In order to predict various phenomena related to flow and heat transfer in space,it is necessary to carry out experiments under microgravity. In this paper,we describe the behavior of a horizontal two-phase flow under microgravity utilizing a drop tower 6.1m in height,which realizes microgravity conditions of less than 0.02G(G=g/go)for about one second when the capsule is falling down. The experiment was carried out in a horizontal transparent acrylic resin tube of 10mm I.D. and 250mm length,using Freon-22 and water as the working fluid,in a superficial gas velocity range of 0.021m/s to 5.05m/s(ReG=58ï½ 1.4Ã 10^4)and a superficial water velocity of 0.022m/s to 0.456m/s(ReL=246ï½ 5.1Ã 10^3). The flow patterns obtained under microgravity were compared with other data under actual microgravity utilizing a drop tower. Furthermore,the base liquid film thickness,the height of waves and the period of waves in the region of annular flow,were obtained from a measured shape of waves. Then,the relationship between these values,gas Reynolds number and liquid film Reynolds number was obtained. Also,the void fraction under microgravity could be expressed using the distribution parameter and the Martinelli parameter.
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