There are lots of engineering systems that consist of heat transfer through multiple layers. These layers are attached in different means. In this attachment, there is a phenomenon that occurs between the layers which is called thermal contact resistance. Here, we will try to explain the thermal contact resistance between the heat transfer layers.
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What is the Thermal Contact Resistance?
If there are contacting layers where heat transfer is intended, there is a contact area between these layers. This contact area will lead to a drop in temperature. So, heat transfer is affected in a negative way on this contact surface. This contact area leads to a thermal resistance called thermal contact resistance.
The surfaces of the contacting layers are expected as perfect contact. But in real applications, the perfect contact does not happen. Because of the surface characteristics of contacting layers, there will always be micro air gaps which will lead to the thermal contact resistances. There are some applications to eliminate this thermal contact resistance between heat transfer layers.
Calculation of Thermal Contact Resistance
The calculation of the thermal contact resistance is very simple actually. The general formulation to calculate the thermal contact resistance is like this;
According to this formula, with the increasing amount of temperature difference of the contacting surfaces, the thermal resistance value increases. So, the temperature difference is preferred in these systems to eliminate the thermal contact resistance.
There is an inverse proportion between the thermal contact resistance and total heat transfer between the contact surfaces. With the increasing total heat transfer, thermal contact resistance decreases. But in design, total heat transfer is not a changeable value to optimize the thermal contact resistance.
With the increasing total area, thermal contact resistance increases. Because there is a much more area and surface defects in the contact surfaces which means more thermal contact resistance. But also in general, the total area is a pre-defined design condition before eliminating the thermal contact resistance in multilayer heat transfer mechanisms.
How to Eliminate the Thermal Contact Resistance?
The elimination of the thermal contact resistance is made by the application of thin conductive metal layers between the layers. This conductive metal takes the place of air which is responsible for the thermal contact resistance. Heat transfer layers are generally contacted with high pressures, by attaching smooth metal layers between them to minimize the thermal contact resistances.
Thermal grease applications are also general applications between the heat transfer contact sections. Thermally conductive greases fill the air gaps between layers to facilitate the thermal conduction between the layers.
Conclusion
This can be a general explanation of the thermal contact resistance phenomenon in thermal and heat transfer applications.
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