Modulated flow pattern in a condenser tube with two-phase flow interacting with mesh screen surface at micro-gravity

•Mesh cylinder creates an annular region and a core region over tube cross section.•The two-phases are thoroughly separated with gas flowing in the annular region.•The modulated liquid film thicknesses are decreased to 1/30–1/10.•The modulated condensation rates per unit wall area are enhanced to 10–100 times.•The effectiveness of phase separation condenser tube at micro-gravity is proved.

Two-phase loop systems are important to maintain low temperature in a spacecraft at micro-gravity. It is known that the condenser size at micro-gravity can be one order magnitude larger than that at the earth gravity. This paper explores the effectiveness of the modulated flow technique at micro-gravity for the condensation heat transfer enhancement. A mesh cylinder is suspended in a tube, dividing the tube cross section into annular region and core region. When an intermittent two-phase flow interacts with the mesh screen structure, gas bubbles are prevented from entering the mesh cylinder thus they flow in the annular region to form the thin liquid film on the wall. Liquid can be separated to flow in the core region. Here the bubble dynamics in the bare tube section and modulated flow section are investigated for three different slug flow cases. It is found that the mesh cylinder modulates the slug flows in the bare tube section to form the elongated-ring-slug bubble train in the modulated flow section. Liquid plugs can disappear due to the continuous liquid flow from the annular region to the core region. Thus the two-phases are thoroughly separated with gas flowing in the annular region, forming ultra-thin liquid film thicknesses on the wall at micro-gravity. The modulated flow pattern forms the liquid film thicknesses to be about 1/30–1/10 of those in the bare tube section for the three cases. Based on the modulated bubble dynamics and parameters, the condensation rates per unit wall area (ṁ) can be about 10–100 times of those in the bare tube section for the three cases. The modulated flow pattern and enhanced heat transfer are more obvious when the gas volume flow rates are decreased. This study provides a new approach to enhance the condensation heat transfer for space applications under micro-gravity environment.