Simple Flow-Pattern Based Heat Transfer Correlations for Flow Boiling in Micro/Minichannels

An improved conventional-to-micro/minichannel threshold was proposed as Bo = 4 and BoRe(1)(0.5) = 200, where Bo is the Bond number and Re-1 is the liquid Reynolds number. The region Bo < 4 and BoRe(1)(0.5) < 200 is termed as micro/minichannel because bubbles tend to be confined and elongated in the channel and the conventional two-phase flow theory loses its applicability. Flow-pattern based heat transfer correlations for elongated bubbly flow and annular flow in flow boiling micro/minichannels were developed separately based on a collected micro/minichannel heat-transfer database. As significant disagreement in experimental trends and heat transfer mechanisms was reported for flow boiling in micro/minichannels in the literature, it is not possible to explain the discrepancy and predict all data points by a single correlation without considering the different flow patterns. The newly developed flow-pattern based predictive tool can not only present a decent overall accuracy, but also estimate the parametric trends correctly. Over 95% of the data points can be predicted by the proposed correlations within a +/- 50% error band for both elongated bubbly flow and annular flow. Therefore, the simple flow-pattern based correlations can be applied for heat exchanger design, improve understanding of the underlying heat transfer mechanisms, and guide development of further enhancement techniques for flow boiling in micro/minichannels

Numerical analysis of non-isothermal Newtonian flows in plate heat exchangers

Associar ao Dep. de Tecnologia Química e Biológica - docente Ricardo DiasNumerical analysis of non-isothermal Newtonian flows in plate heat exchanger passages is carried out in the laminar flow region. The results of this analysis are compared with information available in the literature. Some interesting trends are observed for both heat transfer and pressure drop with varying chevron angle. Areas of further work are delineated and it is emphasised that practical ranges of inter-plate distance, corrugation pitch and the development ratio need to be studied to fully understand the practical implications of the current numerical work