Numerical investigations on pressure wave refrigerators for sizing the dump tank and studying its effect on the operating frequency at first peak efficiency

Abstract Pressure Wave Refrigerators (PWRs), in principle, work with thermal separation through shock waves. A PWR typically comprises a rotating gas distributor that periodically injects high-pressure gas into one or more stationary receiving tubes. The sudden release of high-pressure gas in a tube or channel produces shock waves that heat up the residual gas towards the dead end, while the rarefied waves produce refrigeration in the driver gas at the nozzle end. Upon connection to the outlet port, the refrigerated gas flows out of the receiving tube into a receiver. PWRs have several advantages, such as simple design, low cost, high reliability, low rotational speed, and high efficiency comparable to conventional turbo-expanders. Reflected shock waves from the dead end of the receiving tube of a PWR seriously affect the performance through heating of the fluid inside the tube. A dump tank, is usually fitted at the end of the receiving tube so that the reflected shock waves are attenuated. The effects of the size of the dump tank in terms of the volume of the stationary receiving tube are studied for different tube lengths and pressure ratios. The isentropic efficiency of a 2m tube increases from 54% to 78 % by using a dump tank having volume ten times that of the receiving tube. During the operation of a PWR, there are peaks in isentropic efficiency at certain operating cycle frequencies. In this work, appearance of the first peak efficiency is also investigated for different sizes of the dump tank.