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What are “Thermal Conductivity”, “Thermal Resistance”, and “Thermal Impedance”?

日期：2018-09-14 20:43:19

What are “Thermal Conductivity”, “Thermal Resistance”, and “Thermal Impedance”?

Answer: Thermal Conductivity means that under the condition of 1 degree(K，℃) temperature difference between two sides of 1m thick material, how much heat will be transmitted through 1 square meter area. The unit is W/(m·K). The “K” can be adopted by℃ instead. According to Fourier’s Law, thermal conductivity K is calculated as below:

 

 

Thermal conductivity is the inherent characteristics of the material, not changing with the thickness or area of the material.

 

Thermal resistance is resistance that heat encounters in the flow path, which reflects heat transfer capacity between medium. It indicates temperature rising degrees caused by 1W heat quantity. Thermal resistance R is calculated as below:

 


 

 

Thermal resistance is in proportion to material’s thickness, but in inverse proportion to material’s area.

 

Thermal Impedance is the unit area of thermal resistance, whose unit is (℃*m2)/W or (K*m2)/W. It is calculated as below:

 

 

Thermal impedance is in proportion to material’s thickness.
K：Thermal conductivity, W/ (m*K);
Q：Heat flow perpendicular to the transversal surface of heat transfer, W;
H：Sample’s thickness, m;
A：Sample’s cross-sectional area perpendicular to heat flow path, m2;
△T：Sample’s surface temperature difference perpendicular to heat flow,  K.


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