Math 2.0

Classical thermodynamics, heat transfer Definition

Thermal resistance

Builds on Steady-state heat conductionHeat fluxThermal conductivityTemperature

Definition

Let an object carry heat in steady state between two surfaces held at uniform temperatures T1T_1 and T2T_2. Let Q≠0Q \ne 0 be the heat rate, in watts, from the first surface to the second. The thermal resistance of the object between the two surfaces is R=T1−T2Q.R = \frac{T_1 - T_2}{Q}. Its unit is K W−1\mathrm{K \, W^{-1}}. The reciprocal 1/R1/R is the thermal conductance.

Remarks

Example: a flat wall of thickness LL, area AA and conductivity kk has Q=kA(T1−T2)/LQ = k A (T_1 - T_2) / L by the linear steady profile. So R=L/(kA)R = L / (k A).

Non-example: the heat flux per kelvin, q/(T1−T2)q / (T_1 - T_2), is not a resistance. It is a conductance per unit area, and its unit is W m−2 K−1\mathrm{W \, m^{-2} \, K^{-1}}.

For layers in series that carry the same heat rate, the resistances add: R=R1+R2R = R_1 + R_2. For paths in parallel with the same end temperatures, the conductances add.

Reading path

To understand this page from the ground up, read these 5 pages in order. The foundations come first.

Show the path as a graph
Heat flux, concept, no evidence levelHeat fluxconceptSteady-state heat conduction, concept, no evidence levelSteady-state heat con…conceptTemperature, concept, no evidence levelTemperatureconceptThermal conductivity, concept, no evidence levelThermal conductivityconceptThermal resistance, definition, no evidence levelThermal resistancedefinition
Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
  • no evidence level
  1. Heat flux concept
  2. Steady-state heat conduction concept
  3. Temperature concept
  4. Thermal conductivity concept
  5. Thermal resistance definition

Further reading

  1. Web https://en.wikipedia.org/wiki/Thermal_conductance_and_resistance
About this page
TagZWE9BFVQ37
URIm2://ZWE9BFVQ37
Kinddefinition
WritingW0 stub
MSC80A19
DefinesThermal resistance
UsesSteady-state heat conduction, Heat flux, Thermal conductivity, Temperature
Changed3 November 2026

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