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# Thermal Resistance definition for thermal contact

In thermal analysis of assemblies, SOLIDWORKS Simulation lets you define thermal contact resistance values. This allows you to model the thermal effect of a layer of a material which is too thin to mesh in 3D. However, the user needs to input the value of the resistance. Here is a primer on how to calculate the thermal resistance:

The expected value is either the total or distributed resistance, respectively in K/W or (K.m²)/W in the SI unit system.

The basic formula for temperature drop in a thin layer of material between two parts is given by:

DT = q * [t / (k * A)]

where:

DT= temperature drop at the contact zone in K

q = heat power flowing through the contact in W

t = thickness of the layer in m

k = thermal conductivity of the layer material in W/(mK)

A = surface area of the contact in m²

The total thermal resistance is t/(k*A) and the distributed resistance is t/k.

Thermal conductivity required to have a given thermal resistance

You can also determine the thermal conductivity required to have a given thermal resistance.

For a material of constant thickness, the total thermal resistance is Rt =  t/(k*A) and the distributed resistance is Rd = t/k.

With:

t = thickness of the layer in m

k = thermal conductivity of the layer material in W/(mK)

A = surface area of the contact in m²

Therefore, you can calculate the required thermal conductivity k to use in a material of thickness t to have the thermal resistance you need: k =  t/(Rt*A) or k = t/Rd.