Amelioration of pool boiling thermal performance utilizing graphene-silver hybrid nanofluids

Abstract

Graphene nanoplatelets (GNP) have natural hydrophobicity and are not easy to disperse in deionized (DI) water. In this study, Ag modified functionalized GNP (f-GNP) was used to prepare novel hybrid nanoparticles. Through phase and structural analysis, it is found that the material has high purity, and is dispersed in DI water to produce the nanofluids that are stable. The boiling heat transfer properties of GNP nanofluids, GNP/Ag mixed nanofluids and GNP-Ag hybrid nanofluids of three weight concentrations (wt% = 0.001, 0.002, 0.003) were investigated. Among the nine samples, the GNP-Ag hybrid nanofluids with weight concentration of 0.001% has the best heat transfer property, with a critical heat flux (CHF) of 170.74 W/cm2, which is 52.31% more than the one of DI water. After the boiling experiment, the heating surface was analyzed by scanning electron microscope (SEM) to observe the deposition structure of nanoparticles. It is found that the self-assembled structure of the hybrid nanoparticle deposition is more complex. Under the combined action of the oxygen-containing functional groups of the nanoparticles, the lateral heat transfer of the working medium is strengthened, and the separation of the vapor bubbles is promoted. In the wettability analysis, the contact angle of the nanofluids were measured, and it was found that the hybrid nanofluids was hydrophilic, which improved the liquid supply mechanism on the heating surface and was beneficial to increase the CHF. The bubble formation characteristics of nanofluids were observed by high-speed camera, and it was found that the bubble formation period of hybrid nanofluids was short and the bubble separation diameter was small. Results from tests and experiments indicate that covalent modified hybrid nanofluids have good heat transfer performances.