Numerical study of cryogenic micro-slush particle production using a two-fluid nozzle

Abstract

The fundamental characteristics of the atomization behavior of micro-slush nitrogen ( SN 2 ) jet flow through a two-fluid nozzle was numerically investigated and visualized by a new type of integrated simulation technique. Computational fluid dynamics (CFD) analysis is focused on the production mechanism of micro-slush nitrogen particles in a two-fluid nozzle and on the consecutive atomizing spray flow characteristics of the micro-slush jet. Based on the numerically predicted nozzle atomization performance, a new type of superadiabatic two-fluid ejector nozzle is developed. This nozzle is capable of generating and atomizing micro-slush nitrogen by means of liquid–gas impingement of a pressurized subcooled liquid nitrogen ( LN 2 ) flow and a low-temperature, high-speed gaseous helium (GHe) flow. The application of micro-slush as a refrigerant for long-distance high-temperature superconducting cables (HTS) is anticipated, and its production technology is expected to result in an extensive improvement in the effective cooling performance of superconducting systems. Computation indicates that the cryogenic micro-slush atomization rate and the multiphase spraying flow characteristics are affected by rapid LN 2 – GHe mixing and turbulence perturbation upstream of the two-fluid nozzle, hydrodynamic instabilities at the gas–liquid interface, and shear stress between the liquid core and periphery of the LN 2 jet. Calculation of the effect of micro-slush atomization on the jet thermal field revealed that high-speed mixing of LN 2 – GHe swirling flow extensively enhances the heat transfer between the LN 2-phase and the GHe-phase. Furthermore, the performance of the micro-slush production nozzle was experimentally investigated by particle image velocimetry (PIV), which confirmed that the measurement results were in reasonable agreement with the numerical results.