Cryogens, such as liquid hydrogen and oxygen, are used for future space explorations, which require long-term storage in a closed tank. During long-term storage of cryogens in the tank, thermal stratification is formed near the liquid surface due to heat flow into the tank from the surrounding environment. Therefore, boiloff gas is generated from the surface, which increases the pressure in the tank. An effective way to reduce boiloff gas is to destroy the temperature stratification by mixing cold jet issuing from the bottom of the tank. In this paper, drop tower experiments are conducted to investigate the detailed jet behavior, especially jet's flow pattern and jet-tip height in microgravity. In the experiment, deionized water, which blends red food coloring, was used, and the mixing jet behavior was observed using a CCD camera. The jet-flow pattern was investigated under various experimental conditions. Consequently, six flow patterns, including distinctive flow patterns obtained only in microgravity, were observed, and the predicted model for jet-tip height proposed by the authors in submitted paper agrees considerably with the microgravity experimental data within the MAE 4.37 mm.

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