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The thermal conductivities of cyclic hydrocarbons Perris, George 1947

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THE THERMAL CONDUCTIVITIES OF CYCLIC HYDROCARBONS  by  George P e r r i s  A Thesis Submitted i n P a r t i a l ' F u l f i l m e n t of The Requirements f o r the Degree of MASTER OF APPLIED SCIENCE i n the Department of CHEMICAL ENGINEERING  The University of B r i t i s h Columbia April 4  ^  /  ^  /  ^  1947.  Ui^cpt^  li^rf^Z^  *f~  ACKNOWLEDGEMENT  The a u t h o r w i s h e s t o acknowledge t h e a d v i c e and h e l p f u l s u g g e s t i o n s g i v e n by Dr. W. 3 ? . S e y e r under whose d i r e c t i o m t h i s i n v e s t i g a t i o n o n c y c l i c hydrocarbons was undertaken.  TABLE OF CONTENTS Page I, II. III.  . . . " 1  Introduction D e s c r i p t i o n o f Apparatus  2  Remodelling o f Test C e l l . . .  4  A. E x p e r i m e n t s w i t h V a r i o u s Cements  IV. V. VI.  . . . . .  B. The Mew T e s t C e l l  6  C. Replacement o f Thermocouple W e l l s . . . . .  7  D. Replacement o f Thermocouples  8  Procedure  9  ••  Theory o f Measurement  . . . . . . . . . . . .  11  A. Thermal C o n d u c t i v i t y o f Water . . . . . . .  11  Thermal C o n d u c t i v i t y o f C i s and T r a n s Decahydronaphthalene . . . . . . . . . . . 1.  VIII.  10  Results  B.  VII.  4  16  . . . . . . . . .  16  2. Trans Decahydronaphthalene . . . . . . . .  16  3 . C i s Decahydronaphthalene . . . . . . . .  17  C. Thermal C o n d u c t i v i t y o f Cyclohexane . . . .  17  Discussion of Results  18  P r e p a r a t i o n o f Sample  Suggestions f o r Future Research  . . . . . . .  19  LIST OF ILLUSTRATIONS  Figure  F a c i n g Page  1.  G e n e r a l Assembly o f T e s t C e l l  2.  Thermocouple P o s i t i o n s  3.  Thermocouple C i r c u i t  4  4.  Heating C i r c u i t  4  j>.  G e n e r a l Assembly o f New T e s t C e l l . . . . .  7  6.  Temperature G r a d i e n t Curves . . . . . . . .  12  7.  C a l i b r a t i o n Curves  14  8.  Temperature V a r i a t i o n o f Thermal Conductivities  •  2  . . . .  3  . . . . . . . . . . . .  .  16  1.  THE THERMAL CONDUCTIVITIES OE CYCLIC HYDROCARBONS  INTRODUCTION  In 194-6, Robinson and Younger b u i l t an apparatus 1  f o r the measurement of the true c o e f f i c i e n t s of thermal cond u c t i v i t y of the c i s and trans isomers of decahydronaphthalene (abbreviated decalin), a hydrocarbon which has had many of i t s physical properties investigated i n t h i s laboratory.  Their apparatus was an adaption of one o r i g i n a l l y  designed by 0. K. Bates »5 2  a  t M.I.T. i n 1932  employing the  thick disk method. In t h i s method, the test l i q u i d i s placed i n an insulated c y l i n d r i c a l container and i s heated from the top and cooled from the bottom thereby preventing convection currents.  The true c o e f f i c i e n t of thermal conductivity over  a temperature range i s obtained by t h i s method by means of a single t e s t , Robinson and Younger encountered great d i f f i c u l t y •^Robinson and Younger, M.A.Sc. Thesis (1946). I n d . and Eng. Chem. 23, 431 (1953). 3lnd. and Eng. Chem. 28, 494 (1926). 2  2. i n making the test c e l l ( J i g . 1) impervious to decalin owing to t h i s hydrocarbon*s solvent action.  Decalin would seep  through the g l y c e r i n e - l i t h a r g e cement used to fasten the two copper calorimeters together which form the bottom watercooled surface of the c e l l . I t i s the object of the present research to make t h i s test c e l l impervious to decalin, and to measure the thermal conductivities of decalin as w e l l as other c y c l i c hydrocarbons.  DESCRIPTION OF APPARATUS  The test ©ell ( F i g . 1} consists e s s e n t i a l l y of a shallow c y l i n d r i c a l container with two c i r c u l a r plane faces placed approximately  2 cnu apart, the upper face being  e l e c t r i c a l l y heated, and the bottom face water-cooled.  The  l i q u i d i s contained between these two faces. The water-cooled meters j  surface consists of two c a l o r i -  a centre calorimeter made from a disk of copper  with p a r a l l e l s p i r a l grooves cut i n i t and a copper plate soldered over the open grooved side, and a guard r i n g c a l o r i meter consisting of an annular disk of copper with copper tubing wound S p i r a l l y and soldered t o the underside.  Thermo-  couple wells are placed at the entrance and exit of the water paths of both calorimeters.  The space between these  two calorimeters was f i l l e d with l i t h a r g e - g l y o e r o l cement. The c y l i n d r i c a l container was formed from t r a n s i t e  1. T H E R M O C O U P L E 2.  G L A S S  3. T R A N S i T E 4. W A T E R  SPRING  T H E R M O C O U P L E  ARRANGEMENT  5. G U A R D  GUIDES  6. T E S T  CONTAINER  INLETS  AND  7  OUTLETS  RING H E A T E R HEATER  GUARD  8. T E S T  RlING  -  COPPER  COPPER  CALORIMETER  CALORIMETER  -  COPPER  n  FIG. I  GENERAL  ASSEMBLY OF TEST CELL  -  COPPER  3. piping with a change i n diameter near the bottom which forms ^ the support f o r the heater. Horizontal holes were d r i l l e d at each of three equally spaced heights and glass tubes placed through them and cemented i n p o s i t i o n .  These glass tubes act  as guides f o r the thermocouples which measure the temperature gradient through the test l i q u i d *  The guard r i n g calorimeter  was fastened to the underside of the t r a n s i t e container with l i t h a r g e - g l y c e r o l cement. The e l e c t r i c a l l y heated upper face consists of a centre heater surrounded by a guard r i n g heater.  These  heaters were formed from recessed copper disks i n each of which a nichrome wire wound around a mica disk forms the heating element.  Insulation between the inside copper faces  and the heating elements was provided f o r by covering these surfaces with g l y p t a l .  The two heaters were joined by  l i t h a r g e - g l y c e r o l cement.  A t h i n s t e e l cylinder was soldered  to the outside of the guard r i n g heater and f i l l e d with rock wool i n s u l a t i o n to prevent heat loss upwards. The complete c e l l was placed at the centre of a s t e e l drum and packed underneath with 8$% magnesia and around the  sides with rock wool i n s u l a t i o n . A l l temperature readings were obtained by copper-  copel thermocouples.  The cold junctions were kept at a con-  stant temperature of 0°C i n a Dewar f l a s k f i l l e d with cracked ice and water.  F i g . 2 shows the p o s i t i o n of the thermocouples  i n the heaters and calorimeters and also through the test liquid.  4. The potentials were measured with a Leeds and Kforthrup potentiometer Eb. 8662 which enabled the emf»s to be estimated to 1 microvolt.  The thermocouple c i r c u i t i s shown  diagramstioally i n F i g . 3 . The calorimeter water was kept under a constant head of 4 f t . 6 i n . by means of a well s t i r r e d open tank. The temperature  of the water was kept constant within 0.1°C  by two thermostatically controlled heaters. The heating c i r c u i t i s shown i n F i g . 4 with the current being supplied by a 40 v o l t storage battery.  The  switching arrangement enabled the current i n both c i r c u i t s to be read on one ammeter, and both heaters operated whether the ammeter was i n or out of the c i r c u i t .  REMODELLING OF TEST CELL  Experiments With Various Cements As previously mentioned, a l l the leakage  difficul-  t i e s experienced by Robinson and Younger were due to the d i s solving of the l i t h a r g e - g l y c e r o l cement which joins the two calorimeters and the container together whenever decalin came i n contact with the cement f o r any length of time.  This d i f -  f i c u l t y was not experienced by Bates because he used only water and a red o i l i n h i s test c e l l and these l i q u i d s have no solvent action. Glyptal and other patent organic protective coatings were found to be quite soluble i n decalin and hence could not  5. be used to protect the l i t h a r g e - g l y c e r o l cement. Le Pages glue and Cenco l a b e l varnish were used to cover the surfaces coming i n contact with decalin, and, a l though they were resistant to decalin, they d i d not prevent i t from getting underneath them and eventually d i s s o l v i n g the l i t h a r g e - g l y c e r o l cement. Further attempts to f i n d some sort of protective coating f o r the l i t h a r g e - g l y c e r o l cement proved f r u i t l e s s . I t was therefore decided instead by t h i s investigator to t r y and f i n d another cement to replace the l i t h a r g e - g l y c e r o l . The centre calorimeter was removed from the guardr i n g calorimeter which i n turn was separated from the bottom of the t r a n s i t s container.  The glass thermocouple guide  tubes were also removed and a l l the parts thoroughly  cleaned.  The f i r s t material t r i e d as a cement was Weldwood glue, a p l a s t i c r e s i n , since i t was found to be insoluble i n decalin.  A l l the parts were re-assembled with t h i s glue and  several days were allowed f o r the Weldwood to harden. Although no leaks could be detected when the c e l l was f i l l e d with decalin without the heater i n p o s i t i o n , as soon as the heater was placed i n i t and a test run started, many leaks were developed before equilibrium was half-way reached. Several more attempts with Weldwood were t r i e d using i t i n very t h i n layers, and also a l t e r n a t i n g the Weldwood layers with Cenco l a b e l varnish, but these were just as fruitless.  6 These leaks were attributed to the unequal coeff i c i e n t s of expansion of the copper surface and the Weldwood glue, and hence the further use of Weldwood was abandoned. The second cement to be t r i e d was  Smooth-on i r o n  cement since i t s manufacturers claimed i t could withstand many chemicals.  I t was  found, however, that leaks developed  through the annular space between the two calorimeters but that the space between the guard-ring calorimeter and thebottom of the t r a n s i t s container was An attempt was  unaffected.  then made to solder the two c a l o r i -  meters together with a low melting binding a l l o y leaving the guard calorimeter and container cemented together.  A solder  of a higher melting point would have necessitated the heating of the calorimeters to such a temperature that the copper plate on the underside of the centre calorimeter and the s p i r a l l y wound copper tubing of the guard-ring calorimeter would have come o f f .  Several runs were made with the test  c e l l assembled thus but unfortunately, the Smooth-oh cement joining the guard calorimeter and the t r a n s i t s container t o gether eventually deteriorated causing leaks.  Since i t was  impossible to solder the calorimeter to the t r a n s i t s , a  new  test c e l l had to be designed i n which i t would be possible to solder a l l the parts.  The New  Test C e l l The new  c e l l was  constructed as follows.  bottom edge of a t h i n s t e e l cylinder of 13.7  cm.  The  diameter  and 7 cm. high was plate of 12,1 meter.  s i l v e r soldered onto a t h i n s t e e l annular  cm. inside diameter and 13.3  The guard-ring calorimeter was  cm. outside d i a -  soldered to the under-  side of t h i s plate and the center calorimeter i n turn soldered to the guard calorimeter. F i t t i n g snugly on the inside of the s t e e l c y l i n d e r and r e s t i n g on the s t e e l plate i s a 3.4 piping of 12.1 meter.  cm. inside diameter and 13.7  cm. outside d i a -  F i t t i n g around the outside of the s t e e l cylinder i s a  7 cm. length of t r a n s i t e piping of 13•8 and 13.3  cm. length of t r a n s i t s  cm. inside diameter  cm. outside diameter. Horizontal holes of 0.318  cm. i n diameter were  d r i l l e d at opposite sides of the container at eaoh of f i v e equally spaced l e v e l s between top and bottom.  Through these  holes were placed t h i n copper tubes which act as thermocouple guides.  The tubes were soldered to the outside of the  steel cylinder. The construction of t h i s test c e i l i s shown i n F i g . 3.  Replacement of Thermocouple Wells I t had been found with the old test c e l l that the i n l e t thermopile of the centre calorimeter gave a higher temperature reading than the outlet thermopile.  This  was  due to heat conduction to the hot junction at the i n l e t cause of improper depth of immersion of the  thermopile.  In order to remedy t h i s , l a r g e r brass T*s were  be-  I THERMOCOUPLE SPRING ARRANGEMENT 2. LIQUID THERMOCOUPLE 3. COPPER THERMOCOUPLE GUIDE A. OUTER TRAWSlTE CYLVNDEW 5 - INNER TRANSVTF CYLINDER  FIG. 5  6. 7. 8. 3. IO.  STEEL CYLINDER AND PLATE TEST AMD GUARD CALORIMETERS TEST AND GUARD HEATERS TEST CALORIMETER THERMOCOUPLE V/ELLS GUARO CALORIMETER THERMOCOUPLE WELLS  GENERAL ASSEMBLE OF NEW TEST CELL  substituted f o r the ones used previously as thermocouple wells f o r the centre calorimeter and t h e i r position also changed. Since the i n l e t and outlet thermopiles of the guard-ring calorimeter had not given such high readings, and further, since these readings do not enter into the actual c a l c u l a t i o n of the thermal conductivity, the thermocouple wells were not replaced f o r the guard calorimeter. The two types of thermocouple wells are shown i n F i g . 5.  Replacement of Thermocouples Since a standard c a l i b r a t i o n table f o r coppercopel thermocouples has not been published, the calibration! of these thermocouples had been obtained only by comparison with a copper-constantan thermocouple f o r which the Leeds and Northrup Co. have published tables.  Hence, i t was  thought advisable to replace a l l the thermocouples by glass insulated duplex copper-constantan thermocouples. Several of the values as given i n the Leeds and Northrup No. 38 c a l i b r a t i o n table were checked f o r the new thermocouples against a platinum resistance  thermometer  (No. 81412) i n a constant temperature g l y c e r i n ^ bath. values obtained agreed with the ones i n the table. '  The  9..  PROCEDURE  (1)  The t h e r m o s t a t i c a l l y c o n t r o l l e d c o o l i n g w a t e r was a d justed t o the c o r r e c t r a t e of f l o w through the oentre and guard c a l o r i m e t e r s so t h a t t h e r e s u l t i n g  tempera-  t u r e s o f t h e two c a l o r i m e t e r s were as n e a r l y t h e same as p o s s i b l e . (2)  The t e s t c e l l was t h e n f i l l e d up t o t h e o v e r f l o w tube w i t h t h e t e s t l i q u i d w h i c h had p r e v i o u s l y been h e a t e d above t h e h i g h e s t t e s t temperature t o e x c l u d e any d i s s o l v e d gases.  (3)  The h e a t e r was t h e n l o w e r e d u n t i l i t r e s t e d on t h e i n n e r t r a n s i t s p i p i n g s u p p d r t f o r c i n g out t h r o u g h t h e o v e r f l o w tube any excess l i q u i d . the  The c u r r e n t t h r o u g h  c e n t r e and guard h e a t e r s was a d j u s t e d u n t i l t h e  temperatures o f t h e two h e a t e r s were as n e a r l y t h e same as p o s s i b l e . (4)  A p p r o x i m a t e l y seven t o e i g h t hours were r e q u i r e d bef o r e e q u i l i b r i u m was a t t a i n e d .  The f i n a l s e t o f  r e a d i n g s were t a k e n one hour a f t e r e q u i l i b r i u m . (j>)  The t h e r m o p i l e s were r e a d e v e r y 10 minutes f o r 1 hour and t h e w a t e r r a t e t h r o u g h t h e o e n t r e c a l o r i m e t e r checked e v e r y 15 minutes.  The average s e t o f t h e s e  r e a d i n g s were used i n t h e f i n a l c a l c u l a t i o n s .  10.  THEORY OF MEASUREMENT  The t r u e calculated  coefficient  by means o f  the k  of  thermal conductivity  Fourier = £ A  steady  state  is  equation,  dx dt  where q,.=* h e a t f l o w «=• ©c.  in  gram.cal./sec.  o f water passing through the  centre  meter per second under e q u i l i b r i u m times  the  increase  i n temperature  calori-  conditions i n degrees  centigrade. A -  effective  •jj-g = s l o p e at  the  area of  of  temperature  temperature  termined. at  the  against  2  gradient  the  true  curve  coefficient drawn  thermocouple temperature  to  in  cm/degree was  de-  graphically  points.  their respective  calorimeter surface  calorimeter i n cm. .  The t a n g e n t s were  desired  The l i q u i d plotted  centre  g i v e the  heights  readings  above the  were  oentre  r e s u l t i n g temperature  gradient  curve. Whereas o n l y t h r e e used i n the  original test  thermocouples.• straight  line,  shape  the  of  Since the then,  liquid  cell,  the  gradient  thermocouples had  been  new t e s t  five  curve  i n using only three  is  c e l l has not  generally  thermocouples,  c u r v e w o u l d be m a t e r i a l l y a l t e r e d i f  one o f  a  the the  11. thermocouples were to give a wrong reading.  This i s not pos-  s i b l e i n the new test c e l l because of the two extra thermocouples.  RESULTS  Thermal Conductivity of Water The apparatus was f i r s t tested by measuring the c o e f f i c i e n t of thermal conductivity of water since t h i s value has been obtained by many other investigators i n r e cent years. It was found that i n a l l the runs made with d i s t i l l e d water, the temperature gradient curves were s l i g h t l y concave to the temperature axis instead of being convex since the thermal conductivity of water increases with temperature. This difference i n the shape of the gradient curve indicates heat losses through the walls of the test c e l l and can be eliminated probably by the addition of a secondary guard-ring heater around the top of the test c e l l , and the substitution of a l a r g e r guard-ring calorimeter f o r the present one. Because of these heat losses, a correction f a c t o r had to be introduced i n the c a l c u l a t i o n of the true coefficients.  Test run #22 was used to obtain the c o r r e c t i o n  factor as shown i n the following sample c a l c u l a t i o n which also i l l u s t r a t e s how the true c o e f f i c i e n t i s obtained by means of a single run.  12. Sample Calculation (Test Run #32) Temperatures  &  M  'fei  51.87°C 43.37°C  37-24°C  £6  Centre Water Rate, Cal. Centre C a l . At «C. cc/min.  fe.  30.12°C 22.32°C 0.63°C  48.2  Heights of Thermocouples above Calorimeter Surface #1 - 2.78 cm.  #6  1.01  cm.  #18- 2*14 cm.  #11-0.29  cm.  #19- 1.61 cm.  -  Centre C a l . -  0.00  cm.  The f i v e " l i q u i d " temperature readings were then plotted against the respective heights of the thermocouples above the calorimeter surface.  This gave the r e s u l t i n g tempera-  ture gradient curve shown i n F i g . 6. True Coefficient of Thermal Conductivity The e f f e c t i v e area "A" under test » 37-66 cm . 2  Value of heat flow, £ = (cc/sec)(At °C) = (48.2^0.6?) . ^ 0  o  6  c a l / s e c  .  The equation f o r the true c o e f f i c i e n t becomes A dt  The following slopes were obtained from the gradient curve in Fig. 6  f  jjf at 25°C - 0.0920 | | at 30°C - 0.0893  9 cO  o m  P N  in ~  o •»  <n 0  0  12. H  a t 25°C = 0.0854 a t 40°C = 0.0838  | | a t 45°C = 0.0797. The  true c o e f f i c i e n t s o f thermal c o n d u c t i v i t y a r e : k 5 - (0.0124)(0.0920J - 0.00124 cal,sec" ,cm.- ,°C- ,ciau 1  2  1  2  = (0.0124)(0.0892) - 0.00120  it  n  k ^ = (0.0124) (0.01054) = 0.00115  "  ft  It  k^O - (0.0124)(0.0838) » 0.00112  «•  It  It  k^  0  k45 The  = (0.0124) (0.0797) - 0.00107  tt  tt  »'  it  v a l u e s f o r t h e t r u e c o e f f i c i e n t s a t t h e same t e m p e r a t u r e s  as above, however, a r e g i v e n by B a t e s and many o t h e r i n v e s t i g a t o r s t o be as f o l l o w s : k £ • 0.00142 cal,sec" ,cm" ,°C" ,cm. 1  2  1  2  k^O = 0.00145  "  £3^ - 0.00147  tt  ti  it  • 0.00149  '»  «»  »  - 0.001505  n  n  «  k4  0  11  •  .  -  These v a l u e s , hence, were s u b s t i t u t e d i n t h e e q u a t i o n , k = 0.0124 | i , dt and  the slopes,  dt  were s o l v e d f o r and found t o be:  • j f a t 25°C - 0.1064 $f a t 20°C m 0.1080 §f a t 35°C = 0.1092  14.  M- at 40°C = 0.1110 at I f . at 42°C = 0.1120 at These are the values that should have been obtained from the temperature  gradient curve i n F i g . 6 i f heat losses  were not present. ,  The experimental and the above calculated slopes  were than plotted as shown i n F i g . 7 and from the deviations . of the two curves the following correction factors were c a l culated which are used to give the corrected slopes  at dt  the particular, temperature. Multiply experimental — at 23°C by 1.1£1 to give corrected | 5 . dt au n  "  « at 30°C by 1.212  «  n  it  n at 35°C by 1.272  "  n  tt  tt  40°o by 1 . 3 3 9  "  n  tt  tt at 43°G by 1.418  a  t  »  " tt  •»  »  »  "  tt  " »  n  "  The r e s u l t s of four runs made on d i s t i l l e d water are shown i n , Table I along with the value of the heat flow f o r that part i c u l a r run.  to  0  in  O  in  0 0  0  O  O 6  O C O  6  O  6  8  00 0 6  O  0  in  0 6  0 0 0  6  15. Table I Heat Plow cal/sec  _23  *30  *35  *40  *45  12  0.440  0.00140  0.00143  0.00148  0.00149  0.00153  13  0.438  0.00139  0.00143  0.00149  0.00152  -  13  0.483  0.00143  0.00146  0.00147  0.00148  -  32  0.306  0.00142  0.00143  0.00146  0.00151  0.00152  0.00142  0.00143  0.00146  0.00151  0.00152  Run No.  Average k  c  T a b l e I I shows v a l u e s o f t h e t r u e c o e f f i c i e n t o f w a t e r a s o b t a i n e d by o t h e r i n v e s t i g a t o r s i n r e c e n t y e a r s .  Con-  s i d e r i n g t h e agreement w i t h t h e v a l u e s g i v e n i n t h i s t a b l e , i t can be assumed t h e n t h a t t h i s a p p a r a t u s i s s u i t a b l e f o r t h e measurement o f t h e t r u e c o e f f i c i e n t s o f t h e r m a l c o n d u c t i v i t y o f 11quids. Table I I Observer  Year  k (true) c  c a l , s e c ~ l , cm"^^OQ-1  Temp. t  c  m  #  OQ  Weber  1903  0.001314  13-31.5  Goldschmidt  1911  0.001500  0  Jakob  1920  0.00143  27.3  Bridgeman  1923  0.00144  30  Davis  1924  0.00144  25  Kaye db H i g g i n s  1928  0.00150  25  Smith'  1930  0.00144  30  Bates  1931  0.00160  30  Bates  1935  0.00145  30  The temperature v a r i a t i o n of k  c  as obtained from  the average of the four runs i s shown plotted i n IPig. 8. Thermal Conductivity of Cis and Trans Decahydronaphthalene Preparation of Sample; The c i s and trans isomers were separated from commercial decalin sold by the Eastman Kodak Co. by r e c t i f i c a t i o n i n a Stedman column^" at 9 mm. pressure. The two isomers thus obtained were then further p u r i f i e d by successive r e c r y s t a l l i z a t i o n s using the method of Seyer and Walker^ u n t i l the trans isomer had a constant freezing point of -30» ]6°0 r  and the c i s isomer had a constant  freezing point of -43.31°C. Trans Decahydronaphthalene: The r e s u l t s of four runs made on the trans isomer are  shown tabulated i n Table I I I . The temperature gradient curve f o r Run 22 i s shown  plotted i n Fig. 6. curves.  A l l other runs had s i m i l a r gradient  The temperature v a r i a t i o n of the true c o e f f i c i e n t  kc as obtained from the average of the four runs i s plotted i n F i g . 8.  r  Augley, Potkins, and Rush, B.A.Sc. Thesis (1942).  'J-.A.CS. 60, 2125 (1938).  O S  O-tr  oe  02  17. Table I I I Run Kb.  Heat Flow cal/sec  1?  25  IC30  *35  *40  0.345  0.00111  0.00110  0.00104  0.00097  0.00085  20  0.356  0.00113  0.00110  0.00106  0.00097  0.00083  22  0.366  0.00110  0.00109  0.00108  0.00099 0.0008?  0.00111  0.00110  0.00109  0.00097  O.OOO86  0.00111  0.00110  O.OOIO7  0.00097  0.00085  23  0.362  Average k Cis  G  k  k  45  Decahydronaphthalene: The r e s u l t s of four runs made on the c i s isomer are  shown tabulated i n Table IV.  The temperature gradient curve  f o r Run 27 i s shown plotted i n F i g . 6 while the temperature v a r i a t i o n of the true c o e f f i c i e n t k  0  as obtained from the  average of the four runs i s plotted i n Fig. 8. Table IV Run Nib.  Heat Flow cal/sec  24  0.399  0.00114  0.00113  0.00112  0.00100  0.00096  25  0.400  0.00114  0.00113  0.00113  0.00101  0.00094  26  0.412  0.00117  0.00115  0.00113  0.00101  0.00097  27  0.390  0.00113  0.00112  0.00110  0.00100  0.00092  0.00114  0.00113  0.00112  0.00101  0.00095  Average k  c  k  25  k  30  k  35  k  40  k  45  Thermal Conductivity o f Cyclohexane The f i n a l c y c l i c hydrocarbon to have i t s true coeff i c i e n t of thermal conductivity calculated was cyclohexane; Several runs were made on t h i s hydrocarbon with the  1  18. v a l u e o f t h e heat f l o w a p p r o x i m a t e l y t h e same as t h a t used i n t h e w a t e r and d e c a l i n r u n s b u t i t was f o u n d t h a t t h e c y c l o hexane e v a p o r a t e d b e f o r e e q u i l i b r i u m c o u l d be r e a c h e d . I n order t o prevent t h i s evaporation, t h e heaters were a d j u s t e d t o g i v e l o w e r t e m p e r a t u r e s t h u s r e d u c i n g t h e amount o f heat f l o w . Over t h i s s m a l l s m a l l t e m p e r a t u r e r a n g e , t h e t r u e c o e f f i c i e n t s were c a l c u l a t e d a t t e m p e r a t u r e s o f 22°C and 30 °C. The r e s u l t a n t g r a d i e n t c u r v e i s shown i n F i g . 6. The v a l u e o f t h e heat f l o w was 0.058 c a l . / s e c . and t h e v a l u e s o f t h e t r u e c o e f f i c i e n t s were as f o l l o w s : k 5 = 0.00028 2  kjo - 0.00024  DISCUSSION OF RESULTS  The v a l u e s o f t h e t r u e c o e f f i c i e n t o f t h e r m a l cond u c t i v i t y o f w a t e r o b t a i n e d a r e comparable t o t h o s e o b t a i n e d by o t h e r i n v e s t i g a t o r s . A l t h o u g h t h e t r u e c o e f f i c i e n t s f o r t h e c i s and t r a n s i s o m e r s a r e h i g h e r t h a n t h o s e o b t a i n e d by R o b i n s o n a n d Younger, i t has been found t h a t j u s t a s i n t h e i r r e s u l t s , t h e . c i s i s o m e r has a h i g h e r c o n d u c t i v i t y t h a n t h e t r a n s i s o m e r . A p o s s i b l e explanation f o r t h e i r lower r e s u l t s might be t h a t i n o r d e r t o o b t a i n t h e i n l e t t e m p e r a t u r e o f t h e c a l o r i m e t e r w a t e r , t h e y had t o remove t h e h e a t e r and r u n w a t e r t h r o u g h t h e c a l o r i m e t e r a s f a s t as p o s s i b l e , and u s i n g  19. the reading given by the exit thermopile as the i n l e t temperature.  This procedure was necessary because the i n l e t thermo-  p i l e read too high due to inadequate immersion.  In so doing,  i t i s very probable that some heat was picked up giving an indicated i n l e t temperature higher than i t should be. The consequence of t h i s would be a smaller temperature difference with a resultant smaller heat flow and c o e f f i c i e n t since A dt  SUGGESTIONS FOR FUTURE RESEARCH  In order to prevent the heat losses present i n t h i s test c e l l , i t i s suggested that a secondary  guard-ring  heater be wound around the top of the c e l l , and also that a larger guard calorimeter replace the present one. The temperature range over which the true coeff i c i e n t s can be determined  i s l i m i t e d by the size of the  heating elements i n the two heaters.  I t i s suggested, there-  fore, that larger heating elements be substituted f o r the present ones which allow only a temperature range up to 45°C.  

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