TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)

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A production method for micro-slush nitrogen particles is investigated using a two-fluid atomization nozzle to apply micro-slush as a refrigerant for long-distance superconducting cables; a process that is expected to result in an extensive improvement in effective cooling performance for superconducting systems. The principle of the micro-slush production nozzle and the performance of the nozzle investigated by Particle Image Velocimetry (PIV) measurement and Computational Fluid Dynamics (CFD) analysis are herein presented. We mainly focus on the development of a new type of two-fluid ejector nozzle, which is capable of generating and atomizing solid nitrogen using liquid-gas impingement of a pressurized subcooled liquid nitrogen (LN₂) flow and by a low-temperature, high-speed gaseous helium (GHe) flow. In addition, we constructed a micro-slush particle production system using this new type of two-fluid nozzle and then investigated the effect of the mass flow rate of GHe on the characteristics of the micro-slush two-phase atomizing flow by PIV. Furthermore, the measurement results are compared with those of CFD simulation under the same experimental conditions. The results of this research show that it is possible to produce fine micro-slush nitrogen particles using this newly developed two-fluid nozzle under high-speed atomizing flow conditions, and by applying the appropriate mass-flow rate of subcooled LN₂ and cryogenic GHe. Based on the optimized thermal flow conditions of cryogenic micro-slush particulate atomizing two-phase flow and the practical use of its multiphase functionality, utilization in the development of a new type of superconducting cooling system is predicted.

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