Thermal resistance analysis of battery thermal management design
Thermal resistance (Thermal resistance) definition
Under normal conditions, heat transfer is carried out through three ways: conduction, convection, and radiation. Conduction is the transfer of heat flow from high temperature to low temperature through the contact of objects. The better the thermal conductivity of the object, the better the thermal conductivity. Generally speaking, metal has the best thermal conductivity; convection is the transfer of heat flow through the flow of objects. The faster the flow rate of liquid and gas, the more heat is taken away; radiation does not require a specific intermediate medium, and directly sends heat out, and the effect is better in a vacuum. Poor thermal conductivity is the resistance encountered by heat on the heat flow path, reflecting the size of the heat transfer capacity of the medium or between media. When heat is transferred inside an object (usually from high temperature to low temperature), the resistance encountered is called thermal resistance. When heat flows through the interface of two contacting solids, the interface itself presents a significant thermal resistance to the heat flow, which is called contact thermal resistance. In the process of convective heat transfer, the thermal resistance between the solid wall and the fluid is called convective heat transfer thermal resistance. The thermal resistance when two objects with different temperatures radiate heat to each other is called radiation thermal resistance.
Causes of thermal resistance
The main causes of thermal resistance are as follows: Thermal conductivity of materials: Different materials have different thermal conductivities. Materials with low thermal conductivity, such as some insulating materials, will have a greater obstruction to heat flow, resulting in increased thermal resistance. For example, the thermal conductivity of air is low, and heat transfer will be significantly hindered in the presence of an air layer. Contact thermal resistance: When two solid surfaces are in contact, the actual contact area is smaller than the apparent contact area due to factors such as surface roughness, insufficient pressure, the presence of impurities or oxide layers, resulting in contact thermal resistance. For example, in electronic devices, contact thermal resistance will result if the contact between the chip and the heat sink is not completely tight. Geometry and size: Geometric factors such as the shape, thickness, and length of an object affect the heat transfer path, resulting in thermal resistance. Longer and thinner objects have a longer path for heat flow, and the thermal resistance is relatively large. Thermal radiation obstruction: Thermal radiation is an important way of heat transfer in high temperature environments. However, thermal resistance will occur if there are objects or surfaces that block thermal radiation. Fluid flow resistance: In the case of heat transfer involving fluid (liquid or gas), factors such as the flow rate, viscosity, shape and size of the channel will affect the heat transfer effect and generate thermal resistance.
How to reduce the contact thermal resistance in battery pack thermal management
1. Optimize the roughness of the contact surface: Through fine processing, reduce the roughness of the contact surface, make the contact more compact and smooth, thereby reducing the contact thermal resistance.
2. Select suitable contact materials: Use interface materials with good thermal conductivity, such as thermal conductive silicone pads, thermal conductive gels, etc., to fill the tiny gaps between the contact surfaces and improve heat transfer.
3. Increase contact pressure: Appropriately increase the contact pressure between the battery and the heat dissipation component, but be careful not to exceed the battery's tolerance range to reduce the contact gap and improve the heat transfer efficiency.
4. Surface treatment: Perform special surface treatment on the contact surface, such as silver plating, gold plating, etc., to improve the surface's thermal conductivity.
5. Optimize the installation process: Ensure accuracy and consistency during the installation process to avoid installation deviations that lead to poor contact.
6. Regular maintenance and inspection: Clean the dirt, oxides, etc. on the contact surface in time to keep the contact surface clean and have good thermal conductivity.
