Abstract:

A numerical investigation is conducted to study the pure magnetohydrodynamic (MHD) mixed convective flow of Al2O3-water nanofluid inside a vented H-shaped cavity with a total of four discrete heaters on the side walls, representing a cooling unit for compact electrical and electronic appliances. Two inlet configurations (top and bottom opening) are analyzed under inclined magnetic fields to enhance heat transfer and control flow structure. The coupled mass, momentum, and energy equations are solved using the finite element method-based COMSOL Multiphysics software for a wide range of governing parameters: Grashof (103 ≤ Gr ≤ 106), Reynolds (31.62 ≤ Re ≤ 103), and Hartmann (5.62 ≤ Ha ≤ 31.62) numbers, with the varying magnetic field inclination angle (γ) between 0° and 90°. Results show that simultaneously increasing Gr, Re, and Ha intensifies the primary circulation and alters the secondary vortices. At the same time, the rotation of the magnetic field from horizontal orientation suppresses these secondary cells. The vertical orientation of the magnetic field eliminates recirculation zones, resulting in a reduction in overall heat transfer. The top-inlet configuration provides the maximum Nusselt number (at γ = 45°) and the best thermo-hydraulic performance (at γ = 55°). In contrast, the bottom-inlet configuration achieves the superior ecological thermal effectiveness (at γ = 30°). All these performance evaluations exhibit their maximum at the maximum limit of the governing parameters (Gr = 106, Re = 103, and Ha = 31.62), underscoring the significance of maintaining a higher value of the governing parameters for magneto-thermo-fluid flows in such non-regularly shaped vented cavities. These findings can serve as a guide to optimize the designs of magnetically assisted nanofluid cooling systems in thermal management applications.

Abstract:

Mixed convection within a ventilated square cavity with a baffle at the bottom wall and heating elements at the side walls has been analyzed. The inlet opening has been set at the bottom of the left wall, while the exit opening is put at the bottom of the right wall. Considering air (Pr = 0.71), dimensionless and steady form of mass, momentum and energy equations are solved by implementing proper boundary conditions with the help of the Galerkin method-based finite element scheme. Maintaining pure mixed convection (Ri = 1), baffle length is changed from 0 to 0.95L, and heater location is varied from 0.1L to 0.7L across Re = 10 to 1000. Qualitative changes of the domain are observed with the help of streamlining and isothermal plots. For quantitative comparison, average temperature, Nusselt number, pressure drop and performance index have been considered. The counteracting effects of the increase in Nusselt number and pressure drop are accounted for together with the help of the performance index, which yielded the most economical and optimum baffle height and heater location. The final evaluation shows that the optimum length of the baffle and the position of the heaters can perform most effectively in the range of Re = 20 – 400.

Abstract:

This computational study examines how varying porosity and pore density in vertical tubes, which contain aluminium and copper metal foams, affect the flow boiling behavior of various nanofluids. To investigate water-based nanofluids with alumina and copper oxide nanoparticles alongside plain water as a baseline, mass flow inlet and pressure outlet boundary conditions are employed in the simulation along with heat flux to the pipe wall. This work utilizes CFD analysis using RANS equations and the RPI boiling model with Eulerian-Eulerian approach for each phase, along with the standard k-ω turbulence model to simulate subcooled nanofluid flow boiling. The study demonstrates that porous copper tubes exhibit superior thermal performance to aluminium tubes, and further identifies a significant enhancement in heat transfer when nanoparticles are added to the base water. In addition, substantial increment is also noted in heat transfer coefficient due to moderate porosity and greater pore density. Ultimately, the simulations identify an optimal foam configuration that achieves a balance between improved heat transfer and manageable pressure drop.