A Micro-Orifice Throttle Valve Design for The Joule-Thomson Cryocooler

Abstract

Compact cryocoolers are crucial for applications requiring temperatures as low as 6 K under micro-scale cooling loads. Among various cryocooler types, the Joule-Thomson (JT) cryocooler stands out due to its compactness, zero vibration, and low noise characteristics, making it ideal for sensitive and space-constrained environments. To enhance the miniaturization of such systems, micro-orifice throttle valves are employed to create a significant pressure drop, enabling effective cooling in the positive JT coefficient region. In this study, the flow behaviour within a 30-micrometre micro-orifice was numerically investigated using helium as the working fluid. The gas expanded from 0.7 MPa to 0.05 MPa, resulting in a temperature reduction from 15 K to 6.8 K. The simulation revealed that during this expansion, density changes were more strongly influenced by pressure variations than temperature. Moreover, the velocity of helium increased sharply within the orifice, reaching a supersonic Mach number of 1.8. However, the sudden geometric expansion at the outlet triggered the formation of shock waves, leading to downstream flow instabilities. These instabilities highlight the need for optimized orifice geometry to reduce shock losses and enhance flow uniformity, thereby improving the overall performance and efficiency of JT cryocoolers in compact cryogenic systems.