Magnetic field effect on laminar heat transfer in a pipe for thermal entry region

Abstract

The influence of a transverse magnetic field on the local heat transfer of an electrically-conducting laminar fluid flow with high Prandtl number through a pipe was studied experimentally. Experiments indicated an increase in the local Nusselt number. The coupled set of the equations of motion and the energy equation including the viscous and Joule dissipation terms becomes non-linear and is solved numerically using a finite difference scheme. Favorable comparisons with experimental results confirm the correctness of the numerical results. It is found that the influence of magnetic field can be diminished by reducing the angle between the flow direction and the direction of magnetic field. The wall temperature reduces as the value of Hartmann number increases and the reduction rate of the wall temperature decreases as the value of Hartmann number exceeds a certain value. The average Nusselt number asymptotically approaches its limit as the Hartmann number becomes larger. Also, curve fitting can be employed to derive an equation for the average Nusselt number as a function of the Hartmann number. This equation is similar to the Sieder-Tate equation. It is observed that increasing the Hartmann number has no considerable effect on the thermal boundary layer thickness but decreases the temperature of fluid layers inside the boundary layer.

Numerical analysis of magnetic field effects on the heat transfer enhancement in ferrofluids for a parabolic trough solar collector

“…Moreover, the ferrofluid viscosity can be controlled by the magnetic field applied. The enhanced thermal conductivity of ferrofluid results in improving the heat conduction during chain-like particle assembly formation under the external magnetic field [25], [26].There are different numerical investigations of the ferrofluids HTC performance with/without presence of the magnetic field: Jafari et al [27] have simulated the heat transfer of a ferrofluid under a magnetic field based on kerosene into a cylinder; Huminic et al [28] numerically examined the heat transfer of nanofluid in a helical double pipe heat exchanger in laminar flow; Aminossadati et al [29] studied laminar forced CHT of Al2O3/water nanofluid in a horizontal micro-channel; Malekzadeh et al [30] presented a numerical analysis of the effect of magnetic field on HT in a laminar flow through a tube; Aminfar et al [31]- [34] numerically investigated in several works the effect of non-uniform transverse/axial magnetic fields on hydrothermal as well as hydro-dynamic behaviors of ferrofluids; magnetic field effects on natural CHT of copper/water and copper oxide/water nanofluids were numerically investigated by Sheikholeslami et al [35] and Mahmoudi et al [36], respectively; magnetic field effects on the convection onset for the nanofluid were examined by Yadav et al…”