CFD investigation on the radial heat transfer in a two stage co-axial pulse tube cooler working at liquid hydrogen temperature

Co-axial pulse tube coolers are very popular in practical applications due to their compactness, while radial heat transfer between regenerator and pulse tube due to temperature mismatch at the same axial location affects the cooling performance. Two stage pulse tube coolers are commonly used at liquid hydrogen temperature, and multiple radial heat transfer occurs in gas-coupled co-axial pulse tube cooler system due to the first stage annular pulse tube. CFD simulation models with and without radial heat transfer based on an actual gas-coupled two stage co-axial pulse tube cooler have been conducted to analyze the mechanism and effect. The heat transfer processes between the gas and pulse tube wall are analyzed and compared. Simulation results indicate that after introducing radial heat transfer, expansion efficiency of the second stage pulse tube is improved from 74% to 90.9% with radial heat flow from it to the regenerator and the first stage pulse tube. The cooling power at the second stage is notably increased compared to the model without radial heat transfer, while minor performance reduction at the first stage. This study may provide a valuable reference for the design of multi-stage pulse tube coolers.