Experimental study of boiling heat transfer for a novel type of GNP-Fe3O4 hybrid nanofluids blended with different nanoparticles

Abstract

This work is based on a new research direction to ameliorate the hydrophobicity of graphene nanoplatelets (GNP) by functionalizing it without affecting its good thermal properties and to prepare novel hybrid nanofluids for enhancing heat transfer. In this work, a novel type of GNP-Fe3O4 hybrid nanoparticles is prepared, and the crystal structure test proves that it has high purity, contains a variety of hydrophilic functional groups, and has a strong binding force between elements. The blending of metal or non-metal nanoparticles in the GNP-Fe3O4 hybrid nanofluids is beneficial to improve the deposition effect of the nanofluids and reduces the heat transfer resistance of the heating surface. Therefore, the boiling heat transfer characteristics of GNP nanofluids, GNP-Fe3O4 hybrid nanofluids, GNP-Fe3O4 + Al2O3 hybrid nanofluids, and GNP-Fe3O4 + SiO2 hybrid nanofluids with different mass concentrations (0.0005 wt%, 0.001 wt%, 0.002 wt%, and 0.003 wt%) were studied experimentally. The heat transfer effects of different nanofluids at the same concentration were also compared. The experimental results show that the heat transfer characteristics of nanofluids are significantly enhanced compared with the deionized water (DI water). Among them, GNP-Fe3O4 + Al2O3 hybrid nanofluids and GNP-Fe3O4 + SiO2 hybrid nanofluids have the best heat transfer effect, when the mass concentration is 0.003 wt% critical heat flux (CHF) is 180.23 W/cm2 and 185.29 W/cm2, which are 60.61% and 65.12% higher than DI water. Also, the maximum heat transfer coefficient (HTC) is 9.73 W/cm2K and 10.23 W/cm2K, which are 82.74% and 92.13% higher than DI water. Both of them have similar heat transfer intensity at the same mass concentration. Through the observation of the macroscopic morphology and microstructure of the deposition surface, the wettability test and the study of the bubble generation characteristics, the boiling heat transfer mechanism of the new hybrid nanofluid is qualitatively analyzed. The results show that the wettability and deposition characteristics of GNP-Fe3O4 hybrid nanofluids are significantly improved after blended with other nanoparticles, the microscopic deposition structure is more complex and porous, the macroscopic deposition amount is significantly reduced, and the heat transfer resistance is reduced; the characteristics of bubble formation show that the fluid is violently disturbed and the heat transfer intensity is greatly improved. At the same time, the functional groups introduced by acid mixing treatment and metal modification in the preparation of the new hybrid nanoparticles also plays a great role in promoting the heat transfer of the fluid.