| description abstract | Transformer-oil with low thermal conductivity and large viscosity has poor heat dissipation capability, which leads to the thermal drive failure caused by transient overload. To improve its cooling capability, this paper has proposed first the method which combined the periodically direction-switching electric field and graphene nanofluid to enhance the mixed convective heat transfer properties of transformer-oil, and analyzed the effects of switching periods, nanofluid concentration, electric field strength, heat flux, and Reynolds number on mixed convection heat transfer experimentally. The results show that the heat transfer characteristic of transformer-oil is improved up to 52% by the periodically direction-switching electric field and graphene nanofluid. As the switching period decreases, the thermal performance of the suspension is enhanced more significantly. Moreover, by analyzing the heat transfer mechanism, the periodically direction-switching electric field causes the nanoparticles to move reciprocally, repeatedly impacting and breaking the boundary layer of the heat exchange surface to enhance the perturbation, thus enhancing the heat transfer effect. Meanwhile, the predicted correlation has been proposed on the basis of influence factors, which are in good agreement with the experimental data. | |
