Design, Optimisation and Performance Analysis of Orifice Pulse Tube Cryogenic Refrigerators

Pulse Tube Refrigerator (PTR), a regenerative cryocooler is used in cryogenic cooling applications. Thermodynamic and numerical models help in estimating the operation parameters, analysing and thereby predicting the performance of a PTR. A one dimensional simulation model for analytical studies, design and optimization of the regenerator geometry for improving the performance of the PTR is developed. The simulation program is based on the equations obtained from applying the ideal gas laws, energy and mass balances in the Orifice PTR (OPTR). Predictions by the simulation program of the thermodynamic performance are compared with published experimental results (Kral et al , 1992) to validate the program. At 274 K, the refrigerating effect predicted by the program is 12.689 W, whereas the experimental value is 11.57 W, a difference of around 9%. Conflicting requirements for regeneration are satisfied by selecting appropriate material and size of wire screen mesh type regenerator. Based on empirical understanding hybrid regenerators have been used instead of single mesh, showing improved performances. A mathematical model simulating the regenerator is developed and solved numerically. Unconstrained optimisation technique with univariate search method is adopted to design optimal hybrid regenerators and is integrated with the simulation program. Using a hybrid regenerator, instead of single mesh regenerator used in Kral's experiments, the regenerator effectiveness increases by 0.16% and pressure drop decreases by 29.2% when compared to single mesh regenerators. Hybrid regenerators improve the refrigeration capacity of the OPTR system by as much as 40%. The validated simulation program can be used for the design and development of high performance OPTR.