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Bubble growth, departure and the following flow pattern evolution during flow boiling in a mini-tube

机译：微型管内沸腾过程中气泡的生长，离开和随后的流型演变

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摘要

In the present study, the bubble growth, departure and the following flow pattern evolution during flow boiling in the mini-tube were visualized and quantitatively investigated, along with the simultaneous measurement of the local heat transfer coefficient around a specified nucleation site. Liquid nitrogen was employed as the working fluid and the test section was a segment of vertically upward quartz glass tube with the inner diameter range of 1.3-1.5 mm, which was coated by a layer of transparent ITO film as the heater on the outer surface. The growth rates of bubbles had similar and constant growth rate in two periods of time, i.e., before and after the bubbles departing from the nucleation site, which indicated the bubble growth was primarily governed by the inertial force. The bubble departure diameter and bubble period were investigated and the corresponding correlation was obtained based on the experimental data, which showed that the tube size of the mini-tube had no notable effect on the bubble departure and the trend of the bubble departure was similar to that in macro-tubes. Whereas the following flow pattern evolution was apparently confined due to the size effect, which presented desirable heat transfer performance in mini-tubes. The heat transfer coefficients for different flow patterns along the mini-tube were obtained in terms of bubbly, slug, annular flow and the flow regimes of flow reversal and post dry-out. It was found that the dominant heat transfer mechanism was the liquid film evaporation which offered desirable heat transfer capability. The heat transfer performance would be deteriorated in the post dryout regime, while flow reversal could somewhat enhance the heat transfer upstream of the nucleation site. Boiling curves around the specified nucleation site were recorded and analyzed based on the recorded flow patterns.
机译：在本研究中，对微型管中的沸腾过程中的气泡生长，离开和随后的流型演变进行了可视化和定量研究，并同时测量了特定成核位置附近的局部传热系数。使用液氮作为工作流体，并且测试部分是垂直向上的石英玻璃管的一部分，其内径范围为1.3-1.5mm，其在外表面上覆盖有一层透明的ITO膜作为加热器。在两个时间段内，即气泡离开成核位置之前和之后，气泡的增长率具有相似且恒定的增长率，这表明气泡的生长主要由惯性力控制。研究了气泡离开的直径和气泡的持续时间，并根据实验数据获得了相应的相关性，表明微型管的管径对气泡离开的影响不显着，气泡离开的趋势类似于在宏管中。然而，由于尺寸效应，显然以下流动形式的演化受到限制，这在微型管中表现出理想的传热性能。根据气泡，团状，环形流动以及逆流和干燥后的流动方式，获得了沿着微型管的不同流动方式的传热系数。发现主要的传热机理是液膜蒸发，其提供了理想的传热能力。在变干后的状态中，传热性能将降低，而流动逆转会在一定程度上增强成核位点上游的传热。记录指定成核位置周围的沸腾曲线，并根据记录的流动模式进行分析。

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  • 来源
    《International Journal of Heat and Mass Transfer》 |2010年第22期|p.4819-4831|共13页
  • 作者

    X. Fu; P. Zhang; C.J. Huang; R.Z. Wang;

  • 作者单位

    Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China;

    rnInstitute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China;

    rnInstitute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China;

    Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China;

  • 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

    mini-tube; bubble growth; bubble departure; flow reversal; post dryout;

    机译：迷你管泡沫增长;泡沫离去;逆流干燥后;

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