Experimental And Modeling Study On A High-low Temperature Environment Chamber With LN₂ And Helium As Coolants

Aerospace equipment and parts withstand extremely harsh environments such as high vacuum, cold, black background in space. To ensure the reliability and stability of its proper work, space environment simulation test is usually required on the ground. In some special occasion extreme low temperature, high cooling rate, etc. are even required. In such occasions, cryostat device by filling medium to enhance heat transfer efficiency enhancement becomes the main solution. In this paper, experimental and simulation characteristics of the high-low temperature environment chamber with liquid nitrogen / helium as coolants were studied, the main results of which are as follows:（1） Investigated the cooling performance of LN₂ as single coolant and LN₂ / helium as double coolants where the chamber is filled with helium under the condition of absolute pressure 90 kPa. When the LN₂ as single cold source, the heat sink can meet the average cooling rate-3℃/min during the room temperature to-170℃,the space meet the average space cooling rate-3℃/min during the room temperature to-120℃. After equilibration, the heat sink temperature stabilized at-185 ±4℃, space temperature stabilized at-171±3℃.（2） Stirling refrigerator and LN₂ as dual coolants compared to using LN₂ as single coolant can achieve a greater cooling rate. The heat sink can meet the average cooling rate is greater than-3℃/min during the room temperature to-180℃, the space can meet the average cooling rate is greater than-3℃/min during the room temperature to-130℃. When reach the final equilibrium state, the heat sink temperature stabilized at-191±5℃, space temperature stabilized at-182±5℃. The heat sink can be stabilized at an average temperature of-215±5 ℃ and the corresponding space field temperature stabilized at-208±8℃ through pumping operation of helium and cooling by Stirling refrigerator, which breaking the cooling limit caused by using LN₂ alone.（3） In contrast to the test condition, a numerical model was conducted to simulate the regular cooling of the space and specimen. Space cooling rate and specimen cooling curve showed good agreement with the experimental results, verifying the accuracy of the simulation model. And by the temperature distribution and heat transfer coefficient around the heat sink and the specimen, it is considered that the convection heat transfer occupy a larger proportion than radiation during the cooling process that close to the target temperature. So the high-low temperature chamber has a greater advantage than the thermal vacuum tank.（4） Comparing the cool conditions under four filling pressures（90k Pa/40kPa/10kPa/100Pa）. The results show that the uniformity of the space temperature field and the cooling performance of the specimen are both deteriorated with the decreasing of space filling pressure. It can be seen, the chamber filled 90 k Pa gaseous helium both provide certain negative atmosphere, but also enhance heat transfer in the chamber than thermal vacuum chamber.