Non-Uniform Magnetic Field Effect on Forced Convection Heat Transfer of Flattened Tubes Using Two-Phase Mixture Model

Abstract

The effect of non-uniform magnetic field on forced convection heat transfer of ferrofluids in flattened tubes has been investigated numerically using two-phase mixture model. The equilibrium magnetization for the ferrofluids is considered, and the linear relationship of magnetization with applied magnetic field intensity is assumed to relax. The main goal of the current research is to study the effect of tube flattening under the non-uniform magnetic field and influence of three various positions of current-carrying wires on flow structure and thermal-hydraulic performance of laminar ferrofluids flow in flattened tubes. Numerical results have been presented within the electric current range of 1–5 A. Results demonstrated that the heat transfer coefficient has been varied from 300 to 1800 W/m2 K. In addition, the non-uniform magnetic field with a wire affects the flow structure, and creates two major and four minor vortices in the flattened tubes; but, in the presence of two parallel wires, only four major vortices are created. It is also observed that when the two parallel wires are located in the flat parts of the flattened tubes, the average heat transfer has been reached to its maximum (the heat transfer enhancement is about 240%). However, in contrast to this enhancement, the pressure drop also increases about 82%. Finally, the position of two wires in flat parts is appropriate to enhance the heat transfer while flattening the tube.