This study attempts to numerically investigate the hydro-thermal characteristics of a ferrofluid (water and 4 vol% ) in a counter-current horizontal double pipe heat exchanger, which is exposed to a non-uniform transverse magnetic field with different intensities. The magnetic field is generated by an electric current going through a wire parallelly located close to the inner tube and between two pipes. The single phase model and the control volume technique have been used to study the flow. The effects of magnetic field has been added to momentum equation by applying C++ codes in Ansys Fluent 14. The results show that applying this kind of magnetic field causes to produce kelvin force perpendicular to the ferrofluid flow changing axial velocity profile and creating a pair of vortices leads to increase the Nusselt number, friction factor and pressure drop. Comparing the enhancement percentage of Nusselt number, friction factor and pressure drop demonstrate that the optimum value of magnetic number for Re_ff=50 is between Mn=1.33*10^6 and Mn=2.37*10^6 So applying non-uniform transverse magnetic field can control the flow of ferrofluid and improve heat transfer process of double pipe heat exchanger.

Keywords: Ferrohydrodynamics, Magnetohydrodynamics, Mixed convection, Ferrofluid, Double pipe heat exchanger

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