Mechanical texturing of microporous surfaces to enhance pool boiling heat transfer
Ha, Min Seok
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Boiling heat transfer is one of the most promising solutions for the thermal management of systems that require high heat flux removal, presenting orders of magnitude higher heat transfer coefficient than forced liquid convection. Two important aspect of boiling heat transfer is critical heat flux (CHF) and heat transfer coefficient (HTC), and increasing CHF and HTC has been a subject of research for several decades. One of the highest CHFs is seen with microporous surfaces among various surface features, however, there is a tradeoff between CHF and HTC with respect to the microporous coating thickness. The thick coatings show an increase in CHF and a decrease in HTC while the thin coatings show opposite trend. For that reason, optimal coating thickness has been studied, which maximizes HTC, to be 2-4 times of particle diameter for the coatings sintered with spherical particles. Nonetheless, since the optimal thickness has relatively low CHF compared to thick microporous coatings, maximizing both CHF and HTC using the microporous surfaces is investigated in this study. This is conducted through experimental investigation of pool boiling characteristics on microporous surfaces for DI water by leveraging the theories from previous studies. A better understanding on boiling mechanism of the microporous surfaces is provided that a vapor layer forms and grows in the microporous coatings during boiling, and that preventing the growth is the key to the enhancement. By fabricating vapor channels into microporous coatings and by releasing the vapor efficiently, a significant enhancement is achieved both in CHF and in HTC, more than four times over those of the flat surfaces.