ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN NARBOR CREW-SPACE HEAT TRANSFER FOR A -MEDIUM COMBAT TANK; -RAYMOiD - JE PHTILLIP- L. JACt0S.N ' RICHARDB. -,.:MOIRRPISON Project 2167 DETROIT ORDNANC. DISTRICT, U.S. ARMY CONTA'..CT _NO. DA-20-0-ORD-1 314. SPONSOR NO. DA-DOD-53-19 PROJECT NO. TT1-696 DETROIT, MICHIGAN May 1955

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ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE OF CONTENTSPage LIST OF TABLES iii LIST OF ILLUSTRATIONS v ABSTRACT vii OBJECTIVE viii NOMENCLATURE ix DEFINITIONS xi INTRODUCTION 1 PERSONNEL HEATER CHARACTERISTICS 1 THE CYLINDER ANALOGY 16 CREW-SPACE SURFACE INSULATION 18 COOLED AIR INTRODUCTION INTO TBE CREW SPACE OF THE TEST TANK 24 INSULATION AND REFRIGERATION REQUIREMENT 32 AIR CONDITIONING OF BUSES, AIRCRAFT, AND PASSENGER CARS 39 INTERCITY BUSES 39 AIRCRAFT 40 PASSENGER CARS 40 AREA OF AIR-L;EAKAGE OPENINGS IN THE ARMOR SURROUNDING THE CREW SPACE 4o CONCLUSIONS 46 TITLES CITED 49 BIBLIOGRAPHY 50 APPENDIX, ELECTRIC ANALOGS FOR COMBAT TANK HEAT TRANSFER 51 ii

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN LIST OF TABLES Page I. SPECIFICATION OF MODEL 978 PERSONNEL HEATER INSTALLED IN TEST VEHICLE 2 IIa. PERFORMANCE OF MODEL 978 HEATER IN TEST VEHICLE 3 IIb. MEASURED AIR VELOCITIES IN CREW SPACE 4 IIc. MEASURED AIR VELOCITIES IN CREW SPACE DUE TO PERSONNEL HEATER OPERATION 5 IId. MEASURED AIR VELOCITIES IN CREW SPACE DUE TO TURRETVENTILATION AIR-BLOWER OPERATION 6 IIII. CALCULATED PERSONNEL BEATER -DELIVERY AIR TEMPERATURES VERSUS BEATER-AIR FLOWRATE AND THERMAL CAPACITY 11 IV. THERMAL CHARACTERISTICS FOR STEEL AND CORK 19 V. NUMERICAL COMPUTATION OF INTERIOR SURFACE TEMPERATURES OF 4-INCH-THICK STEEL-CYLINDER ANALOGY TO CREW SPACE FOR A HEAT ADDITION OF 60,000 BTU PER HOUR 20 VI. NUMERICAL COMPUTATION OF INTERIOR SURFACE TEMPERATURES OF 1/4-INCH-THICK CORK-CYLINDER ANALOGY TO AN INSULATED CREW SPACE FOR A BEAT ADDITION zOF >60,000 BTU PER HOUR 22 VII. INTERIOR SURFACE TEMPERATURES FOR SEVERAL THICKNESSES OF CORK INSULATION ON THE CREV-SPACE ARMOR FOR A HEAT ADDITION OF 60,000 BTU PER HOUR 23 VIII. AVERAGE TEST- CONDITIONS, AIR-CYCLE REFRIGERATION UNIT DISCHARGING COOLED AIR INTO CREW SPACE OF TEST COMBAT TANK 30 IX. AVERAGE TEST-CONDITIONS, AIR-CYCLE REFRIGERATION UNIT DISCHARGING COOLED AIR INTO CREW SPACE OF TEST COMBAT TANK 31 i ii -

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN LIST OF TABLES (continued) Page X. MINIMUM AND MAXIMUM AIR VELOCITIES (FPM)I MEASURED DURING COMBAT TANK CREW-SPACE COOLING TESTS 32 XI. COMBAT.TANK rCREW-SPACE REFRIGERATION CAPACITY REQUIRED DUE TO LOSSES THROUGH TEE ARMOR FOR SEVERAL THICKNESSES OF INSULATION 3 XII. AIR-LEAKAGE TEST CONDITIONS 42 XIII. EXPERIMENTAL DATA, CREW-SPACE LEAKAGE AREA TESTS 43 XIV. INSTRUMENTS AND EQUIPMENT USED IN EXPERIMENTS 44 iv

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN LIST OF ILLUSTRATIONS Figure Page 1. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, +40~F. 12 2. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, O0~F 13 35 Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, -400F. 14 4. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, -700F. 15 5. Calculated personnel heater fuel consumption vs heater output, Btu per hour. 17 6. Conventional air-cycle expansion system. 28 7. Turbine-fan operation for air-cycle cooling system, 28 8. Air-cycle cooling system used to cool combat tank crew space. 29 9. Thermodynamic process for air-cooling system used to cool combat tank crew space. 29 10. Combined coefficient hcc for convection and radiation from flat insulated surfaces in a room at 700F; assumed e = 0.90. 34 11. Total refrigeration requirement for a combat tank as a function of crew-space air leakage and insulation thickness. 37 12. Total refrigeration requirement for a combat tank as a function of insulation thickness and crew-space air leakage. 38 13. Air flow into crew space vs;AP/p. 47

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN LIST OF ILLUSTRATIONS (continued) Figure Page 14. Schematic of a metal box as a thermal analog of a combat tank. 52 15. First electric analog for body heat transfer of tank crew member. 54 16. Thermal idealization of human body. 54 17. Second electric analog for body heat transfer of tank crew member. 55 18. Electric analog for crew-space heat transfer. 56 19o Electric analog for heat flow to crew space due to main power plant operation. 57 Photograph 1. Mock-up of air-cycle refrigeration unit mounted on test vehicle. 26 2. Air-cycle refrigeration unit mounted in steel box. 27 vi

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN ABSTRACT.The literature covering physiological effects due to changes in the quality and quantity of air supplied to enclosed living spaces is extensive. There is some agreement concerning the desirability for control of some or all the common -environmental variables: temperature, pressure, humidity, velocity, distribution, and impurities. It is known that there are upper and lower limits of environmental conditions under which men are able to perform certain work, or to perform efficiently. A combat tank crew is subject to these limitations. This report. is concerned with the temperature and velocity parameters for the crew space of a medium combat tank subjected to extreme atmospheric temperatures. Effects due to design changes involving crew-space heat addition, heat subtraction, and air delivery rate are considered. A minimum heat addition of.60,000 Btu per hour is required for crew space heating. The use of crew-space insulation, reduction of air leakage, and superior warm-air distribution throughout the-crew space adds to heating effectiveness. Temperature differentials across the uninsulated armor are usually less than 20F. For no crew-space air leakage a minimum of 5-1/2 tons of refrigeration is required to maintain the crew-space ambient at 800F for most adverse atmosphere conditions. One-quarter-inch thickness of insulation, thermal conductivity of 0.04 Btu per (ft)(hr)(~F), applied to the crew-space surfaces reduces the requirement to 2-1/2 tons. An experimental method for finding the total leakage area of. a buttoned-down combat tank is described. -For the tank tested this total leakage area is 27 square inches. Air velocity in the crew space due to heater operation, except in the region. 1 to 2 feet from the Cheater -outlet, is less than 15 fpm. Air velocity in the crew space due to turret-ventilation-blower operation ranges from 35 to 450 fpm in the turret-basket region and from 13 to 45 fpm in the driver region. A description is given of electric analogs representing heat transfers for the crew -space of medium combat tanks. 'vii

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN OBJECTIVE The objective of this project was to determine the feasibility of ventilating and heating, or ventilating and cooling, the crew compartment of a medium combat tank in environments characterized by extreme temperatures. The upper limit of environmental temperature anticipated by the project is 120~F and the lower limit is -30~F. The possibility of controlling temperature in the main engine compartment was also to be studied, and an estimate was to be made of the practicability of attaining all the above objectives through the design of a universal package system which could be fitted to all tanks without the necessity for redesign. viii

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN NOMENCLATURE A area, square feet A2 area of leakage openings in-armor surrounding tank crew, square feet Btu British thermal unit -c specific heat at constant pressure, Btu/(lb)(OF) C1 air leakage coefficient, C1 = 60 A2ig C armor leakage coefficient, C = 294 A2 cfm cubic feet per minute e vapor- pressure, feet of- water F gasoline consumption rate, TU.S. gallons per hour F' emissivity factor fpm feet per minute g acceleration due to gravity, 32.2 ft/(sec2) or 4.18 x 108 ft/(hr2) G solar.radiation, Btu/(ft2)(hr) h film coefficient for heat transfer, Btu/(hr)(ft2)(~F) H head, feet H' thermal -heating value, Btu/lb k thermal conductivity, Btu/ (hr) (ft2) (~F/ft) 1, L, X a thickness dimension, feet m' flowrate, pounds per minute mt" flowrate, pounds per hour M a dimensionless modulus mph miles per hour n some numbfer, dimensionless P pressure, pounds per square foot psf pounds per squre foot q heat flowrate, Btu/hr q' heat flowrate, Btu/(hr)(ft2) Q' rate of temperature change per time increment due to heat addition, ~F/. r ratio-of surface area to volume of a material, l/ft R gas constant, ft-b/(lb/)(~R) R thermal resistance,, = L/kA rpm revolutions per minute t temperature, degrees Fahrenheit t t' hheater air inlet temperature, ~F tft theater -delivery air -temperature, 0F T temperature, degrees Rankine U over-all heat.-transfer coeffi'c. ient, Btu/(hr)(ft2)(~F) ix

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN NOMENCLATURE.(continued V velocity, feet per second w specific weight, pounds per U.S. gallon W flowrate, cubic feet -per minute thermal diffusivity, A = k/pc, ft2/hr thermal coefficient of expansion, 1/0F 4P' pressure difference, inches CH30H AP pressure difference, pounds per- square foot At temperature difference, degrees Fahrenheit AT temperature difference, degrees Rankine AX thickness increment, feet O time, hours NA time increment, hours e emissivity, dimensionless ratio T1 thermal efficiency, dimensionless IJ~ absolute -viscosity, lb-/(hr)(ft) p density, pounds per cubic foot a Stefan - Boltzmann constant, a = 0.173 x 108 Btu/(hr)(ft )(~R4) Subscript Notation 1, 2 reference points a amb ient A.atmosphere b human body c convection cc combined coefficient cl clothing e engine compartment h.heater i interior is insulation surface o exterior p armor plate r, R radiation t crew compartment v evaporation x skin Script notation in Appendix, used to emphasize fluid as opposed to solid conditions.

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN DEFINITIONS| Buttoned-dtown tank The- combat tank with all hatches closed Crew space Volume within the combat tank provided for crew Equation of state P = pRT Exterior Remote location from viewpoint of:combat tank crew member in crew space Heater thermal efficiency Ratio of net heat delivered to warm air stream and heating value of gasoline used Insulation A material having low thermal- conductivity Interior Near location from viewpoint of combat tank crew member in crew space Radiation absorptivity Fraction of impinging radiation which is absorbed directly Radiation emissivity Ratio of total radiating power. of a nonb-lack sur-| face to that of a black surface at same temperature Radiation reflectivity Ratio,of reflected to incident -radiation xi

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN INTRODUCTION Provisions for operation of a combat tank in atmospheric temperatures ranging from 1200 to -65~F should enable the tank personnel to act efficiently throughout-this climatic temperature range. This investigation deals with temperature and heat-flow parameters of concern to the tank personnel for the given range of atmospheric temperatures. An M-47 medium combat tank, Designation USA 30169766 (DE-29), was used for experimental study. PERSONNEL -HEATER CHARACTERISTICS The M-47 combat tank is equipped with one personnel air heater of the combustion type which uses gasoline-air fuel. Air to be heated enters the heater from the-crew space, is heated, and discharges from heater ducts in the region of the feet of the driver and the feet of the machine gunner. A fan is an integral part of the heater. Combustion air enters the heater from the crew space and exhaust products are dumped overboard. The manufacturer's specification for the personnel heater unit installed in the vehicle tested is tabulated in.Table I. The heating effects produced by this heater were investigated and the test data are given in Table IIa, b, and c. For each test, crew-space temperatures were permitted to reach steady values by letting the unbuttoned vehicle stand. The vehicle then was buttoned down and crew-space air temperatures and velocities were recorded. The personnel heater then was started and operated until.steady crew-space temperature readings were again obtained and recorded, Crew-space air velocities then were measured and recorded. Iron-constantan thermocouples and a recording potentiometer were used to measure air temperatures and a hotwire anemometer was used to measure air velocities. The instruments are listed in Table XIV. All temperature and velocity measurements were made in

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN the region of each crew member approximately at face level, A temperature differential not greater than 7~F and averaging less than 5~F was observed for the heated air discharged from the two outlet ducts and an average is reported. TABLE I SPECIFICATION OF MODEL 978 PERSONNMEL HEATER INSTALLED -IN TEST 'VEHICLZE Fuel -consumption (gal/hr approx.) high heat 0.25 low heat 0.125 Heat output (Btu/hr fresh air) high heat 20,000 low heat 10,000 Heat input (total Btu/hr) high heat 30,000 low heat 11 340 Air temperature rise, ~F high heat 220 Fresh heated air delivery (cfm) 85 Electrical consumption (watts) 24v 12v 6v Start 264 144 75 Run 60 60o 60 Physical size, overall Weight, pounds 23 Height, inches 9-3/4 Length, inches 18-1/2 Width, inches 8-1/4 Installation space, cubic feet 0.859 Starting time (normal voltage ) 10 seconds Starting time at -65~F 30-45 seconds 2..

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE - IIa PERFORMANCE OF MODEL 978 HIEATER IN TEST VEHICLE (All heater operation on "high fire-*") Test Number A B C Date 1-27-55 1-31-55 2-11-55 Duration, hours 1 1 3 Vehicle storage prior to test In Bldg. 7 In Bldg. 7 Outdoors 6 hr prior to test Atmosphere temperature, OF 38-53 65 16-19 Tank and gun position, facing East East South Hatch position for -test -Buttoned Buttoned Buttoned Auxiliary engine operation Operating Operating Operating Main engine operation No No No Avg. turret temp, ~F, start 63 65 40 stop 79 84 57 rise 16 19 17 Avg. driver, machine gunner Temperature, OF, start 61 65 30 stop 110 103 76 rise 49 38 46 Avig. heater-duct outlet temp., ~F 272 269 * Avg. temp. rise, heater and duct, ~F 166 167 * Heat addition, Btu/hr 14,200 14,500 U. Btu/(hr )(f t2) (oF) 1.97 1.7 *No reading due to thermocouple failure.

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABTLE IIb MEASURED AIR VELOCITIES IN CREW SPACE (Tests A, B and C) Air Velocity, fpm Location -Prior to Operation With Heater of- Heater Operating Driver 0 - 21 (8) 10 - 31 (17)* Machine gunner 0 - 15 (7) 12 - 15 (13) Loader 0 - 12 (3) 0 - 20 (12) Commander 0 - 10 (3) 0 - 12 (5) Gunner 0 - 14 (7) 14 - 40 (19) Heater outlet duct, driver side -1000 Brackets enclose, average of velocity readings.

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE IIc MEASURED AIR VELOCITIES IN CREW SPACE DUE TO PERSONNEL -EATER OPERATION Test Conditions: Buttoned-down tank indoors with gun pointed forward between driver -and machine-gunner cockpits; observer in crew space; observations made December-7, 1954, using hot-wire, anemometer; all heater operation on"'thigh fire."' Location __ Air Velocity, Air Velocity, Location of fpm (No Heater fpm (Heater Hot;-Wire Anemometer Probe:Operation) Operation) 1 Air into heater, 12 inches upstream 180 2 Air from heater, 12 -inches from outlet duct 15 360 3 6 inches from wall, 16 inches above loader's seat 12 14 4 Diametrically opposed to (3) above 13 15 5 16 inches above top edge of rebound pad, rear of turret basket -12 14 -6 12 inches above shell rack forward of loader's seat 12 17 7 Symmetrical to (6), referred to longitudinal plane 15 16 8 6 inches above driver's seat 12 23 9 6 inches above machine gunner's seat 12 18 - -- -~ ~ -5

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE IId MEASURED AIR VELOCITIES IN CREW SPACE DUE TO TURRET-VENTILATION AIR-BLOWER OPERATION Test Conditions: Buttoned-down tank indoors with gun pointed forward between driver and machine-gunner cockpits; observer in crew space; observations made December 7, 1954, using hot-wire anemometer. Location of Hot- Air Velocity, fpm Wire Anemometer Beneath Rear of Beneath Central Probe below Upper Loader's Gun Commander's Driver Interior surface, Hatch Breech Hatch Cockpit in. 6 50-90 -75 -130 30-45 12 50-70 -200 150-200 -13 18 40-100 100-120 70-100 -25 24 -35 150-240 -150 -20 30 35-L00 150-400 -150 -20 36 50-90 -450 50-60 40 _-300 44 50-100.....6

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN Heater- and duct-installed performance is calculated from temperature data of Table IIa based on the assumption that the heated air delivery equals the manufacturer's rated 85 cfm. For Test A, Table IIa, the heat addition to the crew space due to heater operation is qh = 60p We Ath (1) = 60(0.07)(85)(0.241)(272 - 110) = 13,900 Btu/hr. With the assumption that the total surface area surrounding the crew space is 450 square feet (see pages 16-18 for discussion of this area) and noting that a steady-state temperature condition exists, the over-all heat-transfer coefficient U is found based on the average temperature of the turret-basket region: qt = U At(tt tA); (2) 13,900 - U(450)(79 - 53) and U = 1.2 Btu/(hr)(ft2) ( F ) For Test A, Equation (2) may be rewritten qt -= 1.2(450)(tt - tA) = 540(tt - tA)- (2a) Using data of Test B, Table IIa, similar calculations yield qh.=.14,600 Btu/hr; U = 1.7 Btu/(hr ) (ft2) ( ~F ), and qt -= 765(tt - tA)'

ENGINEERING RESEARCH INSTITUTE *~ UNIVERSITY OF MICHIGAN A reasonable assumption is that for the turret-basket region of the uninsulated combat tank crew space, the heater-duct installation, and practical heat addition to the crew space, the values for U and UA fall in the range 1 < U < 2, and (3) 450 < UA < 900, and the average for Tests A and B, Table IIa, is approximately at the midpoint of the extremess. If the average steady-state heated-air temperatures of the driver and machine-gunner region (listed in Table IIa) are used instead of the average turret-basket region heated-air temperatures, and the same assumptions are made, values of U approximately one half of those calculated are obtained and the corresponding temperature rises for the driver and machine-gunner region are approximately double those calculated. The method is available for estimation of the crew-space temperature rise due to a given known heat addition. As an example, suppose consideration is given to installation of a 60,000-Btu-per-hour heater to replace the rated 20,000-Btu-per-hour heater tested in the vehicle. With the expression qt = 1.5(450)(tt - tA) = 675(tt - tA), the predicted temperature rise of the turret-basket region due to operation of the 60,000-Btu-per-hour heater is tt - tA = 60,000 890~F 675 For the above assumption, if the heater installed in the test vehicle actually added the rated 20,000 Btu per hr to the heated-air stream, the predicted temperature rise in the turret-basket region of the crew space approaches 30~F. Crew-space temperature rises due to a fixed heat addition, wit-ch the test combat tank located in a fixed atmosphere, vary with-heater location, the number, location, and direction of warm-air discharge ducts, air discharge

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN velocity from the duct, and the location and area of air-leakage openings in the armor surrounding the crew space. The method of warm-air -distribution in the crew space is an important heating factor. The difference between the average air temperature of the turret-basket region and the average air temperature of the driver and machine-gunner region (Table IIa) indicates that the heater-duct installation tested does not produce uniform warm-air distribution throughout the crew space. This is not surprising when it is noted (Table IIb) that at face level the average warm-air motion when the test heater is in operation is always less than 20 fpm and usually less than 15 fpm. By inference from the quotation which follows, which refers to air distribution for an occupied zone, an average warm-air movement less than 15 fpm is not satisfactory: "With reference to permissible room air motion it is not possible to establish a specific standard covering the entire complex problem of air distribution. Velocities less than 15 fpm generally, cause a feeling of air stagnation, whereas velocities higher than 65 fpm will disturb loose paper sheets on desks and may result in a sensation of draft. Air velocities of 25 to 35 fpm in the occupied zone are most satisfactory, but air motion of 20 to 50 fpm will usually be acceptable, particularly when the lower part of this range of velocity is used in cooling applications, and-the higher values on heating jobs. In any case, it is certain that the effect of room air motion on comfort or discomfort depends on air temperature and direction as well as on velocity."1 Although unit-heater warm-air discharge velocities usually vary from about 400 to 2,500 fpm, depending on a number of factors including the distance (blow) the discharged air is to be projected, the presence of obstacles to air motion in the crew space of a combat tank leads to the assumption that an increase in heater warm-air discharge velocity will not solve the air-distribution problem. Provision of additional well-located warm-air outlets is the solution. Equation (1) is useful in the comparison of heater parameters when it is written t" = t, +.60pWc (la) Equation (la) permits calculation of heater-air discharge temperature for fixed heater-air entry temperature, fixed heat addition to the freshair stream through the heater, and known fresh-air flowrate. Data from calculations for a range of heat additions, air flowrates and for fixed heater

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN ambient air-entry temperatures of 40~, 0, -400, and -700F are listed in Table III and shown in Figures 1, 2, 3, and 4, These data illustrate the sensitive relation between -heater-air delivery temperature and heater-air flow for low-air flows. Figures 1 through 4 are useful only if the air-discharge temperature for a heater of given capacity is known. The heater manufacturer usually lists the air-temperature rise for a given heat addition to the fresh-air stream corresponding to fixed fresh-air-stream flowrate. Usually, the specification does not include either the heater entrance or discharge temperatures of the fresh-air stream. These air temperatures may be found by use of Equation (1) and the state equation where p is evaluated for the heater entrance condition th 1 = 60c W, (1) P i\ h / and with the state equation t = O W - 460o By approximation, the air.pressure at the heater entrance is taken as standard atmosphere pressure (2116 psf) and for air the previous expression reduces to t' = 574 W-h) 46o. (4) \ qh also t" = Ath + t'. (5) Two objections are anticipated to the selection of a combat tank heater installation having higher performance than that of the heater installation tested. The objections are the physical size of the heater and its fuel consumption rate. The first objection is a design consideration. Fuel consumption rate, however, for a combustion-type air heater may be estimated by F = (6) w H' 10

TABLE III m CALCULATED PERSONNEL HEATER-DELIVERY AIR EMPERARS Z VERSUS HEATER-AIR FLOWRATTE AND THERMAL CAPACITY Fresh- Fresh- Heater-Air Discharge Temperatures, 0F, for Fixed Heat Addition, Heater-Air Air Flow Air Flow. —. Btu per Hour. Entry through through Temp., ~F Heater Heater. cfm No./hr 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 10,000 +40 100 477 214 301 388 475 200 954 127 170 214 258 302 344 388 431 Z 400 1908 83 105 127 149 170 192 213 236 247 H 600 2862 69 83 98 112 127 141 156 171 185 0 1006 160 241 321 401 482 200 1032 80 120 161 201 241 281 321 361 401 400 2064 40 60 80 100 120 140 160 180 200 600 3096 27 40 53 67 80 94 107 121 134 m -40 100 567 106 179 252 325 396 200 1134 33 70 106 143 180 216 253 289 325 -~ 400 2268 -4 15 33 51 70 88 106 124 142 600 3402 -16 -3 9 21 33 45 58 70 82 O -70 100 611 66 134 202 270 338 395 200 1222 -2 32 66 100 134 168 202 236 270 f% 400 2443 -36 -19 -2 15 32 49 66 83 100 600 3665 -47 -36 -25 -13 -2 9 20 32 43

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN 320 280 LL 240 0 uLJ W 200 w cz BTU/HR 160 _J w 0 100 200 300 400 500 600 AIR~ FLOW THROUGH HEATER, CFM Figure 1. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, +40~F. 12

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN 320 280 240! 200 rL w cr 160 -J 80 40 0 100 200 300 400 500 600 AIR FLOW THROUGH HEATER, CFM Figure 2. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, O~F. 13

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN 320 300 280 260 240 220 0 W m 200 w 180 0. w 1 160 140 w > 120 -J w 80 0 Po 60 ~ 40 20 0 100 200 300 400 500 600 AIR FLOW THROUGH HEATER, CFM Figure 3. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, -40~F. 14

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN 320 280 240 LIJ 200 <~ OLOE >- 80 0 w 120 -- 80 40 CCB 40. 0 100 200 300 400 500 600 AIR FLOW THROUGH HEATERCFM Figure 4I. Calculated personnel heater-delivery air temperature vs heater air capacity and heat-release rate; heater ambient air temperature, -70~F. 15

ENGINEERING RESEARCH INSTITUTE ' UNIVERSITY OF MICHIGAN From Table: I, l1 = 0.66 for the heater installed in the test combat tank, based on the high heat-release rate and the higher heating value for gasoline. If ( oI = 0.66) is assumed, for gasoline, Equation (6) becomes F = 0.125(10-4)qh (6a) Equation (6a) is plotted in Figure 5. If a gasoline consumption rate up to one gallon per hour is admissible, any heater having up to 80,000 Btu per hour heat release may be considered. THE CYLINDER ANALOGY A problem in the- estimation of the heat flow for the crew space of a combat tank is the identification of the surface area concerned. The surfaces surrounding the crew space vary in surface finish, roughness, and in thickness which varies from 1 to 7 inches. The armored surfaces may be plane or curved, with orientation and curvature varying irregularly with respect to- the horizontal and vertical planes. Interior and exterior surface environments may vary from point to point due to the physical dimensions of the combat tank. Suppose then that for heat-transfer-purposes the complex surface design surrounding the crew space is considered as a simple shape, the thermal characteristics of which can be evaluated In the absence of the combat tank bustle and forward control space, the crew space approaches the shape of a vertical cylinder. For heat-transfer purposes, therefore, it is assumed that the combat tank crew space is analogous to a vertical cylinder, the height of which is equivalent to the combat tank dimension from the hull floor to the turret deck, and the diameter of which corresponds to the maximumn turret dimension seen in plan view, and including the bustle projection if any. The dimensions of the analogous vertical cylinder are taken as equivalent to the flat surface area required to -endlose all the hull and the turret-basket space utilized for crew space. For the M-48 combat tank, the pertinent dimensions are2 height, hull floor to turret deck, 90 inches turret, maximum plan-view dimension, 132 inches 16 -

., e~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'' 2.0 < z 1 t 5 ' 0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PME-N48E(2 HEATER S) z -1 -z _ _ _ _ l 10 U-' 0 rlLILii ~~~M-47(lHEATER) "0.z Il II__ _ _ ' __I 20 40 60 80 100 120 140 160 " PERSONNEL HEATER OUTPUT) BTU / HR X I0' Figure 5. Calculated personnel heater fuel consumption vs heater output, Btu per hour. z

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN The dimensions of the analogous cylinder are height, 7-1/2 feet -diameter, 11 feet. Total cylinder surface area is 450 square feet, the vertical walls are 260 square feet in area, and each of the end plates have an area of 95 square feet. CREW-SPACE SURFACE INSULATION For given heat addition and other conditions fixed, the application of insulation to the armor surrounding the crew space causes an increased crew-space ambient air temperature and a rise in armor temperature. Due to the exchange of heat by radiation between the body of the crew member and the surrounding armor surfaces, the temperature of these surfaces is of considerable importance to comfort. Interior crew-space surface-temperature evaluation for fixed heat addition of both the noninsulated and the insulated case is required for any study of the usefulness of crew-space surface insulation. The effect of insulation on crew-space armor temperature is investigated by means of the analogous cylinder idealization, where the cylinder is airtight and constructed of 4-inch-thick armor plate. A heat source is located within the cylinder so that the heat density is applied uniformly over the inner surface. Atmospheric conditions external to the cylinder are fixed and no wind effects are considered. For such assumptions the heat flow -is one-dimensional, with a heat source at the inner surface and a constant temperature at the outer surface. A method of numerical heat flow analysis outlined by Dusinberres is followed. The development of numerical heat-transfer procedures is lengthy and will not be treated in detail as the reader may consult the reference text. The general -approach is that if the tmperature at each surface of a homogeneous body remains uniform over the entire surface and changes with time, and if at the initial time temperatures within the body are known, at any subsequent time the body temperatures can be approximated by: (a) Dividing the body into Tr imaginary laminae of equal thickness AX. Any value may be chosen for q but the greater the value the greater the accuracy of this method. (b) Temperatures t, t0, t1..., tp at the boundaries of these imaginary 18

ENGINEERING RESEARCH INSTITUTE: UNIVERSITY OF MICHIGAN laminae are determined at equal successive time intervals AQ, where the value of A- is k V) (7) (c) Known initial body temperatures are inserted in -a body-temperature — time-increment table for AG = 0 hour. Successive body temperatures are determined for every time interval 4A from an average of preceding adjacent body temperatures where the averaging method is governed by the selection-of the modulus M, In the general case, the time dimension attached to the first few numerical cycles is not a valid approximation. Suppose that consideration is given to the fixed heat addition to the analogous cylinder of 60,000 Btu per hour for the -case where insulation is present and for the case where no crew-space surface insulation is used. Any insulation may be selected for the comparison but to accentuate differenceS an insulation with excellent thermal qualities is chosen. Cork is such an insulation and is chosen for the comparison. The cork insulation is not proposed for actual application to the combat tank, since a number -of factors in addition to the thermal characteristics of the insulation require examination. Thermal characteristics for the steel armor and the cork insulation are listed in Table IV. TABLE IV THERMAL CHARACTERISTICS FOR STEEL AND CORK Nomenclature Symbol Steel Cork Dimensions Thermal conductivity k 25 0.0208 Btu/(hr) (ft2) (~F/ft) Specific heat c O.13 o.485 Btu/(lb)(0F) Density p 490 10 lb/ft3 Thermal diffusivity a 0392 0.0,043 ft2a/hr cp 63.6 4.85 Btu/(ft3)(0F) 19

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN CASE 1. The analogous cylinder, 4-inch-thick steel walls, and no insulation, a heat source of 60,000 Btu per hour is located within the cylinder. For this case, g = oo = 133 Btu/(hr)(ft2) 450 Choosing M = 3 and AX = 4 inches = 1/3 foot, then in,201 @ -= - -c 9(0*392)3 = 0.0942 hour, r = 2(450) 6 ft2/ft3, and 1/3(450) Q' r= r (j) 133(6) (0*0942) = 1.18oF/AQ. =p....63.6 Since the outer surface of the cylinder is constant, it is necessary to calculate only the inner surface temperature ti. With the atmospheric temperature as datum, the; numerical computation is given in Table V. TABLE V NUMERICAL CONUTATION OF INTERIOR SURFACE TEMPERATURES OF 4-INCH-THIdK STEEL-CYLINDER ANALOGY TO CREW SPACE FOR A HEAT ADDITION OF 60,000 BTU PER HOUR, No. of Time Interior No of Tnterior Time Cycles Increment, Surface Temp, Time Cycles Increment, Surface Temp, 0 hjr- ti ~F @Q hr ti ~F O 0 0 4 0.377 1.75 1.18 0o.58 1*18 20

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE V (continued.) No. of Time Interior No of Time InteriorTime Cycles Increment, Surface Temp, Time Cycles Increment, Surface Temp, - Ghr t ~F Qhr. ti F 1 0.094 1.18 5 0.471 1.76 0.*37 0*59 1,.18 1.*18 2 0.188 1.55 6 0.*565 1.77 0.52 0.59 1.18 1.18 3 0.283 1.70 7 0. 659 1.77 0.57 1.18 The numerical computation of Table V demonstrates that with a heat source of 60,000.Btu per hour located in the interior. of the 4-inch wall thickness, uninsulated steel cylinder, the teperature -.of the inside surface of the cylinder rises only 1.770F above the atmospheric datum in a time period of 0.565 hour or 34 minutes. This computation for -the analogy to the uninsulated armor surrounding the crew space indicates that with a 60,000-Btu-perhour-heatadadition to the crew space, uninsulated cold. armor surrounding the crew space remains cold. Since the armor is not effective as a heat-flow barrier, the thermal effect of the cork insulation on the crew-space armor surfaces is approximated by consideration of the analogous cylinder composed of the cork insulation only. CASE 2. The analogous cylinder, 1/4-inch-thick cork walls, and no steel armor; heat source of.60,000.Btu per hour is located within the cylinder. For this case, q' = 133 Btu/(hr)(ft2). 21

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN Choosing M = 53 and AX = 1/4 inch = 1/48 foot, then AG = 0.05537 hour r = 96 ft2/fts, and Q, -= 88.80F/A@. With atmospheric temperature as datumn, the numerical computation follows in Table VI. TABLE VI NUMERICAL COMPUTATIQON 0F INTERIOR SURFACE T:MPERATUES OCF 1/4-INCH-THICK CORK-CYIJNDER ANALOGY: TO AN -INSULATED CREW SPACE FOR A HEAT:ADDITIONOF 60, 000.:BTU PER' HOUR No. of Time Interior No. of Time Interior Time Cycles Incrent, Sface Te, ementy, Surfacece Temp, Q hr t. ~F Q hr ti OF 0 0 0 5 0.169 132.3 88.8 44.1 88.8 1.0034 88.8 6 0.202 132.9 29.6 44-3 88 &. 88.8 2 0.067 118.4 7 0.236 133.1 39-5. 44,4 88.8 88.8 3 0.101 128.3 8 0.270 133.2 42.8 44.4 88.8 88.8 22

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY. OF MICHIGAN TABLE VI (continued) Time Cycles Increment, Surface Temp, Time Cycles Increment, Surface Temp, 0 hr.ti ~F 0 hr ti ~F I-;.... 4 0.135 131.6 9 0.303 133.2 43.5 88:.8 The numerical computation of-Table VI indicates that with a heat source of 60,000 Btu per hour located in the interior space of the analogous cork cylinder having 1/4-inch-thick cork walls, the temperature of the inside surface of the cork cylinder risues 1330F above the atmospheric datum in 0.27.hour or 16 minutes. With an atmospheric ambient temperature-of -65~F, the interior surface of the cork cylinder rises: to a temperature of +68QF. This computation for the analogy to the -case of- the amor surrounding the crew space, where the armor is insulated with a 1/4-inch thickness of cork, is in contrast to Casel (Table V) and removes any doubt concerning the desirability of insulated crew-space armor* Data from additional numerical computations are given in Table VII for several thicknesses of cork insulation and a heat addition of 60,000 Btu per hour. TABLE VII INTERIOR SURFACE TEPERATURES FOR SEVERAL THICKESSES OF CORK INSULATION ON THE CREW-SPACE ARMOR FOR A HEAT ADDITION OF 6o;00o-BTU PER HOUR Cork Wall Interior iW-1- Interior Walli Thickness, Surface Temp Surface Temp for..in.; Rise, ~F.a -650F A.0sphere 1/32 16.7 -48.3 1/16 33.3 -31*7 1/8 66*7 + 2.7 1/4 133.2 +68.2 23

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN The numerical computation method.do.-es not consider.any exchange of air.between the atmosphere and the interior of the analogous cylinder and so it is not possible to obtain all the predicted temperature rises in the combat tank where an air exchange exists between the crew space and the atmosphere. To obtain every.adantage from insulation on the armor surrounding the crew space, unplanned air exchange between the combat tank crew space and the atmosphere should be minimized. InsulatiOn may be attached either to one or both surfaces of the armor surrounding the crew space. For insulation on the crew space surface side (on the interior surface of the.vehicle) the temperature of the armor mass approaches the atmospheric temperature. Neglecting radiation effects and where the absorptivity.of the insulation surface equals the absorptivity of the armor surface, for insulation on the atmospheric side of the armor, the temperature of the armor approaches the crew-space air temperature. These observations are based on the readily demonstrable fact that only a small temperature differential.may -occur across a steel wall. A principal thermal effect due to attachment of insulation on the armor surface facing the atmosphere is that a time delay is introduced in the achievement of the near steady-state condition due to the heat flow to or from the armor mass. A greater time is required to heat the crew space to a given temperature level, and a longer time is required to cool the -crew space to a given level, as compared to placement of insulation on the interior or crew-space -armor surface. The time parameters of the numerical computations, Tables V and VI, are indicative that the time delay is not great and for a crew-space heat addition of 60,000 Btu per hour this lag probably is less than 1 hour. From the thermal viewpoint, where radiation effects are neglected, as both the steel armor surface and the insulation surface are subject to similar surface treatment, placement of given insulation on the interior armor surface, the exterior armor surface, or on both surfaces, produces almost equivalent results. While the observation is beyond the scope of this report, it has been suggested that placement of insulation on the atmospheric surface of the armor, with consequent armor heating for any crew-space heat addition, conceivable -.could result in reduced armor embrittlement at low atmospheric temperatures. The observation may have significance. COOLED AIR:TINTRODUCTION INTO THE CREW SPACE OF THE TEST TANK -To obtain -some heat-flow data. for the crew space.of the testc tank, refrigerated air was introduced into the crew space. Air introduction time,

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN atmospheric temperature and pressure, armor surface and crew-space air temperatures, solar radiation, cooling-air flow, air-cycle turbine air temperature, and pressure drop all-ere measured using instrunentation indicated in Table XIV. The refrigerator unit was mounted in a steel box which was set on top of the test-vehicle turret bustle as shown in the test mock-up in Photograph 1. The air-cycle refrigeration unit mounted in the box, with the box cover plate removed, appears in Photograph 2. The test procedure began with "buttoning" the test vehicle and measurement of initial conditions. Cooled air then was introduced into the crew space:and at time intervals the test parameters were measured and recorded. Because of the availability of -both an air-cycle expansion turbine and a source of compressed air, the air-cycle cooling unit was used to supply cooled air to the crew space of the combat tank. 'The air inlet of the aireycle turbine was connected to the laboratory high-pressure air supply so that -inlet air pressure to the turbine could be controlled by means of a pressure reducing valve* Discharge air from the air-cycle turbine was ducted into the combat tank crew space through an opening in a steel plate covering the opening in the tank bustle remaining after the turret ventilation blower was removed. The cooled-air delivery hose was of fiber, 4 inches in diameter, and was about 1 foot in length so as to limit thermal losses. The aircraft-type air-cycle refrigeration unit was manufactured by AiReseaxch Manufacturing Company of Los Angeles, and is identified as follows: Drawing No. - 52021-150 Type - Turbine Assembly No. - 52022-150 Order Serial - 9-104 Patent No. - 2,398,655 The above designation was submitted to the manufacturer to obtain performance data, but since the unit is an old model, no data were obtained. Measured turbine and fan diameters are 2*125 and 2.75 inches, respectively. -The overall length of the air-cycle unit approximates 8 inches, and the width about 7 inches. Total unit weight is 6 pounds. No heat exchanger was obtained with this unit. Air-cycle- refrigeration uses a Brayton cycle except that the directions of the processes are reversed. The necessary processes are: (a) an air compression, (b) reduction of the heat of compression, usually by means of a heat exchanger, and

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ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN (c) an expansion of the air by means of a turbine or other expansion device. All three processes are requirements. Figure 6 'is a schematic drawing of a conventional air-cycle cooling system where listed values are typical. Figure 7 illustrates turbine-fan operation and typical data. Figure 8 is a schematic drawing of the system used to supply cooled air to the crew space of the test vehicle, together with some typical performance numbers. Note that the heat exchanger requirement is supplied by storage bottle surface. Figure 9 shows the thermodynamic process for the air-cycle system which is shown in Figure 8 and used in the cooling tests. 15 PSIA. 30 PSIA EXCHANGER 30 PSIA 16 PSIA 900 F I 1 240 OF 140 OF WORK. HEAT Figure 6b Conventional air-cycle expansion system. 2 < 30 PSIA PA c"I E CR COOL AIR I\ I - - AIR TO._>:JWORK ATMOSPHERE TURBINE -FAN Figure 7 Turbine-an operationfor air-cycle cooling system.

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN MULTISTAGE STORAGE PRESSURE z ~15 PSIA | P ~SI- I 000 PSIA VALVE 30 PSIA 16 PSIA 90~ 90~ goo 900 -100 WORK HEAT LOSS TO ATMOSPHERE FROM STORAGE BOTTLE SURFACE Figure 8. Air-cycle cooling system used to cool combat tank crew space. HEAT HEAT EXCHANGER EXCHANGER COMPRESSION EXPANS ION COMPRESSION (WORK IN) (WORK) (WORK IN) k OUT EXPANSION WORK) W O I / ~ -OUT - TEMPERATURE IN TEMPERATURE OUT S V Figure 9. Thermodynamic process for air.cooling system used to cool combat tank crew space. The noise intensity of the air-cycle unit used in the cooling tests was high and probably would not be tolerated in the field,. No noise-intensity measurements were made since lower speed and less noisy air-cycle units are available-. In the cooling tests, the refrigeration effect was varied from about 1/2 to 1-1/2 tons with free air flows ranging from 90 to 145 efm. Atmospheric temperatures varied from 680 to 840F and solar inputs varied as listed in Table IX. Mixing of the cooled air made it practical to reduce test data to average values:which are tabulated in Tables VIII, IX, and X. The largest refrigeration effect produced by the cooling system (1-1/2 tons) did not comfortably cool the uninsulated crew space Qf the test vehicle. The largest crew-space average anient temperature drop was 180F and there was a small 29

m z rn TABLE VIII AVERAGE TEST -CONDITIONS, AIR-CYCLE REFRIGERATION UNIT. DISCHARGING COOLED AIR INTO CREW SPACE OF TEST COMBAT: TANK 4 6~~~~~~~~~6 Test- Number ' 1 3 4 5 6 7 8 9 m ), Date 7-23-54 8-6-54 8-9-54 8-11-54 8-12-54 8-13-54 8-18-T4 8-20-54 8-26-54 Time, Start 15:40 13:08 12:50 15:55 14:00 13:18 14:05 14:40 15:57: Stop 15:52 16:30 16:00 16:50 16: 30 15:10 14:48 15:50 16:10 Duration, hr andmin. 0-12 5-05 3-10 2-5 2-50 -1-52 0-43 -50 0-1 - Refrigeration, tons 0,54 0.685.956 1.16 i.34 1 43 1.47 1.57 1.5 Refrigeration, Btu/hr 6480 8220 11,472 13,920 7,160 17,600 18,800 17,940 - Air flow, lb/min 6.69 6.91 8.19 9-.0 10.01 10.05 10.67 10.81 105 Free air flow, ft3/min 90 92 109 120 133 134 142 144 138 Exterior armor temp, 0F, start 86 93 88 80 87 89 72 90 90 c stop 85 89 85 78 83 91 7 90 84 Interior armor temp, ~F, start 86 92 86 79 86 87 71 91 89 < stop 83 88 82 76 81 89 71 89 78 Crew-space air temp., 0FO start 79 83 78 74 76 78 68 86 79 stop 74 71 64 63 58 66 53 72 65 Crew-space air temp drop, ~F 5 12 14 11 18 12 15 14 14 Atmospheric temp., F, start - 84 8 68 77 77 68 86 74 P ~~~ ~~~~~77 77 6 67 stop -- 80 79 72 77 79 71 8 7 777 z

TABLE IX ~ ~ ~ ~ ~ ~ AVEAGETET ~ONITINS AI:,y L'RFRIMU 'O'UIT-ISHARIz COOLED AIR 'INTO CPIEW SPACE OF TEST'..C.OMBAT VEHICLE~~~~~~~~~~C~ Test Nwaber~~ 1., 2 3 4 6. T 8. ~~ Solar radiation (br) (ft2)~~ Meter~~aime at sun'rABL I36X10 2 28 8 1 'Metervertial 66 1 5o 8 11.0 6 74 z AVErhriznaGE TETC.63TOS AR-YL RERIERTIN 7N3 ISCH3GIN TL~bin prssrato.-WO 1 4 283*27 3 - 376 376 8 96

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN (l-50F) change in armor temperature, probably due mainly- to change in atmospheric conditions The- mini and maximum cooling-air velocities in the crew space are reported in Table X and were believed to be too high for comfort It -is noted that the test air velocities usually exceed the 20-fpm cooling-air velocity recommended in Reference 1, page 9 of this report. TABLE X MINIMUM AND MAXIMUM AIR VELOCITIES (FPM) MEASURED DURING COMBAT TANK CREW-SPACE COOLING TESTS* Test Number 2 5 6 8 COmmnander -region, face 25-50 20-120 5-85 waist 20-45 - 16-150 120-400 50-55 knee 25 -65 18-65 10-130 20.-25 Gunner region, face 15-30 17-200 45-100 10-13 waist 20-50 15-80 45-100 20-28 knee 15-30 16-80 25 -60 15-22 Loader region, face 30-55 38-200 30-100 20-45 waist 60-95 26-1530 80-250 14-20-.knee 85 -130.30-100 70-120 20-35 Driver region, face 10-20 15-40 10-60 25-30 waist 10-17 15-25 18-25 14-18 knee 10-19 15-35 16-20 18-25 Machine gunner region, face 10-30 18-35 22-50 18-28 waist 10-15 15-24 17-27 16-19 knee 10-21 15-20 15-22 15-21 Air velocity measurements made only for the cooling tests reported in table. INSULATION AND REFRIGERATION REQUIREMENT Colburn and Hougen4 demonstrated that for either —natural convection or for forced convection where the velocities are low, the film coefficient of convection for gases heated on vertical plates is defined-by 32

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN hc 0.128 (ks p c B g [At0/3 / (8) Griffiths and. Davis5 found that the film coefficient for horizontal plates facing upward is about 27 percent higher than for vertical plates; and for horizontalplates facing downward, about:33 percent lower. The combined. coefficient for convection and radiation from flat or.cylindrical surfaces in-a room is given by he 2= h + e hr. (9) The expressiohr of Colbn and Hougen and. the findings of Griffiths and Davis may be used - to calculate the film coefficient -of convection for heated.vertical and-horizontal flat.surfaces located in a -space having a given air temperature. If the surfaces are insulated with insulation of known emissivity, then the combined coefficient 3 may be found usi hcc hc + Ehr'.c = he +-hr This.was.done for an assumed insulation emissivity of 09 and - for heated surfaces located in a room, or space where the air temperature is 70OF.e Data from these calcuations are given in Figure 10. The combined coefficient is a function of the temperature of the free surface of the insuilation, but for practical purposes useful values of the combined. cooeffficient may be obtained by assuming a reasonable surface temperature. More accurate.predictions for. the surface temperature then are obtained by -trial-and-error solution. Average temperature of the insulation is assumed as the arithmetic average of the insulated. s:urface and the room air temperatures:. For vertical cylindrical -surfaces of large radius compared to surface thickness, the values of the -combined coefficient almost agree with values calculated for the vertical flat plate -For flat surfaces the rate of the heat loss through insulation is k A(tis - ta) (10) 33

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN 3.01_ _ _ _ 2.8 2.6 2.4 2.2 2.0 I0 1.. 1.6 I.6 0 100 200 300 SURFACE TEMPERATURE, OF Figure 10. Combined coefficient hcc for convection and radiation from flat insulated surfaces in a room at 700F; assumed ~ = 0.90. 34

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN The cylinder analogy will -be;used to calculate the refrigeration re quirement -of a combat tank and the effect -of insulation thickness on the refrigeration requirement for the initial condition of elevated armor temperature accompanied by high atmospheric temperature. -Limited observation and the literature concerned with high temperature- conitions suggest that armor termperatures of the order -of 150OF are not unreasonable -The calculations are based on this armor temerate of l50~F which is assumed to exist -due to solar radiation when the atmospheric temperature is 120Fi. The desired crewspace temperature is taken to be 80~F'. When insulation is considered, the calculations are -for insulation on the crew side of the armor. Insulation of fair quality is considered for which a typical value of thermal conductivity is used as follows: taverage = 100F, k = 0039 Btu/(hr)(ft2) (F/ft) = 2009F, k = 0-041, Based on the outlined considerations, the refrigeration requirement, due to heat loss through the armor surrounding the crew space of a combat tank, has been calculated as a function:-of insulation thickness.* The data of the calculations are listed in Table XM and shown in Figures 11 and 12. TAB: XI COMBAT TANK CREW-SPACE REFRIGERATION CAPACITY REQUIRED DUE TO LOSSES THROUGH THE ARMOR FOR SEVERALI THICKNESSES- OF INSULATION k - 0.04 Btu/(hr)(ft2)(~F/ft) for atmospheric temperature = 1200F armor surface temperature - 150F crew-space air temperature = 80~F REFRIGERATION REQUIRWMENT DUE TO LOSSES TBROUGH ALL SURFACES SIRROUNDING CREW SPACE Insulation Heat Flow Refrigeration. of Zero Thickness, q, Capacity, Insulation in. Btu/hr Ton Load 0 64,900 5. 4 100 1/32 55,3Qo00 4 85 1/16 48,800 41.1 75 1/8 40,300 3.*4 62 1/4 29,000 2.4 45 1/2 19,200 1.6 30 '35.

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE XI (continued) DSTRIUTINON OF HEAT LOSSES THROUGH THE ARMOR STIOUNDING 'THE CREW SPACE A. Losses for Deck Surface and Turret Deck Region Insulation Heat Flow Heat Flow Refrigeration % of Thicknes, q' q, Capacity Total Armor in.- Bt (h.r) (ft Btu/br Ton Loss O 124 11,800 0.98 17.6 1/32 108 10,300 0.86 18.6 1/16 97 9,240 0.77 18.8 1/8 80 7,650 0.64 19.0 1/4 61 5.,760 0.48 19.9 1/2 41 5,880 0.32 20.2 B. Losses for Hull and Turret Side-Wall Armor 0 145 37,700 3.14 58.:3 1/32 123 32,000 2.68 58.1 1/16 109 28,300 2.36 58.1 1/8 91 23,600 1.97 58.6 1/4 64 16,700 1.39 57.6 1/2 43 11,100 0.92 57.7 C Losses for Hull Armor Facing the Ground O 162 15,400 1.28 23.9 1/32 137 13,000 1.08 23.4 1/16 119 11,300 0.94 23.1 1/8 95 9,050 0-.75 22.4 1/4 68 6,500 0.54 22.5 1/2 45 4,240 0.35 22,1 The refrigeration capacity required due to heat loss through the armor is not the entire refrigeration requirement. An additional load is introduced due to. leakage, The maximum air'leakage occurs when the tlurret ventilation blower is operating at maximum capacity, which for the test tank is 1500 cfm. Total refrigeration requirement may include capacity accounting 3,6

12: m'l ~ I ATMOSPHERE AMBIENT TEMPERATURE-1200F INITIAL INTERIOR ARMOR SURFACE TEMP. - 150~F REFRIGERATED CREW-SPACE TEMP.- 800F Im I I I I I z 900 CFM =1 LL OZ CW z Z 0 16 8 4 2 INSULATION THICKNESS, IN. Figure 11. Total refrigeration requirement for a combat tank as a Z function of crew-space air leakage and insulation thickness.

12 1 r r I~~~ I I z-I~ I I (TEMPERATURE STATES, SAME AS FIGURE II) m 10o - Iz m m 8 ~ " Z z~~~~~~~~~~~~~ 0 I W6 \4-I oC)_ CD s _x m n- r b_ LiL w z m 2 0 I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l 0 2 4 6 8 0 o 12 14 16 18 CREW-SPACE AIR LEAKAGE - FT3/MIN' 10 Figure 12. Total refrigeration requirement for a combat tank as a Z function of insulation thickness and crew-space air leakage.

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN for this air leakage - However, for- a crew space having a cooled-air introducti on the turret ventilation blower probably operates only infrequently, perhaps only to expel -gun fumes. Refr-igeration capacities equivalent to convective air-leakage rates of 1500, 900, and 300 cfm are added to the zero-leakage refrigeration requireme-nt; these oerall refrigeration requirents also are shown in Figures 11 ~and 12. For the 400~F air temperature differene, -(120-80), the refrigeration capacity to account for air-leakage rates of 1500, 900, and 300 cfm is about 5, 3, and i tons, respectively. AIR CONDITIONING OF BUSES, AIRCRAFT, 7 AND PASSENGER CARS An outline of some -current air-conditioning practices in the transportation field follows, as such -pratices may be copared to pre-dicted combat tank cooling requirements. IETERCITY -BUSES The capacity -of the average refrigeration system in an intercity bus is about 4 tons. This capacity usually is sufficient to maintain an inside condition of 780F dry-bulb temperature, and 67~F wet-bulb- temperature, when the atmospheric condition is 95~F dry-bulb and 78F wet-bulb temperature. Bus cooling requirements are minimized by reduction of air infiltration and the ue of body insulation. Heat-absorbing glass is used to reduce the solar radiation load. Outer surfaces of window shades and the exterior surfaces of the vehicle arretreated to obtain high reflectivity. A typical 55-foot-long intercity bus with a surface area approximately 1250 square feet weighss about 20,000 pounds,, of which 1200 pounds represent air-conditioning equipment. -Mechanical compression, usually with Freon-l2 as the refrigeras the commonly used system. The refrigeration compressor is driven either by the main propulsion or an auxiliary engine. The auxiliary engine, for a 4-ton refrigeration capacity, develops about 20 brake horsepower at 2000 rpm. About 10 cfm of fresh air per passenger is introduced into the bus. The air introdction maintains a small.pressre within the vehicle so that only air letakage out of the vehicle body occur-s. -No exhaust-air openings are provided. Cooled-air distribution throughout the passenger space is accom39

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN plished by the use of perforated ceiling ducts; there are no return-air ducts. The air-conditioning controls are simple and as few as possible, to reduce nonoperation due to control failure'. AIRCRAFT In aircraft, refrigeration capacities vary fromabout 1 ton for the fighter airplane with -a cockpit volime of 40 to: 60 cubic feet up to about 10 tons for commercial pressurized aircraft having some 6000 cubic feet of cabin volume. Satisfactory airliner ~cabin air conditions are 73~ to 75~F dry -bulb temperature, a relative humidity of 50 percent, an air movement of 15 to 25 fpm about the passengerts body, and no heat loss or gain frome the- body to the surrounding surfaces. PASSENGER CARS Air conditioning in passenger cars is a recent development. Main engine powered mechanical compression with Freon-12 as the refrigerant is the common system, Total weight of the system is about 200 pounds and the installed cost approximates $500Q*,.~ Typical data are:8 dar speed, mph 20 40 60 dompressor, rpm 1090 2185 3280 Aefrigeration dffect, Btu/hr 13,750 25,250 33,000 ~tefrigeration effect, ton 1.1 2.1 2.7 AREA OF AIR-LEAKAGE OPENINGS IN HE ARMOR SURR0ING -TIE CRIEW SPACE Thermal losses occur for the crew space of a combat tank due to convective air flow through openings in the armor surrounding the crew space. The magnitude of such losses may be estimated only after the area of leakage is known. If the area of air leakage is large, in the case of crew-space could have important military significane.i For these reasons, it is important that the area of the air-leakage openings in the armor surronding the crew space of the combat tank be known, Direct measurement of the areas of the several small openings is 40

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN difficult and probably not accurate. An indirect approach is made where a known air flow is introduced into the buttoned-down crew space of the test vehicle through an opening in a steel plate covering the well remaining after removal of the turret air ventilation blower. Subsequent to the establishment of a steady-state condition for the known air introduction, the air pressure difference was measured between the crew space and the atmosphere and pressure and temperature parameters so that air densities may be calculated. Actual parameters measured for each test point were: atmospheric temperature and pressure, air pressure difference between crew space and atmosphere, average air temperature in crew space, and air introduction parameters including (a) ASME orifice air pressure, (b) ASME orifice differential air pressure, and (c) air temperature. The test apparatus and instrumentation are listed in Table XIV, and test conditions for each test are given in Table XII. The calculations are based on consideration of the Bernoulli equation Pi + en = P2 + e2Va1 where subscript (1) denotes air conditions within the crew space, and subscript (2) refers to conditions immediately downstream of the air-leakage opening. If the assumption is made that the air velocity within the crew space approaches zero, then Equation (11) reduces to V2 = (P1 - P2) - 2g 4 (11a) P2 Pa But m' = 6o pA2 V (12) and m' = 60 A2 JP4217 AP; m" = CJ2.- (13)

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE XII AIR-LEAKAGE.TEST CONDITIONS.Test Conditions Common to All Tests Vehicle location Test vehicle standing in the open, east of Building Number 8-1/2, Willow Run Airport, Ypsilanti, Michigan. Vehicle orientation Driver cockpit and main gun facing north. Vehicle condition Turret -ventilation blower removed and well-capped with a steel plate. All hatches buttoned-down, canvas cover of gun muzzle and gun breech shroud in position. Air supply Air from high-pressure storage flows through a pressure reducing and regulating valve and then through as ASMEE-type calibrated square-edge flat plate measuring orifice.: Air then flows either to the aircycle refrigeration-unit and into the crew space through an entry in the steel cap on the well of the air ventilation blower or directly from the orifice to the entry in this cap. Test Conditions Particular to Tests Tests 1 and 2 Test 3 Test 4 Test 5 Air supplied to Similar to tests Similar to Test 3 Air directly into air-cycle turf' 1 and 2 except except that main crew space; no bine sitting on that air-filter engine operating air-cycle: refrigturret bustle- passages between at idle speed.- eration unit; no a-d discharged crew space and. measured by ve- engines operating; -from turbine. i'n- engine space hicle tachometer. air-filter pas,;to crew space, open. sages between crew::main and auxili- space and engine ary engines not space closed. operating; air filter passages between crew space and engine!space blocked. 42

T A B L E X I I I E X P E R I ME N T A L D A T A, C R E W - S P A C E LEAKAGE A R E A T E S T S Z Crew- Orifice Crew- C' Corrected Crew Space Cre-Oicerw-) Corrected Crew Space Space Orifice Orifice Pressure Orifice Crew-Space Space Ap Atmospheric to Time Pre e Atmosphhi tAir Air Air Drop Air Flow Average Air Air (Ap\1 2 C C Z Pr e Atoph Pressure Temperature, Pressure, AP', m', W Temperature, Density?p 2 rr9 PA,2 Aft2 Pi, ~R psia in. lb/min, cfm OR P, s in, lb/ftb/ft lb/ft2 CH3(O) lb/ft 3 Z Test No. 1, October 8, 1954 C 15.50 - Start test 15.55 2083 0.140 2083 509 30.47 0.35 6.67 82.3 510 0.077 1.35 66.1 32.4 16.00 2083 0.312 2083 505 47.67 0.56 8.95 117.2 507 0.077 2.01 57.8 28.3 16.05 2084 0.51 2083 501 59.27 0.68 11.08 145 504 0.077 2.56 54.3 26.6 16.10 - Stop test Test No. 2, October 1i, 1954 I 13.20 - Start test 13.26 2048 0.078 2048 528 24.02 0.25 4.14 54.1 528 0.073 1.03 54.5 26.7 13.31 2048 0.187 2048 524 34.42 0.43 6.59 86.1 526 0.073 1.6 57.2 28.0 Z 13.36 2048 0.328 2048 521 46.62 0.59 8.96 117.3 523 0.074 2.21 57.4 28.1 13.37 - Stop test Test No. 3, October 11, 1954 13.50 - Start test m 13.55 2112 0.094 2112 525 25.12 0.26 4.41 57.6 527 0.075 1.12 52.3 25.6 14.00 2112 0.166 2112 523 34.12 o.4 6.4 83.6 526 0.075 1.49 57.1 28.0 14.05 2111 0.296 2111 521 43.91 0.49 7.93 103.8 525 0.076 1.98 52.8 25.9 14.06 - Stop test Test No. 4, October ll, 1954 Z 14.18 - Start test < 14.25 2111 0.281 2111 524 24.31 0.26 4.3 56.6 530 0.075 1.94 29.6 14.5 14.30 2111 0.354 2111 522 33.31 0.4 6.25 82.2 529 0.075 2.17 38.1 18.7 14.35 2111 0.477 2111 520 44.66 0.55 8.48 114 529 0.075 2.52 43.8 21.4 14.36 - Stop test (Main engine idle speed set at 1200 rpm at 14.18; at 14.37 main engine speed was 1500 rpm.) Test No. 5, October 13, 1954 Q 15.53 - Start test 15.58 2069 1.45 2068 518 25.6 3.7 16.6 217 535 0.073 4.45 52.5 25.7 16.03 2069 3.09 2066 508 35.6 5.4 24 313 532 0.073 6.5 50.3 24.6 16.08 2069 5.77 2063 506 46.8 9.0 38.6 505 529 0.073 8.87 59.5 29.1 16.13 2069 8.88 2060 505 64.3 11.5 45 588 528 0.073 11.0 56.0 27.4 16.18 2069 11.53 2057 503 70.3 13.8 54 710 526 0.073 12.6 54.8 26.8 16.19 - Stop test. (Air supply check showed an additional point could be run.) 16.21 - Start test Z 16.26 2069 15.15 2054 505 78.8 15.7 61 796 526 0.073 14.4 58.1 28.5 16.27 - Stop test

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE XIV INSTRUMENTS AND EQUIPMENT USED IN EXPERIMENTS 1. M-47 combat tank, Designation USA 30169766 (DE-29). 2. Brown electronik temperlature recorder; 16 points; Model No. 153X(67)P16-X-(106)A4K; Serial No. 746819, range, -150~ to 200~F in 2~F subdivisions. 3. Brown electronik temperature recorder; 16 points; Model No,.153X62P16 -X-13; Serial No. 568497; range, 0~0 to 350OF in 2'F subdivisions. 4. Mercury-filled thermometers; range, 0~ to 220~F in 2~F subdivisions, Cenco Cat. No. 19297. 5. Toluol-filled thermometers; range, -100~ to 50iC in 1C -subdivisions; Cenco Cat. No..19370. 6. 24-gauge, polyvinyl, insulated, double-conductor, iron-constantan wire; M-H Cat. No. 9B3N4. 7. Laboratory-type mercury-filled barometer for measurement of atmospheric air pressure; Cenco Cat. No. 76890. 8. Meriam inclined manometer, calibrated in 0.001 inch of water; Serial No. 47B253; Model A-763. This instrument used to determine air pressure difference between crew space and atmosphere. 9. ASME-type flat plate orifice, calibrated by A. Weir, Jr.9 The orifice was used to measure:the air -flow -into the crew space of the tank. 10. Vacuum-thermocouple type radiation meter, calibrated in O.to 2 gramcalories per square centimeter per minute; Cenco Cat. No. 81085. Instrument.used to measure solar radiation. Il. Hot-wire anemometer; Type 8500; Serial No. TA-387; manufactured by Illinois Testing Laboratories; dual range: 5 to 300 fpm and 70 to 2000 fpm. Instrument used to measure air movement. 12. Air-cycle xrefrigeration unit, Assembly No. 52022-150; Serial No. 9-104; manufactured by Ai;Research Manufacturing Company. Equipment used to obtain cooled.air for introduction into.crew space. 44

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE XIV (continued) 15. Miscellaneous instruments and equipment include a high-pressure airstorage facility along with nitrogen-controlled air-pressure regulating valves, manometers, pressure and temperature gauges. 14. A Brown recorder and gas-welded iron-constantan thermocouples suspended in air were used to measure crew-space -air temperatures. Thermometers were used as a check. 15. Armor surface temperatures were measured with equipment similar to (14) above except that the thermocouples were fastened to the surface with a mixture of powdered copped metal DuPont Duco cement. No attempt was made to remove surface finish or oxidation. Equation (13) may be rewritten: W = c - ' (14) With reference to Equation (13), if m' and 4p27 aare determined by experiment, the constant C, is known and the air stream area immediately deownstream of the leakage opening is C-1 A2 6o0 The air stream area is related to the area of the leakage openings in the armor -by assuming that the openings are sharp-edged orifices for which the air stream vena contracta.effect is known. The cross-sectional area of a contracted air stream flowing from a sharp-edged orifice is about 0.62 of the- sharp-edged orifice area and the average air 'velocity in the contracted stream section is about 0.9912g AP/p2. Equation (13), for these values, reduces to nm' = 294 A2 Jp C =, (13a) and Equation (14) becomes 45

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN W = 294A2 / = C. (14ka) - P2 - P2 The area of the openings in the armor surrounding the crew space is:A2 i= (15) 294 ' A graph of Equation (13a) or of Equation (14a) is a straight line with slope C. The-air density P2 was assumed to correspond to air density Pj in the experimental work. The experimental data of Table XIII were used to plot Figure 13. The armor leakage coefficient C.determined from Figure 13 is C = 56, and by Equation (15), A2 _ 27 square inches. The area A2. may be used to estimate the heat loss due to convective air leakage from the crew space of the b-uttoned-down combat tank when the personnel heater is in operation.. The maximum heat loss by convective air leakage occurs when air leakage from the crew space leaves at highest velocity and temperature. Data from -Test A, Table IIa, are used as an example. -Highest crew-spaee ambient.temperature recorded in Test A is 1100F, atmospheric temperature is 530~F and the highest crew-space air.velocity is 40 fpm. Using these data, the A2 value, and standard atmospheric pressure in the crew. space, the heat loss from the crew space due to convective air leak-age is 430 Btu per hour. CONCLUSIONS 1. Operation -of the personnel heater.installed in the test vehicle results in a 160 to 190F temperature rise in the turret-basket region of the crew space and a 38~ to 490F temperature rise in the cockpit regions. The air velocity of the personnel heater outlet duct approximates 1000 fpm. Dur - ing heater-operation the air velocity in the cockpit region was up to 31 fpm and usually less than 20 fpm.in the turret-basket region. 2, During heater operation the distribution of the warmed air throughout the-crew space is not uniform as indicated by the air temperature variation and low air velocities recorded in Tables Ha, b, and c. 46

10~~1r CGRAPH 5 8 -C~ ~ 019FT227.41IN.2O UL 06~~~~~~~~~~~~~ P 1/2 ~ ~ ~ ~ ~ * (/)~~~~~~~~~~HADI T U~~~~~~Fgr 3 i o noce pc sA/

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN 3. Heater performande as installed in the test tank is approxi;mated -by the expressions: qt = 675(tt - tA), t' = 574 - 460, and tl' = t' + Ath. 4. Personnel heater fuel consumption in U.S. gallons per hour: is approximated by the expression F = 0.125(10) -4qh. If the maximum allowable fuel consumption is 1 gallon per hour, a heater with thermal capcity up to 80,000 Btu per hour may be used. 5* The total of the leakage openings in the buttoned-down test combat tank is 27 square inches. The expression W = 56AP/p predicts the air-leakage rate through these openings. For one test, the heat loss by convection through the openings was 430 Btu per hour. 6. A heat addition of 60,000 Btu per hour in the crew -space results in a calculated maximum temperature rise for the noninsulated.armor surface surrounding the crew space of less than 20F. In the absence of winds and other -thermal -effects, the 20F temperature rise occurs in 34 minutes. 7. In the case of insulated. armor, where the insulation is 1/4 -inch-thick cork:on the interior armor surface, a heat addition of 60,000 Btu per hour to the crew-space results in a calculated maximum temperature rise for the exposed cork.urface of 133F*- In the absence of winds and other thermal effbcts this temperature is reached in 16 minutes. 8. The crew-space cooling tests in which up to 1-1/2 tons of refrigeration effect were obtained and -up to 145 cfm of cooled air were introduced into the crew space through a single opening in the turret bustle, produced a maximum crew-space temperature drop of 18~F with turret-basket air velocities..up to 250 fpm and.air.velocities in the cockpit-of 10 to 50 fpm. These maximum conditions did not give condlitions satisfactory for body comfort due to nonuniform cooled air distribution and the high (over 50 fpln) crew-space air velocities. 9. At atmospheric conditions near the upper limit obtained in practice, and for an air-leakage rate from the crew space of 300 cfm, 6-1/2 tons

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN of refrigeration are required to maintain an 800F crew-space ambient. For the same conditions, 3-1/2 tons of refrigeration effect are required to maintain the 80~F crew-space ambient when 1/4 inch of insulation [k = 0.04 Btu/(hr)(ft2)(~F/ft)] is applied to the crew-space armor. 10. Insulation is thermally effective when placed on either surface of the crew-space armor. Insulation on the exterior surface of the armor introduces a time lag for both heating and cooling in a cold atmosphere. Insulation on the exterior-armor surface, when the insulation has a reflectivity greater than that of the armor, assists crew-space cooling when solar radiation is an. important thermal load. T.TIT CITED 1. "Heating Ventilating Air Conditioning:Guide 1953", ASHVE, 31, pp. 661 -662, (1953). 2. Technical Manual TM9-718B, 904-Mm Gun Tank T-48, Department of the Army, pp. 8, 9, 14, 339 (August, 1952). 3. Dusinberre, G. M,, Numerical Analysis of Heat Flow, First Edition, McGraw-Hill, New York, pp. 212-215, 1949. 4. Colburn, A. P. and Hougen, 0. A., Ind. Eng. Chem., 22, 522 (1930). 5. Griffiths, E. and Davis, A. H., "The Transmission of Heat by Radiation and Convection", Special Report 9, Department of Scientific and Industrial Research, H. M. Stationery Office, London, 1922. 6. Stoever, H. J,J* Applied Heat Transmission, First Edition, McGraw-Hill, New York, p. 200, 1941. 7. Refrigeration Data Book, Applications Volume, ASRE, Fourth Edition, Section VII, Chapters 55 and 57, 1952. 8. Catalog No. 162, The Harry Alter Company, Inc., Chicago, pp. 82-73, 1955. 9. Weir, A., Jr.,"Two- and Three-Dimensional Flow of Air Through SquareEdged Sonic Orifices", Ph..D. Dissertation, University of Michigan, 1954. 49

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN BIBLIOGRAPHY 1. Anderson, D. B., "Heat Loss Studies in Four Identical Buildings to Determine the Effect Of Insulation", ASHVE Trans., 48, 471 (1942). 2. Blockley, W. V. and Taylor, C. L., 'Human: Tolerance Limits for Extreme Heat", Heating Piping and Air Conditioning (May, 1949). 3. Brunt, Da, "Radiation in the Atmosphere" Supplement to Quart(.-J. Roy. Meteor. Soc., 66 (1940). 4. Carrier, W. H., Cherne, R. E., and Grant, W. A., Modern Air Conditioning, Heating and;Ventilating, Pitman, 1940. 5. Cartwright, K., "Passenger Car Cooling Methods", Refrigerating Engineering, p. 83 (February, 1936), and. p. 158 (March, 1936). 6. De Rosa, G. P., 'Development and. Testing of Heater-Ventilator, GasolineBurning, for Reproduction Vans", ASTIA No. 77031,. December 8, 1949. 7. Eckert, E. R. G., Introduction to the Transfer of Heat and Mass, McGrawHill, New York, 1950. 8. Jakob, Max, Heat Transfer, John Wiley and Sons, Vol. l, 1949. 9. Jakob, Max, Elements of Heat Transfer and. Insulation., John Wiley and Sons, New York, 1942* 1Q. Lovelace, W. R, et al., "Pulmonary Ventilation of Flyers", Department of Commerce, PB 5128. 11. Linsenmeyer, F. J., "Problems in Air -Conditioning Automobiles", SAE Journal, July,.1939. 12. McAdams, W. H., Heat Transmission, McGraw-Hill, New York,, 1950. 13. Mallinckrodt, A. J. and Hanson, L., "Bus Air Conditioning", Refrigerating Engineering, p. 388, (June, 1929). 14. Messinger, B. L., "Refrigeration for Air Conditioning Pressurized Transport Aircraft", Heating and Ventilating, p. 63, (January, 1946). 15. Norris, R. H. and Streid, D. D., Laminar-Flow Heat-Transfer Coefficients for Ducts, Trans. ASME, 62, No. 6, 525 (August, 1940). ~ _ _~ ~ ~ 5

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN 16. Paschkis, V., '"Method for Determining Unsteady-State Heat Transfer by Means of Electrical Analogy", Trans. ASME, 64, 105, (1942). 17. Parmelee, G. V. and Huebscher, R. G., Forced Convection Heat Transfer from Flat Surfaces, ASHVE:Trans., 53, 245 (1947). 18. Simonson, E. T., "German Refrigeration Industry", ASTIA No. 59620, pp. 22-23, June 7, 1945. 19. Scofield, P. C., "'Air Cycle Refrigeration", Refrigerating Engineering, 57, No. 6, 558, (June, 1949). 20. Todd, E. T. and Gadd, F. 0., "Bus Heating", Heating and Ventilating, p. 83 (December, 1946). 21. Tribus, M., "Elementary Heat Transfer", University of California Press, Revised Edition, 1950. 22. "Human and Space Engineering Study Based on Tank 90 Mm Gun, T42", Parts Four and Five, H. L.. Yoh.Company, Inc., Detroit Arsenal Contract No. DA20-089-ORD-35558, April, 1953. APPENDIX ELECTRIC ANALOGS FOR COMBAT TANK HEAT TRANSFER No application is made in this report of an electrical analogy for combat tank heat flow, but preliminary consideration was given to this area and is reported. The analogs were prepared in consultation with Dr. Myron Tribus, visiting Assistant Professor of Chemi.cal Engineering and Director of Icing Research, 1952-1954, University of Michigan; now Associate Professor, University of California, Los Angeles. A combat tank is visualized as a metal container having walls of variour thicknesses and. orientations. The crew space and. the:engine space are considered to be adjacent subcontainers, as in Figure 14. Consider the case where the crew space is cooled and the armor facing the crew is colder than human body tempDerature. The temperature state is maintained by refrigeration. 51

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN G.. pi _ ~ ~ ~ ~ ~ ~.A CREW MEMBER Figure 14. Schematic of a metal-box as a thermal analog of a combat tank. The possible ways for heat transfer to occur are: (a) radiation - sun to tank armor, etc., (b) re-radiation - from armor- to earth, surroundings and space, (c) conduction - flow through the armor, (d) convection - transport through openings, (e) radiation, conduction and convection from main power plant, (f) radiation, conduction and convection from auxiliary equipment and instrumentation, (g) radiation and convection from human body to the armor, and (h) evaporation of human body perspiration. The general forms of the equations representing the transfers are: conduction: q = k At; (16) convection: q = hc A At; and (17) radiation: q = 6c A AT4. (18) The equation for heat flow due to radiation may be expressed as q = hrF' A At. (19) 52...

ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN For a refrigerated crew space where the armor facing the crew is:colder than human body temperature, the radiation from the human body to the interior armor plate- surface is qR = hr Ab (tb tPi).(20) The average body surface area of a human adult male usually is taken at somewhat less than 20 square feet (19.6). The radiation — coefficient for the human-body is assumed to be 0.9 < hr < 1.2. Cooling due to -evaporation of human body perspiration is expressed by hb AL (eb - et), (21) and for the resistance concept of conductive heat transfer W;V = k At At (22) L' L/7kA R= Then RC ~ (17a) RR q 2tL"'.b... L- %. A(23) hbt AL.,- et

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN By virtue of Equations (17a, 19a, and 23), a crude electrical analog representing the heat transfer concerned with the human body in the crew space of a combat tank is shown in Figure 15. tp z t 0 ~z 1 o o -I Figure 15. First electric analog for body heat transfer of tank crew member. Heat flow for the "body circuit" of Figure 15 due to convection and radiation could proceed in either direction, but the heat flow from the;human body due to the evaporative process must result in body cooling. A more sophisticated ' ody circuit" is obtained by consideration of an idealization of the human body shown in Figure 16. Figure 16. Thermal idealization of human body. When the idealization of the human body of Figure 16 is surrounded by the combat tank crew space, the human 'body circuit" could appear as shown in Figure 17.

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN METABOLIC INPUT tb 0 O 0 _ Z O o z z 0 03 tx 0 _ _ _ 0o z 0 tcyi _j z "' Figure 17. Scom.nd electric analog for body heat t ranser of tank crew member.

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN INPUT FROM AUXILIARY EQUIPMENT INPUT FROM CREW BODIES INPUT FROM MAIN POWER PLANT INPUT DUE TO SOLAR RADIATION THROUGH WINDOWS AND OPENINGS-a G SOLAR CONVECTION RADIATION ARMOR RE- RADIATION TO REFRIGERATION CONDUCTION SURROU N DINGS creT4 'm1. 'n ATMOSPHERIC AMBIENT 1 AIR z. AIR LEAKAGE Figure 1 Eectric analg for rew-spa hat transer. Fiur.8 Elcti anlo fo rwsaeharnfr U. on~~5

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN concerns heat addition to the crew space due to passage of heated air from the engine conrpartment to the crew space via openings. The heat addition is q = mfc (te - tt). (24) In the electric analogy, the resistance representing the air leakage in question is proportional to l/m~tc, The electric analogy for the heat input to the combat tank crew space due to the main power plant is given in Figure 19. w w w WW 4Z o Z Q~5ZZ OZ _ 0 0. rrcr. uaot__ 4W 4c1) zW- W C.) WW LJ Z4 WZ 0 1Z wW 0 zo> W 0 C)4 C cr ZI.-C. ZCI)~~~~~~~~~~~M 0 r0 O W Lz- Z0L U M. N T D T 0 U1 - C3 main poe ln oeain OI O -Z 3, te (4a. 0 a. 0 0 0~ INPUT TO CREW SPACE DUE TO MAIN ENGINE OPERATION Figure 19. Electric analog for heat flow to crew-space due to main -power plant - operation. An analytic solution of the heat transfer for the crew space of a combat tank for even one set of conditions is a tedious operation. An electric analog of the heat flow permits ready solution of both the transient and steady-state conditions for any given problem. The analog circuits may be adapted for several combat tank designs. The complexity of the required circuits is a function of the degree of accuracy demanded. The major he-at flows may be found by ignoring circuits representing comparatively low-valued heat transfers. Circuits which may be neglected are determined by comparison of calculated or feasible maximum values.

UNIVERSITY OF MICHIGAN 3 0502519 6687