Estimation of the tip-height of mixing jet issuing from a nozzle by one-dimensional droplet model

Abstract

This study newly proposes a one-dimensional droplet model to estimate the jet-tip height of a subcooling mixing jet issuing from the bottom to the top of tank. Cryogenic liquids, such as liquid hydrogen and liquid oxygen, are used as propellants and oxidants in spacecraft propulsion systems that require long-term storage in a closed tank. However, thermal stratification forms near the gas–liquid interface during long-term storage of cryogens due to heat flowing into the tank from the surrounding environment. In addition, boil-off gas (BOG) is generated from the interface, which causes increased pressure in the tank. To reduce the BOG, it is effective to destroy the thermal stratification by mixing in the cold jet issuing from the bottom of the tank. In this case, the tip-height of mixing jet issuing from the bottom of the tank is an important factor for mixing performance. Ground experiments using FC-72 and water as test fluids are conducted to investigate the jet behavior which is visualized using the Shadowgraph system. The height of the jet-tip is investigated under various experimental conditions, and the experimental results compared to the proposed one-dimensional spherical droplet model as the tip of the jet. The proposed model is also verified by comparison with experimental data available in the literature. The results show that the proposed model aligns well with the experimental data.