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Microgravity Fluid Physics & Heat Transfer

ISBN Druckformat: 978-1-56700-147-1

ISBN Online: 978-1-56700-444-1

PRESSURE DROP MEASUREMENTS OF TWO-PHASE FLOW IN HELICAL COILS UNDER MICROGRAVITY CONDITIONS

Abstrakt

This paper describes tests conducted to obtain measurements of two-phase flow under the microgravity conditions of aircraft parabolic flight trajectories. Due to the space restrictions on channel length typical of facilities available for conducting tests under microgravity conditions (i.e. aircraft or drop towers), helical coil test sections were employed to provide a sufficient length of channel to insure a large enough pressure drop as to be readily measurable. Results are presented for downward air/water two-phase flow through a stainless steel coil (inside tube diameter 0.95 cm, coil diameter of 25.4 cm, L/d = 678) with a vertically oriented coil axis. Measurements were also made for the same flow conditions in a straight length of tubing of the same diameter immediately preceding the coiled test section, both for 1-g and microgravity aircraft flight conditions. Comparative results are presented for the coiled and straight-length test sections in the form of pressure gradient per unit length of flow channel. The pressure gradients for the two-phase flow in the coiled test section were unexpectedly found to be smaller than those in the straight sections for the same mass flow rates of the individual phases. This behavior is opposite to that observed in single-­ phase flows. The different behavior was attributed to the apparently modified flow pattern configuration within the coil turns arising from the centripetal acceleration of the fluids associated with the channel curvature. Additionally, the fundamental changes in two-phase flow characteristics arising from channel curvature suggested a perspective of flow regime transitions that underscores the value of utilizing generalized flow regime transition criteria.
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