What is thermal resistance
In the thermal industry, thermal conductivity is an important parameter reflecting the thermal conductivity of materials. However, in practical application, it is often not enough to evaluate the applicability of products only by thermal conductivity. We often need to introduce another parameter - thermal resistance or thermal resistance to help judge.
Define:
Thermal resistance is defined as the ratio between the temperature difference at both ends of the object and the power of the heat source when heat is transmitted in the object. It can be understood that the resistance encountered by heat on the heat flow path reflects the heat transfer capacity of the medium or between the media, and indicates the temperature rise caused by 1W heat, in K / W or ℃ / W.
Thermal Impedance:
Thermal impedance refers to the thermal resistance per unit area of a material, and its unit is ℃ · cm2 / W or ℃ · in2 / W. Compared with thermal resistance, the calculation of thermal impedance takes more consideration of area. The thermal resistance is for a single material, and the thermal resistance of the interface material will also depend on the actual assembly conditions.
When heat flows through the interface of two contacting solids, the interface itself presents obvious thermal resistance to heat flow, which is called contact thermal resistance. The main reason for the contact thermal resistance is that for any two objects that appear to be in good contact, the actual area of direct contact is only a part of the interface (Figure), and the rest are gaps. The heat is transferred by the heat conduction and heat radiation of the gas in the gap, and their heat transfer ability is far less than that of ordinary solid materials. When the heat flow flows through the interface, the contact thermal resistance will greatly reduce the heat transfer efficiency and make the temperature t drop sharply along the heat flow direction. This phenomenon needs to be avoided in engineering application.
How to calculate thermal resistance:
How to reduce thermal resistance：
1. Increase the pressure on the indirect contact surface of the object to deform the protruding part on the interface of the object, so as to reduce the gap and increase the contact surface.
2. Fill the gap at the interface between the two objects with heat-conducting material and exhaust the air as much as possible, such as using thermal grease.
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