Study of pool boiling on hydrophilic surfaces developed using electric discharge coating technique

Abstract

The emergence of high performing micro-sized devices in the recent decades have led to significant increment in heat generation rate, which is challenging to be dissipated by single-phase cooling schemes such as air or liquid cooling. As such, two-phase mechanism like boiling heat transfer have gained prominence to resolve this challenge. The boiling heat transfer process is usually assessed on the basis of parameters such as critical heat flux (CHF) and nucleate boiling heat transfer coefficient (NBHTC). The process of boiling is most efficient in the nucleate boiling phase which involves bubble generation and detachment. The occurrence of bubble generation can be increased by development of micro/nano-structured surfaces, finally leading to significant enhancement in boiling performance. A variety of surface modification techniques have been adopted in the past to improve boiling heat transfer. But certain issues could be found in few of the techniques. In order to address those issues, the present work has employed the method of Electric Discharge Coating (EDC) for developing microstructured boiling surfaces. The coating deposited was a mixture of zinc-copper (Zn-Cu) composite microparticles, at different current settings, on a copper surface. The EDC process performs the deposition in a layer by layer manner, in subsequent pulse-on and pulse-off cycles, thus ensuring a stable layer. Surface preparation was followed by surface characterization that involved wettability analysis, porosity and pore size estimation, mean roughness measurement and elemental analysis. The surfaces obtained were hydrophilic in nature where the contact angle varied from 62° to 40°. Consequently, the CHF and NBHTC showed enhancements of 48.5% and 195% respectively for the best performing surface in comparison with the bare/uncoated surface.