# Thermal Resistor

Heat transfer by conduction through a layer of material

## Library

Semiconductors / Fundamental Components / Thermal

## Description

The Thermal Resistor block represents heat transfer by conduction through a layer of material. The heat transfer is:

• Governed by Fourier’s law

• Proportional to the temperature difference across the layer of material

• Inversely proportional to the thermal resistance of the material

The equation for conductive heat transfer is:

`${Q}_{AB}=\frac{{T}_{AB}}{{R}_{thermal}},$`
where:

• QAB is the heat flow through the material.

• TAB is the temperature difference across the layer of material.

• Rthermal is the thermal resistance of the material.

Thermal resistance can be calculated as:

`${R}_{thermal}=\frac{D}{kA},$`
where:

• D is the thickness of the layer of material.

• k is the thermal conductivity of the material.

• A is the area normal to the heat flow direction.

Use the Thermal Resistor block to parameterize an equivalent component in terms of thermal resistance of the material layer. To parameterize an equivalent component in terms of the thickness, thermal conductivity, and area of the material layer, use the Conductive Heat Transfer block from the Simscape™ Foundation library.

## Parameters

### Parameters Tab

Thermal resistance

The default value for the thermal resistance, Rthermal, is `1e-3` `K/W`.

### Variables Tab

Use the Variables tab to set the priority and initial target values for the block variables before simulation. For more information, see Set Priority and Initial Target for Block Variables (Simscape) .

Unlike block parameters, variables do not have conditional visibility. The Variables tab lists all the existing block variables. If a variable is not used in the set of equations corresponding to the selected block configuration, the values specified for this variable are ignored.

## Ports

The block has the following ports:

A

Thermal conserving port associated with surface A of the material that the heat flows through.

B

Thermal conserving port associated with surface B of the material that the heat flows through.