Investigation of flow characteristics and heat transfer performance in heat exchangers with magnetic field effect

In the first part of the thesis, the hydrothermal flow and entropy generation properties of ferrofluid (water and Fe3O4) on a cylindrical body in the rectangular channel subjected to the non-uniform magnetic field going through current-carrying wires are numerically explored. The effect of various parameters, such as ferroparticle volume fraction, Φ the strength of the non-uniform magnetic field, Ha, and Reynolds number, Re on the flow characteristics, and forced convection heat transfer is investigated using finite-volume based Ansys Fluent 20. Obtained results demonstrate that the applied magnetic field shortens the length of recirculating wake downstream of the cylinder at Re=25 and makes unsteady flow with alternate vortex shedding as a time-independent steady flow for Hartmann numbers greater than, Ha≥6 at Re=100. At Re=50, the total drag coefficient, CD gets higher by almost 20% when Ha increases from Ha=0 to Ha=6 and subsequently grows by 61% at Ha=10. The findings show that the average Nusselt number, Nuavg demonstrates monotonic behavior with the Ha and it augments when the strength of the non-uniform magnetic field increases. The Nuavg improvement is in the vicinity of 11.71% at Ha=10 and 23.26% at Ha=18 for Re=25. The maximum value of entropy generation, SL reduces when the non-uniform magnetic field is applied. Moreover, increasing the Hartmann number, Ha influences the high levels region of entropy production by relatively extending this zone towards the downstream of the channel and covering more area around the cylinder. According to the outcomes of numerical simulation, there is an increase in Nuavg with 3.98% and 3.88% for Ha=2 and 18 respectively when the ferroparticle volume fraction rises from Φ=0% to Φ=4% at Re=25. Finally, the optimum thermal performance criterion, ξ is obtained at Re=150 for Ha=0 and Φ=4%. In the second part of the thesis, the hydrothermal and entropy generation characteristics of nanofluid (water and CuO) in a rectangular grooved channel exposed to a uniform magnetic field in a transverse direction are numerically investigated. The influence of different parameters, such as volume fraction of nanoparticles, Φ Hartmann number, Ha indicating the intensity of the uniform magnetic field, and Reynolds numbers, Re on the flow behaviors and forced convection heat transfer is explored using finite-volume based Ansys Fluent 20. The acquired outcomes demonstrated that applying a uniform magnetic field in a rectangular grooved channel causes major variations in the streamline patterns and reduces the extent of the recirculation zone in rectangular grooves at both Re=250 and 1250. But the required Hartmann number, Ha for the beginning of recirculation region suppression increases with the rise in Reynolds numbers, from Re=250 to Re=1250. The Lorentz force resulting from the uniform magnetic field attenuates the velocity of nanofluid flow at the center of the channel and considering constant mass flow throughout the channel, the flow velocity remarkably augments near the heated walls. This situation increases the velocity gradient and temperature gradient near the hot walls and heat exchange between hot walls and nanofluid flow improves. According to the results of the numerical simulation, the average Nusselt number, Nuavg augmentation is in the vicinity of 9.08% for Ha=8 and 30.42% for Ha=24 at Re=250 and 0.087% for Ha=8 and 21.13% for Ha=24 at Re=1250 compared to the absence of uniform magnetic field application case, Ha=0.