Heat transfer in two-phase flow through a circular tube at reduced gravity

Abstract

A two-phase, two-component flow test loop was flown onboard NASA's KC-135 Zero-g aircraft in October 1992. During the flights, flow regime, pressure gradient, and heat transfer data were simultaneously gathered for an air-water mixture in vertical, cocurrent, upward flow through a circular tube with a diameter of 9.53 mm. The range of flow rates studied consisted of superficial liquid velocities from 0.24 to 3.0 m/s, and superficial gas velocities between 0.2-17 m/s. Heat transfer measurements taken during fji-g were compared with heat transfer data gathered at 1 g with the same test loop. This comparison indicated that at low liquid and gas velocities heat transfer coefficients at 1 g were up to 15% greater than those measured in /*-g. At higher liquid or gas velocities this trend was reversed, and microgravity flows yielded heat transfer coefficients approximately 10% higher than the corresponding 1 g flows. It was found that a change in the flow regime was not responsible for this difference in heat transfer coefficients.