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Why is contact pressure so important? Explore the key factors in the heat transfer process!
In physics, thermal contact thermal conductivity is the study of heat transfer between solids or liquids in thermal contact. When two solid objects like A and B come into contact, heat flows from the hotter object to the cooler object. However, this process is not as simple as imagined because there is a thermal contact resistance between the contact surfaces.
Thermal contact resistance is defined as the ratio of this temperature drop to the average heat flow across the interface.
This phenomenon means that the thermal conductivity between the two is uneven. Even when the two solides are in perfect contact, there is a thermal resistance between the contact surfaces. Many studies have shown that thermal contact thermal conductivity is not only an important factor in solid industry and construction technology, but also plays a vital role in multiple applications such as nuclear reactor cooling, electronic packaging, heat exchangers, etc.
Factors affecting thermal conductivity of thermal contact
Thermal contact thermal conductivity is a complex phenomenon, with multiple factors affecting its effectiveness. According to research, here are some of the most important factors:
Contact pressure
Contact pressure is one of the most important factors affecting heat transfer between two contacting objects. When the contact pressure increases, the real contact area of the contact surface increases, resulting in an increase in contact thermal conductivity, that is, a decrease in thermal contact resistance. This is why most studies measure and model contact thermal conductivity and contact pressure as interrelated topics.
Gap material
There is no completely smooth surface. When two surfaces come into contact, a small range of contact points will be formed with relatively large gaps between these points. The gas or liquid filling these gaps affects the total amount of heat flow. The thermal conductivity of the gap material and its pressure affect the contact thermal conductivity.
Surface roughness and ripples
After a surface undergoes certain machining procedures, these properties can be described in terms of roughness, ripples and fractal dimensions. In particular, the effect of surface roughness on thermal conductivity can be compared to the concept of electrical contact resistance.
When two objects come into contact, plastic or elastic deformation may occur on the surface. Such deformation will increase the actual contact area and thereby reduce the contact impedance.
Surface cleanliness
The cleanliness of the surface may also have an impact on contact thermal conductivity. Dust, acid or other impurities will reduce contact efficiency and affect the transfer of heat flow.
Measuring thermal contact thermal conductivity
Calculation of thermal contact conductivity is often difficult because measuring the contact area A is often challenging. Therefore, this property is usually obtained experimentally, and there are related reports and data in many engineering literatures.
However, there is a lack of a centralized thermal contact thermal conductivity database, which results in many companies potentially using outdated or irrelevant data. The CoCoE project, started in 2006, aims to solve this problem by creating a centralized database of contact thermal conductivity data and developing corresponding computer programs.
Thermal boundary thermal conductivity
Even when the contact surface is ideal, there is still a certain thermal boundary thermal conductivity due to different electronic and vibrational characteristics between materials. This thermal conductivity is often particularly important in nanomaterial systems.
In general, thermal contact thermal conductivity not only has important applications in scientific experiments, but also has a profound impact on our daily lives and industrial processes. Have you ever wondered how the quality of thermal contact in the equipment we use every day affects its performance and longevity?
