The Experimental Study Of Flow And Heat Transfer Process In Circular Tube Of A New Nanofluid

As a new type of high efficient heat transfer fluid,nanofluid has a wide application prospect in the fields of solar thermal energy(STE),industrial waste heat recovery,phase change material(PCM),hydrogen internal combustion engine cooling and so on.In this paper,the preparation,stability,thermal conductivity,viscosity,flow and heat transferof graphene nanofluid were studied through experiment and numerical simulation.And the experimental results were preliminarily analysed,which offeres support forthe theoretical research and practical application of nanofluid.Graphene nanofluid was prepared by "two steps" method.The graphene nanofluid was prepared under laboratory conditions,and the deposition study demonstrates that it is stable.The comparison of stability of graphene nanofluids with different based-fluids shows that the larger the matrix viscosity is,the better the stabilityof nanofluid is.The thermal conductivity of graphene nanofluid was measured using a liquid thermal conductivity tester,which is based on the transient heated probe method,and the experimental results were compared with the values calculated by solid-liquid suspension thermal conductivity models.The result shows that the addition of graphene nanoparticles enhances the thermal conductivity of the based-fluids.The mass fraction of graphene nanoparticles,the thermal conductivity and temperature of based-fluid are important factors to thermal conductivity of nanofluid.Accroding to the experimental results,the mechanism of thermal conductivity enhancement of nanofluid was preliminarily analyzed in some aspects,such as brown motion,the properties of solution and agglomeration of particles.The viscosity of water-based graphene nanofluid was measured by ubbelohde viscometer,and the experimental results were compared with the values calculated by the solid-liquid suspension viscosity models.It is found that the addition of graphene nanoparticles increases the viscosity of the base-fluid.The mass fraction,shape,size of nanoparticle and fluid temperature are the factors that affect the viscosity of nanofluid,and fluid temperature is the main factor among them.An experimental system of flow and heat transfer in the tube was designed and built,which was used to test the convective heat transfer coefficient of water-based graphene nanofluid with different particle concentrations in the range of Re=8000-12000.The result shows that the addition of graphene nanoparticle increases the convective heat transfer performance of basefluid.Moreover,the enhancement of the convective heat transfer coefficient is greater than that of the thermal conductivity.The heat transfer rate,particle concentration,turbulence intensity are the factors that affect the convective heat transfer coefficient of nanofluid.The modification of the inner wall of the circular tube by nanoparticles is beneficial to the transmission of energy.The flow and heat transfer numerical simulation of water-based graphene nanofluid in circular tube,which is based on the experimental system,was conducted using ANSYS Workbench.Comparing the experimental results with the simulation results,it is found that the irregular brown motion of particles in nanofluid is an important factor to enhance the convective heat transfer performance.The law of the flow and heat transfer of nanofluid in circular tube was analysed through temperature field and velocity field and pressure field.