Thermodynamics
Thermal Resistance
Thermal analog of electrical resistance. ΔT = P × R_th.
Variables
R_thK/W
Thermal resistance
Resistance to heat flow
Lm
Length
Thickness of material
kW/(m·K)
Thermal conductivity
Material property
Am²
Cross-sectional area
Area of heat flow
Derivation
From P = kAΔT/L, define R_th = L/(kA) so ΔT = P·R_th. Resistances add in series.
Your notes
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Common questions
What is the Thermal Resistance formula?
Thermal Resistance is written Rₜₕ = L/kA. Thermal analog of electrical resistance. ΔT = P × R_th. It belongs to Thermodynamics, under Heat & Temperature.
What are the units in Rₜₕ = L/kA?
In SI units, R_th is thermal resistance, measured in s³·K/(kg·m²); L is length, measured in m; k is thermal conductivity, measured in kg·m/(s³·K); A is cross-sectional area, measured in m².
How is the Thermal Resistance formula derived?
From P = kAΔT/L, define R_th = L/(kA) so ΔT = P·R_th. Resistances add in series. The result is Rₜₕ = L/kA.