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Abstract:The plate fin heat exchanger is the compact heat exchanger applied in many industries because of its high thermal performance. To enhance the heat transfer of plate fin heat exchanger in further, three new kinds of wavy plate fins, namely perforated wavy fin, staggered wavy fin and discontinuous wavy fin are proposed and investigated by CFD simulations. The effects of key design parameters, including that of waviness aspect ratios, perforation diameters, stagger ratios and breaking distance are investigated, respectively, with the Reynolds number changes from 500 to 4500. It is found that due to the swirl flow and efficient mixing of fluid, the perforation, serration and breaking techniques are beneficial for the enhancement of heat transfer compared to the traditional wavy fin. At the same time, serration is beneficial to reduce the friction factor, and the breaking technique can reduce heat transfer area as well as enhance heat transfer performance. Through the performance evaluation criteria, the staggered wavy fin has an advantage over the small waviness aspect ratio compared to the perforated wavy fin. The maximum performance evaluation criteria (PEC), as high as 1.24, can be obtained for the perforated wavy fin at the largest waviness aspect ratio.

Numerical simulations were conducted to study thermal and hydraulic performance of liquid-cooled heat sink on power electronics cooling, in particular with water/glycol mixture. Considering non-uniform and discrete heat sources, geometry and number of cooling channels were analyzed. The results show that alternating rectangular channel has high thermal performance with a little penalty in hydraulic resistance. The number of cooling channels can be optimized to provide the best thermal performance, as 40 channels for the analyzed case. Performance difference resulting from working coolants was studied, with 100% de-ionized water, mixture of 50% ethylene glycol and 50% de-ionized water (EGW) by weight, and mixture of 60% propylene glycol and 40% de-ionized water (PGW) by weight. The variations of fluid physical properties with temperature were taken into account. It has been concluded that lower coolant temperature does not necessarily lead to better cooling capacity, i.e. a specific coolant has an optimum operation temperature to provide the maximum cooling performance.

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