Heat Transfer Enhancement by Electromagnetic Forcing in Duct Flow

National audienceElectromagnetic forcing could be used to produce streamwise vortices in order to enhance the heat and mass transfer processes in ducts and pipes. In our current study we take this novel method to a more practical use, to suggest a Magneto hydrodynamic heat exchanger in which several transverse Lorentz forces are arranged along the streamwise direction to produce secondary flow structures and enhance mixing of hot fluid particles near the wall with cold fluid particles near the center. The Reynolds number based on the mean flow velocity and hydraulic diameter is taken 1000. The flow structures, the local heat transfer and the thermal performances are quantitatively analyzed to show the effectiveness of this concept. Increases by more than 100% in the global Nusselt number and the thermal performance were detected. Several configurations of forcings were tested, where it was found that the increase in local and global Nusselt is more efficient with subsequent forces of the same direction, rather than changing directions. Nomenclature A overall area of heat transfer, m 2 B magnetic field, T c heat capacity of the fluid, J/kgK F Lorentz force, N/m 3 GCI Grid convergence index h convective heat transfer coefficient, W/m 2 K J current density, A/m 3 k bulk fluid thermal conductivity, W/mK N u global Nusselt number N u z local Nusselt number p c apparent order of converge q overall rate of heat transfer, W S exchange area, m 2 T temperature, K ∆T lm log mean temperature difference, K u velocity vector field, m/s Greek symbols ρ density, kg/m 3 µ dynamic viscosity, Pa.s φ electric field scalar potential, V σ electric conductivity of the fluid,