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首页> 外文期刊>International Journal of Heat and Mass Transfer >Numerical investigation of hydrodynamics and heat transfer of elongated bubbles during flow boiling in a microchannel
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Numerical investigation of hydrodynamics and heat transfer of elongated bubbles during flow boiling in a microchannel

机译：微通道内流动沸腾过程中细长气泡的流体动力学和传热的数值研究

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摘要

Flow boiling within microchannels has been explored intensively in the last decade due to their capability to remove high heat fluxes from microelectronic devices. However, the contribution of experiments to the understanding of the local features of the flow is still severely limited by the small scales involved. Instead, multiphase CFD simulations with appropriate modeling of interfacial effects overcome the current limitations in experimental techniques. Presently, numerical simulations of single elongated bubbles in flow boiling conditions within circular microchannels were performed. The numerical framework is the commercial CFD code ANSYS Fluent 12 with a Volume Of Fluid interface capturing method, which was improved here by implementing, as external functions, a Height Function method to better estimate the local capillary effects and an evaporation model to compute the local rates of mass and energy exchange at the interface. A detailed insight on bubble dynamics and local patterns enhancing the wall heat transfer is achievable utilizing this improved solver. The numerical results show that, under operating conditions typical for flow boiling experiments in microchannels, the bubble accelerates dow_Nstream following an exponential time-law, in good agreement with theoretical models. Thin-film evaporation is proved to be the dominant heat transfer mechanism in the liquid film region between the wall and the elongated bubble, while transient heat convection is found to strongly enhance the heat transfer performance in the bubble wake in the liquid slug between two bubbles. A transient-heat-conduction-based boiling heat transfer model for the liquid film region, which is an extension of a widely quoted mechanistic model, is proposed here. It provides estimations of the local heat transfer coefficient that are in excellent agreement with simulations and it might be included in next-generation predictive methods.
机译：由于微通道能够从微电子器件中去除高热通量，因此在过去的十年中，人们对微通道内的沸腾沸腾进行了深入的研究。但是，实验对理解水流局部特征的贡献仍然受到所涉及的小尺度的严重限制。取而代之的是，对界面效应进行适当建模的多相CFD模拟克服了实验技术中的当前限制。目前，在圆形微通道内的流动沸腾条件下，对单个细长气泡进行了数值模拟。数值框架是商业CFD代码ANSYS Fluent 12，具有“流体体积”接口捕获方法，在此通过将“高度函数”方法实现为更好地估计局部毛细作用，并使用蒸发模型来计算局部函数来进行改进。界面处的质量和能量交换速率。利用这种改进的求解器，可以获得有关气泡动力学和增强壁热传递的局部模式的详细信息。数值结果表明，在典型的微通道沸腾实验操作条件下，气泡按照指数时间规律加速dow_Nstream，与理论模型吻合良好。事实证明，薄膜蒸发是壁和细长气泡之间的液膜区域的主要传热机制，而瞬态热对流则可显着增强两个气泡之间的液团中气泡尾流的传热性能。 。本文提出了一种基于瞬态导热的液膜区域沸腾传热模型，该模型是被广泛引用的力学模型的扩展。它提供的局部传热系数估计与仿真非常吻合，并且可能会包含在下一代预测方法中。

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  • 作者

    M. Magnini; B. Pulvirenti; J.R. Thome;

  • 作者单位

    Dipartimento di Ingegneria Energetica, Nucleare e del Controllo Ambientale, Universita di Bologna, Bologna, Italy;

    Dipartimento di Ingegneria Energetica, Nucleare e del Controllo Ambientale, Universita di Bologna, Bologna, Italy;

    Laboratory of Heat and Mass Transfer (LTCM), Ecole Polytechnique Federate de Lausanne (EPFL), Lausanne CH-1015, Switzerland;

  • 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
  • 中图分类
  • 关键词

    Flow boiling; MicroChannel; Volume Of Fluid; Evaporation; Heat transfer;

    机译：流沸腾;微通道;液体量;蒸发;传播热量;

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