Surface wettability change on TF nanocoated surfaces during pool boiling heat transfer of refrigerant R-141b

Abstract

Experiments were performed to demonstrate the impact of surface wettability on the nucleate boiling heat transfer of Silicon Dioxide (SiO2) Thin Film (TF) nanocoated surfaces using the saturated refrigerant R-141b at atmospheric pressure. Six numbers of circular flat type test sections of copper material having thickness of 0 nm (plain surface), 125 nm, 250 nm 375 nm, 500 nmand 625 nm surface coating thicknesses were fabricated with the Sol-Gel method followed by spin coating process and characterized through atomic force microscope (AFM), field emission scanning electronmicroscopy (FE-SEM), TelescopeMicro-Goniometer (TMG), and Energy – Dispersive X-Ray spectroscopy (EDX) etc. The experimental results from plain and nanocoated copper surfaces were validated with well-established correlations to predict the pool boiling curve. In comparisons with plain surface, results obtained from other surfaces show that the reduction of wall superheat and additional improvement of heat transfer coefficient (HTC), for all TF nanocoated surfaces at atmospheric pressure. It has been revealed that surface wettability improves the vapor bubble departure radius for hydrophilic surfaces and decreases the frequency of bubble emissions.