Thermal conductivity - Revision history

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Energy>Jmdonev: /* For Further Reading */

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For Further Reading

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	<onlyinclude>'''Thermal conductivity''', frequently represented by <math>\kappa</math>, is a property that relates the rate of [[heat]] loss per unit area of a material to its rate of change of [[temperature]].<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction\|conducts]] heat.</onlyinclude> In [[SI\|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] <math>\left(\frac{W}{m K}\right)</math><ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units\|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] <math>\left(\frac{BTU}{h ft ^{\circ}F}\right)</math>.<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.		<onlyinclude>'''Thermal conductivity''', frequently represented by <math>\kappa</math>, is a property that relates the rate of [[heat]] loss per unit area of a material to its rate of change of [[temperature]].<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction\|conducts]] heat.</onlyinclude> In [[SI\|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] <math>\left(\frac{W}{m K}\right)</math><ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units\|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] <math>\left(\frac{BTU}{h ft ^{\circ}F}\right)</math>.<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.

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	==Values for Common Materials==		==Values for Common Materials==
	{\| class="wikitable ~~floatleft~~"		{\| class="wikitable floatright"
	\|+Thermal Conductivity, <math>\kappa</math><ref>The Engineering Toolbox. (May 12, 2015). ''Thermal Conductivity of Common Materials and Gases'' [Online]. Available: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html </ref>		\|+Thermal Conductivity, <math>\kappa</math><ref>The Engineering Toolbox. (May 12, 2015). ''Thermal Conductivity of Common Materials and Gases'' [Online]. Available: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html </ref>
	\|-		\|-
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	\|}		\|}
	<br/>		<br/>
	From the table to the ~~left~~, it can be seen that most materials generally associated with being good [[conductor]]s have a high thermal conductivity. Mainly metals have very high thermal conductivity which compares well to what is known about [[metal]]s. As well, insulating materials such as aerogel and insulation used in homes has a low thermal conductivity, indicating that they do not let heat pass through them easily. Thus a low thermal conductivity indicates a good insulating material.		From the table to the right, it can be seen that most materials generally associated with being good [[conductor]]s have a high thermal conductivity. Mainly metals have very high thermal conductivity which compares well to what is known about [[metal]]s. As well, insulating materials such as aerogel and insulation used in homes has a low thermal conductivity, indicating that they do not let heat pass through them easily. Thus a low thermal conductivity indicates a good insulating material.

	Materials in between these have neither significant insulating or conducting properties. Cement and glass neither conduct extremely large amounts of heat nor do they insulate extremely well.		Materials in between these have neither significant insulating or conducting properties. Cement and glass neither conduct extremely large amounts of heat nor do they insulate extremely well.

	The idea that the thermal conductivity of certain materials are linked to how well they insulate provides a connection between thermal conductivity, and [[R-value]]s/ [[U-value]]s. Since U and R-values to express how well a certain material resists the flow of heat, thermal conductivity plays a role in shaping these values. However, the U and R values also are dependent on the thickness of the material whereas thermal conductivity does not account for this.		The idea that the thermal conductivity of certain materials are linked to how well they insulate provides a connection between thermal conductivity, and [[R-value]]s/ [[U-value]]s. Since U and R-values to express how well a certain material resists the flow of heat, thermal conductivity plays a role in shaping these values. However, the U and R values also are dependent on the thickness of the material whereas thermal conductivity does not account for this.
	~~<br/><br/><br/>~~

	==~~Thermal and Electrical Conductivity~~==		==For Further Reading==
	~~The values for thermal conductivity and electrical conductivity of metals can be expressed and compared using a ratio known as the Wiedemann-Franz Ratio. This ratio is expressed as:<ref name=hp/>~~		*[[Thermal conduction]]
			*[[Electrical conduction]]
	~~<center><math>L = \frac{\kappa}{\sigma T} = \frac{\pi^2k^2}{3e^2}</math></center>~~		*[[Insulation]]
			*[[Thermal insulation]]
	~~Where:~~		*[[Electrical insulator]]
			*Or explore a [[Special:Random\|random page]]
	* ~~<math>L</math> is a constant known as the ''Lorentz number'', equal to 2.44 x 10<sup>-8</sup> WΩ/K<sup>2</sup>~~
	* ~~<math>\kappa</math> is the thermal conductivity of the material~~
	* ~~<math>\sigma</math> is the~~ [[~~electrical conductivity~~]] ~~of the material~~
	* ~~<math>T</math> is the temperature of the material, in Kelvin~~
	* ~~<math>k</math> is the~~ [[~~Boltzmann's constant~~]]
	* ~~<math>e</math> is the elementary charge of an~~ [[~~electron~~]]

	==References==		==References==
	{{reflist}}		{{reflist}}
	[[Category:Uploaded]]		[[Category:Uploaded]]

Jmdonev: 1 revision imported: Doing upload, largely of old redirects.

2018-06-04T16:52:31Z

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Jmdonev at 21:28, 1 June 2018

2018-06-01T21:28:56Z

← Older revision		Revision as of 21:28, 1 June 2018
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	<onlyinclude>'''Thermal conductivity''', frequently represented by <math>\kappa</math>, is a property that relates the rate of [[heat]] loss per unit area of a material to its rate of change of [[temperature]].<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction\|conducts]] heat.</onlyinclude> In [[SI\|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] <math>\left(\frac{W}{m K}\right)</math><ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units\|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] <math>\left(\frac{BTU}{h ft ^{\circ}F}\right)</math>.<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.		<onlyinclude>'''Thermal conductivity''', frequently represented by <math>\kappa</math>, is a property that relates the rate of [[heat]] loss per unit area of a material to its rate of change of [[temperature]].<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction\|conducts]] heat.</onlyinclude> In [[SI\|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] <math>\left(\frac{W}{m K}\right)</math><ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units\|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] <math>\left(\frac{BTU}{h ft ^{\circ}F}\right)</math>.<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.

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	* <math>\sigma</math> is the [[electrical conductivity]] of the material		* <math>\sigma</math> is the [[electrical conductivity]] of the material
	* <math>T</math> is the temperature of the material, in Kelvin		* <math>T</math> is the temperature of the material, in Kelvin
	* <math>k</math> is the [[Boltzmann constant]]		* <math>k</math> is the [[Boltzmann's constant]]
	* <math>e</math> is the elementary charge of an [[electron]]		* <math>e</math> is the elementary charge of an [[electron]]

Jmdonev: 1 revision imported

2018-05-18T22:53:12Z

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Jmdonev at 22:32, 11 May 2018

2018-05-11T22:32:07Z

← Older revision		Revision as of 22:32, 11 May 2018
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	[[Category:Done ~~2015~~-06-01]]		[[Category:Done 2018-05-18]]
	<onlyinclude>'''Thermal conductivity''', frequently represented by <m>\kappa</m>, is a property ~~of a material~~ that relates the rate of [[heat]] loss per unit area of ~~the~~ material to ~~the~~ rate of change of [[temperature]] ~~of the material~~.<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction\|conducts]] heat.</onlyinclude> In [[SI\|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] (<m>\frac{W}{m K}</m>)<ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units\|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] (<m>\frac{BTU}{h ft ^{\circ}F}</m>).<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.		<onlyinclude>'''Thermal conductivity''', frequently represented by <math>\kappa</math>, is a property that relates the rate of [[heat]] loss per unit area of a material to its rate of change of [[temperature]].<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction\|conducts]] heat.</onlyinclude> In [[SI\|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] <math>\left(\frac{W}{m K}\right)</math><ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units\|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] <math>\left(\frac{BTU}{h ft ^{\circ}F}\right)</math>.<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.

	Since [[heat transfer mechanisms\|heat transfer]] by [[conduction]] involves transferring energy without motion of the material, it is logical that the rate of the transfer of heat would depend only on the temperature difference between two locations and the thermal conductivity of the material.		Since [[heat transfer mechanisms\|heat transfer]] by [[conduction]] involves transferring energy without motion of the material, it is logical that the rate of the transfer of heat would depend only on the temperature difference between two locations and the thermal conductivity of the material.
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	==Values for Common Materials==		==Values for Common Materials==
	{\| class="wikitable floatleft"		{\| class="wikitable floatleft"
	\|+Thermal Conductivity, <m>\kappa</m><ref>The Engineering Toolbox. (May 12, 2015). ''Thermal Conductivity of Common Materials and Gases'' [Online]. Available: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html </ref>		\|+Thermal Conductivity, <math>\kappa</math><ref>The Engineering Toolbox. (May 12, 2015). ''Thermal Conductivity of Common Materials and Gases'' [Online]. Available: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html </ref>
	\|-		\|-
	! Material !! Conductivity at 25<sup>o</sup>C		! Material !! Conductivity at 25<sup>o</sup>C
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	Materials in between these have neither significant insulating or conducting properties. Cement and glass neither conduct extremely large amounts of heat nor do they insulate extremely well.		Materials in between these have neither significant insulating or conducting properties. Cement and glass neither conduct extremely large amounts of heat nor do they insulate extremely well.

	The idea that the thermal conductivity of certain materials are linked to how well they insulate provides a connection between thermal conductivity and [[R-value]]s ~~and~~ [[U-value]]s. ~~The construction industry uses the~~ U and R-values to express how well a certain material resists the flow of heat ~~across the material~~, ~~which partially has to do with the~~ thermal conductivity ~~of the material itself~~. However, the U and R values also are dependent on the thickness of the material whereas thermal conductivity does not account for this.		The idea that the thermal conductivity of certain materials are linked to how well they insulate provides a connection between thermal conductivity, and [[R-value]]s/ [[U-value]]s. Since U and R-values to express how well a certain material resists the flow of heat, thermal conductivity plays a role in shaping these values. However, the U and R values also are dependent on the thickness of the material whereas thermal conductivity does not account for this.
	<br/><br/><br/>		<br/><br/><br/>

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	The values for thermal conductivity and electrical conductivity of metals can be expressed and compared using a ratio known as the Wiedemann-Franz Ratio. This ratio is expressed as:<ref name=hp/>		The values for thermal conductivity and electrical conductivity of metals can be expressed and compared using a ratio known as the Wiedemann-Franz Ratio. This ratio is expressed as:<ref name=hp/>

	<center><m>L = \frac{\kappa}{\sigma T} = \frac{\pi^2k^2}{3e^2}</m></center>		<center><math>L = \frac{\kappa}{\sigma T} = \frac{\pi^2k^2}{3e^2}</math></center>

	Where:		Where:

	* <m>L</m> is a constant known as the ''Lorentz number'', equal to 2.44 x 10<sup>-8</sup> WΩ/K<sup>2</sup>		* <math>L</math> is a constant known as the ''Lorentz number'', equal to 2.44 x 10<sup>-8</sup> WΩ/K<sup>2</sup>
	* <m>\kappa</m> is the thermal conductivity of the material		* <math>\kappa</math> is the thermal conductivity of the material
	* <m>\sigma</m> is the [[electrical conductivity]] of the material		* <math>\sigma</math> is the [[electrical conductivity]] of the material
	* <m>T</m> is the temperature of the material, in Kelvin		* <math>T</math> is the temperature of the material, in Kelvin
	* <m>k</m> is the [[Boltzmann constant]]		* <math>k</math> is the [[Boltzmann constant]]
	* <m>e</m> is the elementary charge of an [[electron]]		* <math>e</math> is the elementary charge of an [[electron]]

	==References==		==References==
	{{reflist}}		{{reflist}}
	[[Category:Uploaded]]		[[Category:Uploaded]]

J.williams: 1 revision imported

2015-08-26T21:31:43Z

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J.williams at 17:00, 12 August 2015

2015-08-12T17:00:13Z

New page

[[Category:Done 2015-06-01]]
<onlyinclude>'''Thermal conductivity''', frequently represented by <m>\kappa</m>, is a property of a material that relates the rate of [[heat]] loss per unit area of the material to the rate of change of [[temperature]] of the material.<ref name=hp>HyperPhysics. (May 12, 2015). ''Thermal Conductivity'' [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html</ref> Essentially, it is a value that accounts for any property of the material that could change the way it [[conduction|conducts]] heat.</onlyinclude> In [[SI|SI units]], thermal conductivity is expressed in [[watt]]s per [[meter]] [[kelvin]] (<m>\frac{W}{m K}</m>)<ref name="text1">R. Chabay, B. Sherwood. (May 12, 2015). ''Matter & Interactions'', 3rd ed., Hoboken, NJ, U.S.A.: John Wiley & Sons, 2011</ref> whereas in [[imperial system of units|imperial units]] it can be expressed in [[BTU]] per [[hour]] per [[foot]] [[Fahrenheit]] (<m>\frac{BTU}{h ft ^{\circ}F}</m>).<ref>D Green, R Perry. (May 12, 2015). ''Perry's Chemical Engineers' Handbook'', 7th ed., McGraw-Hill, 1997.</ref> Materials with a higher thermal conductivity are good conductors of thermal energy.

Since [[heat transfer mechanisms|heat transfer]] by [[conduction]] involves transferring energy without motion of the material, it is logical that the rate of the transfer of heat would depend only on the temperature difference between two locations and the thermal conductivity of the material.

For more information on thermal conductivity, see [http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html Hyperphysics].

==Values for Common Materials==
{| class="wikitable floatleft"
|+Thermal Conductivity, <m>\kappa</m><ref>The Engineering Toolbox. (May 12, 2015). ''Thermal Conductivity of Common Materials and Gases'' [Online]. Available: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html </ref>
|-
! Material !! Conductivity at 25oC
|-
| Acrylic || 0.2
|-
| Air || 0.024
|-
| Aluminum || 205
|-
| [[Bitumen]] || 0.17
|-
| Brass || 109
|-
| Cement || 1.73
|-
| [[Copper]] || 401
|-
| Diamond || 1000
|-
| Felt [[Insulation]] || 0.04
|-
| Glass || 1.05
|-
| Iron || 80
|-
| [[Oxygen]] || 0.024
|-
| Paper || 0.05
|-
| Silica Aerogel || 0.02
|-
| [[Vacuum]] || 0
|-
| [[Water]] || 0.58
|}
 
From the table to the left, it can be seen that most materials generally associated with being good [[conductor]]s have a high thermal conductivity. Mainly metals have very high thermal conductivity which compares well to what is known about [[metal]]s. As well, insulating materials such as aerogel and insulation used in homes has a low thermal conductivity, indicating that they do not let heat pass through them easily. Thus a low thermal conductivity indicates a good insulating material.

Materials in between these have neither significant insulating or conducting properties. Cement and glass neither conduct extremely large amounts of heat nor do they insulate extremely well.

The idea that the thermal conductivity of certain materials are linked to how well they insulate provides a connection between thermal conductivity and [[R-value]]s and [[U-value]]s. The construction industry uses the U and R-values to express how well a certain material resists the flow of heat across the material, which partially has to do with the thermal conductivity of the material itself. However, the U and R values also are dependent on the thickness of the material whereas thermal conductivity does not account for this.
 

==Thermal and Electrical Conductivity==
The values for thermal conductivity and electrical conductivity of metals can be expressed and compared using a ratio known as the Wiedemann-Franz Ratio. This ratio is expressed as:<ref name=hp/>

<center><m>L = \frac{\kappa}{\sigma T} = \frac{\pi^2k^2}{3e^2}</m></center>

Where:

* <m>L</m> is a constant known as the ''Lorentz number'', equal to 2.44 x 10-8 WΩ/K2
* <m>\kappa</m> is the thermal conductivity of the material
* <m>\sigma</m> is the [[electrical conductivity]] of the material
* <m>T</m> is the temperature of the material, in Kelvin
* <m>k</m> is the [[Boltzmann constant]]
* <m>e</m> is the elementary charge of an [[electron]]

==References==
{{reflist}}
[[Category:Uploaded]]