air by some
means such as water injection or compact low weight heat exchangers may become
attractive. Louis and Wu (1984) have studied this aspect of the problem and have
concluded that the enhancement performance of combined cycles using steam cooled gas
turbines, particularly ﬁlm steam cooling, is very favorable. The advantages of this
technique derives from the high speciﬁc heat of steam, negligible pumping power, but
most signiﬁcantly from the fact that the steam is developed using the waste heat from the
gas turbine and then expands through the gas turbine with the combustion gases.
Rice(1982), in his work on the reheat gas turbine with steam blade cooling, stated that the
reheat pressure and hence the reheat temperature can be appreciably increased by
applying steam cooling to the gas generator turbine blades. It has been found by Rice that
as the reheat pressure level is increased, the performance of the gas turbine cycle is
increased, and at the same time the physical size of the reheat combustor is reduced,

thereby enhancing its practicality.

Aircraft technology can be successfully implemented for industrial applications. Studies
have shown that steam extracted from the associated steam turbine cycle in a combined
cycle can be substituted for air as the blade coolant to achieve an inlet turbine
temperature of 2400°F. Wu and Louis (1984) have found that superheated steam could be

introduced with minimum design changes in air cooled gas turbine technology. They

17

proved that the efﬁciency of a steam cooled combined cycle optimized at higher values of
turbine inlet temperature, gas turbine pressure ratio and steam inlet pressure than the

comparable cycles using air as a coolant.

Arseniev et.al(199l) in their work on combined cycle plant based on high temperature
steam cooled gas turbine have indicated that it would be advantageous to employ steam
for gas turbine cooling systems. They extracted the steam for the cooling system from the
steam turbines and returned it back for superheating purposes. Their work conﬁrmed the
practical realization of combined plant cycle while providing higher turbine output cycle

efﬁciencies.

Film cooling has been used for protecting turbine blades and vanes from the surrounding
high temperature gas stream. In aircraft turbine applications, the majority of the studies
have used air as the cooling ﬂuid. A theoretical study by Han et.al (1986) predicted that
ﬁlm cooling effectiveness of steam is about twice that of air under the same operating
conditions due to its favorable thermal properties such as speciﬁc heat and prandtl
number. Conklin, et.al (1983) have studied ﬁlm cooling effectiveness with steam
injection through three staggered rows of holes that are inclined at an angle of 60 degrees
over a symmetric aluminum airfoil. They found that ﬁlm cooling effectiveness increased

50-150% over air cooling when steam injection was used.

Han et.al(l986) have studied the heat transfer and ﬁlm cooling of a single row of inclined

18

holes on a stainless steel ﬂat plate. The results showed that the ﬁlm cooling effectiveness
using steam was about 30 to 60 percent higher than that when air was used. The heat
transfer was about 10 to 15 percent higher for all test data. They studied the ﬁlm cooling
effectiveness of one row and two rows of 35 degree inclined holes over a ﬂat plate with
both steam and air injection. Their experiments proved that steam injection provided
about 50 to 100 percent higher ﬁlm cooling effectiveness than that for air injection. They
found that in the two dimensional ﬁlm cooling region i.e, at lower blowing rates and/or
farther downstream locations, steam injection provided 80 to 100 percent higher
effectiveness because of the favorable speciﬁc heat. However, in the three dimensional
ﬁlm cooling regions, i.e, higher blowing rates and/or near injection hole regions, the
increase in ﬁlm cooling effectiveness is reduced because the advantage of higher speciﬁc

heat is reduced due to mixing of the secondary ﬂuid and the mainstream ﬂuid.

Rice has also looked at the possibility of using steam as a coolant for compressors and
combustors. He had found that while considering a continuous turbine inlet temperature
of 2400°F to 2700°F for industrial gas generators, there exists a critical ducting area
between the high pressure turbine blading and the low pressure turbine blading which is
subjected to a much higher temperature. The main support strut passes through this
ducting area to tie the inner barrel, seals, and the rear blading to the outer casing. It is not
practical to use steam as a disk and casing coolant in aircraft engines due to weight
restrictions. Industrial gas turbines, on the other hand, do not have these restrictions, and

steam, a far superior coolant with twice the speciﬁc heat and a lower viscosity, can be

19

applied as a coolant, particularly when a combined cycle using a bottoming steam turbine

is contemplated.

Steam can be extracted from the steam turbine, used as a coolant and readmitted into the
steam turbine at a higher temperature to Obtain additional steam turbine work before
being condensed. A closed system is thus possible without losing steam to the
atmosphere. A higher gas turbine reheat temperature can be realized through cooling the

power turbine in this manner.

lkeguchi and Kawaike (1994) have done work on the effects of a closed circuit gas
turbine cooling system on combined cycle performance. In this work they have presented
comparative studies taking into account the required cooling ﬂow to cool the blade. They
compared a basic conventional blade cooling system, which used an open circuit air as its
coolant with two closed circuit blade cooling systems; one using as coolant the steam
extracted from and returned to the bottoming cycle, and the other using air from the
compressor and fed back to the combustor. The results indicate that the full closed circuit
cooling system provides signiﬁcant improvements in performance over conventional

open circuit air cooling systems.

Steam cooling, in some respects, is simpler than air cooling. Steam is easy to pipe and has
twice the speciﬁc heat which reduces the Size of cooling lines. Pressure drop is not as

critical as it is for air, and greater pressure differentials are available to allow more design

20

freedom for heat exchange surfaces. Combining these beneﬁts of steam in a way so as to
address the present problems of heat transfer and cooling gas turbine engine components
would enhance the turbine cooling design process by optimizing combinations of
minimum use of coolant, minimum interference with hot gas side aerodynamics, and

minimum component temperature and temperature gradient levels

Thus, the overall motivation for this work is the need for incorporating the above
mentioned beneﬁts in advancing the existing cooling techniques by using superheated
steam as a coolant for turbine blades in an industrial combined gas and steam turbine
cycle. The discussion concentrates on comparing the heat transfer characteristics of
compressed air and super heated steam in a one pass internal cooling conﬁguration, both
experimentally and numerically. The experiments are to establish base line data for the
internal coolant capabilities of steam and air on the basis of heating tests on a simple ﬂat
blade geometry. Once the base line data have been established, the coolant properties of
air and steam are compared and ﬁnally evaluation of existing analytical tools for
conduction and convective heat transfer for this geometry is performed to compare the

experimental results with the analytical predictions.

EXPERIMENTAL APPARATUS

A specially designed suction type wind tunnel shown in Figure 3, was constructed for
these studies. This wind tunnel is powered by a Dayton blower run by a 3.73kW electric
motor and is capable of creating air ﬂows up to 1811 cfm. The ﬂow rate of the air is
controlled by a ball valve which is located just upstream of the blower. The ﬂow control
valve is connected to the tunnel by a 22 cm diameter tube which expands in transition
from a circular cross section to the 15 cm by 20 cm rectangular cross section of the tunnel
test section. The tunnel test section is about 3m long and is made up of multiple
interchangeable sections made of clear plexiglass. The model blades are mounted in the
ﬂow of the stream in a section which is 0.3m long, upstream of the blade is an entrance
length section which is connected to a honeycomb structure at the inlet of the tunnel for
straightening the ﬂow in the tunnel. The maximum external side Reynolds Number that

can be realized in this set of experiments is about 150,000.

Figures 4 and 5 Show the overall schematic of the experimental setup for the internally
heated blade experimental conﬁgurations, using hot air and super heated steam,

respectively.

21

22

 

Figure 3. Photograph of the Experimental Setup

23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a \
.9 ﬂ~~
Compressed Mass flow Direction of Inline Heating
air Controllers internal flow Chamber
Inlet where P,T [Test Blade
are measured 1’
“*1:
g Wind Tunnel <3
0 I
"‘ I
m u ”T, '
Outlet whe‘re P,'r 7 Direction of
are measured external flow

Figure 4. Experimental Setup for the Hot air conﬁguration.

AS shown in Figure 4, the compressed air from the compressor lines is passed through
three Porter fast response mass ﬂow meters and controllers (200F series). Once the
required mass ﬂow rate of air has been attained by using the built in solenoid control
valve, the air is then passed through the inline heating chamber (heat exchanger) where
the air is heated to the prescribed temperature. This hot air is then passed through the

Single pass blade, thus heating the blade internally.

24

 

 

\
\

 

 

 

 

 

 

 

 

 

===::=" c:;:>
I ‘0'
I ’0
' Direction of flow of
Steam Direction of Steam superheated steam
generator steam flow Superheater through the test

section

Inlet where P,T
are measured

 

 

 

V

I

Condensor

Test Blade
I
I

 

 

Blower

 

 

 

 

 

 

 

 

‘t:
Wind Tunnel <:.
I
l
-ca '
‘--“l- '
Outlet where P,T Direction of
are measured external flow

To condensor

Figure 5. Experimental Setup for Super Heated Steam Conﬁguration.

Figure 5 shows the schematic of the experimental setup for the super heated steam blade

conﬁguration. This is similar to the hot air experimental setup, with the difference being

the steam generated from a Chromolax steam generator replacing the compressed air as

the source. The steam, which is generated at just above saturation conditions, is then

passed through a by pass valve which is used to control the mass ﬂow rate of steam. The

super heater that is present in the line is then used to superheat the steam to the prescribed

state conditions, and this is then passed through the single pass blade. The steam is ﬁnally

condensed in a condensor unit and the mass ﬂow rate of the steam is measured by the

condensate.

25

The test piece is a single pass blade made of a ﬂattened copper tube. A cylindrical copper
tube of outside diameter 169.56mm and wall thickness 1.75mm was heated and ﬂattened
to form the tube. The ﬂattened tube consisted of three sections; a ﬂat middle section with
a cross section of 76.2mm x 6.05mm; and two curved half elliptical shaped cross
sections, one at the front and the other at the back end of this rectangular cross section,
with a half curvature length of 4.29mm. A sketch of the test piece used for this

investigation is shown

Internal ﬂow direction

WConnecting Pipe

.......4....

 

4—

Test Piece

4—-:

304.8mm

External ﬂow direction

 

 

 

...... .V..."

 

 

 

 

II 76.2mm '.

 

84.78mm

Figure 6. Schematic Of the One pass test blade

26

in Figure 6. The entire tube is 304.8mm long. This tube is placed in the wind tunnel in

such a way that the 304.8mm long section is perpendicular to the ﬂow direction.

In order to connect this to the super heated steam and compressed air lines, a pipe ﬁxture
was mounted at the two ends of the test piece. The outer surface of the blade is coated
with liquid crystals, which allows the temperature distribution on the blade surface to be
determined. Before using the liquid crystals on this blade they are ﬁrst calibrated in a
constant temperature bath. A detailed report about the calibration procedure is attached in

Appendix A and Appendix B.

Figure 7 shows the liquid crystal calibration setup. The temperature bath is ﬁt with a PID
controller unit which helps in maintaining a temperature constant to 01°C during the
entire calibration process. To provide for the most uniform surface temperature, the liquid
crystals are sprayed over a thin layer of black paint coating onto a large copper block.
This block is 76.2mm square by 128.6mm high. The top is notched so that the area that
the liquid crystals cover is slightly smaller than the rest of the block at only 63.5mm

square. The block is placed in the constant temperature bath.

27

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Video System
Adapter
1 >
L' h ' T I:
1g ting . ........ CCD Camera
. ................. 4 .........
H : V Computing System
tical l s . :1
OP g as ‘Il ........ - TLC Black Paint
———!==s ............. C
Constant E: ’ opper Block
Temperature "
Bath

 

 

 

 

 

 

 

 

 

Figure 7. Calibration Facility of Liquid Crystals

This layer of liquid crystals is checked with a micrometer to ensure that they are the same
thickness as the layer on the test surface. The liquid crystals used for this purpose were
supplied by Hallcrest, Inc., and were of BM/R25ClW/C17-10, BM/R29C4W/Cl7-10,
BM/R30C15W/ C17-10 and BM/R45ClW/C17-10 types. These liquid crystals showed
color exhibits over a wide range off temperatures starting from 25°C to 55°C. A Sony
CCD RGB camera system, including a VHS video recorder is interfaced with a 100
megahertz Pentium class computer with a Matrox Marvel image processing system using

the Matlab Image Processing Tool box

The copper block is partially submerged in a constant temperature water bath which is
insulated on the top by a layer of air trapped between the copper block and a ﬂat plate of

optical glass. The optical glass serves to insulate, to prevent glare, and to simulate

28

experimental viewing conditions. The CCD camera is set up at approximately the same
angle with relation to the surface of the liquid crystals and to the lighting source as it is in
the test section. A T-type thermocouple is ﬂush mounted to one side of the copper block
at a distance of 12.8mm from the top surface. This thermocouple is used to measure the
temperature of the copper block during the calibration purpose. An air gap ( which acts as
an thermal insulating medium ) is created between the coated surface and the optical

glass. The illumination source is the same source used in the experimental setups.

Under steady state conditions, the optical information required to process the response of
liquid crystals is recorded with the CCD RGB camera ( whose position, with respect to
the coated surface, was maintained constant for the calibration and for the actual
experimental setup) and was either recorded on a VHS tape recorder or sent directly to
the computer. A Matrox Marvel color frame grabber along with an analog processor
converts the color into red green and blue components. The image data ( 8 bit/ 24 bit )
from selected frames are processed using the software package developed for this purpose
with the help of Matlab image processing toolbox to give hue, saturation and intensity

content exhibited by the liquid crystals at distinct surface temperatures

After the calibration of the liquid crystals, the test piece was coated with the same type of
liquid crystals. Since the test piece consisted of three different cross sections, a series of
tests were initially performed on an electrically heated ﬂat plate with a cross section
similar to the one corresponding to the test piece. This was done in order to establish the

measurement technique and the analysis procedure that were to be implemented, while

29

running tests on the internally cooled/heated test piece itself. The electrical power that
was supplied to this ﬂat blade was measured using a TEK 157 digital multimeter, which

allowed both voltage and ammeter readings to be read.

These tunnel calibration experiments were carried out with an electrically heated ﬂat plate
with a curved leading edge. Its dimensions are 25.4cm long, 7.62cm wide and 0.508cm
thick. The plate is capable of being operated between 0 - 600W. TO measure the surface
temperature of the electrically heated it was coated with a thin layer of liquid crystals.
This setup enables the measurement of the whole surface temperature distribution as well
as local temperature distribution in the operating temperature range of liquid crystals
with the help of a frame grabber which has a capability of grabbing 30 frames/sec. With
this technique of measurement, it is possible to accurately and precisely measure the
surface temperature ( with a temperature resolution of 005°C and a spatial resolution of

0.02mm ) and subsequently the heat transfer on the external blade surface.

RESULTS AND DISCUSSION

The ﬁrst blade that was tested was an electrically heated ﬂat blade. The blade was ﬁrst
coated with a very thin layer of black background paint over which 2-3 very thin coatings
(~20-30 urn thick) of liquid crystals are spray painted. The uniformity of the heat ﬂux
over the blade surface is tested by supplying and measuring the power supplied, using a
TEK 157 Digital MultiMeter, to the liquid crystal coated electrically heated blade which

is positioned horizontally in still air.

The calibration curves of the Hue, Saturation and Intensity values of the colors exhibited
versus temperatures are shown in Figure 8. Among these three, the hue is the one that is
used for this calibration because of its sensitivity and its capability to exhibit unique
values at different temperatures under steady state conditions. The calibration curves

compare well with those predicted by other researchers.

30

31

 

 

 

 

 

 

 

 

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1818528888R8888899355§§999339
Tommtun In Degree Colclua

Figure 8. Typical HSI signals used for calibration of Liquid Crystals

The images were analyzed both as a 24 bit image and as an 8 bit image. It was found that
under steady state conditions, these values are not very different. But because of the
resolution and precise color information recorded by a 24 bit image, this was used as a

standard throughout this analysis even though both the values are almost comparable.

A curve ﬁt of second order polynomial, as Shown in Figure 9, in general, agreed well with
the experimental hue values. The points on this curve were within a scatter of 0.8% of
the actual hue values. With this technique, it is believed that measurements can be made

with a spatial resolution of 0.02mm and a temperature resolution of 001°C.

32

 

  

y = 0.000t3x2 - 0.0811x + 35.858
F? = 0.9899

 
 

 

 

35 1 : : 1 t t .
100 120 140 160 180 200 220 240 260

line Measured

 

Figure 9. Polynomial ﬁt for the calibration data of Liquid crystals

After the calibration of liquid crystals, the experiments with the electrically heated blade
were conducted. The ﬂat blade coated with the calibrated liquid crystals was connected to
an AC power source through a variac and is placed in the test section of the wind tunnel.
By adjusting the variac and measuring the voltage and the current with help of a
voltmeter and an ammeter connected to the power source, the power supplied to the blade
is controlled. Under steady state conditions the temperature on the surface was measured
using the calibrated liquid crystals. The velocity distribution at six strearnwise locations
on the blade was measured using a total pressure probe and a factory calibrated I-IHP-
102A electronic manometer, which is capable of providing both the total pressure and
the static pressure at a particular location to 0.2% accuracy. Also, a specially constructed
thermocouple probe whose tip is 0.0762mm, was used for measuring the temperature

gradients above the surface of the plate to determine the local heat transfer coefﬁcient.

33

Using the variac, the desired heat ﬂux is provided to the plate and calibrated liquid
crystals are used to provide the steady state surface temperatures with a precision of
001°C and with an accuracy of 01°C. The air temperature was measured using a
thermocouple probe which traversed in a direction normal to the surface of the plate at

increments down to 0.2m with an accuracy of 015°C.

The blade is analyzed as a ﬂat blade taking into account the curvature effect of the
leading edge and the stagnation region that develops due to the blunt leading edge as
shown in Figure 10. The curvature of the blade is accounted for by measuring the arc
length of the leading edge and ﬂattening it out. After that, the boundary layer thickness
that is created due to the blunt nose effect is calculated and the virtual length (
corresponding to the equivalent boundary layer thickness for a ﬂat blade ) is added to the
existing ﬂat section and the arc length of the leading edge to give the virtual starting point
of boundary layer development. This correction in the leading edge was necessary in

order to account for the stagnation and curvature effect at the leading edge of the blade.

34

Internal ﬂow direction

WConnecting Pipe

 

....................... - . _ . ‘——'
1 External ﬂow direction

Test Piece

*—1

 

 

 

 

F"
'. I. - -0

Note

_ virtual length due to boundary layer development at the blunt edge

— ﬂattened section of the blunt edge at the tip of the balde
- existing ﬂat section

Figure 10. Corrected Conﬁguration of the blade

The velocity and temperature proﬁles measured at the dimensionless location x/L = 0.72,
using the procedure outlined above is shown in Figures 11 and Figure 12. In Figure 11,

the

35

 

   

 

   

 

 

 

 

 

 

 

30
25.. ---------------
0
Baa--
.E
e. 15 ~- It Theoretical values(SiriaﬂtySolution)
E10 [:1 Experimentalvanes
g Polynom'al fit for Experimental data
5«- ------- SirilarityVelocityprofile
0 t + L .L
D (D N N v— (D (D (D 1—
g E: g e ta :1 a: g
z N e e E S 19 Q
1:) o o o :5 o d t:

Hatlo of dletance neutral to the surface at the plate TO the ﬂuid boundary
layer thickness

Figure 11. A typical velocity proﬁle on the electrically heated ﬂat blade
(At the location x/L = 0.72, from the leading edge)

velocity proﬁle measured using the experimental data is compared against the velocity
proﬁle of the similarity solution for laminar ﬂow. This shows that the corrected virtual

length analysis discussed previously agrees well with the ﬂat blade assumption.

In Figure 12, the measured temperature proﬁle generated is shown. This is compared
against the temperature proﬁle that Prolhac used while obtaining the integral solution for
the energy equation. The linear temperature proﬁle very close to the wall is typically used
for computing the temperature gradients at various streamwise locations on the blade
surface which are then used to compute the local heat transfer coefﬁcient using

hex! = -( k C” / dY)ext/ ( Ts'Tamb ).

Using this the external local Nusselt Numbers are calculated Nuxm = he,“ x/km.

36

 

0.3 ~0-

R' c 0.007.

 

0'2 ii 0 3rd order Integral eoiutlon

I eaeerlmenteldeta
0.1 J“ —Poly. (3rd order integral eolution)
-——Poly. (experirn entai date)

 

 

 

 

 

 

0 0.1 0.2 0.: 0.4 0.5 0.0 0.1 0.0 0.0 1
Din eneiealeee Dietaaee

Figure 12. A typical temperature proﬁle over the electrically heated blade surface
( At the location x/L = 0.72, from the leading edge )

10 V V T VVVVV' V V V V VVVV' V V V VVVVT
1

_ Nux= 0.364Re .5 P 1/3 Bejané: 995: f
3

 

 

— -Nux= 0.417Re .5 P 1/3 Began 1995
- ~ ' Nux= 0.424Rex .5 P 1/3 Bejan 1995
~ Nux=0.464Re .5 P 1/3 Churc I||(19
. ——Nux=0.453Rex .5 P 1/3 Bejan(1995)

" T I 7"

 

 

 

0 Current experimetal values

Nusselt Nunber
3N

 

 

 

10 I I I I I I PII I I I I I I I I l I I I I L I I I
103 1o4 105 10°
Reynolds Number

 

Figure 13. Local Nusselt Number versus Local
Reynolds Number for an Electrically heated plate

37

Figure 13 shows the external Nusselt Number plotted against the external Reynolds
Number on a log-log scale. The dashed lines in this ﬁgure indicate the theoretical
predictions, and the '0' represents the experimental data that have been generated using
the procedure outlined above. This demonstrates that the Nusselt Number varies as 1/2
power of the Reynolds Number which is consistent with the existing theories for laminar

ﬂow over ﬂat surfaces.

These experimental results clearly Show that the above procedure can be employed to
accurately determine external Nusselt Numbers. The aims of this phase Of the project
were to establish conﬁdence in the liquid crystal surface thermography technique and to

determine the relation for the external side heat transfer for the model blade.

Tovt

/v:"/v T. y
(r w) lg

J X

 

 

 

Note:

External ﬂow is in the ‘x’ direction
Internal ﬂow is in the ‘z’ direction
The direction of heat transfer depicted
is in the ‘y’ direction

1 I hextAext tcu / kculA‘cu l I hinAin

Tm —M ‘—/\/\/——/\/\F—’ Tm

Figure 14. Illustration of the electrical analogy model set up to compute 'hin'

38

Having established a standard procedure for evaluating the external heat transfer
coefﬁcient, a similar set of experiments was conducted on an internally heated/cooled
blade. These experiments involve heating the blade internally by passing either dry steam
or hot air through the blade and cooling by the external ﬂow of air in the wind tunnel. The
conﬁguration being tested is similar to the electrically heated blade. The blade that was
studied is a single pass rectangular cross sectioned blade with a curved leading edge made

out of copper.

The external heat transfer coefﬁcient determined by the above procedure is used to
evaluate the internal heat transfer coefﬁcient using the heat resistance model as modeled
in Figure 14. The following equation is used to compute the heat transfer coefﬁcients on
the internal side once the external heat transfer coefﬁcient is known.

Q = (Tin - ext ) / ( 1 / hextAext)+( WA )w + (l/hinA'm)
The only unknown in the above equation, hm, is evaluated after determining 'hw' from the

procedure outlined above.

The measurements and data reduction made on the single pass internally cooled blade are
shown in Figures 15 through 18 for different experimental runs. Figures 15 and 16 Show
the temperature proﬁles measured at a distance of 4.194cm from the corrected leading
edge of the plate for hot air case and super heated steam case respectively. These
measurements have been compared with the dimensionless temperature proﬁle for a ﬂat
plate analysis. From these ﬁgures, it is clear that the temperature proﬁles measured agree

well with the theoretical predictions of the 3rd order integral solution.

39

 

A

 

 

 

 

 

 

 

.’....x...-..E|I....-.i"lI .
g 0.9 A’ ..... 9‘
0.8 -» ...... ll
2 A 07 x ..... p 9
8 E ' n w"
0.6 '1’ .e'..
g h? .."
0.5 1+
.- E ..’..
3 E 0.4 «- z.
5 E. 0 3 ﬂ .,.-’ xTheoretlcel Solution ( Integral Solution)
v ° .313 nHotAlr (#1)
g 0.2 « ’x AHotalr (#2)
_ I- xHotAlrUtS)
a 0-1 ‘3' eHotAlr (#4)
0 i. 4 : : : t : 4. : : t : :
0.00 0.13 0.19 0.25 0.38 0.39 0.50 0.58 0.63 0.75 0.78 0.88 0.97 1.00

Ratio of 'dletance normal to the plate euriace' to 'Thermal Boundary layer thicltneea'

Figure 15. Dimensionless Temperature Proﬁle at 4.194cm from the leading edge

with hot air being circulated internally.

 

 

 

 

 

 

 

09.. swam} I
.a 0'"
c 0.0 4 o"
t .r- a
I. 0.7 J- J."
g 0.6 ~» a".
t.- .0!
S 0.5 "’ ‘0'.
r- .r"
0.4 1- '.’.
E 0.3 «- ﬁx"
1! . .- 3 Theoretical Solution ( htegral Solution )
0.2 «~ ’3‘ nSteam It
.- Asgeam :3
I. s. X 08'"
0'1 . 0 Steam M
0 i . 1‘ c : : e + : J. : . c
0.00 0.13 0.19 0.25 0.38 0.39 0.50 0.58 0.63 0.75 0.78 0.88 0.97 1.00

Ratio of 'dletance normal to the plate eurtace' to 'Therrn al Boundary layer thickneee'

Figure 16. Dimensionless Temperature Proﬁle at 4.194cm from the leading edge
with super heated steam being circulated internally.

Once these temperature proﬁles were measured, the external Nusselt Numbers were

evaluated, using the gradient of the temperature proﬁle at the wall. And using these local

40

external Nusselt Numbers, the local internal Nusselt Numbers have been evaluated using

the procedure discussed earlier.

The average internal Nusselt Number versus Reynolds Number relationship is shown in
Figure 17. This is compared with the theoretical predictions for a turbulent ﬂow within a
rectangular duct. From this ﬁgure, it is clear that for the conﬁguration under Study, the
internal Nusselt Numbers for both the hot air and the super heated steam cases vary as
4/5th power of the Reynolds Number which is expected for a turbulent duct ﬂow. And as
a further result, for identical Reynolds Number ﬂows, the heat transfer coefﬁcient would

be higher for ﬂuids which have a higher thermal conductivity, in this case steam.

 

   

 

 
 

 

 

 

 

 

 

1000
'- 100 . ,,,,,
.8
E
3
z
‘i
g 10 q ’ o Nu(air)exp
' ' A Nu(Steam)exp
Nu = 0.023 Re"0.8 was (Pr = 0.7)
— . — . — Nu = 0.023 R9008 Pr"0.6 (Pr = 0.96)
1 .
1000 10000 100000

Reynolds Mun ber

Figure 17. Average Internal Nusselt Number versus Average Internal Reynolds Number

Figure 18 shows the internal Nusselt Number as a function of dimensionless distance
along the internal ﬂuid ﬂow direction. It can be seen that the experimentally averaged
Nusselt Numbers for both the hot air and superheated steam case lie in the ﬂattened part
of the curve indicating that the ﬂow is close to reaching the thermally fully developed
state. Since the instrumentation available, cannot determine the internal temperature
proﬁle in the experiments,

conditions was developed using ANSYS 53 analysis tool, and the results of this analysis

41

an analytical model with the experimental boundary

is presented in Figures 19 through 22.

120

 

 

  
   
   
 
      

 

Nu Air ) Current experimental \aluee

a Nu Steam)currentexpenmental alone
at Nu stt
A NU 812
0 N0 313
9 Nu at
V MI 32

 

—Nu Air =Nuo' 1+2.4254/ z/tR‘JBJm
-----Nu Air -Nuo' 1+0.9756/ z/ )0.
—Nu Steam sNuo'1+2.42 I z/D . A
......-Nu Steam uNuo' 1+0.9758/ 21d “.87 )

 

 

 

vvvnnv v

 

 

 

0.00

0.67

1.33

Figure 18. Local Nusselt Number versus dimensional distance

in the direction of internal ﬂow

42

Figure 19 shows the numerical model built for this purpose using ANSYS 53. This 3D
model is composed of 13200 3D Flotranl42 type elements. The boundary conditions that
were imposed on this were the results that are obtained from the experiments. A constant
heat ﬂux boundary condition was imposed on the exterior surfaces of the ﬂat test section,
and the measured experimental temperatures were imposed on the inlet and the outlet
along the internal ﬂow direction. Adiabatic boundary conditions are imposed on the
entrance and exit pipe sections of the test blade. Also at the inlet and outlet, measured
velocity and pressures are imposed as the boundary condition. All along the boundary, a

no slip velocity boundary condition is imposed.

 

ANSYS 5.3
DEC 11 1997

-> Internal ﬂow direction xv -1

ZV -3
DIST-.435335
XF 3.415

YF 8.0375
Z? -.0065
Z-BUFFER
EDGE

  
 
  
 
 
   

1 External ﬂow direction

 

 

 

Figure 19. AN SYS 3D Numerical Model that was built to verify
the experimental assumptions

43

Figure 20 shows the velocity proﬁle along the centerline of the test blade at z/Z=0.5,
y/Y=0.5. The velocity proﬁle along the cross section at this location is a parabolic fully
developed proﬁle as shown in the ﬁgure, with the maximum velocity occurring at the mid
section of the cross section. At either ends of the cross section, the velocity proﬁle does
not have the same smoothness as the mid sectional velocity proﬁle because of the
geometry of the blade being investigated. This irregularity in the velocity proﬁle did not
affect the results in the experiments as the experimental data were measured in the
sections where the velocity proﬁle has the parabolic behavior. This provides the
conﬁdence in the assumption that the ﬂow was fully developed at the measurement

locations.

 

x 10xx-1
a .301

2.007"

a rut

l.”‘

3.33.1

I 81“

Velocity g

I 8.3“

t

 

°.. I I... I L I I”? I. I 'Lf:’°”‘°’

.73 2.28 3.73 3.- $.75

 

Distance along external. flow (m)

 

 

 

Figure 20. Computed velocity proﬁle of the internal ﬂuid at the center cross section in the
external ﬂow direction

In Figure 21, the temperature proﬁle that is obtained from the steady state analysis of the

numerical model at the same cross section, as discussed above, is shown. This shows that

the temperature proﬁle is ﬂat along the cross section at the speciﬁed location where

measurements were made, with no spikes in between which justiﬁes the assumption of a

thermally developed ﬂow. Figures 20 and 21 show that the internal ﬂow is close to being

hydrodynamically as well as thermally fully developed.

45

 

 

 

as 07.1 -f ~— .—
3‘0. mq (Ii
904 'M1

27'. on“

2.3. 361‘

 

 

.017 “3'1

-- M"

Temperature (K)

28.. m“

 

 

I“. m“

 

 

1‘. on o I I I L I 3.. I I. I l’f:im-Ol
73 2.25 3.73 l.m O.”

0131:. along int. flow direct.(m)

 

 

 

Figure 21. Temperature Proﬁle of the internal ﬂuid across the middle along the external
ﬂow direction
Figure 22 shows the temperature proﬁle of the ﬂuid along the central line of the internal
ﬂow (y/Y = 0.5, z/Z = 0.5). This ﬁgure shows that the temperature drop of the internal
ﬂuid along the ﬂow direction is close to being linear in the section of the model blade
which is inside the test section of the wind tunnel, which provided the necessary
justiﬁcation for the experimental assumption that the internal temperature proﬁle is linear
from the inlet to the outlet section of the test blade. Near the inlet and the outlet sections,
there is a deviation in temperature proﬁle from the linearity because the ﬂow is suddenly
being expanded/constricted to ﬁt into the inlet/outlet pipe ﬁxture. These two regions did

not affect the results as they were outside the test sections of the wind tunnel.

46

 

no {9'7“
no. 765‘
an. 075‘
”7.35"
as. “7"
”I 034']

:22. 221 ‘1

Ionporaiura {K}

to. DO.“

SIC. 79“

8L7. 0.3-

 

 

(aroma-t)
:ats m

o I I I laIseo I Lesa I inane I 5.101
.310 .92!) 1.8!) 2.171 9.79!

Dist. along int. flow direct.(m)

 

 

 

Figure 22. Temperature Proﬁle of the internal ﬂuid from inlet to exit

The measurement uncertainty analysis on the experimental parameters was carried out
based on Moffat(l992). The uncertainties due to mass ﬂow raterof air, velocity of air,
external Nusslet Number, internal Nusslet Number and the heat energy delivered are
estimated to be .0225 gm/s, 0.069m/s, 11.1431, 4.09 and .9W respectively. The

uncertainty of the liquid crystal temperature measurement was 02°C.

CONCLUSIONS

Distributions of external and internal heat transfer coefﬁcients and Nusslet Numbers for
hot air and superheated steam along the single pass blade was obtained in the specially
designed wind tunnel using the liquid crystal technique. Several conclusions can be made

from this study

0 Application of the Liquid Crystal Technique for determining the temperature
distribution and hence the heat transfer distribution on a one pass blade conﬁguration
presents an attractive and efﬁcient way of obtaining experimental data with low
uncertainty values. This technique also provides a way of measuring data in a manner
that is non obstructive to the ﬂow.

0 The experimental analysis approach of unwrapping the blunt leading edge into a
virtual sharp edged ﬂat blade, in order to correct for the leading edge effect, for this
blade geometry agreed well with the data analysis.

0 The use of ANSYSS3 as a numerical tool to justify the experimental assumptions
worked well for the experimental velocity as well as the temperature proﬁles. This
analysis provided the necessary conﬁdence in the experimental approach adopted.

0 The internal Nusselt number comparisons between steam and air indicate that they
both vary as the 0.8 power of the Reynolds Numbers. Since the heat transfer
coefﬁcient of the ﬂuid is directly proportional to the thermal conductivity of the ﬂuid,
and because of steam’s higher thermal conductivity and speciﬁc heat capacity, we
would expect a much higher heat transfer from steam compared to air. At higher
pressures and temperatures, this effect would be more pronounced. As the
dimensionless numbers indicate, for the same kind of ﬂow conditions, steam has a
much higher heat transfer coefﬁcient compared to that of air. All these experimental
results look promising towards using steam as an alternative for air for the cooling of

the turbine blades.

47

APPENDIX A

Appendix A
Experimental Apparatus

The wind tunnel designed and constructed for this purpose is powered by a Dayton
Blower. The tunnel test section is about 1.2m long (including the entrance length) and is
made up of multiple interchangeable sections made of clear plexiglass, to allow optical
measurements to be made. The model blades are mounted in the ﬂow of the stream in a
section which is 0.3m long, upstream of the blade is an entrance length section which is
connected to a honeycomb structure at the inlet of the tunnel for straightening the ﬂow in
the tunnel. The velocity proﬁle of the ﬂow with the honeycomb at the entrance, is shown
in the following ﬁgures. The velocities at different locations were measured using a pitot

probe and hand held manometer.

Figures A1, A2 and A3 Show the velocity proﬁle across the test section with different
entrance lengths of 0.9m, 1.2m, and 2.1m respectively. The velocity proﬁles shown in
these ﬁgures indicate that the ﬂow is fully developed and laminar, in all three cases. The
ﬂow also appears to be ﬂat at the center portion of the test section, which is were all the

temperature gradient and pressure gradient measurements are made.

49

50

 

 

 

000
068
148
228
308
388
68
48
28
08
88
68
48
028
1108
1268
1348
1428
1498

Figure A1. Velocity proﬁle of the air ﬂow across the width of the
test section for an entrance length of 0.9m.

 

 

 

 

§§3§883338883§3

d d o d m h h m m

1268
1348
1428
1498

8:
DIatancealongthewtdthottheteeteectlon.cm

Figure A2. Velocity proﬁle of the air ﬂow across the width of the
test section for an entrance length of 1.2m.

 

51

 

28

24 -~

20 ..

A
Q
l
I

d
N
1
r

 

Velocity in rule

 

 

 

'v’uito'ro'h'edoioo

83838338988333883338
OOPNNC’) '- (9“?

Dietancealongthewldthottheteeteection,cm

Figure A3. Velocity proﬁle of the air ﬂow across the width of the
test section for an entrance length of 2.1m.
Figures A4, A5 and A6 Show the velocity proﬁle in the test section, from top to bottom,
with different entrance lengths of 0.9m, 1.2m, and 2.1m respectively. The velocity
proﬁles shown in these ﬁgures again indicate that the ﬂow is fully developed and laminar.
In addition to this, it is ﬂat at the center of the test section which is where the temperature

and pressure gradients are measured.

52

 

 

 

 

 

 

e
833338883333333333333
OOFNMVWONDOOPNOVMONQQ

DIetancetromtoptobottomottheteeteectlon,cm

Figure A4. Velocity proﬁle of the air ﬂow from top to bottom of the
test section for an entrance length of 0.9m.

 

25 e»

20 +

 

Velocity, min
a

 

 

888388338833833388838
OOFNOVW‘DNQQOFNQVDONQQ

Dietancetromtoptobottomottheteeteectlon,cm

Figure A5. Velocity proﬁle of the air from top to bottom of the
test section for an entrance length of 1.2m.

53

 

M
Q

N
.5

N
O

.a
a:
l
r

.a
N

 

Veictty In mle

 

 

 

§§3§333888383§8888§§§

MVIDCDh-OQO

DIetancetromtoptobottomotﬂreteeteectIonmm

Figure A6. Velocity proﬁle of the air ﬂow from top to bottom of the
test section for an entrance length of 2.1m.

It is clear from the above ﬁgures that the entrance lengths do not affect the ﬂow ﬁeld
within the test section. Because of this, the entrance lengths for all measurements in the
experiments were chosen as 0.9m arbitrarily. Furthermore, since the center of the test
section indicated that there were no pressure gradients at that section, the measurements

made above the model blade were solely due to the blade.

APPENDIX B

APPENDIX B

LIQUID CRYSTAL HEAT TRANSFER MEASUREMENT TECHNIQUE

Introduction

In 1888, an Austrian botanist, Friedrich Reinitzer, observed that certain organic
compounds appeared to possess two melting points, an initial melting point that turned
the solid phase to a cloudy liquid and a second melting point at which the cloudy liquid
turned clear. Further research revealed that an intermediate phase, or “mesophase” did
indeed exist between pure solid phase and pure liquid phase of some organic compounds.
Reinitzer termed this phase a “liquid crystal phase”. Since his work, a great deal of
research concerning the structure of liquid crystals has been carried out resulting in the
classiﬁcation of liquid crystals into one of three categories: smetic, nematic, or

cholesteric; the particular category being determined by the molecular structure.

Liquid Crystals are frequently used in applications for measuring the local surface
temperature. This type of thermometer enables the surface temperature to be determined
over a complete area and, in the absence of lateral heat conduction, allows the local heat
transfer coefﬁcient to be calculated. This measured heat transfer distribution can be used

directly in the design of components or in the development of ﬂow predictive methods.

55

56

Temperature sensitive liquid crystals provide one of the most convenient and accurate
ways of measuring surface temperature distributions. They have been used both in
transient and steady state heat transfer measurements. One of the basic assumptions
considered in all these applications is that the crystal coating is hydraulically smooth and,
geometrically and thermally very thin. Under these conditions, the temperature sensitive

coating is non-intrusive.

Thermochromic Liquid Crystals

Liquid Crystals are substance which in certain phases have the mechanical properties of
liquids but the optical character of a crystal. Under speciﬁc conditions, the optical
properties can be dependent on physical factors such as the stress, electrical, magnetic or
temperature ﬁelds. Substance which exhibit liquid crystal behavior with temperature
changes are known as thermotropic. These organic molecules are generally of the order of
20-30 angstroms long and about 5 angstroms in diameter. On heating, from the solid
state, the materials melt but long range order is sustained by intermolecular forces until
the ﬁnal melting temperature to the isotropic state. Whilst in the liquid crystal
mesophases, the molecular anisotropy causes long range ordering of molecules which
gives rise to anisotropy in physical properties such as refractive index, conductivity and
viscosity. This ordering of molecules traces a helix, and this structure becomes optically
active when the pitch of the helix is of the order of the wavelength of the incident light. A
change in the pitch with temperature is responsible for the change in surface color on

heating.

57

A variety of externally applied ﬁelds including electrical, magnetic, shear, pressure and
thermal ﬁelds have been found to produce a change in the optical properties of liquid
crystals. Cholesteric liquid crystals, as the name implies, are formed from the esters of
cholesterol. The property of interest, from the heat transfer point of view, of the
cholesteric type liquid crystal concerns its response to temperature. Over a known,
reproducible range of temperature, the “event temperature range”, the cholesteric liquid
crystal will progressively exhibit all colors of the visible spectrum as it is heated through
the event temperature range. The phenomenon is reversible, repeatable and with proper

care, color can be accurately calibrated with temperature.

At present, the liquid crystals are commercially available with event temperature ranging
from a few degrees below zero t several hundred degrees Celsius. Liquid crystals can be

obtained with event temperature spans as small as 1°C to as large as 50°C.

Pure liquid crystals, although exhibiting brilliant colors, pose several problems from the
point of view of usage. Once applied to a specimen, the pure liquid crystals deteriorate
rapidly with age permitting only a few hours of experimentation. They are also
susceptible to contamination with marked alteration in their performance. Further, the

detection of temperature by change of color is strongly inﬂuenced by viewing angle.

Many of the problems associated with the use of pure cholesteric liquid crystals have

either been eliminated or greatly reduced through an encapsulating process developed by

58

National Cash Register Company. The encapsulated liquid crystals are coated with gelatin
in a polyvinyl alcohol binder. In addition to extending the life of the liquid crystals, the
encapsulation also greatly reduces the variation of color due to the viewing angle.
Encapsulated liquid crystals can be obtained as precoated on a blackened substrate of
paper or mylar, or in water based slurry. For our experiments, the encapsulated liquid
crystals were obtained in slurry form which allowed manual coating of the specimen

surface using an air brush.

Coatings

In all the work that is detailed in this report, the liquid crystals were applied in an
encapsulated form. Care must be taken to ensure that the surface is fully dry before the
crystal mixture is applied. A thin coating ( approximately 20pm ) is developed by
spraying many thin coats with interim drying using an air heater. This coating is applied
over a thin coating of black paint. This allows an enhancement of the color display
contrast. Also the black substrate insures that all light transmitted through the liquid
crystal ﬁlm is absorbed and, therefore, is not reﬂected to compete with the desired signal.
An overall layer of between 20-30pm is sufﬁcient since the response does not improve

with increased thickness.

59

Time Response

The accuracy of the measured temperature during a transient test depends on the rate at
which the liquid crystals can respond to the surface temperature change. The earliest
measurement of the time response was made by Parker who investigated a material
derived from cholesterol. Ireland and Jones also measured the time response. These
experiments showed that the delay between the time at which the surface reached the
steady state color display temperature and the occurrence of the color display was no
more than a few milliseconds. Bonnet investigated the time constant of several liquid
crystal materials by pulsing an indium tin oxide heater on a glass substrate. He used a
bridge circuit to monitor the resistance of the heater and hence record the temperature of
one surface of a covering 10-15um layer of encapsulated liquid crystals. He was able to
show that time constant for a typical chiral nematic mixture with color display close to
room temperature is about lOms whereas a room temperature cholesteryl ester mixture
has a time constant of over 100ms. This led to the conclusion that the actual time delays
observed during heating tests are shorter than the measured time constants. ( Ireland RT.

(1992) )

Cholesteric liquid crystals have been employed in a number of interesting applications
over the past several years. In the ﬁeld of non destructive testing, Dowden (1967) used
liquid crystals to check for irregularities in the bonded structures, to observe regions of

overheating on electronics equipment. Woodmansee (1968) used these liquid crystals to

 

60

check for ﬂow blockages in heat exchangers, as crack detectors in aircraft structure, and
to check the effectiveness of windshield heaters, to name a few typical applications. In the
medical ﬁeld, Crissey (1965) used cholesteric liquid crystals to observe surface blood
ﬂow patterns in humans and as a diagnostic tool for detection of breast cancer. Cook

(1971) used cholesteric liquid crystals to study the characteristics of ultrasonic beams.

Several investigators have employed liquid crystals as a temperature transducer in
engineering heat transfer studies. Raad and Myer(l97l) used liquid crystals to observe
nucleation sites in a study of pool boiling. Ennulat and Fergason(l97l) employed a liquid
crystal ﬁlm as the display device in a non contacting thermal imaging system.
Maple(l972) studied the transient and steady state temperature ﬁelds that develop on the
exterior of an active sonar transducer by coating the surface of the transducer with liquid
crystal. Cooper and Groff (1973), Katz and Cooper (1973), and Cooper and Petrovic
(1974) employed liquid crystals coated on a thin mylar sheet to observe temperature ﬁelds

produced by resistively heated, radio frequency, and cryosurgical cannulas, respectively.

The use of cholestric liquid crystals in wind tunnel experiments was ﬁrst investigated by
Klein in 1968. McElderry(1970) in an investigation similar in principle to the one
conducted by Klein, used unencapsulated cholesteric liquid crystals as a means of

determining boundary layer transition on a ﬂat plate placed in supersonic air stream.

I-Iippensteele et.al (1981) investigated the performance of heat transfer measurements

using liquid crystal coatings on a commercially available composite sheet and found it to

61

provide a simple, convenient, accurate and low cost measuring device for use in heat
transfer research. Simonich and Moffat (1982) used liquid crystals to map heat transfer
contours quickly and easily. They conducted the tests to qualify the technique for
quantitative determination of heat transfer coefﬁcient and found that the results agreed
well with the measurements taken with conventional techniques. Simonich and
Moffat(1984) used liquid crystals to study heat transfer on a concavely curved turbulent
boundary layer. They developed a technique for instantaneous heat transfer measurement
to provide a clear picture of local surface heat transfer coefﬁcient on concave surfaces
such as the ones existing on turbine blades. Hippensteele et. al(1985) used liquid crystals
to map the local heat transfer coefﬁcients along the mid chord of a ﬁve times size turbine
blade airfoil in a static cascade operated at room temperature over a range of Reynolds
numbers. They compared these results with the analytical values of heat transfer
coefﬁcients obtained from the STAN 5 boundary layer code. Their results indicated that
the composite of liquid crystals and the heater element sheet bonded to a model turbine
blade provides an accurate, quantitative, and continuous map of heat transfer coefﬁcients

on the blade surface.

Hippensteele et.al (1987) used liquid crystals for quantitative, high resolution heat
transfer coefﬁcients on a turbine airfoil, including turbulence and surface roughness
effects. In 1988, the same authors made use of liquid crystals for heat transfer
measurements on the end wall of a turbine passage. Jones and Hippensteele (1988) used
liquid crystals for heat transfer coefﬁcient maps applicable to compound curve surfaces in

a transient wind tunnel. Akimo et. al (1989) used a set of sharp band optical ﬁlters to

62

draw isothermal lines with the aid of digital image processing technique( Black and

White ) that excludes human color sensation.

Hollingsworth et.al (1989) used a wide band liquid crystal on a ﬂat plate along with a true
color digital image processing technique to measure the temperature distribution on a
specimen. from its color image. Baughn et. al (1989) used liquid crystals to measure the

local heat transfer coefﬁcients on a pin ﬁn.

The above digital image processing techniques used the RGB signals for associating color
to temperature. Camci et. a1 (1991) developed a hue capturing technique for quantitative
interpretation of liquid crystal images. They performed their experiments on the bottom
surface of square to rectangular transition duct. Their interpretation included the use of a
linear hue versus temperature relation as an accurate measuring tool and a transient heat
transfer model for the conversion of time accurate temperature information into heat
transfer coefﬁcient maps. Camci et.al (1992) used the HSI technique to discuss the effect
of the strength of the illuminating source, the heat transfer surface, effect of orientation of
the illuminating source with respect to the surface, crystal layer uniformity, and the
repeatability of the process. In 1993, Camci et.al used the above technique for evaluating
the convective heat transfer coefﬁcient maps on complex surfaces, and concluded that the
usage of a narrow band of liquid crystal provided accurate results with very low

uncertainty values.

63

Wang et. al.(1993) used a new method for processing liquid crystal signals from transient
heat transfer experiments. They used the entire intensity history recorded during an
experiment to obtain an accurate measurement of surface heat transfer coefﬁcient. Farina
et.al (1994) developed the HSI technique in which the results from the liquid crystal
images were not dependent on the light source. Praisner et.al (1997) have used liquid

crystal for spatial heat transfer distribution in the end wall junctions of a turbine passage.

This above discussion details on the various applications of liquid crystals in the heat
transfer ﬁeld. The following section discusses the calibration and data measurement
technique employed in Michigan State University for mapping heat transfer/temperature

distribution technique on a ﬂat surface.

Calibration

The response of the encapsulated liquid crystals can differ between nominally the same
coating composition. In the experiments performed, a particular liquid crystal coating is
always calibrated in a calibration facility which approximates the experimental conditions

very closely.

A sketch of the Calibration facility is shown in Figure B 1.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Video System
Adapter
l l ,
Lighting . ..... CCD Camera
5 : v Computing System
Optical 81885. T """"" TLC Black Paint :3

5—4 ..... ‘ ..........
Constant 5‘ Copper BIOCk
Temperature ' '
Bath

 

 

 

 

 

 

 

 

 

 

 

 

Figure B 1. Calibration Facility of Liquid Crystals

Calibration is performed by coating the top of a copper block with a thin layer of liquid
crystal coating over a thin layer of black paint coating. This block is 76.2mm square by
128.6mm high. The top is notched so that the area that the liquid crystals cover is slightly
smaller than the rest of the block at only 63.5mm square. This layer of liquid crystals is
checked with a micrometer to ensure that they are the same thickness as the layer on the
test surface. The copper block is partially submerged in a constant temperature water
bath which is insulated on the top by a layer of air trapped between the copper block and
a ﬂat plate of optical glass. The optical glass serves to insulate, to prevent glare, and to
simulate experimental viewing conditions. The digital camera is set up at approximately
the same angle with relation to the surface of the liquid crystals and lighting source as it is
in the test section. A T-type thermocouple is ﬂush mounted to side of the copper block at

a distance of 12.8mm from the top surface. This thermocouple is used for determining the

65

temperature of the copper block during the calibration purpose. Care should be taken to
insure that the temperature reading from the thermocouple matches with the constant
temperature bath reading during the calibration process, which serves to act as a method

for determining the insulation provided for the copper block.

Calibration is performed for the entire band of liquid crystals. Images are recorded every
0.5°C between the lower end and the higher end of the sensitive range of the liquid
crystals. Once steady state is reached for a certain speciﬁed temperature, the liquid crystal
image is grabbed using a Sony CCD Camera attached to a Matrox Marvel 11 frame
grabber board ﬁt into an IBM PC and saved into a ﬁle or the images can be recorded
using a VCR and analyzed later. The Matrox Marvel II board is capable of grabbing 24
bit images at 30 frames per second, which is useful for both transient as well as steady
state measurements. As soon as an image is grabbed, it is analyzed frame by frame using
standard Image processing tools ( MATLAB, in this case ) at each of the temperatures to
determine the average hue values corresponding to each temperature. These images have

been analyzed both as 8 bit ( 256 colors ) as well as 24 bit images (16 million colors ).

66

 

 

 

 

 

 

 

 

230
I
210" n
8 200 ~-
5 52
3 .90
g 1.0..
170 xHuetrom a24 bit Image
nHueiromaSbit Image
160
150 . : i : t 4
49 50 51 52 53 54 55

Temperature in Degree Ceiciue

FigureB2. Comparison of 8 bit versus 24 bit values

Using the MATLAB toolbox, the grabbed images are converted into Red, Green and Blue
( RGB ) signals, pixel by pixel. These images have been analyzed both as 8 bit ( 256
colors ) as well as 24 bit images (16 million colors ) ( Figure BZ ). Using standard
conversion factors, these three signals are converted into hue, saturation and intensity

values. The equations for conversion from RGB to HSI are as follows

To ease the process of collecting and analyzing the data, a program written using
LABVIEW software provided a step by step procedure for the user to follow when
calibrating and collecting data. LABVIEW served as a controlling software which called
various subroutines which were capable of performing different tasks depending on the
users desires. This program had the capability to calibrate liquid crystals as well as

analyze data that had been collected. LABVIEW uses a MATLAB program to convert the

 

67

hue values found on the plate into temperature data using the calibration values that were
generated prior to performing the experiment. A detailed report on the LABVIEW

software is attached in APPENDD( C.

APPENDIX C

APPENDIX C

LABVIEW SOFTWARE REPORT

This software is written primarily for the image acquisition and analysis process for a
liquid crystal thermal image. It links this with the temperature/pressure data acquisition

done by the HP Data Acquisition system through the network, using LABVIEW.

The overall control ﬂow for this entire process is shown in Figure C1. There are
principally two computers, one(GATEWAY) for the image acquisition and analysis
process using the image grabbing card and the other (DEL) for collecting thermocouple
and pressure transducer data using the GPIB card, which is connected with the HP data
Acquisition System. These two computers are linked by a transfer control protocol
written in LABVIEW, so that the temperature/pressure data and the image data are
collected simultaneously in the two different computers using the networking facility
available. This entire process is done in real time. The overall control program for this
entire process resides in the GATEWAY computer because the image processing (which

takes up a lot of time) is done in this computer.

69

70

 

 

 

TCP/IP

 

   

 

 

 

 

Image Grabber Gateway DEL GPIB

 

 

 

 

 

 

 

 

 

 

 

 

indicates the trigger path sent from Computer I to the
Grabber and also through the NetWork to Computer

--------------- > indicates the data path from Computer II, Image
to Computer I

Figure C1. Overall System Design

As mentioned earlier, the gateway computer acts as the controller for this entire routine.
When the experiment is run at steady state conditions, a button is pressed in the
LABVIEW software which sends two signals simultaneously. One of them triggers the
image acquisition process while the second one acquires the pressure and temperature
data using the thermocouples and pressure sensors connected to the HP Data Acquisition
System. As a recap, the image acquisition is done using the GATEWAY System, and the

other parameters are acquired using the DEL System.

71

Having given a brief introduction about the overall control logic for the entire software,
now we concentrate on the image acquisition and analysis part of the software. The

ﬂowchart for the image acquisition part is provided in Figure C2.
Initializing the Software

In order to start the software the user has to click on the LABVIEW icon. A list of sub

directories are shown and the user has to choose the Liquid crystal program directory

 

| Main |

I Calibration Run I W

|Calibration Initialization | IEXPeﬁmem “thumb“ I

1 / - ,
Talk To Image Grabbelgl Grab Image I GPIB I
I \ TCP/IP I-j

Image Analysis

I ~ Temperature 7
I Calibration Curve I Plot 7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Temperature/
Pressure Arra

 

 

 

Figure C2. Flowchart of the control algorithm

folder ( Make sure that this is shared with the other computer DEL). Once into this folder,
there are a list of virtual instruments which would be used for this entire process. ChOose

the Output Panell.vi by double clicking on it and this brings up the ﬁrst screen in the

 

72

software. The Run button is activated in LABVIEW (the small => in the tool bar), and the
RUN EXPERIMENT button is pressed. This brings up another window which gives the
user an option of using either the calibration process or the experimental grabbing
process. One of the options is used for calibrating the liquid crystals, and the other option

is used for experimental testing.

Calibration

The calibration ﬂow path is characterized by three sub programs. The ﬁrst one is called
calibration initialization.vi. This vi offers a list of checks that are to be taken care before
going ahead with the calibration process. The user has to click on the rectangular buttons
whenever he has completed the mentioned tasks. Once the user clicks the rectangular
button, the circular indicator on the right side of that button changes color (from Green to
Red) indicating that the particular step has been completed. Once the user has clicked all

three rectangular buttons, the next subprogram calgrab.vi is initiated.

The calgrab vi performs the image grabbing process. The user has to specify the total
number of images that he wishes to grab during the calibration process in the speciﬁed
rectangular control box. Once he has speciﬁed the number, he has to press the ENTER
button to register that value. After this, the user waits for steady state conditions to be
reached for the ﬁrst calibration point or temperature. As soon as steady state is reached,
the user presses the GRAB button at the lower left hand comer of the screen. This triggers

a signal to be sent to the image grabbing board and a frame of the image at that particular

 

73

temperature is brought up on the screen, and a dialog box asking for the ﬁlename under
which the image is to be saved is brought up. (Note: The ﬁle is always saved on the D:\
drive. The ﬁle, at this point of time cannot be saved in any other directory or drive). The
user has to type in an appropriate name in the ﬁlename box and hit the OK button. This
will save that particular ﬁle under that name. Also there would be an update of the
number of images that have been grabbed till that point of time in the indicator box on the
right hand top comer of the screen. This process of pressing the GRAB button and saving
the ﬁle is repeated for all the calibration points ( i.e.,= to the total number of images ).
Once all the images have been grabbed the image analysis sub program called calib
analy.vi is brought up. Before this is activated, there is message prompt which says that
MATLAB would be loaded for the image analysis purposes, and that the user has to use
the MATLAB program named cal (which stands for calibration) for this analysis purpose.
The user has to pay careful attention to the instructions that are brought up at this point of
time, because the user has to be careful while selecting the window within which the

image analysis is to be performed.

In the image analysis sub program, MATLAB is started and the program written for
analyzing the images is loaded by typing “cal” at the matlab prompt. After this, a few
inputs as to the name of the image ﬁle, the number of pixels that need to be skipped while
carrying out the image analysis routine, the window of the image ﬁle within which the
averaging of the pixel values need to be done are chosen using the left and right mouse
button. ( The left mouse button is used to choose the upper left comer of the averaging

area and the right mouse button is used for choosing the lower right hand comer of the

74

averaging area ). After this the program averages the hue value between these two end
points in the window. Once the processing of the image is done( indicated by the mouse
pointer shape) the user closes the image window in MATLAB, and the temperature at
which that particular image was recorded is given as an input to the program. This writes
the hue value associated with the ﬁrst image along with the corresponding temperature
into a ﬁle called calbfile.xls. The program prompts for the second image ﬁle, and the
above process is repeated until all the calibration images have been analyzed. Once all the
images are analyzed, the button which says ‘DONE WITH MATLAB’ is ﬂipped to the
YES position. This initiates a curve ﬁtting routine (a second order polynomial best ﬁt),
and the calibration curve between the temperature and the hue value is thus generated.
The calibration equation is saved under a ﬁle called CALEQU.TXT and the coefﬁcients
of the calibration equation is saved in a ﬁle called CALCOEFFXI‘XT. These two ﬁles are
saved in the ‘D:\’ drive and they are used for the experimental run routine. A typical
calibration curve is shown in Figure C3. And the associated calibration equation of the

best ﬁt second order line is as follows

Tavg = 0.000281 - Hue2 + 0.00657 - Hue + 29.079284 (1)

75

 

  

y = 0.0003x2 - 0.0311): + 35.858
F? = 0.9899

 
 

 

 

 

100 120 140 160 180 200 220 240 260

I‘ll. Measured

Figure C3. Second Order Polynomial Fit for Hue versus Temperature.

This calibration equation is then used for getting the surface temperature distribution of

the image grabbed under steady state when the actual experiment is run .

EXPERIMENTAL RUN

The data for the experiment is collected using a very similar setup as was used during the
calibration phase. This flow path is activated by using the experimental run option instead
of the calibration run option. There are a set of initial conditions that are tested for the
experimental setup, which is done using the experimental initialization.vi. Once all the
conditions are tested, the experimental grabbingvi is activated. This vi grabs the
experimental image, and the image is saved in the D:\ drive (Note: The location of these
ﬁles can’t be altered, and they have to reside in the D:\ drive). The salient feature of this

vi is that when the GRAB button is pressed, a trigger is sent to the image grabbing card to

76

grab the image, and at the same instant another trigger is generated which travels across
the network through the transfer call protocol (Figure Cl), and the pressure and
thermocouple data of the ﬂow is recorded in the DEL computer. Once these sets of data
have been collected, the image analysis is done using MATLAB as before. Before

executing the experimental analysis program, another program called dimes is activated.

The dimens program is used for converting the pixel locations into ‘x’ and ‘y’ coordiante
values in terms of meters. By typing dimens at the MATLAB prompt, this program is
executed and a bunch of inputs such as the name of the image ﬁle, the length of the plate
along the ﬂow direction and across the flow direction and the extremities of the plate
pixel locations(by mouse clicks) are given. These inputs initiate the calculation of the
length of each pixels in both the ‘x’ and ‘y’ directions. These values are stored in

dimensi.txt

After that the image window is closed and the image analysis program is activated. To
activate the experimental image analysis program, the program exper is executed, which
asks for the following inputs namely, the name of the image ﬁle and the window within
which the image is to be analyzed. The user also has to specify the number of pixel that
needs to be skipped for the analysis. (Note: The number of pixels to be skipped
determines the rate at which the results of the analysis are given. i.e, the lower this

number, the longer it takes for the analysis to complete. The default is set to 10).

77

These input speciﬁcations allows the hue values for the image to be computed as before,
and they are converted into corresponding temperatures using the calibration equation.
This entire process is automated. Since the conversion from the image to RGB values to
HUE values to Temperature values involves lot of computation, the process is not
dynamic, though the data part is dynamic. A possible way of altering this could be by
using the board itself to access the data and convert it into hue values instead of using
MATLAB to convert the image into RGB values, which is not currently being done.
Instead the entire process is done by the software. This controlling by the hardware is

required, if one were to run transient analysis on the liquid crystal data.

Once the analysis is done, the MATLAB window closes automatically, and the user can
make use of the ‘DONE WITH MATLAB’ button. Switching this button towards the
YES direction loads all the data into the table, and there are a couple of prompts which
ask whether you want to replace the existing ﬁles. The user takes an appropriate action by
saying REPLACE, and then he has to click the DONE button. This would take the control
to the main window, and when the user clicks on PLOT DATA button, the results which
are originally in a ﬁle which has three columns( Name of the ﬁle is TEMPVALXLS, and
this is in the D:\ drive) is converted into a rectangular matrix depending on the number of
pixels in the X and Y directions, and this resultant ﬁle is stored in the ﬁle

TEMP_MAT.xls.

APPENDIX D

APPENDIX D

Instructions for the MATLAB based Liquid Crystal program

Calibration:

(i) Assume that the calibration setup is ready.

(ii) Using the temperature controller set the ﬁrst temperature for calibration

(iii) allow system to reach steady state

(iv) using MyComputer, go to D:\ double click the grab.exe to grab the ﬁrst image, and
give an appropriate name for the ﬁle. (for testing purposes dy existing ﬁles namely
ME491290, ME491295 etc.,)

(v) Once you have grabbed all the images, go to MyComputer, open up the ﬁle
D:WOFrames.xls and change the ﬁrst number to indicate the number of images that
you have grabbed and save the ﬁle back in the same place using Save As.

(Vi) Now open MATLAB using Stan->Programs->M4TLABf0r windows-> MATLAB

(Vii) Type in cat at the matlab prompt and follow instructions. Once you have analyzed
all the images, the results of the calibration is stored in a ﬁle D:\calbﬁle.xls. Close
MATLAB.

(viii) Open up the D:\calbﬁle.xls ﬁle and plot Temperature versus Hue and not Hue
versus Temperature using scatter plot. To insert a trendline, ﬁrst double click the

chart, and then single click anyone of the data points. Now go to INSERT ->

79

 

8O

Trendline menu option, ﬁt a second order polynomial, and using the OPTIONS
within that window, choose an option so that the equation of the polynomial is shown
in the ﬁgure. Make a note of this polynomial. After this open D:\CALCOEFF.xls, and
enter the coefﬁcients of the calibration equation into this ﬁle in the same order as

present in the equation (i.e., 2nd order ﬁrst, 1St order and the constant).

Emrimental Run

(i) Assume that the experimental setup is ready.

(ii) Wait for steady state to be reached.

(iii) Using D:\grab.exe, grab the image and save it in an appropriate ﬁle name.

(iv) Now open MATLAB using Start->Programs->MA TLAB for windows-> MATLAB

(v) Type in dimens at the MATLAB prompt. This program is used to convert the pixel
coordinates into the xy coorinates positions in terms of meters and follow the
instructions. The output of this ﬁle is stored in D:\Dimensttxt, which contains
information about the pixels lengths in terms of meters. After this close the ﬁgure
window.

(vi) Now type in exper at the MATLAB prompt, and follow the instructions to analyze
the image. Once you have analyzed the image, MATLAB would automatically close,
and the output of the analysis is stored in ﬁles namely D:\Hu_valpi.xls, and

D:\Hu_value.xls

 

81

(vii) The above two ﬁles contains only the Hue values in each pixel location in terms of
pixel coordinates and xy coordinates(meters) respectively. Both the ﬁles are 3 column
ﬁles, and the third column is where the Hue values are stored.

(viii) Now in order to transform the ﬁle from a three column hue values ﬁle to a three
column temperature ﬁle and then to a rectangular matrix, you have to rerun
MATLAB. Open MATLAB as before, and type in transﬁ'm at the MATLAB prompt
and this program automatically creates two output ﬁles namely TEMP_VAL.xls and

temp_mat.xls. For more information about these ﬁles refer to APPENDIX E.

 

 

APPENDIX E

 

APPENDIX E

List of ﬁles and the information stored in them
The names of the ﬁles used in the program

LAB VIE W ﬁles

Output panel 1 .vi

MAIN 1.vi

calibration initialization 1.vi
cal grab.vi

matlab analysis calibration.vi

experimental initialization 1.vi
EXPERIMENTAL GRABBINGI .vi
matlab analysis 1.vi

globalctl.gbl
globa12.gbl
global3.gbl

List of MATLAB program ﬁles

cal.m
exper.m
dimens.m
transfrmm
bmpread4.m

List of DATA ﬁles

Dimensi.txt
Calbﬁle.xls
CALCOEFF.xls
Calequ.txt
NoFrames.xls
Hu_valpi.xls
Hu_value.xls
TEMP_Val.XLS
temp_mat.xls

83

 

84

Output Panell.vi

The front panel in this LABVIEW program is where the entire control algorithm starts for
the liquid crystal calibration as well as the experiment. The are three blocks in this front
panel. One block which can list the temperature and pressure data, of the flow, that is got
from the DAQ. One chart which gives the surface temperature distribution from the liquid
crystal image, when the PLOT DATA button is pressed. And the third button which
causes the entire sequence of this program to execute. The PLOT DATA button is pressed
at the end of the entire sequence of the experimental run. This results in the data that is
stored in three columns in the ‘TEMP_VAL.xls’ to be converted into a rectangular matrix

and stores the rectangular temperature matrix into a ﬁle called ‘temp_mat.xls’.

MAIN 1. Vi
The front panel of this LABVIEW program contains two things namely CALIBRATION
RUN and EXPERIMENTAL RUN, which are self explanatory. The user clicks on either

one of these buttons depending on what needs to be done.

CALIBRATION INTIALIZATION.VI

This part of the LABVIEW front panel has a bunch of controls and indicators. The
controls are the one’s on the left hand side of the panel, and the indicators are on the right
hand side of this panel. Presently all these controls have to be manually done. The idea

behind having this initialization process is to aid any person who uses the liquid crystals

 

85

to take appropriate care to go through all these steps before commencing the calibration
process. When the user clicks on the controls the indicator against these controls
automatically change their colors from GREEN to RED. Also these controls can be used
to activate motors (if the proper instruments are made available, instead of manual

operations, as is currently being done ) to take necessary actions.

CAL GRAB.VI

This program is used for grabbing the images while calibrating the liquid crystals. The
user has to specify the number of images that s/he wants to grab (which is directly
proportional to the number of temperatures that s/he wants to calibrate the liquid crystals
at). The value that the user speciﬁes here is stored in the ‘NoFrames.xls’ ﬁle. Once
speciﬁed, the user waits for steady state to reach for the ﬁrst set temperature (the user has
to watch the TV screen for this purpose). Once s/he is satisﬁed with the steady state
condition, the image is grabbed by clicking on the GRAB button. This would allow the
image to be saved in a ﬁle that is stored in the REMOVABLE DISK DRIVE (D:\). Note
that if the user runs into any problems while grabbing the images s/he can restart the
grabbing process, but the number of images to be grabbed has to be modiﬁed accordingly
when it is run the second time. Also once all the images have been grabbed, before
running the MATLAB program ‘cal’, the user has to open the ﬁle Noframes.xls and
check if the ﬁrst number indicates the total number of images that have been grabbed

during the entire calibration process.

86

MATLAB ANALYSIS CALIBRATION.VI

The front panel of this program has three blocks, one to check whether the MATLAB part
of the analysis is completed, the second to display the hue values corresponding to each
temperature, and the third block is to displace the calibration equation, which relates the
Temperature to the HUB values by means of a second order polynomial. The output ﬁles

created out of this program are

(i) ‘calbﬁle.xls’, where the hue values corresponding to each temperature is
stored

(ii) ‘calequ.txt’, where the calibration equation is stored

(iii) ‘calcoeff.txt’, where the coefﬁcients of the calibration equation is stored.

All the above ﬁles are stored in the REMOVABLE DISK DRIVE (D:\).

EXPERIMENT INITIALIZATION 1.VI

This part of the LABVIEW front panel, similar to the CALIBRATION
INITIALIZATION VI, has a bunch of controls and indicators. The controls are the one’s
on the left hand side of the panel, and the indicators are on the right hand side of this
panel. Presently all these controls have to be manually done. The idea behind having this
initialization process is to aid any person who uses the liquid crystals to take appropriate
care to go through all these steps before commencing the experimental run process. When

the user clicks on the controls the indicator against these controls automatically change

 

87

their colors from GREEN to RED. Also these controls can be used to activate motors (if
the proper instruments are made available, instead of manual operations, as is currently

being done ) to take necessary actions.

EXPERIMENTAL GRABBING 1.VI

This front panel has just one button, which is used for grabbing the steady state image
when the experiment is run. Once s/he is satisﬁed with the steady state condition, the
image is grabbed by clicking on the GRAB button. This would allow the image to be

saved in a ﬁle that is stored in the REMOVABLE DISK DRIVE (D:\).

MATLAB ANALYSIS IN]
The front panel of this program has three blocks, one to check whether the MATLAB part
of the analysis is completed, the second to display the hue values corresponding to each
temperature, and the third block is to displace the calibration equation, which relates the
Temperature to the HUB values by means of a second order polynomial. The output ﬁles
created out of this program are
(i) ‘Hu__ValPi.xls’, which saves the pixel location and the corresponding hue
values in a three column matrix.
(ii) ‘Hu_Value.xls’, which saves the ‘x’ and ‘y’ coordinates and the
corresponding hue values in a three column matrix.
(iii) ‘TEMP_VAL.XLS’, which saves the ‘x’ and ‘y’ coordinates and the

corresponding temperature values in a three column matrix.

 

 

 

88

cal.m

This is a MATLAB ﬁle which is used while the calibration is done. This program
analyzes every image, and computes the average hue value within the speciﬁed window.
The hue value is matched with the corresponding temperature and the results of this is
placed in a ﬁle called Calbﬁle.xls. The inputs that this program needs are the ﬁle name of
the image to be anlayzed, the window within which the hue values have to be computed,
the number of the pixels that need to be skipped during this calculation procedure, and the
temperature at which the calibration is done. Depending on the number of the images that
have been grabbed (this value is stored in NoFrames.xls), the above process has to be

repeated that many times.

dimens.m

This is again a MATLAB ﬁle which is used in converting the pixel locations into x and y
coordinate locations. This ﬁle is executed before exper.m. The basic function of this is to
create an output ﬁle with information about how much each pixel length corresponds to
in terms of distance in meters. For this purpose, the user has to give inputs like the
distance of the plate(that is encompassed in the view) along the ﬂow as well as across the
ﬂow. The user needs to specify the name of the image ﬁle ( NOTE: The image of the
plate has to be at aligned perfectly with the ‘x’ and ‘y’ axis, and cannot be at an angle),
and using the mouse has to pick the pixels at the extremes of the plate location using the
left and right mouse buttons respectively. The output of this program is stored in

dimensi.txt and is made use of by exper.m ﬁle

89

exper.m

This MATLAB ﬁle is used for analyzing the experimental image, and converts the pixel
image into hue values. The inputs that this program requires are the ﬁle name of the
image, number of pixels to skip and the output is a three column matrix which is stored in
two ﬁles namely, Hu_valpi.xls and Hu_value.xls. The ﬁrst two columns in Hu_valpi.xls
are the ‘x’ and ‘y’ pixel locations, while the ﬁrst two columns in Hu_value.xls are the ‘x’
and ‘y’ coordinates in terms of meters. The third column in both these ﬁles is the hue at

that particular location.

transfrm.m
This MATLAB ﬁle is used for the standalone program(Appendix D) only. This is used to
convert the three column matrix got out of exper.m into a rectangular matrix and stores

the output temperature matrix in a ﬁle D:\temp_mat.xls.

If LABVIEW were not being used for the image anlaysis process, then the user needs to
follow the instructions provided in Appendix D to go through the liquid crystal analysis

process.

 

APPENDIX F

Appendix F

Image Acquisition Experiment Setup

Computer Yifiw Camera

 

 

 

 

line line
A B

a 2;»? F

I
thun/

vukx) SVﬁdeotSanuxa

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Camera Adaptor Box

Note: The connection from the video out of the VIDEO to the computer must be

connected through the Video A cable.

91

REFERENCES

92

93

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95

Dini., S., et.al., “ Use of liquid crystal for local heat transfer coefﬁcient measurement
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97

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99

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100

Wang, Z., et. al., “ A color image processing system for transient liquid crystal heat
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