HEAT-TRANSFER IN 2-PHASE FLOW-THROUGH A CIRCULAR TUBE AT REDUCED GRAVITY

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 now through a circular tube with a diameter of 9.53 mm. The range of flow rates stu died 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 measu rements taken during mu-g were compared with heat transfer data gather ed at 1 g with the same test loop. This comparison indicated that at l ow liquid and gas velocities heat transfer coefficients at 1 g were up to 15% greater than those measured in mu-g. At higher liquid or gas v elocities 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 now regime was not respo nsible for this difference in heat transfer coefficients.