Pool boiling enhancement through microporous coatings selectively electrodeposited on fin tops of open microchannels

Open microchannels and microporous coatings have been individually employed by previous investigators for enhancing pool boiling heat transfer. In this paper, their combined effect is investigated by electrodepositing microporous coatings on the fin tops of microchannels. The microporous coatings were applied using the optimal electrodeposition parameters developed in an earlier study. The effect of microchannel geometry on heat transfer performance for water boiling at atmospheric pressure on 10 mm x 10 mm copper chips is reported here. A maximum critical heat flux (CHF) of 3250 kW/m(2) was obtained for Chip 9 with fin width = 200 mu m, channel width = 500 mu m and channel depth = 400 mu m at a wall superheat of 7.3 degrees C. A maximum value of heat transfer coefficient (HTC) of 995 kW/m(2) degrees C was achieved for Chip 12 with a different channel width of 762 mu m for a heat flux of 2480 kW/m(2) at a wall superheat of 2.5 degrees C. Bubble growth and heat transfer processes are altered when nucleation takes place preferentially on the fin tops. Visual studies indicate a microconvective mechanism in which bubbles leaving from the fin tops induce strong localized liquid circulation currents in the microchannels. A liquid microcirculation based theoretical model is developed to predict heat transfer under this mechanistic description. The preliminary results are in good agreement with the experimental data. (C) 2014 Elsevier Ltd. All rights reserved.