An experimental investigation has been carried out on two-phase flow characteristics in a 10 μm circular gap. The inlet of the gap is formed by two circular surfaces with radius 10 mm. The pressure drop is measured between two points placed — respectively — at the inlet and at the outlet of the gap. The upper and lower plates of the test section are transparent. Two-phase flow patterns were determined by video recording. The single flows of liquid FC-72 and nitrogen gas, as well as two-phase flow are investigated. In two-phase flow experiments the gap is filled by liquid. Liquid is maintained continuously by surface tension in the gap and in the meniscus formed between two inlet circular surfaces. The pressure difference includes two components, surface tension component in the meniscus and viscous one. Instability appears at the entrance of the gas into the gap. At small flowrate the gas flows in the gap has the form of chains of bubbles. Part of investigation was done in microgravity during a Parabolic Flights. In order to better understand experimental results, some numerical simulations have been done both in two and three dimensions for the real geometrical configuration for one-phase flows only.

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