The Effect of Liquid Film Evaporation on Flow Boiling Heat Transfer in a Micro Tube
The Effect of Liquid Film Evaporation on Flow Boiling Heat Transfer in a Micro Tube
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DOI：
10.1115/ihtc14-22751
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发表时间：
2012-01
期刊：
影响因子：
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通讯作者：
Youngbae Han;N. Shikazono;N. Kasagi
中科院分区：
文献类型：
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作者：
Youngbae Han;N. Shikazono;N. Kasagi
微通道内流动沸腾因其单位体积换热面积大而备受关注。由于通道壁面的限制，微通道内产生的气泡被拉长，段塞流成为主要流型之一。在弹状流中，连续的气泡被液体弹状物限制，在管壁和气泡之间形成薄液膜。液膜蒸发是微通道内的主要换热机理之一，而液膜厚度是决定换热系数的重要参数。在本研究中，测量了流动沸腾条件下的液膜厚度，并与绝热条件下的关联式进行了比较。研究了液膜厚度与换热系数之间的关系。试管采用内径为D=0.5 mm的PYREX玻璃管。工作液是水和乙醇。采用激光焦移仪测量液膜厚度。在绝热条件下提出的关联式可以很好地预测流动沸腾条件下的初始液膜厚度。然而，在回流和短段塞的情况下，测量的液膜厚度变得比预测值要薄。认为这是由于液塞中速度剖面的变化所致。在流动沸腾条件下，由于汽相速度较高，液膜分布会发生波动，并随时间呈现周期性变化。周期图形的频率随着热流密度的增加而增加。在低质量时，根据测量的液膜厚度计算的换热系数与直接从壁温测量获得的换热系数显示出良好的一致性。版权所有*2010由ASME
Flow boiling in micro channels is attracting large attention since it leads to large heat transfer area per unit volume. Generated vapor bubbles in micro channels are elongated due to the restriction of channel wall, and thus slug flow becomes one of the main flow regimes. In slug flow, sequential bubbles are confined by the liquid slugs, and thin liquid film is formed between tube wall and bubble. Liquid film evaporation is one of the main heat transfer mechanisms in micro channels and liquid film thickness is a very important parameter to determine heat transfer coefficient. In the present study, liquid film thickness is measured under flow boiling condition and compared with the correlation proposed under adiabatic condition. The relationship between liquid film thickness and heat transfer coefficient is also investigated. Pyrex glass tube with inner diameter of D = 0.5 mm is used as a test tube. Working fluids are water and ethanol. Laser focus displacement meter is used to measure the liquid film thickness. Initial liquid film thickness under flow boiling condition can be predicted well by the correlation proposed under adiabatic condition. However, measured liquid film thickness becomes thinner than the predicted values in the cases of back flow and short slugs. These are considered to be due to the change of velocity profile in the liquid slug. Under flow boiling condition, liquid film profile fluctuates due to high vapor velocity and shows periodic pattern against time. Frequency of periodic pattern increases with heat flux. At low quality, heat transfer coefficients calculated from measured liquid film thickness show good accordance with heat transfer coefficients obtained directly from wall temperature measurements.Copyright © 2010 by ASME