Investigation of nanofluid heat transfer in a microchannel under magnetic field via lattice Boltzmann method: effects of surface hydrophobicity, viscous dissipation, and Joule heating

In this paper, effect of Joule heating (JH), viscous dissipations (VD), and super hydrophobic surfaces on heat transfer of water-Al₂O₃ and water-CuO nanofluids in a microchannel has been investigated using lattice Boltzmann method (LBM). The microchannel is under a uniform and transverse magnetic field. The lower wall of the microchannel is insulated and a uniform heat flux has been applied to the upper wall. Results are generated at constant Reynolds number of 150, volume fraction of 2%, and a diameter of 25 nm with variable Hartmann numbers ranging from 0 to 20 and nondimensional slip coefficients from 0 to 0.05. The results of the developed code are in good agreement with other analytical, numerical, and experimental reports. Moreover, the results show that in such case, ignoring the JH and VD leads to a significant error in the prediction of Nusselt number up to 62% and 56%, respectively, for water-Al₂O₃ and water-CuO nanofluids. It has also been shown that using a super hydrophobic surface with a slip coefficient of 0.05 leads to a significant reduction in VD; however, it increases the effect of JH. On the other hand, it is found that, despite JH and viscous dissipation effects, using super hydrophobic surfaces (up to a slip coefficient of 0.05) leads to an increase in Nusselt number and decrease in shear stress for all the studied Hartmann numbers. Finally, it has been concluded that super hydrophobic surfaces can be used as a passive tool to enhance the heat transfer rate and simultaneously decrease the pumping power demand.