Experimental study on pool boiling characteristics of trapezoidal reentrant microchannel grooved surfaces
Rajesh Kumar, B. Premachandran
Abstract
The increased demand of high heat flux dissipation in the thermal management systems necessitates the use of phase change process of boiling. However, the maximum heat flux in boiling is limited by the critical heat flux (CHF). After reaching the CHF, a vapor layer tends to develop over the heated surface, thereby heat transfer coefficient (HTC) decreases significantly. Therefore, simple and inexpensive methods are required to enhance both HTC and CHF to simultaneously increase the efficiency and operational range of systems. Though various surface and fluid modification methods have been reported in the literature for the enhancement of HTC and CHF, they are costly and susceptible to fouling. Moreover, many of these methods are suitable for the enhancement of either HTC or CHF. In this study, surfaces with new microchannel configurations are introduced to simultaneously enhance HTC and CHF in saturated pool boiling. Three structured surfaces, namely rectangular microchannel (RM), trapezoidal reentrant microchannel (TRM) and segmented trapezoidal reentrant microchannel (STRM) are developed and experimentally investigated with water at the atmospheric pressure. Vapour bubble dynamics is studied using shadowgraphic high-speed movies. The top-performing STRM surface shows the CHF of 4555.2 kW/m 2 which is 290 % higher than the plain surface CHF. This surface demonstrates the highest maximum HTC of 842.5 kW/m 2 K compared to 53.8 kW/m 2 K with a plain surface. The enhanced performance of the STRM surface is due to the additional surface area, improved bubble dynamics and effective rewetting. The STRM surface performs better than the other enhanced surfaces reported in literature and has the ease of implementation and cost-effectiveness. Therefore, the proposed microstructured surface has better potential for application in the thermal management systems.