the thermal conductivity

5/17/2018 The Thermal Conductivity

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The thermal conductivity, as defined by Fouriers equation, is a materials ability to transmit heat

by means of conduction, which allows the flow of heat from its warmer surface through the material to

its colder surface shown in Figure ### below:

Figure ###: The illustration for measurement the thermal conductivity of an object.

Thermal conductivity is measured in watts per elvin!meter "$%&'$m&', i.e. ("%$m) or in *+

units "tu$hr&'$ft&'$F&', i.e. tu("hr$ftF). From the Fourier equation, the thermal conductivity of

material is defined as in -q ###

k= Q/A

T/ L "###)

where is the amount of heat transferring through a cross section area of material "/) that

causes a temperature difference " T over a distance " L ). The main difficulty of

measuring thermal conductivity of a liquid is to measure the heat flu0 "(/) because liquid is

subjected to the flow motion of its molecules and does not have a well!defined area.

1onsequently, the heat transfer source is not pure conduction, but it is combination of

conduction, convection or even radiation. The value of thermal conductivity is a material related

property, which is dependent on pressure and temperature. 2owever, in most cases temperature

has higher magnitude effect on thermal conductivity of material than pressure. For solid

materials over certain temperature ranges, thermal conductivity is small enough to be neglected.

2owever, in many cases, such as liquids and gases, the variation of the thermal conductivity with

temperature is significant.

3epending on the thermal properties of material and the medium temperature, there are two

broad categories of measuring thermal conductivity of material: steady!state and transient state.

The steady state technique is used to measure material that has high thermal conductivity such as

solid, while the transient state technique is used to measure material that has low thermal

conductivity such as liquid. *n this e0periment, we use the transient hot wire technique for

measurement of the thermal conductivity of liquid. *t wos based on the detection of the


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temporal temperature rise in a thin wire immersed in the tested liquid, initially at thermal

equilibrium, following the application of a stepwise electrical current. The wire acts as a heat

source and produces a time!dependent temperature field within the liquid. The temperature rise

at the radial distance r from the heat source is given by

T(r , t)= Q

4 k(ln( r2

4 a )+ ln (t))where is the total heat, is thermal conductivity "$%&'$m&'), a is thermal diffusivity of

tested fluid "m4s!') and 5 is a -ulers constant 6.7884'78. The plot of the temperature T"r,t) on alogarithmic scale of time, ln"t), is linear, with the slope m9(";), from that the thermal

conductivity can be derived as -q. ### below:

k= Q

4 m


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MF Name -25 C 0 C 25 C 50 C 75 C 100 C

Cl4 Si ! !

H2O ater ! 6.7>'6 6.>68' 6.>?7 6.>>>@ 6.>8='

Hg Aercury 8.47 8.88 @.47 @.>@ =.68 =.?

CCl 4 Tetrachloromethane ! 6.'6 6.6== 6.6=? 6.6@@ !

CS 2 1arbon disulfide ! 6.'7 6.'= ! ! !

CHCl 3 Trichloromethane 6.'48 6.'44 6.''8 6.''4 6.'68 6.'64

CH 2Br 2 3ibromomethane 6.'46 6.'' 6.'6@ 6.'6? 6.6=8 !

CH 4O Aethanol 6.4' 6.468 6.466 6.'=? ! !

C 2Cl 4 Tetrachloroethylene ! 6.''8 6.''6 6.'6 6.6=8 6.6='

C 2HCl 3 Trichloroethylene 6.'?? 6.'4 6.''> 6.'6@ 6.'66 !

C 2H 3Cl 3 ',','!Trichloroethane ! 6.'6> 6.'6' 6.6=> ! !

C 2H 3N /cetonitrile 6.46@ 6.'=@ 6.'@@ 6.'8@ 6.'>@ !


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C 2H 4O 2 /cetic acid ! ! 6.'7@ 6.'7? 6.'= 6.'

C 2H 5Cl 1hloroethane 6.'7 6.'?4 6.''= 6.'6> 6.6=?

C 2H 5NO N !Aethylformamide ! ! 6.46? 6.46' 6.'== 6.'=>

C 2H 6O -thanol ! 6.'8> 6.'>= 6.'>4 ! !

C 2H 6O 2 -thylene glycol ! 6.47> 6.47> 6.47> 6.47> 6.47>

C 2H 7NO -thanolamine ! ! 6.4== 6.4@> 6.48 6.4>'

C 3H 5ClO -pichlorohydrin 6.'4 6.'?8 6.'?' 6.'47 6.''= 6.''

C 3H 6O /cetone ! 6.'>= 6.'>' ! ! !

C 3H 6O 2 Aethyl acetate 6.'8 6.'> 6.'7? 6.'? 6.'?? 6.'44

C 3H 7NO N,N !3imethylformamide ! ! 6.'@ 6.'8@ 6.'8' 6.'>7

C 3H 8O '!+ropanol 6.'>4 6.'7@ 6.'7 6.'= 6.'7 6.''

C 3H 8O 4!+ropanol 6.'> 6.'' 6.'?7 6.'4= 6.'4 6.''@

C 3H 8O 2 ',4!+ropanediol ! 6.464 6.466 6.'== 6.'=@ 6.'=8

C 3H 8O 3 Blycerol ! ! 6.4=4 6.4=7 6.4=8 6.?66


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C 3H 9N Trimethylamine 6.'? 6.'?? ! ! ! !

C 4H 4O Furan 6.'4 6.'? 6.'4> ! ! !

C 4H 4S Thiophene ! ! 6.'== 6.'=7 6.'=' 6.'@>

C 4H 6 4!utyne 6.'?8 6.'4= 6.'4' ! ! !

C 4H 8O 4!utanone 6.'7@ 6.'7' 6.'7 6.'?= 6.'?? !

C 4 H 8O Tetrahydrofuran 6.'?4 6.'4> 6.'46 6.'' ! !

C 4H 8O 2 ',!3io0ane ! ! 6.'7= 6.'8 6.'?7 6.'4?

C 4H 8O 2 -thyl acetate 6.'>4 6.'7? 6.' 6.'?7 6.'4> !

C 4H 10O '!utanol ! 6.'7@ 6.'7 6.'= ! !

C 4H 10O 3iethyl ether 6.'76 6.'6 6.'?6 6.'46 6.''6 6.'66

C 5H 5N +yridine ! 6.'>= 6.'>7 6.'>' 6.'7@ !

C 5H 8 1yclopentene 6.'? 6.'?> 6.'4= ! ! !

C 5H 10 '!+entene 6.'?' 6.'4 6.''> ! ! !

C 5H 10 1yclopentane 6.'6 6.'?? 6.'4> ! ! !


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C 5H 12 +entane 6.'?4 6.'44 6.''? 6.'6? 6.6=7 6.6@8

C 5H 12O '!+entanol ! 6.'78 6.'7? 6.'= 6.'7 !

C 6H 5Cl 1hlorobenCene 6.'?> 6.'?' 6.'48 6.'44 6.''8 6.''4

For referencehttp://www.engineersedge.com/heat_transfer/thermal_conductivity_of_liquids_9921.htm

http://www.imt.ro/romjist/olum1!/"um#er1!_$/pdf/!1%&odreanu.pdf

http://www.eurotherm2!!'.tue.nl/(roceedings_)urotherm2!!'/papers/&onduction/&*"_1!.pdf

http://www.ime+o.org/pu#lications/wc%2!!$/(,&%2!!$%-&12%!2.pdf

The theoretical model describing the T2 technique is derived from the analytical solution of

the heat conduction equation for a line heat source of radius rD6 and lengthlD' of negligiblethermal mass, which is perfectly embedded, with no thermal contact resistance, in an unbounded

heat sin, initially at uniform temperature T6. The sin is considered of homogeneous and

isotropic material with constant thermal transport properties. hen a constant electric power isstepwise applied, the wire instantly and totally liberates the heat source output per unit length, to

the test sample, where it is conducted outwards and stored entirely.
http://www.engineersedge.com/heat_transfer/thermal_conductivity_of_liquids_9921.htmhttp://www.engineersedge.com/heat_transfer/thermal_conductivity_of_liquids_9921.htmhttp://www.imt.ro/romjist/Volum10/Number10_3/pdf/01-Codreanu.pdfhttp://www.eurotherm2008.tue.nl/Proceedings_Eurotherm2008/papers/Conduction/CON_10.pdfhttp://www.eurotherm2008.tue.nl/Proceedings_Eurotherm2008/papers/Conduction/CON_10.pdfhttp://www.imeko.org/publications/wc-2003/PWC-2003-TC12-027.pdfhttp://www.imt.ro/romjist/Volum10/Number10_3/pdf/01-Codreanu.pdfhttp://www.eurotherm2008.tue.nl/Proceedings_Eurotherm2008/papers/Conduction/CON_10.pdfhttp://www.eurotherm2008.tue.nl/Proceedings_Eurotherm2008/papers/Conduction/CON_10.pdfhttp://www.imeko.org/publications/wc-2003/PWC-2003-TC12-027.pdfhttp://www.engineersedge.com/heat_transfer/thermal_conductivity_of_liquids_9921.htmhttp://www.engineersedge.com/heat_transfer/thermal_conductivity_of_liquids_9921.htm

the thermal conductivity

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