CHF Enhancement of Pool Boiling in Graphene oxide Nanofluid with Chemical Reduction

Abstract

Graphene oxide (GO) can be deposited on a heater surface to produce nanoscale structures that enhance the thermal limit of the heater. GO has shown a very unique feature showing CHF enhancement without wettability improvement in terms of apparent advancing contact angle unlike any other typical nanoparticles. Many studies have analyzed the reason for the enhanced critical heat flux (CHF) of the heater. Three major models have been used for studying the enhanced CHF of the heater in many heat transfer studies: wettability of surface (contact angle), Rayleigh-Taylor instability wavelength, and thermal activity. In this study, scanning electron microscopy (SEM) images and the contact angle were taken to explain the enhanced wettability of a heater surface in a GO nanofluid. GO is composed of carbon and oxygen. This material has good affinity with water because of its polarity. In an electric field, GO reduces into reduced graphene oxide (RGO). This chemical reduction on the surface may be one factor that enhances the CHF. To examine how a GO nanofluid can enhance CHF to more than twice its original magnitude, a wettability model was applied that uses the contact angle of the nichrome wire heater surface after the CHF experiment. The reason why the wettability model could not completely account for the CHF enhancement in a GO nanofluid was also determined. The reduction of GO was considered to explain CHF enhancement.