Choked flow behavior of helium-4 at cryogenic temperature

Abstract

Physical characteristics of choked helium have a significant impact on heat and mass transfer in helium cryogenic systems. Below the liquid hydrogen temperature region, the choked features of helium are numerically calculated, analyzed, and experimentally validated. Stable, one-dimensional, isentropic flows are assumed in the calculations. To analyze cryogenic helium single-phase and two-phase choked states, the developed algorithm with a mass flux criterion includes homogeneous models and different slip models. At stagnation temperatures ranging from 4 to 20 K and larger stagnation pressures (from 0.02 to 2.3 MPa), the choked parameters (pressure, temperature, sound velocity, mass flux, and critical pressure ratio) are calculated. According to the results of the analysis, two-phase choking occurs when the stagnation pressure is less than 300 kPa and the stagnation temperature is less than 6.0 K. In the experiment, the mass flow rates were tested by varying the inlet pressure and temperature of the micro-orifice (34  μm). The trends of mass fluxes calculated using the homogeneous model well match the experimental data. The reason for the difference between experimental and theoretical values is that the computational model does not account for actual fluid losses (structural impedance) and deviation of the helium physical property assumption in the two-phase region. The present study's findings are expected to improve the understanding of a cryogenic helium choked flow behavior and the limitations of theoretically choked flow models currently used in cryogenic systems.