TEC Science Class：How does the thermal resistance on both sides of a semiconductor refrigerator significantly affect the refrigeration performance?
Welcome to TEC Science Lesson! This issue will describe in detail the influence of thermal resistance on both sides of semiconductor refrigeration performance. If you have questions about this article or want to learn more about TEC, please leave a comment in the comments section
01 What is thermal resistance?
Simply put, thermal resistance is the degree to which an object impedes the transfer of heat. For semiconductor refrigeration, the thermal resistance on both sides mainly comes fromThe thermal conductivity material in contact with it, the contact thermal resistance between interfaces and the external heat dissipation environmentLet's wait.
▲ Schematic diagram of refrigeration unit
Above is a schematic diagram of the structure of the cooling unit: the entire unit is composed of a semiconductor cooler, thermal materials on both sides, a heat sink and a fan. For users, it is important to pay attention to the temperature and cooling capacity on both sides of the refrigeration unit. The temperature on both sides of the refrigeration unit is affected by the thermal conductivity of the thermal conductivity material, and when the thermal resistance of the thermal conductivity material is large, it will hinder the transfer of heat. Therefore, thermal resistance has a significant influence on the key parameters of semiconductor refrigeration system.
02 Influence of thermal resistance on key parameters
Take the standard TEC-12706 as an example:
1. The influence of thermal resistance on cold and hot end temperature (Tc/Th) and temperature difference (DT) : As shown in the figure, when the cooling capacity (Qc=10W) and the temperature on both sides of the refrigeration unit (Th '=50℃, Tc' =20) are set to a fixed value, it can be seen that the semiconductor refrigerator as a "barrier" forms a temperature gradient inside the thermal conductivity material. When the thermal resistance increases, the temperature on the hot side increases, the temperature on the cold side decreases, the temperature gradient increases, and the temperature difference on both sides of the semiconductor cooler will also increase.
▲ The temperature and temperature difference on both sides of the semiconductor refrigerator change with thermal resistance curve
2. The influence of thermal resistance on cooling capacity (Qc) : As shown in the figure, when the input current (I=3A) and the temperature on both sides of the refrigeration unit (Th '=50℃, Tc' =20) are set to a fixed value, the thermal resistance is increased, the power consumption is increased, and the cooling capacity is decreased. It can be seen that in a semiconductor refrigeration system, increasing the thermal resistance will increase the temperature difference, which will lead to a decrease in cooling capacity. On the contrary, reducing the thermal resistance can improve the heat transfer efficiency and quickly remove the cold end heat, thereby increasing the cooling capacity.
▲ Cooling capacity and power consumption with thermal resistance change curve
3.The effect of thermal resistance on refrigeration efficiency (COP) : refrigeration efficiency (ratio of refrigeration capacity to input power) is an important indicator to measure the performance of semiconductor refrigeration. As shown in the figure, when the cooling capacity (Qc=10W) and the temperature on both sides of the refrigeration unit (Th '=50℃, Tc' =20) are set to a fixed value, the electrical power consumption increases with the increase of thermal resistance, and the COP decreases. It can be seen that in a semiconductor refrigeration system, if the thermal resistance on both sides increases, the temperature gradient will increase, in order to keep the cold side temperature of the refrigeration unit unchanged, and achieve the same cooling effect, the input power needs to increase, then the COP will decrease.
▲ Cooling efficiency with thermal resistance curve
03 Cold/hot end thermal resistance simulation experiment
When we assemble the semiconductor cooler, in order to fix it on the target plane and ensure maximum heat conduction, we will apply thermal grease, solder paste welding or attach thermal gaskets. The thermal resistance of different thermal conductive materials is closely related to its thickness, thermal conductivity and cross-sectional area.Here is a set of simulation experiments to test the extent to which the addition of thermal resistance on the cold/hot side affects the cooling performance of the semiconductor.
Take the standard TEC-12706 as an example:
In this simulation experiment, the input current is 3A, the heat load on the cold side is 10W, the thickness of the thermal pad is 0.3mm, the thermal conductivity is 5W/ (m•k), the temperature on the hot side is 50℃ (if the thermal pad is installed, the temperature on the external surface is the ambient side), and the size of the semiconductor cooler is 39.7*39.7mm. Because of the thermal resistance of the thermal gasket itself, it can be divided into four simulation groups: (1) no thermal resistance; ② cold side heating resistance; ③ heating resistance on the hot side; ④ Bilateral heating resistance. Please swipe the image to see the simulation results in four different states.
It can be seen from the experimental results that the state of no thermal resistance on both sides can ensure the smooth conduction of heat. When thermal resistance is added to the cold side, the cold side temperature increases slightly, but the amplitude is small. When thermal resistance is added to the hot side, the temperature of the cold side increases obviously, indicating that the thermal resistance has affected the heat transfer. When thermal resistance is added to both sides, the temperature of the cold side reaches the highest. In summary, it can be seen that when there is thermal resistance on the hot side of the semiconductor refrigerator, the heat transfer is most affected.
04 Reduce thermal resistance - Optimize TEC performance
So far, we have verified that the fluctuation of thermal resistance on both sides of TEC (especially the hot side) will affect the performance stability of TEC. Therefore, it is very important to maintain the stability of thermal resistance, and the following points need to be done:
1. Optimize thermal conductivity materials: select materials with high thermal conductivity, such as aluminum, copper, etc., to reduce thermal resistance.
2. Improve the interface contact process: reduce the contact thermal resistance between the interfaces by surface treatment, increasing contact pressure and other methods.
3. Strengthen external heat dissipation design: Use efficient radiators, fans, etc., to improve heat dissipation efficiency and reduce thermal resistance.
Through this lesson, we realized that in the design of semiconductor refrigeration, in addition to reasonable selection of TEC models that meet the needs, effectively reducing the thermal resistance on both sides is also the key to improve the refrigeration performance. Only when these factors are considered comprehensively, can efficient and stable refrigeration effects be achieved.
