Thermophysical and rheological properties of water-based graphene quantum dots nanofluids

Abstract

Application of the suspended solid particles in the base fluids is one of the novel methods to increase the thermal performance of heat transfer fluids. However, the major problems with this technique are the short time colloidal stability, low thermal conductivity of additive as well as significant negative effects on rheological properties once loading nanoparticles. The present study explores, for the first time, the impacts of graphene quantum dot (GQD) on the colloidal stability and thermophysical properties of water-based GQD suspensions as a new generation of heat transfer fluid. To this end, amine-treated GQD (A-GQD) were synthesized with a novel method. Surface functionality groups on A-GQD were analyzed by XPS. Atomic-force microscopy (AFM), UV–vis spectrometry, zeta potential and average particle size techniques have been used in order to measure and evaluate the colloidal stability, size and thickness of A-GQD. After applying A-GQD as an additive, colloidal stability results indicate no sedimentation after a 30-day period. In addition, all the thermophysical properties e.g. thermal conductivity, density and viscosity were measured experimentally. The viscosity of the water-based A-GQD samples was tested at various shear rates, concentrations and temperatures. Further, it has shown that by loading A-GODs in the water, the increasing rate of the density and viscosity is not significant. Interestingly, the water-based A-GQD nanofluids at very low concentration significantly increase the thermal conductivity in comparison with that of pure water.