Post-CHF Swirl Flow Heat Transfer with Low Wall Superheat

本研究的目的是：1)测量和预测低壁过热度下大参数范围内旋流条件下后临界热流（后chf）两相流的换热；2)验证最近发现的质量通量效应；3)确定流场中的物理条件。流动旋流对后chf状态的好处是巨大的，最近在UIC获得的数据，用于管内插入物引起的旋流换热器，表明了当壁面过热度低而质量通量高时，直接滴壁传热是一个重要的因素。文献中存在的低壁过热轴流或旋流的chf后数据很少，而大多数高壁过热和轴流的数据没有显示出这种效应。UIC相对独特的液体加热流动沸腾实验设施允许在chf后区域进行稳态测试，将用于获得更大范围内的质量通量数据，以提供与有限的现有数据重叠，以验证质量通量对chf后传热的影响，并支持该两相流的建模验证。UIC将使用闪光x射线、激光多普勒测速仪和摄影仪器来测量流体中的液滴大小分布，以扩大建模工作。第二个实验设备将测量空气/水分散流中的涡流流滴大小。验证质量通量效应的实验也将扩大数据库，包括一种环境上可接受的制冷剂作为沸腾流体。测试截面的方向和尺寸也会发生变化，以便根据更大范围的参数进行预测。实验结果将用于发展半经验现象学模型和基本分析。这两种方法都已在有限的数据范围内制定并成功验证，并且期望通过这种实验/分析结合的努力，在通用性和建模方法方面取得重大进展。

The objectives of this investigation are to: 1) measure and predict heat transfer to post-critical heat flux (post-CHF) two-phase flow under swirling flow conditions at low wall superheat over a broad parameter range, 2) verify the mass flux effect recently identified, and 3) identify physical conditions in the flow field. The benefit of flow swirl to the post-CHF regime is substantial, and recent data obtained at UIC, for application to heat exchangers with swirl flow induced by inserts inside tubes, suggest that direct drop-wall heat transfer is an important contributor when the wall superheat is low and the mass flux is high. Minimal post-CHF data exist in the literature at low wall superheat axial or swirl flow - and most data at high wall superheat and axial flow do not exhibit this effect. The relatively unique liquid-heated flow boiling experimental facility at UIC, which allows steady-state testing in the post-CHF region, will be used to obtain data over an extended range of mass flux to provide overlap with limited existing data necessary to verify the mass flux effect on this post-CHF heat transfer and to support modeling verification of this two-phase flow. Flash X-ray, laser Doppler velocimetry and photographic instrumentation available at UIC will be used to measure drop size distributions in the flow for use with an expanded modeling effort. A second experimental facility will measure swirl flow drop size in air/water dispersed flows. Experiments to verify the mass flux effect will also broaden the data base by including an environmentally acceptable refrigerant as the boiling fluid. Test section orientation and size will also be varied to produce predictions based on a wider range of parameters. Experimental results will be used in the development of both semi-empirical phenomenological models and basic analysis. Both approaches have been formulated and successfully verified over a limited data range, and significant advancement in both generality and modeling approach is expec ted from this combined experimental/analytical effort.