The condenser performance deteriorates sharply with the reduction of gravity.An order of magnitude increase in tube length is required to achieve complete condensation in a tube under microgravity as compared with a tube under normal gravity.The phase distribution and heat transfer are not coordinated under microgravity so that the heat transfer is deteriorated.The new phase separation condenser tube proposed using the passive phase separation concept to modulate flow patterns and enhance heat transfer is suitable for different gravities.This paper focuses on the numerical simulation of the air-water flow pattern modulation process in the vertical phase separation condenser tube under normal gravity

low gravity and microgravity.Three conclusions could be drawn.(1)The phase distributions of “gas near the tube wall and liquid in the tube core” are obtained under the three gravitational conditions.Under microgravity

the annular region is completely occupied by the gas and almost all liquid flows in the core region.(2)Smaller gravity makes the liquid film thickness much less by the flow pattern modulation.Under microgravity

the thickness is decreased to 1/32.(3)Smaller gravity enhances the condensation heat transfer dominated by the thin liquid film more greatly by the flow pattern modulation.Under microgravity

the condensation heat transfer is enhanced 57.4 times.In general

the flow pattern modulation is more helpful to enhance the condensation heat transfer at smaller gravity.