Experimental analysis of electrical field combining nanofluids to enhance the mixed convective heat transfer in the rectangular channel

Owing to the disadvantages of low thermal conductivity and large viscosity, the mixed convective heat transfer efficiency of transformer oil can not meet the cooling demand of transformer. Furthermore, the electrical field force could manipulate the motion of nanoparticles, so as to further strengthen the heat transfer of nanofluids. Therefore, the electrical field and nanofluid are combined in the present study to enhance the thermal performance for cooling transformer. Meanwhile, the effects of electrical field strength, the nanofluid concentration and heat flux on heat transfer as well as mechanism are discussed. Then, a semi empirical correlation is proposed by considering the effects of electrical field and nanoparticles. The result shows that the heat transfer is greatly strengthened up to 65% with the increment of the electrical fields, and there exists an optimal concentration of nanofluid for the best enhanced effect. According to the mechanism analysis, the electrical field force pulls nanoparticles to high potential area and the fluid molecules move with nanoparticles, which impacts the boundary layer. Then, disturbances of nanofluids increase and the boundary layer thickness is decreased. Thus, the boundary layer thickness is reduced and fluid disturbance is strengthened, which significantly enhances heat transfer. Moreover, the predicted values calculated by the semi empirical equations fit the experimental data well.