5" I ',1 I " ii i. ." f i "uw‘v-w~ -_ W—fiW"—Jw 'v- m’ _ ." - I- . -.. . . .~.—. - "["'IUA0‘~..J¢'. W; N: DYEUZATION 0F RADIANT HEAT FOR THE PROTECTION OF 'VEGETATiON FROM FROST DAMAGE Thesis for the Demo 0! M. S. MkCHlGAN STATE COLLEGE Francis Jefferson Hassler 1948 I495 Thlslstooerflfgthntthe thesis entitled Utilisation of Radiant Beat for the Protection of Vegetation from Frost Damage presented by Francis Jefferson Hauler has been accepted towards fulfillment of the requirements for l. 8. degree in Agricultural Engineering Major professor Date—”W. —---—.—‘ —. UTILIZATION OF RADIANT HEAT FOR THE PROTMTIOII OF VEGETATI ON FRO! FROST DAMAGE B! Francis Jefferson gguler A THESIS Sunnitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree or EASTER OF SOIBICE Department of Agricultural Mgineering 1948 THFQIS é ’5 Y/%5 ACKNOWLEDGMENTS The writer is deeply indebted to Professor AJI. Farrell, Head of the Department of Agricultural En- gineering at Michigan State College, who originated the idea of radiant heat for frost protection, directed the preliminary work done on this subject at Iichigan State College, suggested this investigation, and gave valuable assistance and guidance throughout the entire study. The funds for the project were made available through the Agricultural Experiment Station under the direction of v.3. Gardner. The Research Board of the Detroit Chamber of Commerce aided in solving commercial problems. It would be impossible to mention specifically all the numerous people who gave valuable assistance to this project, but it is the wish of the writer to especially thank Ir. George Gibson and Professor Clarence Hansen for many days and nights of hard work, and llr. JJI. Rice]: for the arrangement and correction of the manuscript. 208050 TABLE OF CONTENTS PAGE I. INTRODUCTION . . . . . . . . . . . . . . . l A. Nature of the Problem . . . . . . . . 2 B. Radiation-type frost . . . . . . . . . 5 C. lethods used for the protection of vegetation from frost damage . . . . . 6 D. Preliminary tests made at Iichigan State College . . . . . . . . . . . . . 9 II. DESIGNING AN EFFECTIVE, PRACTICAL OIL-BURNING INFRARED RADIANT HEATER FOR LARGE AREA FROST PROTECTION . . . . . . . . . . . . . . . . 14 A. Objectives . . . . . . . . . . . . . . 15 B. The theory of radiation . . . . . . . 16 0. Laboratory testing . . . . . . . . . . 27 l. laterials . . . . . . . . . . . . 28 2. Instruments . . . . . . . . . . . 29 3. The first laboratory investigation 31 4. The second laboratory investigation 40 D. Designing and building the units . . . 63 1. Burner . . . . . . . . . . . . . 54 2. The first design: Type A.unit . . 66 ..... ...... 000000 iv 3. The field test . . . . . . . . . 61 4.TypeBunit.......... es 5. Heat balance for the Type B . . 68 6. Type C unit . . . . . . . . . ._ 73 7. The commercial design: Type AA.unit 78 E. Tests under natural frost conditions 83 1. Test one . . . . . . . . . . . . 84 2. Test two . . . . . . . . . . . e 91 III. SUIIARY CONCLUSIONS . . . . . . . . . . . 98 FOOTNOTES................... 100 BIEIIOGR‘PHY O O O O O O O O O O O O O O O O O 103 LIST OF FIGURES FIGURE PAGE 1. The Radiant Energy Spectrum. . . . . . . . . 17 2. Energy Radiated By a Blackbody as a Function of Temperature . . . . . . . . . . . . . . 20 3. Spectral Distribution of the Radiation from a Blackbody at Temperatures of IOOOOF. and 1500°F 2S 4. The Application of Lamberts' Cosine Law of Incidence . . . . . . . . . . . . . . . . . 26 5. The Operation of the Inverse Square Law . . 26 6. Leeds and Northrup Infrared Radiation.leter . SO 7. Apparatus and Set-Up for the First Laboratory Investigation . . . . . . . . . . . . . . . 32 8. Apparatus Used in the First Laboratory Inves- tigation . . . . . . . ... . . . . . . . . . 35 9:15. Typical Results of the First Laboratory Investigation . . . . . . . . . . . . . . 34-58 14. Apparatus and Set-Up for the Second Labora- tory Investigation . . . . . . . . . . . . 41 15. Apparatus Used in the Second Laboratory Inr vestigation . . . . . . . . . . . . . .'. . 46 16. Close-Up of the Labelled Grid‘lith the Three Shapes of Radiating Surfaces Tested . . . 44 FIGURE PAGE 17. Detail of ThermoPile Mounting . . . . . . . 45 18-25. Typical Results of the Second Laboratory Investigation . . . .. . . . .. .. . 46-51 24. 'Aeroil” Burner With Modification . . . . . 55 25. Type "A” Frost Prevention Unit . . . . . . . 59 26. Type A Unit . . . . . . . . . . . . . . . . 60 27. Field Operation Data for Type A Uhit . . . 62 28. Type "B” Frost Prevention Unit . . . . . . . 65 29. Type B Unit . . . . . . . . . . . . . . . . . 66 30. Field Operation Data for Type B Unit . . . . . 67 51. Energy Distribution Curve for Type B Unit . . 7O 32. Type "c" Frost Prevention.Unit . . . . . . . . 74 35. Type G Unit . . . . . . . . . . . . . . . . . 75 34. Field Operation Data for Type 0 Unit . . . . . 76 55. Type "AA" Frost Prevention Unit . . . . . . . . 79 36. Type AA Unit . . . . . . . . . . . . . . . . . 80 37. Field Operation Data for Type AA Unit . . . . 82 58. Diagram of the Set-Up for the First Test Under Natural Frost Conditions . . . . . . . . . . . 85 59. Field Operation Data for the First Test Under Natural Frost Conditions . . . . . . . . ... 88 vii . FIGURE PAGE 40. Coleus Plants Ten Hours After the First Test Under Natural Frast Conditions . . . . 9O 41. Diagram of the Set-Up for the Second Test Under Natural Frost Conditions . . . . . . 92 42. Tomato Plants Used in the Second Test Under Natural Host Conditions . . . . .‘ . . . . 94 45. The Tomato Plants Shown in Figure 42 After Exposure................. 96 ..... I . INTRODUCTION A. Nature of the Problem One of the main hazards to fruit and truck crops is radiation-type frost damage. his damage includes late maturity of crops, poor quality and quantity, and in some instances a total loss of produce.1 In the United States, losses due to frost damage are more pronounced in states such as Florida and Califor- nia where the citrus crop makes up intensive or highly- valued agriculture. The same is true for states that grow truck crops and fruit orchards extensively. Michigan represents this type of agriculture and the annual frost damage in the State of Michigan is es- 2 timated to range from ten to twenty million dollars. I Footnotes are on pages 100-102 B. Radiation-Type Frost The earth.receives its heat from.the sun in the form of radiant energy. This energy is absorbed by plants and transformed into sensible heat. At the same time that heat is being received, plants are radiating a part of this heat back toward the sky. However, there is a net gain on the part of the plants during a twenty-four hour period. \This condition is brought about by the blanketing effect of the atmos- phere on the earth, for the energy of the sun is emitted in short wave length radiation which penetra- tes the atmosphere of the earth with.little loss, while the plants, having absorbed this energy, emit it in long wave length radiation which is readily ab- sorbed by the atmosphere and thereby results in heat being added to the atmosphere. Thus the atmosphere acts as a trap whereby the earth retains sufficient heat to carry it through.the night. The condition of the atmosphere, then, will great- ly influence the net amount of heat gained by plants in any one period of time. For example, the absorbing characteristics of the air become more pronounced as the absolute humidity increases. Conversely, if there is little humidity in the air, as on a clear night, the plants rapidly lose their heat. Radiationvtype frost is common during the early and late parts of the growing season. To set the stage for this type of freeze it is required that there be a preliminary influx of cool to cold air, followed by a calm, clear night. Since the plants under these conditions are radiating heat to the outer space, the not heat transmission is away from the plants. The air will become cooled by conduction to these plants.3 As the air becomes cooled, gravity pulls it down to settle close to the ground. When the plants have lost sufficient heat by radiation and have cooled the sur- rounding air to a low temperature, their temperatures will approach the freezing point. If the plant temper- ature falls below the dew point of the surrounding air, moisture will condense on the vegetation, and when subsequently frozen to ice, will give the familiar frost appearance. Not all freezing however, is visible. One example is when the wind velocity is in the magnitude of five miles per hour and the condensate is carried off the vegetation, leaving no moisture to form.visib1e frost. Another condition is then the dew point is lower than the minimum plant temperature for that freeze.4 This freezing without visible frost is commonly known as “black frost." Except for extremely cold conditions, a four mile per hour wind will cause sufficient turbulence to prevent the air from collecting in strata.5 The moving air also convects heat to the plants, keeping their temperatures above the freezing point. Ihen the pre- liminary influx of air is relatively cold, freezing is likely to occur even if there is a brisk wind, because this cold air cannot oonvect enough heat to the plants to offset the heat that is lost by radiation. C. Nethods Used for the Protection of Vegetation From Frost Damage The basic principle involved in the problem of keeping vegetation from freezing is to maintain the temperature of the vegetation safely above its freezing point. The three approaches to this problem are: (l) conserve the existing heat possessed bv the plants and the ground; (2) utilise the heat in the surrounding air through stirring; (3) add artificial heat. Numerous attempts have been made to gain these three objectives, but the methods tried have either been too expensive or not entirely successful. For example, glass coverings, or a covering of cloth and lath screens, are excellent protection, but far too expensive for the average crOp. Irrigation has been used successfully, but it, too, is expensive to in- stall.6 Flooding is effective, but often causes water damage. Efforts to make artificial clouds have not been successful}, Large motor-driven prOpellors have been used to stir the air, which in turn convects heat to plants, but there is not agreement on the success ‘ 8 of this method. ' The most widely-used and successful means of combating frost damage has been the use of orchard heaters in the citrus groves. The original idea was to blanket the area with dense smoke in order to out down radiation loss. From this practice, the burners came to be called 'smadge pots." The individual units cost little, but one per tree, or two hundred per acre, are required to be effective. The damage from the smoke and the nuisance they cause have led urban com- munities to pass ordinances restricting the use of this type of heater. A larger orchard heater.was then designed to heat the groves by convection. mile these units are more expensive, only about fifty per acre are required. This heater takes advantage of the fact that on a clear calm night there is a thin layer of cold air near the ground, while the air temperature increases with ele- vation to a certain point, above which the temperature again decreases. This phenomenon is called temperature inversion. The purpose of these heaters is to warm the air under the inversion point to the necessary degree. Conditions limit the effectiveness of this method. It is most effective if the day temperature has been highand therefore it is necessary to heat less air. mass. heaters are generally effective for the control of radiation-type frost, but give little pro- tection during cold fronts that are accompanied by cold winds- These units are also expensive, not only because of the initial cost and the fuel cost, but because much labor is required for installation and maintenance. These facts have caused the citrus in- dustry to look for better means for preventing frost damage . D. Preliminary Tests Made at Michigan State College the farmers of Michigan realize the need for pro- tection against frost damage, as a large part of their agricultural industry is devoted to truck gardening and fruit growing. The problem of frost damage, while always important, became more so during World War II when the crop values increased. By 1945 this problem had become so am. that the lichigan Agricultural Experiment Station, a part of Hichigan State College, was asked to develOp a prac- tical means for controlling frost formation. the problqn was subsequently referred to the Agricultural Engineering Department. As a first step, an intensive study was made to determine the relative advantages and disadvantages of all known attempts to control frost. lethods that appeared to be practical were given careful considera- tion, and some of these methods were tested by the Agricultural Engineering Department. In one instance the United States Army Air Forces sent a helicOpter to the college to be used in circulating the air by flying at low altitudes over the areas to be protected. 0 10 It was concluded that while some of these practices are effective under selected conditions, they would be impractical for the conditions surrounding Hichigan agriculture. Careful study showed that convected heat is of limited value because its success depends on the atmospheric conditions. In the fall of 1945, A. W. Farrall, Head of the Department of Agricultural Engi- neering, at Michigan State College, proposed radiant heating as a practical method of solving the problem. Professor Farrall, pointed out that by this method energy can be directed onto the objects to be heated without directly heating the intervening air. In order to test this method, an electrically- powered radiant-type unit was designed and constructed at Michigan State College in the spring of 1946 with the cooperation of the Research Committee of the Detroit Board of Commerce. Information was needed as to the effectiveness of radiant heat in preventing frost damage, the radiation intensity required per unit surface area, and the cost of constructing and operating a practical unit. 11 this unit was designed to cover a plot forty feet square. The heating unit consisted of rod-type chromolox elements with.an imput of twenty‘K.fi. With the use of standard reflector design techniques, this unit was so constructed that practically all of the heat being radiated was uniformly distributed over the designated area. Tests were made during natural radiation-type frosts.9 Although actual temperatures of the vegeta- tion and the surrounding air were not recorded, the tests indicated that a radiation intensity of three watts per square foot would adequately protect vegeta- tion from frost under the conditions most likely to occur during the spring and early fall.10 Although this electrically heated unit was excellent for testing purposes, and supplied the neceSsary basic data, it would be too costly to be commercially feasible. Parthenon, present lines are of insufficient capacity to provide protection for appreciable areas. The next step was to develop a radiant heat source that would be practical. Two factors led to the use of oil-burning equipment. First, on a BTU basis oil is inexpensive; second it was felt that oilaheated radiation units could be constructed at a reasonable cost. the average net heat loss from the surface of the earth.by radiation at night has been found to be at the rate of approximately one million BTU per hour per acre.11 Using this as a basis from.which to start, an oil-burning unit was constructed that would burn fuel at the rate of approximately seven gallons per hour. the radiating surface was made of three steel oil drums welded end to end. Aluminum.reflectors were positioned around the barrels in an attempt to direct the radiation downward. A commercial-type pressure vaporizing burner was used. this unit was tested dur- ing the fall of 1946 under natural frosting conditions. the results were conclusive in establishing the effec- tiveness of the principle of frost control through the use of radiant heat. the area covered was greatly expanded and the originial figure of three watts per square foot was found to be the average intensity requirements for protection against normal frosting conditions during the fall. 13 the object of this study was to collect detailed information regarding the application of radiant heat to large areas, and to determine principles of design which could be incorporated into a practical ccmercial unit. II. DESIGNING AN EFFECTIVE, PRACTICAL OIL-BURNING INFRARED RADIANT HEATER ran LARGE AREA FROST PROTECTION. l) 2) 3) 4) 5) 6) A. Objectives to analyze and summarize that part of radiation theory which.pertains to infrared radiant energy; to study the radiating and reflecting character- istics of materials to determine which.are the most practical; to determine the shapes of both reflectors and radiating surfaces which are the most effective and practical; to study the relative positioning of reflectors and radiating surfaces to determine the most ef- fective combinations; to design and construct test units; to analyse the performance of test units to deter- ‘mine their effectiveness for frost control and their practicality for commercial manufacture. "- “fi‘l-IEJ B. the Theory of Radiation the discussion of radiation in this paper will be limited to radiant heat. the term “radiant heat' names that part of the electromagnetic spectrum which imparts heat to material objects. this interval of the spectrum is ccnonly referred to as the “infrared" range. Radiant heat and infrared, even though used interchangeably, must be used only when illustrating the range of wave length from visible light to radio waves. Prom Figure 1 it is noted that this range in- cludes the wave lengths from 7800 Angstrom Unite to ' approximately 5,000,000 Angstrom Units. there is much published information concerning laws pertaining to radiation. Here, however, only those fundamental laws which will give the reader a working knowledge of the application of radiant heat will be outlined. the theory of radiation states that energy is being transferred by vibrating waves in a medium of ”ether.“ These waves have varying lengths and amplitudes, as is also illustrated in Figure 1. It has been established that all wave lengths traverse equal distances in the .wfiwmbcumm chwfifim BZ¢HQ¢K EVE .H mmwam 7 1 mug; DEPOMJM mm><>> 0.04m L ommdmmg hm..._0_> gumbo m><3 @ met—,5 EOEme< 3:02. ..3 "mmmfizfizmo$165.23.:_ $102. 03.3 ...mmmpmzjninb. 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This brings out the physical ' relationship that wave length times frequency equals a constant which is the speed of light, or approxi- mately 186,000 miles per second. to satisfy this relationship means that the wave length varies in- versely as the frequency. the Stefan-Boltzman.Law gives the total net energy for all wave lengths radiated by a solid in the following. equationxlz s: rut-1'04) .1; Where, I = net energy radiated in BtU per hour per square foot of radiating surface k = constant 0.173 times 10"8 BTU per square foot per hour per degree Rankine4 t = absolute temperature of the radiating body, in degrees Rankine 0-3 O u absolute temperature of the surrounding surface, in degrees Rankine et total emdssivity 19 The total emissivity, °t' is a surface character- istic and varies with the temperature of the radiating body. A blackbody radiator is called the standard radiator and is considered to have a total emissivity of unity. All other materials or objects have radiating characteristics which give them a total emissivity of a fractional part of unity. these values are given in tables in most books dealing with heat transfer.13 The Stefan-Boltsman Law gives the rate or power of radiation as proportional to the fourth power of the absolute temperatures (see Figure 2). This is an important factor when considering the application of radiant heat. In addition heat will be given off by conduction and convection, but the means by which the greatest rate of heat transmission is obtained usually names the system or principle employed. The heat that is being radiated does not leave the heated body in any single wave length. Nor does the heat being radiated change to different wave lengths as the body changes tanperature. The heat will always be given off in the longest wave lengths, but the temperature of the heated body determines the shortest Iv. . .Vw?_w¢r£_m.fiab two ZOHBOFE d. was. ammofiaqfim .< ta QfietqHQdfi NEWLY .m EMLUHL :mzzumzé muumeuamxaaacuazu» . .oo». oo! .03. .onofi .00: K #08. .03 twoos at: .3. . . :, m»... . n9: , no.3. .h \ (IJ'OSNBH) I 01.8 8 3 21 wave length. This is illustrated by the visible light or incandescence of a body as its temperature increases; this visible light that is given off progresses from dull red, which is at the long wave length and of the visible spectrum, to yellow light of shorter wave length. Although the Stefan-Boltzman law gives the total amount of energy radiated at a given temperature for a body at that temperature, it does not yield any information regarding the distribution of the energy over the various wave lengths. This phase is referred to as spectral distribution and can be calculated by 14 Planck's Distribution Law: energy radiated in wave length inter- 3" D. Y I. vals ax, in BTU per hour per square“ foot per micron or cm. x 3 wave length in cm. absolute temperature in degrees Rankine ...g . 1.18 x 10 BTU per square foot per 4 hour times cm. .0 u C; = 2.58 x cm. 1 degrees Rankine 6 = Napierian base of logarithms which is numerically equal to 2.718 This law is represented by the temperature curves of Figure 3, which are for a blackbody radiator. These curves give the relation between energy radiated and. wave length. The ordinate represent the rates of radiation or radiant intensity per unit area of emit- ting surface per element d). of wave length interval at the wave length x . The abscissas are wave length intervals at the wave length )x given in microns. he energy radiated at any wave length interval, d). , is the area of the vertical strip under the curve or the product of the ordinate and the wave length interval. For greater wave length intervals, when the ordinate approximation would introduce appreciable error, a planimeter can be used to determine the area under the on". e The total area is found by summing up the intervals 23 s § ? woxacfi} ! : enaxuo5 o—J—tsoo’F ' 6 ,, 50):”) 5. u V i S a ; ‘ 6 5:44oxuc>é E a EL 5 ' \ 3 , 5 h , .~ on soxuofi‘ : _ - u . * N 0A 3 a “f E ; i N . ...: 20 X IO6 ;_._.. E » an--- -.....___....-+-.a.-.-__ m N z E “’ t ... “ N N N. t +2- onmsm ~ : hr-aooowP 1 -_ g N a E 5 1t v x t: K ; 1S g 0_ h i” --- . [\ XL... 5 IO I54 20 WAVELENGTH " MICRONS (‘ f0 -ANGSTROMS) FIGURE 3. SPECTRAL DISTRIBUTION OF THE RADIATION FROM A BLACKBODY AT TEMPERATURES 0F 1000°F. AND 1500°F. THE CROSS-HATCH PART snows THE INTENSITY FOR A WAVE- LENGTH INTERVAL EQUAL TO DA. 24 of wave lengths from 0 to o . This is: a) -e C. X (1 Ex 2 C X 6 s/XLI which afterointegration gives Stefan-Boltzman Law for a black body: 3 = kT4 me curves in Figure 3 illustrate that the energy passes through a maximum. The wave length at which maximum radiation occurs shifts towards the shorter . wave lengths as the temperature of a body increases. The maximum is at 3.5 microns for a temperature of 110001?" while at 150001'. it is 2'7 microns. The rela- tion between the wave length at which the maximum energy is radiated and the temperature is given by Wien's Displacement Lew: XT = 0.5195 max )s 8 wave length in cm. T = the absolute temperature in degrees Rankine A further point of theorectical interest is Lam- bert's Cosine Law of Incidence, which states that the radiation intensity on a surface is equal to the incident radiation times the sine of the angle which the radiation makes with that surface. This is illus- trated by Figure 4. A point of more than theoretical . interest for this problem is the Inverse Square Law. Briefly, energy radiating from a point source will have an intensity that varies inversely as the square of the distance, or B = I/D2 . See Figure 5. he reflectors on the finished units are used to converge the energy in order to offset this effect, and the laboratory investigations were made mainly to find out how to so arrange the reflectors as to best accom- pli sh this end. 0- . 8. g IOO“ FIGURE 4. THE APPLICATION OF LEMBERT'S COSINE LAW OF INCIDENCE. IN THIS FIGURE THE RADIATION INTEN- SITY ON THE HORIZONTAL SURFACE AT 100 FEET, In, IS EQUAL To I100TIMES COSINE e. FIGURE 5. THE OPERATION OF THE INVERSE SQUARE LAW. C. Laboratory Testing The purposes of the laboratory tests were: 1) To select materials for the radiating surface that would be coalparatively cheap in cost, available, easy to shape, and that would have a relatively high coeffi- cient of emissivity; 2) To select materials for the reflectors that would be cheap, available, flexible, and have a high coefficient of reflec- tivity. The surfaces would have to be of an inert nature to prevent excessive oxidation; 5) To so position and shape the radiating surface and the reflectors as to offset the inverse square law. It was not the purpose of this work to find out only the theoretically best, but also to arrive at a design that would be commercially feasible. 1. Materials Rolled sheet steel satisfies the requirements for the radiating surface. After oxidation through excessive heating it has an emissivity factor of ap- proximately .80. Sheet aluminum with an anodized surface meets the requirements for the reflectors. 2. Instruments Three instruments were used in the laboratory experiments. They were later used for gathering in- formation once the units were constructed. These in- struments were: 1) 2) 3) Leeds and Northrup potentiometer for measur- ing temperatures with thermocouples; Leeds and Northrup Optical pyrometer for measuring the temperature of the radiating surface; Eppley Radiation later, which is illustrated by Figure 6. This instrument consists of a thermopile to expose to the radiation. The thermopile is electrically connected to a potentiometer for measuring the HF, which, by the proper conversion factor of 35.6 microwatts per square cm. per microvolt, gives the radiation intensity. .mHBm-_H H_.~©H._..¢Hm¢m mmmmmmu: mzwmmbmoz mad mflfllamg .0 mngh m0m. .02 w... EOZKMI... mum .Oz EPUZOFZMFOQ 31 5. The First Laboratory Investigation This preliminary investigation was made to study the distribution of radiant heat from a flat radiating surface. Figures 7 and 8 illustrate the apparatus for the first laboratory experiments. The radiating surface consisted of a 'six-inoh commercial strip heater with an’ input of 110 volts, 400 watts. It was so mounted that the angle it made with the so-called horizontal could be changed. The reflectors were made of sheet aluminum with an anodised surface which gave them a specular finish. In this experiment they are left straight, but their length and their position relative to the radiating surface could be changed. Radiation intensities could then be measured with the radiating surface at various angles to the so- called horizontal, and with the reflectors at various positions in relation to the radiating surface. This was done at 100 intervals on a ten-foot radius from the radiating surface. Figures 9 through 15 show the typical results ob- tained from these tests. On each figure, the position- ¢ 52 I000 [’00 1 iomzouna I” _ _ __ _ __ \\\ 0 0° 5' ‘J’ 9° If fz—ARDITRARY GROUND LEVEL’W‘ f @ELECTRICALLY HEATED RADIATING SURFACE @THERMOPILE (PLACED AT IO° INTERVALS ON IO' RADIUS FROM RADIATING SURFACE) @ POTENTIOMETER @COPPER WIRES CONNECTING THERMOPILE AND POTENTIOMETER ©REFLECTORS OF VARYING LENGTH AND POSITION FIGURE 7. APPARATUS AND SET-UP FOR THE FIRST IABORATORY INVESTIGATION. aflbflcadanuv .| ..an 1) Potentiometer. 4) Upper Reflector. 2) Radiating Surface. 5) Mounting for Measuring Angles 5) Lower Reflector. of the Radiating Surface. 6) Thermopile. FIGURE 8. APPARATUS USED IN THE FIRST L.‘.‘:5I_‘E‘.‘.'i"i'i".' TTI‘.’E.3TI’}.‘.TI(‘N. ‘1 .0 £4 01 o f ‘ //A N ' . Z 1 / I,” Q DISTRIBUTION CURVE Fog RADIATION .INTENSITY AT l0 FEET VERTICA (16v & Radiating Surface Scale 1"- l' DIAGRAM OF TEST SET-UP * l Microvolt 235.6 Microwatts per sq.cm. FIGURE 9 ,’ I \xg / , . ' O (,/ \gf /" ~._ /' . ’ I 0 ' O _ ' 0 / - M ' L L 1 DISTRIBUTION CURVE ron RADIATION .INTENSITY AT I0 FEET ANGLE Inten race sity _ \ \\ 3! —— - —F::._\‘/ 4 \__ _ V. ’Y . Reflector _, or... _ — ___.____ - . o -——Radiatina Surface ~ e __ - ..g,‘__ - -—-;:_—_. l/———Reflect.0r _‘ 2'-3"\\1 0 N i ' DIAGRAV CF TEST SETffifle l 3 l * l Microvolt : 35.6 Microwatts per sq.cm. DATA ‘ ' FIGURE 10 l r I I . ‘ LHRLZrthTAI, o :_.rcf -" -. ./'_, // ”-" z’ Z/ / 1 Li” QAIZ DISTRIBUTION CURVE FOR RADIATION .INTENSITY AT IO FEET ANGLE n en race t VERTICA (II/Iv);I eflector ' Scale 1"- 1' DIAGRAM OF TEST SET-UP ' *-1 Microvolt : 55.6 Microwatts per sq.cm. DATA \ ? FIGURE 11 . 0° I 0°\. I3 ° 20‘. \ \ l g \\ 0 VIC" \\ * \‘ R\ \ . \\ \ \ \‘\ \\ \ \x\ K“ g \ -\ \\ \ \ \_\ 1 O I \\ \I \ \ \ \ 4 II \ \ \ \ ‘ ‘IO '7: \ \\ \ k \ \‘ I“ I I N‘ \‘ '-\\ \ I \ “I \‘ , x ‘ “ ' . | \ \ \ , \ \ V \I I I " ‘ I ) 1I ‘ ‘ . I I . I T ‘4 ‘ I ' ' ) I ' I l ' '. I I I ' I 1“ NOTE 1 A . I90" ’ I 1 I; I i I T I I I ‘ O / 3 / l: I. / I I: I II I O I I I I / ‘ / ' I / ‘ o // 8 I I 'I" / / f "I / / O / e 1/ I! ’ {I ? / I O / I, I’ I 7 / / I / / 1/ / t/ I’ / // I / /'/ f/ / . f I’/ / /‘l / I .x l/ // I o f/ I] e o O o e // /' Z/ / A j 1, 0‘, I L DISTRIBUTION CURVE FOR RADIATION . INTENSITY AT IO FEET NO 3.5: $389 VENT (My * AC?— 0 ‘ 100 (\O 1'”6" -——L—— “-4 eflector Scale 1": 1' DIAGRAM OF TEST SET-UP * l Microvolt - 35.6 Microwatts per sq.cm. FIGURE 12. u i k x. ‘l '\ ‘{ ‘ \ X T Q i 1 ‘ . 4 + X 4HfillodTAu . ‘ :39 ’ .‘ l ' ! b I r | I l l . . / ’fl - 0 i A - ' 1 / Z L I” ' DISTRIBUTION CURVE FOR RADIATION .INTENSITY AT IO FEET ANGLE npen FROM Slty \ .JL VER‘HGA (MV )* I? 4 Radiating Surface ----*- w 39 \4 Scale 1": 1' DIAGRAM OF TEST SET-UP * l Microvolt = 35.6 microwatts per sq.cm. DATA FIGURE 13. 39 ing of the radiating surface and the reflectors is shown. Figure 9 shows a symmetrical curve, with an equal distribution of intensity above and below the horizon- tal. The strongest point of intensity was at the hori- zontal or normal to the radiating surface. There were no reflectors to divert the energy from above the horizontal, and all of the energy above the horizontal is considered to be lost. Therefore, the problen.was to so position reflectors of adequate length in rela- tion to the radiating surface that the radiation would be converged below the horizontal. Figures 10 through 13 show other typical results from the various positionings. Figure 13 was especial- 1y interesting, as the results showed.most of the radiation converged within a narrow angle interval. From.this experiment it was conoluded that the inverse square law could be offset. 4. The Seeond Laboratory Investigation The first laboratory investigation demonstrated that the inverse square law could be offset; the second laboratory investigation was made to get further in- formation. ‘Ihe effort in this experiment was to see if the energy could be converged like a beam towards the vegetation to be protected. In this experiment the radiating surface was an eighteen-inch commercial electrical strip heater, which was expected to give more effective results than did the six-inch surface. It was shaped three ways on a hydraulic press with Jig: straight, slightly curved, and curved on a small radius of curvature. The radial-T ting surface was mounted so that its angle with the so- called horizontal could be changed. Figure 14 shows the apparatus for this investi- gation. The reflectors consisted of chrome-plated stainless steel, so they would be affected by magnets. A labelled grid was drawn up, and the shape of the reflectors was changed by changing the position of the magnets on this grid, which made it easy to record the reflector shape in each case. It will also be noticed "I 41 -. ....) . u..(on 3 .8889: 2030”” U5! ghmec . wan: v 022.4548 Fur-4428 gut ‘ UJ§¢U¢ (Ob Uhdd 0235502. ngcg hum u 0. 21¢ m5_o<¢\ mg”; U; 0238.0! con >355 a e 2.3.. 95 a. S 1: 43h: o zoo» sin 4 B .155. .on at F80. 953525 a 2.88.5. c upon a n5“. .3 #3 Old hw.au e .f.. 4.1-0 v.51luuule....hl.§ 4....‘3Nh‘ that the thermopile was so mounted that it could be 42 rotated by a pulley arrangement, and therefore one man could make the investigation. A photograph of the entire apparatus is shown in Figure 15. Figure 16 illustrates how the reflectors were bent by the magnets. Figure 1'7 shows the pulley arrangement whereby the thermopile could be rotated at the ten-foot radius from which the readings were taken. Figures 18 through 23 show the typical results obtained in this investigation. Figure 19 shows an energy distribution curve for the slightly-curved radiating surface when no reflectors are used. It will be noted that a complete and symmetrical curve does not result, and furthermore, there is slight ”beaming” effect from the curving of the radiating surface. Figure 20 shows that curving the radiating surface to a small radius of‘eurvature does give a noticeable beaming; however, in comparison with Figures 9, 18, and 19, a reduced radiation intensity is indica- ted. Figures 21 through 23 show typical results obtain- ed with various shapes and positionings of both the .ZQHB2H >mob¢fi0n338 .53.. d mi 23410 OukérgJJ. 032w ramp 3.» ml; 85 -Il- IIJliIn '3' l.£|~.|§ no .hna .— :23 no Shdoigl .554 8:59.. $2.30 to we: ONE ambit» hmu» ml: U‘j Duhfibm h. 2: Us: p .353 III... at: .55 .6 an: Haiti; 5...: 35%;: £344.. htlal' mks mtz: zonw>wma hmomn. mon— <._.0 29.4? hvlnlml mhdo ; 3 e538 3253.... 5.59.... zg.xe.§la L .. wtz: 20....zw>wma .58“. mo... «.20 hmmk indicated from the test that two units would protect if placed-between l20 feet and 140 feet apart. There is a high intensity near the unit, which dr0ps off rapidly as the distance from the unit increases. Fur- ther experiment with the reflectors may make this unit more effective . 78 7. The Commercial Design: TYPO AA Uhit The primary problem.was to develop a unit that would be feasible for commercial manufacture. The three units constructed were not practical for commercial manufacture. Types A and B were too expensive, while Type 0 did not have the proper energy distribution. The constructed units were now evaluated to determine changes that could be made to cut down construction costs while still retaining effectiveness. Since the radiation intensity varies as the fourth power of the absolute temperature, it was found that the radiating surface area could be reduced to one-half of the original surface area without reducing the effective- ness if the temperature of the radiating surface were raised from 1200°F. to 15000F. This would be a major step towards reducing construction costs. Aluminised steel was tried as a heat-resistant metal for the radiating surface. The unit was then constructed with the same shape as the original Type A unit, but on a reduced scale. Figure 35 shows the cross-sectional drawing, and Figure 36 is a photograph of the unit. L. '79 I- I'—-I 8' I-\ . ‘9 a fill REFLEOTO ,0. t / ,T -.' .3. 95:55.81. 2|- 9" 8 m ’0'; , zlot—J SCALE I/2'=I' FIGURE 35. TYPE "A-A"F80$T PREVENTION UNIT FIGURE 36. TYPE AA TTHIT. 81 the field tests, the results of which.are illustra- ted in Figure 37, showed the unit to Operate satisfac- torily. The fuel consumption of ten gallons per hour is less than that of the A unit. The effective range of one unit was from sixty to seventy feet, and it was indicated that two unite would be effective if placed fron.220 feet to 240 feet apart. The tests also showed that aluminised steel would not withstand the high temperatures which.are necessary. this unit is now being manufactured commercially with stainless steel replacing aluminized steel as the radia- ting surface. 82 04 I ,4 ... ... 4 _ .., c. 4. .4 .1414 x .I EHLL» «a DEE; 00L ¢E¢fl 2055?.me QHLHnH . hm mg...“ Hm .W. «H. .% . . % uo:<5.o H t . . O a o. M ow m On m l 0' N on om . w o» 3 /1y on m [I / on u 8. . r 0.. W / o~. W on. . 4 o... m do. w... i mmhl Man 5 - . ._ bm. Mum flnliglldoglldfla a: .o». .8. o: o . o. o. 2. on 3 0. L? .3 .0. us: dd «in am a“. . %. memo. nub. .50: g 52 8 Eu» 8 us: So: SE45 8:25 cum 0 meh hmwh :23 3.59. mm... a mack us: us: Cum 5.: so 59! oz: .923 film I . .... 2:23 no 20.50.28: i... $04 m 0 Ham-m.) utjm OZ.» u42< 50qu K 02.68 NANNOZ cwzmam . 1 Smash...» .64 523 .6 8842 Jamguzso to K: . a as :3 so a: 4. ..roov: zuxfl. «02.049. mo“ 20 Jr r. A mmuzxmg ...:o...» woodwoiozd >¢Ok<¢on<4 .gzu 694 no 8.2.30 33.. - 023.92 024 >0:.30.. «“1315 29.4.. ..o 8.3 :2: 3 3.343 35:53.: .952 (.138 34: ... «c _n . mtz: zonm>wmm .58.... mo... 3.40 hmu... E. Tests Under Natural Frost Conditions The units had been tried in the field, and their relative radiation intensities determined with.a ra- diation.meter. They were now considered ready to be subjected to natural frost conditions. 20 1. Test One Units A and B were used for this test. Figure 38 shows the positioning of the units. They were plac- ed on an East-West line, with unit A being on the Nest position. The units were 130 feet apart. For this experiment plants with various degrees of resistivity to frost were selected from.the horti- culture greenhouse at Michigan State College. These plants, listed in order of increasing resistivity to frost damage, were: Coleus, tomatoes, Marigold, and Phlox Dru-nondi. The positioning of these plants were: 1. Control plants: one pot of each.variety placed 300 feet East of B unit; 2. Plants placed at ten-foot intervals between the units; 3. Plants placed on a line South of the mid-point I between the units at tenefoct intervals. Climatic conditions were ideal for radiation- type frost. The air was moderately cool, with a clear, starry sky. There was no noticeable wind. At 10:30 P.l. the temperature was 320 one inch.above the ground, and frost began to form. The readings, which were taken \ .\‘\. \“\\ ’W’” ///'/ 453é II/ N o\ \ \ - "’ ’/,. . {A . _ 1’ 3| .3I ;_sI 36 9% 53-0}90 739-” o /, t, z ‘3' 38 39 39 44 63",, ao/SQ._\ \ . .38 . / , ‘ \ \ ‘\V",/ l/ / '1. . ‘ \\ O=COLEUS IN GROUND \ \\ J ’ / » ‘ “x \ //.. / ,. ’ I. \ x. a-.- /_-/’ , x NOTE 356 MICROWATTS PER CM' PER MV FIGURE 58. DIAGRAM OF THE SET-UP FOR THE FIRST TEST UNDER NATURAL FROST CONDITIONS. all night, are given in Table I. The units were started at 10:20 P.l. and were Operated until 6:30 A.l. The data on the units are shown by Figure 39. lo effort was made to Operate the units above normal. They both heated fairly uniform- ly at about 11500F. It will be noted that Type A was burning about 14 gallons of fuel per hour, while Type B was burning about IO gallons of fuel per hour. Radiation intensities, taken at ten-foot inter- vals out to 120 feet from each unit, are given in Figure 39. There was heavy frost on the grass beyond the protected area, and the control plants were badly frost- ed to the height of sixteen inches. The potted plants on the center line between the two units were complete- ly free of frost. There was no frost on the standing vegetation for a distance of eighty feet west of the A unit. Beyond this point there was visible frost on the Phlox Drummondi, a fuzzy-leafed plant, but there was none on the larigold. From fifty feet of either unit the frost on the low-growing grass increased as the distance from.the units increased. However, there TABLE I 87 AIR Tmmmmms IR ° 1. POSITION l 2 Kidpoint 300 Feet east between of "3" unit units unprotected Time control position 10:25 P.M...............,° 34 33 103h5 ' ............... 35. 31. 11:10 ' ..............., 37.8 30.h 1:15 A.M................ 3h 28 2:15 ' .............., 3# 28, 3:15 ' ............... 3“. 27.5 uzoo I .............., 3h.1 27.3 5:35 ' ............... 33, 25.5 6:15 " ............... 31.5 26.“ 7:00 ” ............... 3h 32 (r) HrHEHflzcu Emcmrm mafimphdz mmamre. Emme EmmHm ”AWE mom t Eonb Ear k ., _ . . . . . 91 21 2. Test Two Units A and as were used for this test. The test was made late in the fall, and the temperatures were considerably lower than those from which.the agriculturist would normally have to protect his crepe. The temperature was 360 F. at sundown, and preceding this test there had been several days and nights of sub-freezing weather and the ground had been frozen to an appreciable depth. Tomato, begonia, and geranium plants used for this test were placed as illustrated by Figure 41. It will be noticed that the plants in Group I and II were placed over a blue grass sod with.grass blades to a height I of four inches, while most of the plants of Group III were sitting in Open or fallow ground that had sparsely drilled wheat growing on it. The air temperature was taken with mercury bulb thermometers at different elevations, and at widely separated points. These temperature readings are given in Table 11. However, radiation intensities were not taken during this test. Figure 42 shows the tomato plants from Group III _ [ FRESHLY DRILLED ‘ I. I‘ SMALL GRAIN , I I, I. . ‘\ .‘ “\ ~ ‘\ - I. .« I. ‘ . \ . .‘ \ \-.‘ x: a“. . 6 , ’ _, / I \ . ‘ k . ' I R.‘ . ‘ \H ‘ ‘\ I”, ’t/ / I I/ \\ « . ‘ x ‘ 20.“..1 , / /' . . ,/ p§ 0;; g 0;» .3 egg .;_ BLUE GRASS 500 «f , . ' T H. \ \ \1 \ \ ,' 3/ ' ._/ /GRO}’P -m .- . 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DIAGRAM OF THE SET-UP FOR THE SECOND TEST UNDER NATURAL FROST CONDITIONS. 93 .353» 5 3:5 .45. go 335430 08m 83.. n .umbco ummhu cu paca.sdds Mo umwmzufiom pomh oom |.N . .Aoboo umwum dH uaqs.s