Bubble dynamics and heat transfer on biphilic surfaces

Pool boiling has been proven as a very effective process for heat transfer in cooling applications. Surface wettability plays a vital role in pool boiling heat transfer [1]. Surfaces with customized wetting patterns (hydrophilic surfaces with hydrophobic regions), when properly optimized geometrically, have shown a high potential of enhancing heat transfer [2], by promoting nucleation at lower superheat values and allowing a significant increase in the critical heat flux [3]. However, the scarce number of experimental studies performed so far shows a clear limitation: while authors describe nucleation and bubbles dynamics (and eventually thermal) behavior, with significant detail, very little is known regarding the internal flow inside the bubbles, which nevertheless may strongly affect both dynamic and thermal processes. Hence, a deeper knowledge on the dynamic behavior of both the vapor inside the bubble and the surrounding liquid could provide a deeper insight on the forces acting on the bubble. Such detailed description also allows a clearer analysis of the relation between the geometry and varying wettability patterns of the surface and its performance in terms of an effective heat transfer enhancement. In previous works, a two-phase, CFD, enhanced numerical model for nucleate boiling that uses an enhanced Volume of Fluid (VOF) based method [4] has been developed. In this work, this model will be tested in pool boiling applications for biphilic surfaces and validated based on experimental values.