Effect of Magnetic Baffles and Magnetic Nanofluid on Thermo-Hydraulic Characteristics of Dimple Mini Channel for Thermal Energy Applications

The combined effect of a magnetic baffle and a dimple turbulator on the heat transfer and pressure drop is investigated computationally in a mini channel. Fe3O4 magnetic nanofluid is used as a working fluid. The Reynolds number (Re) is varied from 150 to 210 and the magnetic field intensities range from 1200 G to 2000 G. Finite-volume based commercial computational fluid dynamics (CFD) solver ANSYS-Fluent 18.1 was used for the numerical simulations. A laminar viscous model is used with pressure-velocity coupling along with second-order upwind discretization and QUICK scheme for discretizing the momentum and energy equations. The results show that there is an increase of 3.53%, 10.77%, and 25.39% in the Nusselt numbers when the magnetic fields of 1200 G, 1500 G and 2000 G, respectively, are applied at x = 15 mm, as compared to the flow without a magnetic field when the pitch = 10 mm. These values change to 1.51%, 6.14% and 18.47% for a pitch = 5 mm and 0.85%, 4.33%, and 15.25% for a pitch = 2.5 mm, when compared to the flow without a magnetic field in the respective geometries. When the two sources are placed at x = 7.5 mm and 15 mm, there is an increase of 4.52%, 13.93%, and 33.08% in the Nusselt numbers when magnetic fields of 1200 G, 1500 G, and 2000 G are applied when the pitch = 10 mm. The increment changed to 1.82%, 8.16%, and 22.31% for a pitch = 5 mm and 1.01%, 5.96%, and 21.38% for a pitch = 2.5 mm. This clearly shows that the two sources at the front have a higher increment in the Nusselt numbers compared to one source, due to higher turbulence. In addition, there is a decrease in the pressure drop of 10.82%, 16.778%, and 26.75% when magnetic fields of 1200 G, 1500 G, and 2000 G, respectively, are applied at x = 15 mm, as compared to flow without magnetic field when the pitch = 10 mm. These values change to 2.46%, 4.98%, and 8.54% for a pitch = 5 mm and 1.62%, 3.52%, and 4.78% for a pitch = 2.5 mm, when compared to flow without magnetic field in the respective geometries. When two sources are placed at x = 7.5 mm and 15 mm, there is an decrease of 19.02%, 31.3%, and 50.34% in the pressure drop when the magnetic fields of 1200 G, 1500 G and 2000 G are applied when the pitch = 10 mm. These values change to 4.18%, 9.52%, and 16.52% for a pitch = 5 mm and 3.08%, 6.88%, and 14.88% for a pitch = 2.5 mm. Hence, with the increase in the magnetic field, there is a decrease in pressure drop for both the cases and the pitches. This trend is valid only at lower magnetic field strength, because the decrease in the pressure drop dominates over the increase in pressure drop due to turbulence.This work was funded by the Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Saudi Arabia (Project No. GRANT331). The authors also acknowledge the financial support received for the research project entitled “Performance Improvement of Solar Thermal Systems using Magnetic Nanofluids” funded by the Department of Science and Technology (DST), Govt. of India under India-South Africa Joint Science and Technology Research Collaboration vide Sanction no.: DST/INT/South Africa/P-08/2021 dtd. 16 September 2021

Simulation of natural convective heat transfer and entropy generation of nanoparticles around two spheres in horizontal arrangement

Herein, laminar convective heat transfer from two horizontally arranged spheres has been evaluated by using numerical models inside water-based fluids incorporated with alumina (Al2O3), copper oxide (CuO), and copper (Cu) nanoparticles. The problem was simulated for different Rayleigh numbers ranging from 103 to 106 and various volume fractions including 2, 4, 6, and 8%. The evaluation process included the perspective of both first and second thermodynamic laws. In-house FORTRAN code was provided to solve the equations based upon the finite volume method as well as the Multigrid acceleration. According to the obtained results, the average Nusselt number enhanced by 57.4% for both the spheres and plates with increment of the Rayleigh number from 103 to 106 for the constant volume fraction of 2%. In addition, nanoparticle type played a significant role on the heat transfer rate and generated entropy. Moreover, introduction of the Al2O3 nanoparticles into the water-based fluid resulted in approaching to the highest Bejan number of 0.98. Furthermore, the ecological coefficient of performance of CuO nanoparticles decreased by increment of the volume fraction at all Rayleigh numbers. In the volume fraction of 2%, it raised from 2.89 to 7.8 by increasing of the Rayleigh number from 103 to 106