Investigation of a Helium-adsorption Regenerator using Porous Silica Microspheres

High-frequency regenerative cryocoolers, such as Stirling cryocoolers and pulse tube cryocoolers, are important technologies in the field of miniature cryogenic refrigeration at liquid-helium temperatures. However, the insufficient heat capacity of solid regenerator materials remains a key bottleneck restricting further improvement of system performance. To address this issue, the feasibility of using porous silica microspheres as regenerator materials was preliminarily investigated in this study. First, helium adsorption characteristics were evaluated in the temperature range of 5-20 K, and the equivalent volumetric heat capacity was calculated. The results showed that the equivalent heat capacity of the porous silica was superior to that of conventional materials below 15 K. Subsequently, based on a three-stage Stirling/pulse tube hybrid cryocooler experimental platform, porous silica and HoCu₂ spheres were filled into the regenerator in a layered configuration with a volume ratio of 1∶3, and preliminary experimental tests were carried out. Under operating conditions of an average pressure of 1.6 MPa and a frequency of 16 Hz, a no-load minimum temperature of 6.71 K was achieved experimentally. Numerical simulations indicated that, if the adsorption effect of the porous silica was neglected, the cryocooler could not reach temperatures below 10 K, thereby confirming the positive role of the porous silica microspheres. Meanwhile, a discrepancy was observed between the experimentally measured cooling capacity and the numerical simulation results. This discrepancy is presumed to originate from the limited helium confinement capability of the porous silica, such that mass exchange occurred between the gas adsorbed inside the pores and the mainstream gas, preventing the complete formation of equivalent heat capacity. Future work should focus on adsorption materials with stronger adsorption potential and improved structural stability for application in adsorption-based regenerators.