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首页> 外文期刊>Multiphase science and technology >TWO-PHASE FLOW AND HEAT TRANSFER IN MICRO TUBES UNDER NORMAL AND MICRO-GRAVITY CONDITIONS
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TWO-PHASE FLOW AND HEAT TRANSFER IN MICRO TUBES UNDER NORMAL AND MICRO-GRAVITY CONDITIONS

机译：正常和微重力条件下微管的两相流动和传热

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摘要

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.
机译：已经进行了详细的数值模拟，以研究重力对小直径管道中两相流传热（无相变）的影响。研究了流向相对于重力的影响。总的来说，两相流的排热速率明显高于单相流。下游流的特征可以是围绕每个气泡/块的周期性流，其中夹杂物的形状和它们周围的流达到可重复状态。流动状态，即。发现气泡，团状和团状应变对传热和压降有很大的影响。壁热层受夹杂物的阻挡作用的影响，其表现为叠加在等效单相充分展开的流动上的循环液体流动形式。 Nusselt数分布表明，气泡，团状和团状状态将热量从管壁传递到大流量的热量是纯水流量的三至四倍。对于上流，破裂成气泡/团块的时间更早，发生频率更高。总体而言，相对于重力，流动方向没有显着影响平均Nusselt数。提出了一种基于夹杂物的频率和长度尺度的机械传热模型。此处发现的结果表明，欧洲航天局可以在其太空Fluid-Lab设施上进行涉及空气水系统的微重力实验。

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