RT Journal Article ID 5518f8bb0d4b1606 A1 Narayanan, C. A1 Lakehal, D. T1 TWO-PHASE FLOW AND HEAT TRANSFER IN MICROTUBES UNDER NORMAL AND MICROGRAVITY CONDITIONS JF Multiphase Science and Technology JO MST YR 2009 FD 2009-11-13 VO 21 IS 4 SP 279 OP 295 AB Detailed numerical simulations have been performed to study the effect of gravity on two-phase flow heat transfer (without phase change) in small-diameter pipes. Effect of the flow orientation with respect to gravity is investigated. Overall, the heat removal rate in two-phase flow was shown to be significantly higher than in single-phase flow. The downstream flow can be characterized as a periodic flow around each bubble/slug rather, where the shapes of the inclusions and the flow around them reach a repeatable state. The flow regime, viz. bubbly, slug, and slug-train, is found to have a strong influence on the heat transfer and pressure drop. The wall thermal layer is affected by the blockage effect of the inclusions, which manifests itself in a circulating liquid flow pattern superimposed on the equivalent single-phase fully developed flow. The Nusselt number distribution shows that the bubbly, slug, and slug-train regimes transport as much as three to four times more heat from the tube wall to the bulk flow than pure water flow. For upflow, the breakup into bubbles/slugs occurs earlier and at a larger frequency. Overall, the average Nusselt numbers are not significantly affected by the flow orientation with respect to gravity. A mechanistic heat transfer model is proposed, based on frequency and length scale of inclusions. The results found here suggest that a microgravity experimental campaign dealing with air water systems can be performed by European Space Agency on its space Fluid-Lab facility. PB Begell House LK https://www.dl.begellhouse.com/journals/5af8c23d50e0a883,3879f57d5e4970ad,5518f8bb0d4b1606.html