Amelioration of boiling heat transfer by 3D deposition structure of graphene-silver hybrid nanoparticle

Abstract

• The novel hybrid coating solves the thermal barrier problem of graphene. • Modification makes the coating have rich chemical bonds and complex microstructure. • The oxygen-containing functional groups promote the capillary effect of coating. • Concentration has little effect on structure and element content of hybrid coating. During the boiling process, the heating surface has a substantial influence on the growth of the bubbles, the wetting of dry spots, and the deposition of the particles. Therefore, improving the surface properties is one of the main ways to enhance heat transfer. In this study the heating coatings were prepared by boiling deposition using GNP nanofluids, GNP/Ag mixed nanofluids, and GNP-Ag hybrid nanofluids with different mass fractions (wt% = 0.001,0.002,0.003) as raw materials. The boiling heat transfer characteristics of DI water on the bare copper surface and heating coatings were studied, and the heat transfer mechanism was analyzed. The results show that GNP-Ag hybrid nanoparticle coating has the most outstanding enhanced heat transfer effect. DI water achieves the highest critical heat flux (CHF) of 163.65 W/cm 2 and heat transfer coefficient (HTC) of 9.69 W/cm 2 K on the coating, which are respectively 45.84% and 82.14% higher than the smooth copper surface. The wettability was analyzed by measuring the contact angle. Scanning electron microscope image was used to analyze the microstructure of the coating. The microstructure of Ag modified functionalized GNP nanoparticle has a great change compared with mixed nanoparticles. It was observed that the hybrid nanoparticle deposit into a large number of bulges and cavies, and the bulges accumulate in clusters and form self-assembled flower-shaped bulges. Combined with the energy spectrum test results of the heating coating, the coverage of the nanoparticles in the coating on the copper substrate and the variation trend of each deposited element with the concentration are analyzed. The novel heating coating enhances heat transfer under the combined action of nanoparticle functional groups, coating microstructure, and wettability. GNP-Ag hybrid nanoparticle coating was applied towards the heat dissipation of electronic devices. When the input power is 300 W, the maximum temperature of electronic devices is 108.52 °C, which is much lower than that of other coatings.