WADC TR 58-405 THE UNIVERSITY OF MICHIGAN RESEARCH INSTITUTE ANN ARBOR, MICHIGAN Technical Report THERMAL CONDUCTIVITY OF LUBRICATING OILS AND HYDRAULIC FLUIDS D. W. McCready UMRI Project 2510 UNITED STATES AIR FORCE AIR RESEARCH AND DEVELOPMENT COMMAND WRIGHT AIR DEVELOPMENT CENTER CONTRACT NO. AF 33(616)-3543 WRIGHT!-PATTERSON AIR FORCE BASE, OHIO October 1958

FOREWORD This report was prepared by The University of Michigan Research Institute under USAF Contract No. AF 33(616)-3543. This contract was initiated under Project No. 7360, "Materials Analysis and Evaluation Techniques," Task No. 73603, "Thermodynamics and Heat Transfer." It was administered under the direction of the Materials Laboratory, Directorate of Laboratories, Wright Air Development Center, with Mr. Hyman Marcus acting as project engineer. The principal investigator was D. W. McCready, who was assisted by Edward Heyman and Gerald E. Patow. This report covers work conducted from 1 April 1956 to 31 March 1957, WADC TR 58-405

ABSTRACT An all-metal concentric cylinder type of thermal conductivity cell was designed, fabricated, and calibrated to measure the thermal conductivity of fifteen natural and synthetic base lubricating fluids. Thermal conductivity values in the temperature range of from 70 to 5000F are reported for fluids considered stable to the higher temperature. The maximum temperatures for other fluids were limited by their instabilities under test conditions. Since each fluid has individual characteristics, no correlation of conductivity values appears possible. Values are considered precise and for possible correlation can be compared to those of a fluid chosen as a "standard reference." In general, thermal conductivity of the lubricating fluids decreases with increasing temperature but tends to become asymptotic at the higher temperatures. PUBLICATION REVIEW This report has been reviewed and is approved. FOR THE COMMANDER: L. F. Salzberg Chief, Materials Physics Branch Materials Laboratory WADC TR 58-405 iii

TABLE OF CONTENTS Page I INTRODUCTION. a a 1 II DESIGN OF THERMAL CONDUCTIVITY CELL................ III PROOF OF THE THERMAL CONDUCTIVITY APPARATUS...... 5 IV VALUES OF THERMAL CONDUCTIVITY OF FLUIDS.... 11 V CONCLUSIONS......... 11 APPENDIX I. The Thermal Conductivity Cell........... 19 APPENDIX II. Thermocouples......................... 28 APPENDIX )II. Stability Test....15.............. 32 APPENDIX IV. Calculation of k from Data.5................ 34 APPENDIX V. Operation of Cell...e 0 0 0 0 0 e 0 0 0 I 0.... 36 APPENDIX VI. Identification of Thermal Conductivity Fluids......... 38 REFERENCES. ~ ~ ~................ 39 WADC TR 58-405 iv

LIST OF ILLUSTRATIONS Figure Page 1 Components of cell,..... *. -.......... 3 2 Assembly of cell.......................... 4 3 Front view of apparatus.........,... 6 4 Top view of apparatus.................... 7 5 Thermal conductivity of calibration fluid................ 10 6 Thermal conductivity of 1100, MIL-C-8188, 0-54-23....... 12 7 Thermal conductivity of 0-55-36, 0-55-33, 0-55-18., 13 8 Thermal conductivity of ML0-56-161, 0-55-29, MLO-55-918..... 14 9 Thermal conductivity of MLO-56-278, 0-55-32, 1010...... 15 10 Thermal conductivity of 0-55-22, 0-55-17, 0-55-9,...... 16 11 Conductivity cell, part 101.............. 21 12 Conductivity cell, part 102,............. 22 13 Conductivity cell, part 103,................ 23 14 Conductivity cell, assembly drawing..........,... 24 15 Conductivity cell, parts 105, 106............25 16 Temperature measurement circuit.................. 26 17 Temperature control and heat input systems......... 27 18 Calibration of sheathed couples (constant-temperature bath)... 30 19 Calibration of laboratory-made thermocouples...... 31 20 Temperature distribution in conductivity cell (Gulfpride 10 Base Oil)...............eo.......5... 37 WADC TR 58-405 v

LIST OF TABLES Table Page I Thermal Conductivity Values, Literature....... 9 II Reported Values of Thermal Conductivities... 9 III Thermal Conductivity as a Function of Temperature....... 17 IV Temperature Distribution of Thermocouples............ 36 WADC TR 58-405 vi

I. INTRODUCTION Under Contract No. AF 33(616)-3543, determinations of the thermal conductivity of ten synthetic base and five mineral base lubricating fluids were initiated. Conductivities over the temperature range of 70-5000F were required. The work was initiated because such data are required. for engineering designs of heat transfer equipment. Such data were not available in the literature or from other sources. Many individuals have reported measurements of the thermal conductivity of fluids on about as many modifications of the basic types of apparatus. Reviews of these by Dick,1 Sakaidis and Coates,2 and others were studied, primarily from the standpoint of reported values and designs of apparatus. The final choice of apparatus was greatly influenced by the work of Mason.3 Very few measurements-of thermal conductivities of liquids have beenmade previously at temperatures above about 200~F' Those reported were made on apparatus of doubtful precision. Thus the only references to data in the literature are limited to those of value to this work and they are referred to when used. II. DESIGN OF THERMAL CONDUCTIVITY CELL Apparatus for the measurement of thermal conductivities of fluids may be classified into three general types on a basis of the directions of heat flow: 1) direct flow between flat plates; 2) radial flow through an annulus of fluid (between. concentric cylinders); and 3) flow from a hot wire. All types were considered for this research. A concentric cylinder type of cell was chosen. Several such cells have been used by other investigators and have been proven as precise means of measuring thermal conductivities, Factors considered in this selection were: 1. the high temperature (500QF) which limited materials to ceramics or metals except for.gaskets where Teflon could be usedo 2. the stability of the.fluids to oxidation which required operation in the absence of air. Manuscript released by author 23 October 1958 for publication as a WADC Technical Report. WADC TR 58-405 1

3. the stability of fluids in contact with metals, specifically copper, which accelerate thermal decomposition. 4, the high temperature which made it unfeasible to use a fluid as the final heat sink. 5. the desire for flexibility in that heat fluxes and film dimensions could be readily changed. The metal chosen for the essential parts of the cell was copper because of its high thermal conductivity. Silver was considered too expensive for the initial cell. Corrosion-resistant metals were considered to have too low thermal conductivities, a conclusion drawn after computations of expected temperature differentials. Copper is the least desirable metal to use from the standpoint of stability of the fluids, and so the copper surfaces were plated with chromium. Means of excluding air were devised, and a procedure, discussed later, was initiated to insure that the fluids were not operated under unstable conditions. The concentric cylinder type of cell consists of a central cylinder or core, which is the heat source, surrounded by another cylinder, which is the heat sink. Heat flows from the core to the sink through the sample contained in the annular space between the cylinders. A second sink usually surrounds the whole to maintain controlled conditions; in most cases this is a fluid bath, but in this research a large cylinder of aluminum was used. Thermal conductivity of a fluid may be computed from the known heat input, temperature drop across the annulus, and dimensions of the annulus. The components and method of assembly of the thermal conductivity cell are shown in Figs. 1 and 2. Figure 1 shows the components, the filling and emptying tubes in the foreground, the central electric heater behind them, and in the rear, the bottom seal, seal gaskets, central core with top seal, and Sink I and Sink II. The central core and Sink I are of electrolytic copper and chromium-plated, Sink II is anodized aluminum. The seals are chromium-plated brass. The thermocouple holes (8) in the central core are arranged around the circle, the diameter of which is pictured as about 3 times that of the hole through which the heater is placed. The bottoms of these holes are 1, 2, 3, 4, 4, 5, 6, and 7 inches from the top. The thermocouple holes in Sink I are shown at the 7-, 8-, and 4-inch level, as holes drilled to 1/16 of an inch of inner face and with channels leading from the holes to the top, through which the thermocouple wires pass. This sink is tapered to fit a similar taper in the central hole in Sink II. Figure 2 shows the means of assembling; the heater centered in the central core; the core is centered and bolted by the seals to Sink I, and Sink I is centered in Sink II. WADC TR 58-405 2

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In operation, the whole is insulated and heated by electrical tapes wound around Sink II. The filling and emptying tubes connect to the top and bottom seals as shown with the top seal. Working drawings of the cell and discussion of them are in Appendix I, as are also drawings of the electrical circuits for measuring heat input and temperatures, and for controlling temperature. All units are pictured in Figs. 3 and 4. Figure 3 shows almost all the parts; the K-2* potentiometer, galvanometer, standard cell on the left-hand table, and under the table the battery used with the potentiometer. The left side of the instrument panel is the Wheelco Controller** with the temperature indicating scale near the top and the temperature controlling cam in the center. On the right-hand panel below the clock are the thermocouple switches. Further right are switches and ammeters for control of battery discharge and charge circuits. Power for the central core heater is supplied by the batteries on the floor and they are floating on the 110-volt d-c source in the building. In this way these batteries maintain a constant voltage. Just behind the panel is the volt box for measuring the voltage drop across the central heater. This voltage is measured by the K-2 potentiometer. Next behind is the ice chest which serves as ice storage and thermocouple cold junction. The white unit behind it is the thermal conductivity cell insulated with asbestos winding and blocks. Figure 4 shows the components behind the panel board: the large ice chest with the cold junction tubes apparent at the further end; the core reactor behind the ice chest; and the standard ohm resistance behind the insulated cell. The current to the central heater flows through the standard ohm (.1 2) resistance and is evaluated as a potential drop across the standard ohm resistance by the K-2 potentiometer. III. PROOF OF THE THERMAL CONDUCTIVITY APPARATUS Thermal conductivity values are acceptable only if obtained with an apparatus of proven precision. Such precision is always difficult to confirm and generally *Leeds and Northrupo **Wheelco; Model 72000-5253 Chronotrol, 110 v, 60 cycle, O-600~F range for ironconstantan thermocouple, 1 rev in 3 days; and Saturable Core Reactor. WADC TR 58-405 5

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is determined by comparison with accepted results of other investigations. Or the apparatus may be, after thorough study, considered a precision instrument, and the results obtained as absolute or at least comparable with expected results. The latter is the case with this apparatus. The apparatus was first proven by comparing thermal conductivities obtained with it against reliable values reported in the.literature. Water, toluene, and glycerol were selected as comparison fluids4. Thermal conductivity values were selected from the most recent determinations on well-designed apparatus. These are reported in Table I. The.determinations of this research are reported in Table II. The results cannot be considered good in all cases. Comparisons with toluene and glycerine are fair but with water the results are 10* low. Many adjustments were made in the apparatus and many procedures were tried, but under the conditions used the results were invariably the same. During most of these proving runs, heat was supplied to the central core only. As a result, heat flows through the seals produced a large temperature gradient through the central core, so that temperatures were high in the middle and low on each end. Uniform temperatures were obtained by insulating the cell and supplying heat to Sink II, and preferably operating with a decreasing overall temperature. This meant operating at temperatures above 2000F which were well above the ranges reported in Table I. Thus the proving of the apparatus resulted in the realization that the apparatus was precise only at temperatures above about 250'F with normal ambient temperatures. A "standard of reference" was therefore established to evaluate the apparatus and the test fluids. The "Standard" is a close-cut lubricating oil fraction from Pennsylvania crude without additives and having about the same viscosity as most of the test samples. It was obtained as a standard oil from the Gulf Research organization at Mellon Institute in 1951. At that time it was placed in glass bottles, deaerated, and sealed. Thermal conductivity vs. temperature curves on this oil were obtained at the beginning, the mid point, and the end of the research. The results are plotted in Fig. 5 and the consistency of the results confirms the operation of the cell and the choice of the "standard of reference." Proof of the thermocouples, dimensions of the cell, and other factors are discussed in Appendix II. WADOC TIR 58-405 8

\jI TABLE I TABLE II o THERMAL CONDUCTIVITY VALUES, LITERATURE REPORTED VALUES OF THERMAL CONDUCTIVITIES. Temp, Temp Fluid Fp K Ref. Fluid Tmp, K K(Lit) Water 68 0o.341 4 Toluene 140 0.0750 0.0720 68 0.346 7 0.0825 104 0.361 4 104 O.363 7 168 0.0730 0.0695 104 0.366 9 0.0810 158 0.386 4 168 0 386 9 Glycerine 110 o.1685 0.1685 176 o.387 7 0,1730 '0 g194 0.391 9 0.1800 200 0.401 7 286 0.1755 Glycerine 68 0.165 10 68 o.168 4 Water 125 0.323 0.375 68 0.170 3 180 0.337 0.384 18o o.18o 3 Std Oil 120 0.0825 0 0772 Toluene 68 0.0780 6 200.o0850 to 0.0892 68 0.0800 5 86 o0865 8 168 0.0817 8 175 o.0685 6

~=C.0850 0. o Gulf0pride 10 Base Oil (5 July, 1957) 1-3. 1 I U1~~" 0 0t.080 o _ _ __,.0800 o o Heating curve | Cooling curve ~ A~ o o0 O 10 '0 H_ A Equilibrium I-o.08 50 _ _ _ _ _ _ _ _ GuCooling cI 0 Base Oil (15 August 1957) 50 100 150 200 250 300 350 400 450 500 550 ) a >.0800. o a o.0750 I.08501 ~50 I 00 150 200 250 300 350 400 450 500 550 TEMPERATURE (OF) Fig. 5. Thermal conductivity of calibration fluid.

IV. VALUES OF THERMAL CONDUCTIVITY OF FLUIDS The results of this research are most readily reported as the measured values of thermal conductivities of the fluids as a function of temperature. They are plotted as such in Figs. 6 to 10, and tabulated in Table III. Also apparent in the table are the maximum temperatures to which these oils could be heated for at least 20 hours in contact with copper without apparent decomposition. The details of the test are in Appendix III; typical computations of thermal conductivities are in Appendix IV. Several attempts were made to see if the curves in Figs. 6-10 could be fitted to a typical curve, but all were unsuccessful. Each fluid has individual characteristics. About the only general conclusion is that there is a tendency for the thermal conductivities to become asymptotic at the higher temperatures. Data on stability apply only to the test as made, namely, 20-hr duration. As indicated in Table.III, some fluids were apparently stable after 50 hr. Stabilities under other than test conditions were not measured and are not inferred. No measurements of decomposition of the fluids were made after thermal conductivity determinations, although acid numbers were requested. Most of the fluids showed no visible change during a determination. As a 100% sample could not be obtained, and as apparent changes in the fluids were negative, acid numbers were not run. The method of determining acid numbers would depend on the chemical characteristics of the fluids, and it was considered that the expected small differences between fresh and used fluids would not be sufficient to warrant conclusions concerning stability. Stabilities were considered measured by tests reported in Table III. V. CONCLUSIONS The thermal conductivity apparatus was designed, built, proven, and used for measurements on submitted samples of lubricating fluids. The values of thermal conductivities of the fluids are considered absolute or at least precise in reference to a "standard oil." WADC TR 58-405 11

.0900 Q. 1100 (7 September, 1957) --.0850 -0 0" 0 ' O ' * o 0 ~ o ~ Tn 0o Heating curve * Cooling curve A Equilibrium u..0800_.0950 I M I L-C - 8188 (18 September, 1957):LL t-.0900 IF-, I _ _ 1 F-J 0 ro D.0850 zc | o Heating curve o o Z o o o I ~* Cooling curve A Equilibrium.0800 u.0950 0-54-23 (28 September, 1957).0900 0 Heating curve 0 Cooling curve 01 o o Equilibrium.0850 100 150 200 250 300 350 400 450 500 550 TEMPERATURE (~F) Fig. 6. Thermal conductivity of 1100, MIL-C-8188, 0-54-23.

.0900 I I i; *-" 055-36 (3 August, 1957) -Pm-.0850 0o 0 0 >|0 o Heating curve o * Cooling curve 0 000 0 A Equilibrium ~~ 0 c.0900 055-33 (21 August, 1957) 0 Heating curve > * Cooling curve; C)o 0 ~.0900 r w 0 I ~o 055-18 (29 August, 1957).0850 - 2 > — oo o Heating curve 0 * Cooling curve ____ _ A Equilibrium - 50 100 150 200 250 300 350 400 450 500 550 TEMPERATURE (OF) Fig. 7. Thermal conductivity of o-55-36, 0-55-33, 0-55-18.

.090 I I ~o.Osoo<>; | l l |ML0-56-161 (23 July, 1957) cd o 0o 0 0o I I o I '31.0850 C 0 I o o 0 0 0 '|l o Heating curve 00 o o * Cooling curve _ _ _ o o.0800.0800 Equilibrium _ ~ -.089005 IN..0 80, o 055-29(27 July, 1957):D 08500 o Heating curve o 0 -z* ~ Cooling curve z 0 A Equilibrium o o.0800 _A -J o.0850 w Z 50 100,,, 200 250 300 350 400 450 500 550 Fig. 8. Thermal conductivity of MLO-55-918 (01 July,1957) 0 00 o Heating curve ~ Cooling curve.0750- & Equilibrium 0 50 I00 150 200 250 300 350 400 450 500 550 TEMPERATURE (OF) Fig. 8. Thermal conductivity of ML0-56-161, 0-55-29, ML0-55-918.

.0850 o.0850 |- - - M L0-56-278 (7 August, 1957) 00 O o.0800 o O.0800 l| o Heating curve o ~ * Cooling curve i e ~ ~ A Equilibrium C.0750 n,. I l l llI I ofi n850 l,;>__>_, \ 055-32(10 August, 1957) o Heating curve t * Cooling curve. Equilibrium -- ~ 0 T T W, 0 I |1010 (24 August, 1957).0750 o Heating curve 0.0700 ~ Cooling curve ~- A Equilibrium.0 0 50 100 150 200 250 300 350 400 450 500 550 TEMPERATURE (~F) Fig. 9. Thermal conductivity of ML0-56-278, 0-55-32, 1010.

cl ~~~.0900 ~7d I _ d I.090C055-22 (4 September, 1957) co.085C 0 0 o 0~~~~~~~~~~~~~~~~~~~ U-.0800 01I ~I C.- 0 LL ~ a Heating curve * Cooling curve a:A Equilibrium N.075C 0900 >- ~~~~~~~~~~~~~~0-55-17 (5 October, 1957) ONo~.0850 L Cc 00o Heating curve 0 -I 10 Cooling curve < A Equilibrium 7.0800 ------ cr w.0900 0-55-9 (5 November, 1957).0850 0.080C 50 100 150 200 250 300 350 400 450 500 55 TEMPERATURE (0F) Fic. 10. Thermal conductivity of 0-55-22, 0-55-17, 0-55-9.

TABLE III co THERMAL CONDUCTIVITY AS A FUNCTION OF TEMPERATURE(a) \J1 Oil 100~F 150~F 200~F 250~F 300~F 350~F 400~F 450~F 500~F 1010.0755.0737.0721.0709.0703.0700.o0699.0699gg.0699 1100*.0889.0878.0o868.0859.0854.0851.0o85o.0850.0850 0-54-23.0933.0920.og06.0893.o884.0876 - 0-55-9.0o846 0839.0832.0825 0-55-17.0866.o0856.o0846.0o836.0828.0820.0813 --- 0-55-18.0887.0869.0850.0832.0818.0o808.0802.0798.0794 0-55-22.0873.0853.0833.0816.0804.0796.0791.0787.0783 0-55-29*.0898.0878.0858.0o840.0826.0817.0812.0o808.0804 0-55-32.0o868.0855.0840.0827.0815.o808.0804.0801.0798 0-55-33.0881.0o864.0847.0831.0817.0807.0800.0795.079 2 0-55-36.0893.0871.0850 o.0833.0822.0816.0811 o0808.0805 MIL-C-8188.0902.0889.0875.0861.0o848.0834 --- -- MLO-55-918*.o0841.0825.0o809.0793.0778.0769.0761.0753.0745 MLo-56-161*.0882.o863.o843.0825.0810.0798.0789.0784.0782 MLO-56-278 o0831.0815 o0801.0788.0778.0772.0766.0763.0760 Gulfpride(b) 10 Base.0830.0818.o805.0792.0781.0773.0768.0764.0760 Gulfpride(c) 10 Base.0832.0817.0803.0791.0783.0778.0776.0774.0772 Gulfpride(d) 10 Base,0841.0831 o0820.0809.0800.0794.0791.0789.0787 (a) Thermal conductivity is reported in [Btu/hr ft2 (~F/ft)]. (b) 5 July 1957. (c) 15 August 1957. (d) 28 October 1957. * Stable for 50 hours at 5000F.

APPENDIXES WADC TR 58-405 18

APPENDIX I THE THERMAL CONDUCTIVITY CELL Figure 14 is the assembly drawing of the thermal conductivity cell. It shows three concentric cylinders, the central core, Sink I, and Sink II. Between the central core and Sink I is the annular space that will enclose the specimen under test. Details are shown in the magnified section. CENTRAL CORE The central core is built up of three segments, the centered Calrod tubular heater, on which is a close-fit copper tube part 101, and finally the close-fit tube part 102. The heater is a production item. It was chosen because of the possible high heat output per unit of length. After receiving it, it was checked for regularity of windings and the length of the winding by means of x-rays. The photographs showed the windings to be very uniform and thus the heater is being accepted as an absolute source of heat. Part 101 is close-fitted on the heater for good metallic contact and it serves two purposes. First, it will distribute the heat from the heater uniformly within the central core. Second, it is milled to permit insertion of the thermocouples down the long, small-size slots. The design as shown indicates four slots for two couples each. The part, as made, has eight slots for a single couple each. Part 102 completes the central core. It serves to distribute the heat uniformly and has been carefully machined to give the desired outside diameter with a minimum of eccentricity. SINKS I AND II Sink I (Fig. 13) receives heat from the central core through the fluid layer. Thermocouple wells are drilled from the outside close to the inner surface of the sink. These couples are located opposite couples in the central core, the difference being the temperature drop across the fluid layer. Sink I fits into Sink II with a taper for easy removal and the use of shims between the sinks to control heat flow. Sink II is the final receiver of heat from the central core. It operates at a fixed temperature which controls the entire operation of the cell. Sink II is made of aluminum and is wound with heating tapes as soukrces of heat for control of the temperature of the sink. WADC TR 58-405 19

TEMPERATURE MEASUREMENT The important temperature measurement circuits are shown in Fig. 16. It is the standard method using iron-constantan thermocouples and cold junctions. The emf is measured by a sensitive K-2 potentiometer. TEMPERATURE CONTROL AND HEAT INPUT The.wiring diagrams of the temperature-control and heat-input systems are shown in Fig. 17. Heat is supplied to the central core and flows out to Sink IIo Control of temperature drops through the cell is maintained by control of the temperature of Sink II. The tubular heater in the central core is supplied with current from a bank of storage batteries. These storage batteries deliver a constant voltage, and are connected across the laboratory d-c line so as to give long periods of operation between recharges. Heat input is determined as the watts to the heater as computed from the current and voltage drop across the heater. Current is measured by the emf across a standard shunt in the line. Voltage drop is measured by a proportionating volt box. All emf's are measured on a K-2 potentiometer. Temperature control of Sink II is attained by a controller, operated by a thermocouple located in the sink, which controls the heating cycles of either one or both of two windings of heater tapes on the outside of Sink IIo Input to the tapes is manually controlled by means of powerstats. By this means it is expected that the control is so sensitive that the fluctuations of temperature in Sink II does not materially influence the temperature drops across the fluid layer, WADC TR 58-405 20

K H I I JNOTE' "G" TO BEIN LINE WITH "C" ON DWG 105 1 ''" 1 TSS of I "K" I 1 I lG" BElTO RECEIVE V.P.=,313.750 -Fig. 11. Conductivity cell, part 101. WADC TR 58-405 21

c) O3 0 k-l o X2SEE NOTE XI ON DWG 103 Po no Fig. 12 odutvt cl~pat128" Fig. 12. Conductivity cell, part 102.

DRILL a TAP 8 -10 -32 HOLES BOTH ENDS 8 ALINE SEE DWGS 105 106 SERIES "A"HOLe LAYOUT LIpJ4J I " '" TF- l --- i 36Sll!~ 3.720 4" 4"4D II 6I I - a1.860 - -_.034,. ' I 1 1 NOTE: X, DIMENSION DEPENDS ON THICKNESS a FINISH OF CHROM PLATING -ALSOMI THLLS IS CRITICAL ANNULAR SPACE Fig. 1. Conductivity cell, part 100.4 WADC TR 5 O 28-5 2HOLES 2 wp~c TR 58-4o5 2.5

G.E. TUBULAR HEATER SINK AE SINK I DW1. 104 DWG. 103 1.8.5 1.625 TOP SEAL DWG. 105 e- 10-32 X 5/8 ALLEN SCREWS NOTE: MUST BE CENTERED EXACTLY /CENTRAL ClE SO THAT ANNULAR SPACE IS DWGS. Irg1 & 102 103 I BOTTOM SEAL DWG. 106 ENLARGED VIEW 10i.313 VENDOR PART(V.P) SECTION A-A Fig. 14. Conductivity cell, assembly drawing. WADC TIP 58-405 24

SERIES "A" HOLES DRILL CLEARANCE FOR 8 -10-32 SCREWS 450 APART DRILL I HOLE,+.\ R =-.875 / SERIES "B" HOLES DRILL 4 HOLES-9' 900 A PART DRILL 8 TAP DRILL CENTER HOLE -i*t':~ '/ _6> a REAM AT ASSEMBLY FOR.156 DEEP \ ' PRESS FIT SINGLE OPENING V.P:.313 DIA. FOR CONNECTION R -.156 OF METAL TUBING -_\ - 2.250 450 rDELI 4":" 11.~250 TOP SEAL 105 AS SHOWN BOTTOM SEAL 106 ~ LEAVE OFF,_ _____ SERIES "B" HOLES () CENTER HOLE, DRILL# Fig. 15. Conductivity cell, parts 105, 106. WADC TR 58-405 25

16 THERMOCOUPLES Ox3 0 TO STANDARD SELECTOR SWITCH SHUNT TO VOLT o-, I I BOX GALVANO ~~~~~~~~~~~BA. ~METER STD. CELL POTENTIOMETER Pig. 16. Temperature measurement circuit.

I lOV A.C. TO POTENTIOMETER I IOV D.C. H~~~~~~~~ Qd CONTROL,~ ' UNIT SHUNT 0 TO POTENTIOMETER I I, ---iCELL 4-12.6V RHEO. -~~~~ I I~~~' I I I I I I /~~~~~I.C STORAGE Fg 7TmetueC aVOLT N)~ B OX s~oA~ P~~~~~~, SINK I r I HEATERS RHEOSTAT Fig. 17. Temperature control and heat input systems.

APPENDIX II THERMOC OUPLES Precise determinations of thermal conductivities are dependent on precision temperature measurements. In this research, thermocouples are being used to measure temperature and much effort has been spent in calibrating them. COUPLES CALIBRATED The first couples calibrated were the sheathed couples obtained from Aero Research Company. These are iron-constantan couples, insulated with magnesium oxide, and swaged in stainless steel sheaths (diam = 0.04 in.). They were selected as ideal for research at a temperature of 5000F and the conductivity cell was designed for their use. These proved to be too erratic for precise temperature measurements, as is shown later. The next group of couples calibrated was laboratory-manufactured from 30-gage wires, glass- and silicone-insulated. There was some difficulty in making satisfactory couples. In all about 60 were made, of which 16 were proven satisfactory and are now in use. The procedure of making them follows later. METHODS AND RESULTS OF CALIBRATION IN CONSTANT-TEMPERATURE BATH First calibrations were made using a precision-controlled temperature bath as the hot junction and melting ice as the cold junction. Temperatures of the hot junction were measured by a calibrated mercury thermometer and a calibrated resistance thermometer. Deviations in both the hot and cold junctions were evaluated by Beckmann thermometers. The emf of the thermocouples were measured by a K-2 potentiometer obtained for this research. The first calibrations were very erratic and much effort was spent investigating the methods used, electrical contacts, shielding, and personal factors. But the sheathed couples still gave erratic results and it was considered necessary to abandon them. Typical results with two of the sheathed couples are shown in Fig. 18. The plot shows that over a period of four hours the Beckmann thermometer in the hot junction indicated a maximum temperature variation of O.070F, while the variations for couples 6 and 12 were 0.270F and 0.45~F, respectively. Of greater concern are the actual readings of couples 6 and 12, and the plot shows a difference in them of 1.25~F, WADC TR 58-405 28

CALIBRATION IN A RISING AND FALLING TEMPERATURE BATH Calibrations of couples either sheathed or laboratory-made were always rather erratic in the c~ontrolled-temperature bath under static conditions. Further, the controlled bath was limited to rather low temperatures. Thus a kinetic type of calibration was adopted, using a silicone bath controlled by an automatic temperature controller, the one obtained to operate the cell. First calibrations were made on a rising temperature but were again a bit erratic, although much better than with the constant-temperature bath. The final procedure was to calibrate with a slowly falling temperature. The sheathed couples were again tried but they proved as erratic as before. The calibration of the final group of laboratory-made thermocouples is plotted in part in Fig. 19. Several runs were made in steps from 500~F down to 1000F. The data plotted in Fig. 19 show good agreement between couples, although erratic at the beginning of any one step. From this group of twenty couples, sixteen were selected for use in the thermal conductivity cell. It must be made clear that although most of the tested couples did evaluate the true temperature within the usual limits of accuracy, it is necessary in this work that the couples do so with a uniformity that does not allow temperature differences between couples greater than about 0.10F. It is felt that this last group of uniformly made couples meets this requirement. MANUFACTURING OF COUPLES Two general types of couples are needed. Those couples for the inside core must have the outer insulation removed for a distance of about seven inches to allow for insertion into the deepest well. The couples for Sink I need only to have the insulation removed for a distance of two inches. The following stepwise procedure was instituted in the preparation of the thermocouples for the cell: 1) Remove outer insulation to required distance, being careful not to unravel the inner glass insulation. This may be facilitated by twisting the two wire strands together at the tip. 2) Two coats of thermocouple insulating resin* are then applied. The resin should be diluted so as not to increase the thermocouple diameter appreciably. 3) The wire tips are then barred and twisted together for about 1/8 ino 4) The junction is then made by dipping the twisted end in flux and passing through an electric arc. 5) The thermocouple is completed by removing the excess flux and applying an additional coat of thermocouple insulating resin. *Silicone resin supplied by Dow Corning~ WADC TR 58-405 29

3.780 '7d co1 3.770 THERMOCOUPLES NO.6812 RUN OF OCT. 22,1956 0-6 w o ~ -.12 J1 aA- BECKMANN THERMOMETER 3.760 -w I3.750 + + z 3.7C 3+ + + -1 + + + 2 w > 3.73C z~~~~~~~ 3.72C w 0 3.7 1C 0 0~~~~~~~~~~~ 0 0 3.700 0 z.45'F 3.690:=.070F.950 B P d P p ~~~~~~~~~~~~~~~~~~~~~.900 3.680.850 0 2 3 4 5' TIME IN HOURS FiJ. i8. Calibration of sheathed couples (constant-temperature bath).

, 3 COD CALIBRATION OF THERMOCOUPLE 00.~SAMPLE SECTION END OF FIRST RUN MARCH 10, 1957 0 000 I I 0 1~~ ~~ o oo 0 00 0 0o 0 0 0 0 2019 18 17 16 15 14 12 11 10 9 8 7 65 4 3 2 I z 0 3 U END OF SECOND RUN 120 2O 0)0 0 0 ~O CD O o O O | tBEGINNING OF SECOND RUN oL 20 191,81 17 16 15 14 12 II10 9 8 76 5 4 3 2 I 0 ~ W) 121110 8.64 8.70 8.80 8.90 9.0 9.1 9.2 EMF IN MV Fig. 19. Calibration of laboratory-made thermocouples.

APPENDIX III STABILITY TEST The protection of the thermal conductivity cell against corrosive attack of the fluids or vice versa had to be determined. It was proposed that a test be made on all samples by subjecting them to elevated temperatures in contact with copper, the metal of which the cell is constructed. The following test was devised. A 5/8-in. ID x 6-in. heavy-walled Pyrex test tube is used. Into it is placed a polished and bent piece of copper sheet about 1 inch square. The test tube is than drawn down to a narrow neck to form an open ampoule about 3 inches long. The fluid sample is carefully pipetted into the ampoule to prevent any oil contacting the glass surface that will be heated in sealing the arnpoule. The fluid completely covers the copper; -the fluid sample is then de-aerated under high vacuum with care being taken to avoid vaporization of the fluid. While under vacuum the ampoule is sealed by fusing the glass at the drawn-down portion. The ampoules are then placed in a controlled temperature oven and observed at intervals. Conditions of this test are considered comparable to the conditions within the calorimeter. All fluid samples were placed in the oven at 5000F with the following results: 1. Fluids apparently stable after 50 hours ML0-56-161 0-55-29 MLQ-55-918 1100 2. Fluids apparently stable after 20 hours but decomposed at 50 hours Gulfpride 10 0-55-33 0-55-36 0-55-18 MLO-56-278 0-55-22 0-55-32 1010 3. Fluids apparently stable for less than 10 hours 0-55-17 0-54-23 NIL-C-8188 0-55-9 It was considered that the fluids in the Groups 1 and 2 could be safely run in the apparatus, without deterioration, and without harm to the apparatus. This was done. WADC TR 58-405 32

The fluids in Group 3 had such doubtful stability that it was felt that they might decompose and do harm to the apparatus if run up to and down from the maximum temperature of 5000F. They might well be run to a lower maximum, to be determined by the outlined test. Permission was granted to limit the determination on the fluids in Group 3 to a maximum temperature determined by the test, WADC TR 58-405 33

APPENDIX IV CALCULATION OF k FROM DATA NOMENCLATURE q = heat/time, Btu/hr k = heat/time length temp, Btu/hr ft2 (~F/ft) A = length2 normal to flow, ft2/in. T = temperature, ~F X = distance along direction of flow, ft ro = outside radius of central core, in. ri = inside radius of Sink I, in. V = voltage, volts I = current, amperes emf = emf of thermocouples, millivolts H.L. = heater length, in. d = respective diameters a) q = kA dT dX Since the annular spacing is only.036 in., AX may be used in place of dX. Solving for k, then, b) k = 1 AX A AT AX (rl-ro/12) A = [c(ri+ro)/144] AT = [emf/.0292 mv/OF] ci = (VI) 3. 42 Btu/hr x in. VIBtu/hr watt H.L. \1931 in., j 3.42\ 144l _ 1 (rr-ro).0292 ~ k = (VI) 9531 it (rl+ro) 12 Aemf rL-ro dr-do.0362 ra+r dl+do 1.8072 WADC TR 58-405 34

c) k - VI 3.42 o 12 ~.0292 ~.0362 5.959 10-4 VI Aemf 19.31... 1.8072 Aemf The values used for VI are the average values of the beginning and end of a line. SAMPLE CALCULATION Data from 0-55-17 run of 30 September 1957 EI line 13 = 81.9178 Ea 81.85o6 watts EI line 14 = 81.7835 avg Position: 4A Aemf couples 7 and 8 = 0.4010 k = 3.9590 10-4 81.8506.o808 Btu/hr ft2 (~F/ft) WADC TR 58-405 35

APPENDIX V OPERATION OF CELL The thermal conductivity cell is filled by applying a vacuum, and forcing the fluid into the annulus by the pressure of its own vapor. It is felt that this procedure effectively eliminates entrained air. An example of the temperature distribution of the thermocouples on a cooling cycle and a heating cycle is shown in Table IV and Fig. 20. Outside couples refer to those imbedded in Sink I and inside couples refer to those in the central core. Readings are taken of the thermocouples at one-minute intervals and are repeated every half hour. Thus the time elapsed between reading couples Nos. 1 and 3 is two minutes, The controller regulates the rate of heating and cooling to 20 Fo/houro TABLE IV TEMPERATURE DISTRIBUTION OF THERMOCOUPLES Gulfpride 10 Base Oil Line 30, 13 August 1957 Line 95, 13 August 1957 Thermocouple EPmf (millivolts) Emf (millivolts) 1 10.4454 11.4256 2 10.8436 11o7981 3 10o4905 11,4273 4 10. 8919 11.8152 5 10.5167 11.4186 6 10o.9574 11 8464 7 10.5525 11.4153 8 11.0010 11.8523 9 10o.5985 11,4228 10 11.0510 11.8599 11 10,6220 1153981 12 11.0590 11.8167 13 10o6500 11.3901 14 11.0765 11.8024 15 10.6505 11o3648 16 11.1041 11 8044 WADC TR 58-405 36

OUTSIDE COUPLES INSIDE COUPLES 11.5 11.9 11.4' _ ' ' 1 = 1 - 1 1(= Iw Line 95 L ine 95 13 August 1957 13 August 1957 11.3 I 11.7 10.7 11.1 13 August 1957 13 August 1957 F0.- 10... 1 _1 35 7 9 11 13 15 2 4 6 8 10 12 14 16 THERMOCOUPLE THERMOCOUPLE Fig. 20. Temperature distribution in conductivity cell (Gulfpride 10 Base Oil0). WADC TR 58-405 37

APPENDIX VI IDENTIFICATION OF THERMAL CONDUCTIVITY FLUIDS Sample No. Ident ificat ion 0-54-23 Esso WS 2812 Aviation Oil 0-55-9 Proprietary 0-55-17 Proprietary 0-55-18 GTO 133 SRI Gear Reference Oil 0-55-22 0-55-29 Dow Corning QF-258 0-55-32 Esso Turbo Oil 15 Batch 68 0-55-33 0-55-36 Shell WRGL 21D MIL-C-8188 Esso Turbo Oil P16 ML0-55-918 Disiloxane 8515 Oronite Chemical Company MLO-56-161 Dow Corning XF 4039 MLo-56-278 Monsanto OS-45 1010 Engine Oil (hydrocarbon, natural) 1100 Engine Oil (hydrocarbon, natural) WADC TR 58-405 38

REFERENCES 1. Dick, M., Synthetic Lubricants, Univ. of Mich. Eng. Res. Inst. Final Report M-779, Ann Arbor, Appendix IIIe 2. Sakaides, B. C., and Coates, J., Louisiana State Univ. Eng. Exp. Station Bull. Nos. 34 (1952)g 48 (1954), 35 (1953), and 45 (1954). 3. Mason, H. L., Trans. A.S.M.E., 76 (1954), 817. 4. Bates, K. O., Hazzard, G., and Palmer, G., Ind. Eng. Chem., Anal. Ed., 10 (1938), 314. 5. Briggs, D.K.H., Ind. Eng. Chem., 49 (1957), 418. 6. Reidel, L., Chem. Ing. Tech., 23 (1951), 321 7. Reidel, L., Chem. Ing. Tech., 23 (1951), 465. 8. Smith, J.F,D., Ind. Eng. Chem., 22 (1930), 1246. 9. Smith, J.F.D., Trans. A.S.M.E., 58 (1936), 719. 10. Sakaides, B. C., and Coates, J., Jour. A.I.Ch.E., 1 (1955), 275. WADC TR 58-405 39

UNIVERSITY OF MICHIGAN 1111111113 90 1.5 03483 1 95111111 3 901.5 03483 1951