Effect of temperature and heat input on helium isotope separation driven by an entropy filter

Abstract

To understand the effect of temperature and heat input on helium isotope separation driven by an entropy filter, the thermomechanical flow of superfluid helium through an entropy filter for obtaining high purity 4He is experimentally investigated. For this method, there are two important indicators: separation flow (flow rate) and separation effect (3He concentration). The separation flow rate is examined at various temperatures ranging from 1.6 K to 1.9 K of feed helium. Different heat inputs (Q) are applied to the entropy filter outlet to drive the superfluid 4He flowing through the porous element. The results demonstrate that the flow rate increases as the feed helium temperature decreases and heat input increases. Simultaneously, 3He diffusion is detected as the superfluid helium passes through the entropy filter. The concentration of 3He, filtered at different temperature ranging from 1.6 K to 1.9 K, are analyzed using HELIX SFT Static Vacuum Mass Spectrometer. The findings reveal that the 3He concentration decreases with an increase in the temperature of the feed helium bath. 3He concentration of feed helium is around 3.3×10-8. Specifically, the 3He concentration in the filtered helium at 1.6 K is approximately 3.2×10-10, while at 1.9 K, it reduced to 2.2×10-10. This suggests that 3He diffusion in He II is inversely proportional to the He II temperature from 1.6 K to 1.9 K, resulting in a lower 3He concentration at higher temperatures.