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AIR WM BY INJECTOR

Thu for of nu.

109322 Monan How.

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$2.32.:

THESIS

Lam-«idiom.
The writer tabs this opportunity to 0113:». 111.
silicon muciatin fur the 30mm uni-tune.
1nd cap-ration given bin by tho 01¢: Iotor lorh
in providing fuoilitiu for the nrim tut.

noon“!!! in obtaining the data used in this than“.

:0". m.

10 853 22'}

Introductigg,

lny'systam.of air movement where energy is imparted to an air
stream.of relatively low velocity through the medium of a second air
stream.of relatively high.velccity is here considered as an injector.
The variations in the design of injectors cover a wide range and prob-
ably are as numerous as the air movement problems for which they have
been a solution. This is due to the fact that the air injector is
simple to design, inexpensive to build, and within certain limits -
easily adjusted to produce the results desired.

many attempts have been made to definitely evaluate the
relations of the elements of design of an injector by the use of
empirical formulas. 'Many of these formulas have been published
and are used by industrial ventilating engineers. It is not the
objective of this discourse to discredit either the origin or use
of these formulas. They have been developed by experiment - and
as a rule - represent good design for most practical applications.
They are statements of the practical relations or the elements of
design and rarely have a fundamental aerodynamic origin.

It is the objective or this discourse to make an aerodynamdo
analysis of the air injector and established/a guide to its design and

application.

PROCEDURE.
The subject will be dealt with in somewhat the following manner:
Part 1. Analytical Development.

A. Simple Preliminary Design................... Page 1
l. The Nozzle"............................ Page 1
2. The Air Jet............................. Page 3

3. Stack Diameter.......................... Page

4. Stack Length............................ Page

5. The Test Stack.......................... Page

no T‘ltI to Verify mameeeeeeeeeeeeeeeeeeeeee P380

“#400

Part II. Theoretical Development..................... m.
A. Basis of Theory............................. Page 12
B. Fundamntal lquations....................... Page 12
0. Friction Anaheim.......................... Page lb
D. Stack Nozzle Diameter Ratio................. Page 16
3. Theoretical Sm-ary......................... Page 18
Part III. Vlrietions in Design"..................... Page 19
A. Venturi Stacks............................. Page 20
3. Straight Stack with Deflector-Cone Nozzle.. Page 84
0. Straight Stack with Converging Nozzle and
Gone Deflectors............................ Page 84
n. Stacks with Annular Ring Nozzles........... Bag. 27

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Part IV.
Le
Be
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Applications............................... Page 30
Genus]. Use................................ Page 30
Paint rum Remval......................... Page 31
corrosive lhnne Removal. 3’
ncirouit Injector - 32.

General Notes on Design 33

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A.

PART I.
Analytical DeveIOpment.
Simple Preliminary Design:

Is a basis for discussion the writer has selected an injector
stack of the simplest design - see figure 1 on the following page.
Inasmuch as the primary objective of the injector is the movement
of air, it is analogous to a fan. As a specific example, the cen-
trifugal fan has two essential parts, 1.9., the impeller which
imparts energy to the air, and the housing which confines and
directs the energized air stream. The injector stack is essentially
the same. It has the nozzle for imparting energy to the air and the
stack for confining and directing the energized air. If onedwere
to assemble a fan for a specific purpose, extreme care would be
taken in selecting an impeller and housing whose characteristics
blended together would produce the results desired. The same care
should also be taken in assembling an injector stack. The char-
acteristics of each part should be studied and used as a guide in

obtaining an efficient and balanced assembly.

1. The Nozzle:

The nozzle as the source of energy in the injector should
receive first consideration. .As will be apparent later in this
discussion, the nozzle should produce an air jet with uniform.in-
tensity and a minimum of turbulence. With high.nozzle velocities,
it is also good practice to keep the approach velocity low in order
to reduce the frictional resistance between the primary air supply
and the nozzle. .A study of the characteristics of various nozzle

designs will lead to the selection of the converging orifice type

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of nozzle. The writer recommends a converging orifice nozzle with

an included angle of taper of 13° and an area of entrance three
times the area of discharge. This gives an approach velocity of
one-third the discharge velocity; it also breaks up stratification
and reduces turbulence. This nozzle design and formula for its use
are given in appendix I.

8.The.iir Jet:

The air jet produced by a nozzle has characteristics which
will be recognized as being of considerable importance in the jet's
application to a stack injector. The American Blower Company
gives a very descriptive chart on these characteristics in their
book, “Air Conditioning and Engineering". This chart is given
with some notes by the writer in figure II. By using it for a
guide, tests were made roughly verifying the characteristics given
and developing the following observations:

(£)The discharge opening of a nozzle should be very accurate in
shape. For perfection, it should be smoothly machined to a
true circle. Roughness or irregularity gives a distorted
or one-sided jet.

(b) The included angle of the jets divergence as defined by
distinct lines of force is not effected by the velocity
of discharge.

(c)'I'he stream line confines of the jet are well defined by
force lines up to 15 nozzle diameters distant from the
discharge. Beyond this point, turbulence, lack of confine-

ment, and fading of force lines takes place.

 

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(d)When the air jet is projected into a smoke laden atmosphere,
an induced disturbance takes place adjacent to and parallel
in motion to the jet. The intensity of this motion increases
as the distance from the nozzle increases. (The development
and control of this characteristic is the elementary principle
of the injector.)

From these observations - together with figure II, relative
stack dimensions can be determined. The following analogy was used
by the writer in determining dimensions for a preliminary design.

3.3tack Diameter:

Figure II indicates that the maximum diameter of the jet
defined by distinct lines of force is 5%-nozzle diameters. Assuming
that a stack larger than this ratio would act as an encumbrance on
the air stream.thru turbulence and friction, the writer chose 5%
nozzle diameters for the test design. Subsequent tests proved this
ratio to be a little too high. See Part IIéD.

4.3tack Length:

‘It was observed that an induced motion parallel to the jet
existed. Inasmuch as it is the development of this characteristic
that we are primarily interested in, tests were made to determdne
the amount of the induced volume at varying points along the axis
of the jet. The lines on figure II marked A-B were arbitrarily
drawn to establish the diameters of imaginary circles. Circles
were established at points as indicated, the air volume determined,
and the results plotted in terms of the nozzle volume. See figure
III. From this study, a stack length of 20m nozzle diameters was
established. As will be shown later, this length is insufficient.

See discussion under B-l.

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5. Test Stack:

figure 1‘" ship the test stack. That portion shown in dotted
lines indicates the portion added for test purposes. The bell-mouth
entrance gives a minim entrance loss and is the basis for calcula-
tions. The lugth shown was developed by tests. The nozzle was made
detachable with the idea of varying the nozzle sizes and stuhing
nozzle-stack diueter ratios. .
Tests to Verify Dasign:
The following tests were made and the results were receded. may
of the tests were repeated as many as twenty times under varying con-
ditions ef nozzle sizes. primry air pressures, and entrance and dis-

charge resistances. The results given are either the average or a

. specific, as indicated.

1.

To determine the mini-n lugth of steel: necessary for ‘11.-
efficderaey. '

This test was run for nozzle sizes of 8", 3", d", 5", and .-
diamter. Tb pressures on the nozzles varied from 2" water

gauge en ti: 8" nozzle and 1" water gauge to 6" watergauge on

the .d' nozzle. figure 7. show a speciun test with a 5" diameter
nestle under 5" woe; pressure. It was found that auxin ”trace
vein resulted when the stack was 40 nozzle diameters in length.
This length was verified for the other nozzles at various pressures.
It will be observed tint at this di stance the cross-section of the
discharge becomes practically unifn - indicating a minim of

. stratification. ,

To determine the nature of the ccnfined jets
The results of this test are shown in figm-e' VI. in att-pt was made

to apply this study to each nozzle size; however; the 5" diameter and

‘3

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11.

and 6" din-atol- nozzles were the only successful tests. B! m of
explanation - the writer nuggoatu that the nozzles - manor than

5' dim-tor could not capletoly £111 a stack of 24" dimtor. This
than 1: Mud on the uni. darned jot diameter a: autumnal by

the phylum study or a Jet. Figure '1. 5170: the result- or a tut

_ on n 6" dial-star nozzle at 5' manpnuuro.

hater-inc the «tut of varying the stack-nozzle unnatu- ratio as
indiutod by the Officiant of tho aquipnant.
this test 1- diamond in part II.

A.

mm 11.
‘ Theoretical Development .
Dalia “for Theory - Sea East Stack - Figure No
Tests were Ida by ace of the ecction chown in dottei line.
we waa neeeaeary for making reaaonably accurate neaanrmcnte. hr
theoretical analyeie the atack mat take the torn ahown in heavy

liaee. The condition to be taken into conaidcraticn in the

. analyeie are ac followes

1c

The bell-month entrance often a minim or reaiatance. It forn-

abaeia tron which all development met be in the torn of increaael

’ entrance resistance.

he run discharge length in eeaential for complete mm; of the

. two air atrial ae indicated by teats already diacueeed.

All luau in the primary air atrean previoua to the discharge
opening or the aozale are cmeidered- ae hart cf the princy air
aupply ayatel and not part of the injector atack.
Mute]. Equations:

1.. previously nentioned, the fundamental action or the

injector ia the trader of energy tr. an air atrcan or relatively

' high velocity to another air atre- or relatively low velocity.

Inprceeins thia action in the for. or an equation, we lave

EN = E o + EF 0)
where . .
I. .- energy cf the nozzle. -
lb 3 energy or the air etréam at diecharge.
ii. 3 energy abaorbei by friction.
I: this equation were expressed in tom of the nan-energy eqaatin

fiOIO

E =12; MV" (2)

1‘
C

it would read as follow:

J2‘ MN VNZ = "2. Mo I431 + £7: (3)
where

I 3 no: of prilary air

71; 3 Velocity of diecharge in foot per oeoond.

ID : nu or oocondary air plna primary air at discharge.

VD gulecity of! cabinet! primary and secondary at dioolnrse

in feet per second.

I, 8 energy count-ed by friction.
munch as IS oonoioto or the two menace, prinry and oeocndary air3
equation amber three (3) can be furthor expanded to

JEMNV; 7"; MNV0L+333M5 VDZ+EF (9)
wherc

‘8 : nu of aeoondary air.
Stating in“ in terms or air vain-u and telooitieo the equation

. . ' 'V 8. 'D
é.QNZ.:VN=_LZ.Q~2;ID +é'ghi‘g'l'kEF (s)
whore

because

 

 

Q 3 quantity or air in cubic feet per oecond

3 g acceleration due to gravity in teat per adcond 38.8 .

w 3 weight or air par cubic foot.

I, being a conotant detennined by expel-nut and varying for
different valnoo of Q and 7 ~ equation R can be aancollcd out to
chow a more direct function]. relation between the variables T and Q.

The option baccnoo after clearing

I

14

3QN'VN = VD (QN+QS) +F (L)

"I" being the no! canatant for friction.

m thie relation observe the following:
Leanne the value of the equation remina constant.
1. If % varie-

a. 'N varies indirectly.

b. '11 nriee directly.

c. QB variee indirectly.

d. l' varies directly.

8. If 7 mice
a. a verieo indirectly.

b. QR variee indirectly.
c. Q' vario- directly.
d. 1' mice indirectly.

Let it be cboerved that the mount of energy available for nee
on the eeoondery air in dependent on the amount need in moving the
urinary air. In other words - the anallcr the volnlb of prinry air
the greater the pouibility of high efficiency in term or energy
applied. Following thie logic - the efficiency of tin energy tnnater

depende on the anount or available energy mich can be orpreoaed ea

_ 0. g“ __
Ea~ (n+0, EN E, (7)

where I. an available energy.

 

0. friction Analysis:

This leads no to the necessity of holding I, to a minim.
Motion can be classified as on of two fem, eiflier internal
er external. Internal friction is eons idered as these losses in
energy transfer due to the characteristics of the equip-ant which
can be controlled - to a very great extent by care in design.
Internal friction consists of the physical requiralents of tb
aeolication which are ccntrolable only to a mall degree. It is
on. can friction a fan would hve to .... name if it were
applied to tin cans Job. l'ol' the sake of naking clear tin
effect of desip en the count of energy lost by friction of

either classification - both classes are ennerated below.

Internal h-iction:
l. roorly shaped nozzles can give a oneoeided Jet3epending
energy in a non-effect ive blast-turbulence, and frict ion
.egeinet tin stack calls.
I. hproperly proportioned stack-male dimers can spend
energy in turbnluoe, skin fricthn, or excessive second-
. ary velocity. See Section D.

5. Intel-open: installed nozzles (out of line or loose)
develop the sen troubles with friction as noted in #1.

d. All duct work should be smooth and strcfi-linc.

Internal hiction:
l. llbows, tees, canopies, booths, etc.y
8. High velocities, restrictions, etc.

8. massive lengths of entrance and discharge ducts.

16

4.. Leah in Joints and scan.

5. Sprinkler lines inside stacks, etc. _
Internal friction cannot be evaluated except by test. External
friction can be evaluated in terms of velocity head or static
pressure. lhen known in team of static pressure the energy

eonsuaed can be calculated by use of the equation

EF =(q x P x .0865) 2.....m. (g)

per second.
wbre

r s static pressure in inches w.s. .0068 : fcet pounds per

second required to mvs one cubic foot of air per
second millet one inch pressure water gauge.
1). Stack-leash Dianster Ratio:

In Part I .. rests, a reference was node in regard to a test
for detenining the proper stack-nonale dianeter ratio. The dis-
cussion am results of this test were differed to this later
treabnt due to tin fact that their understanding sinuld be
founded on the foregoing theoretical developsnt. fin results
are shown us figure TII. 3'1'he curve slnws tin percent of pri-ry
air energy actually canceled in air novennt. Stating the curve

in the fol: of an equation

ED = nozzle Ratio Efficiency. (q)
E u

 

a I _ l. A ,
1 , _ _ _ I ._ W
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_ I f , .
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'7

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18

Theoretieel summery:

Le een be oheerved in equation #6, the euooeeeml injeetw

depende on the belenee developed by the designer for the reletion

between five veriehlee. In order to properly deein en injector

for e eeeeirie euplieatien, each or the variablee nnet he evelneted

in term of the condition eet up by the application. If thin in

telleved out in a logical eequenoe - tln deeign ie einele and

definite. A .1... of 1.31.3.1 proeehre 1. here given.

1.

4.

6.

7e

Deternine the velocity of tln eeoondery eir me rum

the neeeeeery etnel: dimter to handle t1. voll-

required.

Detenine the clergy required te move the eeeorlery

eir at the velocity eeleeted - nee equation #2.

Deternine the eddit ienel energy required for over-

ecning eppreeeh reeietenee or friction.

Select the voln-trie retio or urinary to eeeondery air.
Deter-line the aergy required to love tb eahined volu-

d' eeeondery and pram-ya: at the velee ity eetebliehed

in fl. flee equation 5-8.

heternine the energy neeeeeery for evereuing trietien in

the eteet. Thin value on he eeeund to he fr- Si te 5‘

of the energy et the nozzle.

Dyuee otthe meritene 3; 8, end 6, endtheprineryeir
velI- the eree. efl preeeure of the nozzle een he deternined.
M thie - uee either the eeleuletione oi’ eupendix I together
with equatien h «- or the ehert given in epuendix II.

rhe everell effieieney on he figured by dividing the en of
it-eflendflhythepeverinpnt.

19

PART III.

Variations in Design.

The foregoing has dealt entirely with.what has been referred
to as a simple design. An attempt was made to show the fundamentals
of this method of air movement. As will be shown in the following
discussion, this method has been used in several different stack
designs; however, the fundimental principle remains the same and
the fundimental equation given as B-6 on page 14 holds true for each
design. This equation was used by the writer in some 100 tests and
found to be consistent. There are four fundamental deviations from
the simple stack design. Each of these are given in the following dis-
cussion; however, the writer feels safe in stating that an increase
of efficiency, by any one of them, of over 5%‘wculd be unusual and
excessive.

The test stack with the belldmounthed entrance (figure IV)
eliminates all the resistance of approach. This leaves the throat
and discharge end as the only remaining parts that might be improved.
It was stated previously that the friction in a well designed stack
‘might run as high as 5%.cn the discharge. Following this line of
reasoning, it might be said that all that could be eXpected of any
improved stack would be a possible increase of 5% in efficiency -

speaking of available energy only.

1..

Venturi Stack: , f

figures VIII, 1!, and I show veaturi designs of more or less
annirical origin. This tyoe was used by one of our largest indus-
trial ventilation engineering and contracting fix for a amber
of years. It was clained to be the most efficient of all stack
designs; Mover, they adnit now that it never showed an advantage
of ever 5‘ over other designs. Their clai- ccntenled their in-
creased efficiency was due to reduced discharge resistance - and
increased efficiency of energy transfer by high throat velocity.
The reduced discharge resistance is admitted. By use of the
venturi it is possible - under ideal conditions - to reduce this
resistance to a negative quantity - actually creating a slight
suction on the threat. The contention for high threat velocity
seals rather unfounded as it, in itself, requires a mater meat
of energy than if a lower velocity were used.

msically the stack has several characteristics netewortln‘
of -ntion. . V

1. Its design appears difficult; however, it is sigh;

as adjust-ants are always provided to copulate for
’ errors in design. See note on figure It.
8. It is expensive to fabricate as may different patterns
. are necessary.
3. The null throat nabs the upper portion inaccessible

for “suing er naintenance.

u.\

u/
I
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41315-13 Crf’ I 27 j
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B. Straight Stack with Deflector-scene locale .

J'igure II showspa straight stack design with a deflector-
cone nozzle. rho objective ef this tn. of nozzle 1. to obtain an
i-diate nixing ef the two air strea- and thereby aha-ten the nec-
essary lugth of the stack. It is the Opinion of the writer than an
«tulips in“ an. direction is false econouy. changing the diverging
angle of the jet, chewing the course or direction of the Jct, er
changing the course of the secondary air strean involves restrictions
or interference which produce friction. The savings accaplished by
shortening the stack would not pay for very Inch energy consued by
friction when figured over'the anticipated life of the equipnent.

It could also be expected that this type of ncssle would have a greater
action than other nozzle designs in blasting intrained piaent against
the walls of the stack.
Straight Steel: with converging Nozzle and cone-Deflectors: _
figure It: sbwc another design intended to shorten the stack.
This design is patterned after the schntte-Ioerting draft boesters. 'l'hc
idea is good when applied te stack-nonale disnster ratios greater than
I}. The schutte-Iccrting designs were for use in large diameter chineys
with snail high pressure nozzles. The application of this idea to air
novassnt within the scape as here discussed could be criticized in tb
can nanner as followed in discussing the design of figure II. Actual
enerisnce by the writer has proved the criticisns to be true and not

a nattdr of opinion.

 

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D.

Stacks with Annular Ring Nozzles:

l‘igures XIII and m show the latest developments in nozzles
for an injector stack. Ii'his design probably has more arguments in
its favor than any other deviation from the simple stack design.
rigure m is the later develop-ant and is now being used very
successfully. The principal points of cmstruction are tin pro-
tective skin for the stack.- fanned by the primary air, the shorter
required stack desig',’ the lee pressure prinry air, and the ease
of cleaning and naintenanoe.

The only criticisns on this stack are directed against the
dea igner's cleins for higher efficiency. It the efficiency of the
stack is figured on the basis of the whole systn, including the
primary air fan and motor - the contentions could fall beyond
criticisn. If the contention is limited to the stack alone -
it is poorly funded. To bear out this point tin writer has
prepared a graph shown in appendix #II. This graph is based on
calculations only - but it shoes the increase of available energy
by increased prin-ry air pressures. It till be observed that tin
snount of available henetic energy in the primary air, with the
primary air volume constant, is directly proportional to the
prinry air pressure. This is true regardless the desip of the
nozzle.

However, this attack on the contended efficiency of the
annular-ring-venturi stack should be modified. The overall
efficiency is the important consideration in the long run. This
design, although possibly of low efficiency as a unit, has several

characteristics which - when balanced in ultimate results - place

 

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N
23

it in the opinion of the writer as the best of eta-rent practical
design. To support this Opinion the following points are
enmratcd:
l. The stack is simple to design.
I. It is relatively more expensive to build.
3. It is cmvenient to clean.
4. It requires a greater volume but lower pressure
prim air. This results in a greater efficiency
of primary air supply.
5. The venturi stack reduces stack back pressures.
Design au—ry:
To sullnrize the nerits of the various stack designs the
writer has chosen to construct a chart which is given as figure 1?.
fhe qualifications of each stack are given as the opinion of the
writer; they are the result of personal experience, experienc- of
others, and ordinary deduction and study. No stack could be designed
ideal for all applications. Bach steel: has sane one outstanding
characteristic which nay make it ideal for a specific application.
An attenut has been node to bring out the chief characteristics of
each design and pick out the one stack dcsip which - in the opinion
of the writer - would be most satisfactorily used for the average

applications 0

.bH earn

goon Madam Ho 2:3 {firearm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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A.

30
PART IV. _
dpplication.
General Use:

All problems of air handling can be solved more efficiently and
more cconcnically than by use of the injector, when cmsidered from
the power standpoint alone. The use of the injector should be the
result of careful deliberation on all the circumstances influencing
the application. Relatively speaking, the injector is low in first
cost but costly to operate. Keeping this thought in mind its use
will generally fall in one of the following applicat ions:

1. Increase draw of furnace stack for periodic operation.

2. Remove snobs or steam from process operations when use is

ally occasional.
3. Renove corrosive funss from process Operations.
4. Remove funes and fog fr:- spray painting operations.
5. mulling air where epaoe will not permit the installation
of a direct operating fa. I

6. Handling air where the investment in a direct operating fa
is prohibitive when capered to using a high pressure low
volun blower that may be on hand.

Statements have been made to the effect that an injector stack
should never be used in a position where the jet notion is not up.
The impression scene to be prevalent that the success cf the injecta'
largely depends on a natural draft action. The writer tabs the
liberty of correcting this impression. Tests have proved that the
advantage realized by use of the natural draft created in a sheet
metal stack (except where heated air is handled) is very stall and

not dependable. The writer advises the use of the injector in any

B.

0.

31

position advantageous to the application, providing sufficient
length of straight stack is available for proper approach and
discharge conditions. less friction is encountered if the in-
jector is located near the discharge when long runs are necessary.
I'hether the injector or a fan is used, provision for replacement
air is necessary.

Paint It Removal:

The injector stack has worm very satisfactory in removing
pig-ant or varnish laden fumes from paint spraying operations.
There is equipment on the market now that works on this application
more efficiently and economically than the injector. The air is
drawn through a scrubber and filter, thence into a fan and die-
charged to the atmosphere. It is high in first cost but lee in
cleaning and power costs. If a job is to be alert in life and
will not require excessive cleaning, the injector will probably
figure out to be the best investment. I
Corrosive rule Removal:

This type of application is a very good annals of on air
handling job where the injector is most successful. The parts of
the equipmnt coming in contact with the fumes are standard gauge
sheet metal, easily treated for corrosive resistance. The fan can
be standard design and not risk the necessity of frequent replace-
ment. The injector figures to be the most advisable investment for
this application when compared with the cost of a fan of special

material or special treatment.

D.

Incircuit Injector Fan:

Many applications of the injector stack require the movement
of air that is relatively clean and would not be detrimental to
the fan. In cases of this nature - the fan may be connected some-
what as shown in figure XVI. li'his arrangement saves the energy
lost in handling the primary air and increases the overall efficiency
considerably.

General Notes on Design:

Although the injector normlly would not be used for back presence
as high as would be the case with a fan, the same precautions in design
must be folloIed. Losses due to poor desig are more costly with an
injector than with a fan - due to the share of energy necessary for
conveying away the primary air. Sons itenn not to be overlooked are
as follow:

1. Plan the duct velocities law to avoid unnecessary friction,

1,800 to 1,500 feet velocity.

8. Plan all hoods, elbows, tees, branches, and canopies for a

minim of resistance.

5. Plan all systems with a means of replacing the air exhausted.

4. Take the primary air from outside to avoid heat loss. This

does not apply to air inoircuit hook-up.

5. Locate the nozzle in a straight run of pipe - at least four

pipe diamters from any elbow and have sufficient stack to
give at least 50 nozzle disneters before a discharge elbow

is enc cuntercd.

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