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Enhanced Macroconvection Mechanism With Separate Liquid-Vapor Pathways to Improve Pool Boiling Performance

机译：增强的宏观对流机制，具有独立的液-气通道，可改善池沸腾性能

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摘要

Understanding heat transfer mechanisms is crucial in developing new enhancement techniques in pool boiling. In this paper, the available literature on fundamental mechanisms and their role in some of the outstanding enhancement techniques is critically evaluated. Such an understanding is essential in our quest to extend the critical heat flux (CHF) while maintaining low wall superheats. A new heat transfer mechanism related to macro-convection is introduced and its ability to simultaneously enhance both CHF and heat transfer coefficient (HTC) is presented. In the earlier works, increasing nucleation site density by coating a porous layer, providing hierarchical multiscale structures with different surface energies, and nanoscale surface modifications were some of the widely used techniques which relied on enhancing transient conduction, microconvection, microlayer evaporation, or contact line evaporation mechanisms. The microconvection around a bubble is related to convection currents in its immediate vicinity, referred to as the influence region (within one to two times the departing bubble diameter). Bubble-induced convection, which is active beyond the influence region on a heater surface, is introduced in this paper as a new macroconvection mechanism. It results from the macro-convection currents created by the motion of bubbles as they grow and depart from the nucleating sites along a specific trajectory. Directing these bubble-induced macroconvection currents so as to create separate vapor-liquid pathways provides a highly effective enhancement mechanism, improving both CHF and HTC. The incoming liquid as well as the departing bubbles in some cases play a major role in enhancing the heat transfer. Significant performance improvements have been reported in the literature based on enhanced macroconvection contribution. One such microstructure has yielded a CHF of 420 W/cm~2 with a wall superheat of only 1.7℃ in pool boiling with water at atmospheric pressure. Further enhancements that can be expected through geometrical refinements and integration of different techniques with macroconvection enhancement mechanism are discussed here.
机译：了解传热机制对于开发池沸腾的新强化技术至关重要。在本文中，对基本机制及其在某些杰出的增强技术中的作用的现有文献进行了严格评估。这种理解对于我们在维持低壁过热的同时扩展临界热通量（CHF）至关重要。介绍了一种与宏观对流有关的新型传热机制，并提出了同时提高CHF和传热系数（HTC）的能力。在较早的工作中，通过涂覆多孔层来增加成核位点密度，提供具有不同表面能的分层多尺度结构，以及纳米尺度的表面改性是依赖于增强瞬态传导，微对流，微层蒸发或接触线的一些广泛使用的技术。蒸发机制。气泡周围的微对流与在其附近的对流有关，称为影响区域（在气泡直径的一到二倍之内）。本文介绍了气泡引起的对流，该对流在加热器表面的影响区域之外有效，是一种新的宏观对流机制。它是由气泡在沿着特定轨迹生长和离开成核位置时运动所产生的宏观对流引起的。引导这些气泡引起的大对流，以创建独立的气液通道提供了一种高效的增强机制，可同时改善CHF和HTC。在某些情况下，进入的液体以及离开的气泡在增强热传递方面起着重要作用。基于增强的宏观对流作用，已有文献报道了性能的显着提高。一种这样的微结构在大气压下用水沸腾的池中产生的CHF为420 W / cm〜2，壁过热仅为1.7℃。此处讨论了通过几何改进和将不同技术与宏观对流增强机制集成在一起可以预期得到的进一步增强。

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  • 来源
    《Journal of Heat Transfer》 |2017年第5期|051501.1-051501.11|共11页
  • 作者

    Satish G.Kandlikar;

  • 作者单位

    Mechanical Engineering Department, Rochester Institute of Technology, 76 Lomb Memorial Drive, Rochester, NY 14623;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
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