Effect of nitrogen contamination on the performance of pulse tube cryocoolers

With no moving parts at the cold end, pulse tube cryocooler has the advantages of high reliability and long lifetime, which makes it widely used in infrared detection. The contamination of working medium is one of the typical failure mechanisms of pulse tube cryocoolers. With the development of pulse tube cryocooler from the temperature of liquid nitrogen to lower temperatures, nitrogen has become a main kind of impurity gas that deteriorates the performance of pulse tube cryocooler. It is of great significance to study the influence mechanism of nitrogen contamination for improving the service life of pulse tube cryocooler at temperatures lower than liquid nitrogen. A real-time gas adding device has been developed to add nitrogen to the pulse tube cryocooler to obtain the critical values and the principles of gas impurity affecting pulse tube cryocoolers. By comparing the experimental and numerical simulation data, we know that the main reason for the performance deterioration is the adhesion of solid nitrogen in a tiny part of the regenerator , and the temperature fluctuation is caused by the repeated phase transition of nitrogen. Based on this, the method of standing after shutdown and then restarting can be used to avoid the temperature fluctuation.