Multi-phase modeling considering the nanofluid heterogeneity and slip velocity is not explored in simulating nanofluid flow and heat transfer at higher Reynolds numbers (Re). A comprehensive study of turbulent flow around hot circular cylinders is lacking. The flow patterns are not tackled, and the relationship between flow behaviors and force variations due to the influencing parameters is not established. The heat transfer enhancement and hydrodynamics with forced convection in a rectangular duct are investigated using Ansys FLUENT 15.0, applying a nodal spectral-element method based on the Eulerian-mixture model. The current investigation focuses on demonstrating the correlation between high Re values, size of the bluff body in relation to duct height, nanoparticle volume fraction, magnetic field strength, and heat transfer for magnetohydrodynamic flow. In general, the Nusselt number (Nu) increases with Re, cylinder diameter in relation to duct height, and nanoparticle volume fraction (ϕ) and decreases with the Hartmann number (Ha), except at Ha 0 ≤ 20. Nu increases with Ha from 0 to 20 with a drastic increase up to Ha = 10 and moderate from 10 to 20 with augment of Ha. The best heat transfer enhancement case is reported with the identification of ideal influencing parameters. The significant finding is that the control of flow over a circular cylinder for heat transfer enhancement using different parameters significantly changes vortical structures in the wake and reduces mean drag and lift fluctuations, destabilizes the shear layer and reattaches the flow on the surface before main separation, which delays main separation and decreases drag, and finally reduces the lift fluctuations.

The present study analyses the influence of magnetohydrodynamics on endwall heat transfer in turbine blades using computational fluid dynamics simulations. The simulations consider the three-dimensional geometry of the turbine blade, the magnetic intensity, and the boundary conditions. The outcome revealed the existence of a magnetic field can outstandingly increase the pitch-averaged film cooling effectiveness and endwall heat transfer, particularly near the edges of the turbine vane with an optimal magnetic field. This results in a more uniform distribution of heat transfer along the endwall and can help to reduce hot spots and prevent thermal damage to the blade. The research also highlights the importance of considering the magnetic intensity and its impact on the flow characteristics and heat transfer when designing turbine blades for high-speed applications. By optimizing the design of the turbine blades to take into account the magnetohydrodynamic effect, engineers can improve the overall performance and lifespan of these critical components. Numerical simulations had been utilized to forecast the impacts of contouring of endwalls efficiently, employing the secondary kinetic energy coefficient as the accomplished parameter demonstrated in the current investigation. A reduction in endwall heat load with enhanced net heat flux reduction and aerodynamic performance is reported for a non-axisymmetrically contoured endwall subjected to optimal magnetic field strength. The novelty of the present study is the establishment of the impact of vortices on endwall heat transfer with respect to the vane under the influence of magnetohydrodynamics to reduce the weight and cost of a turbine engine.

The lattice Boltzmann-Bhatnagar-Gross-Krook method was used to simulate Al2O3-water nanofluid to find the effects of Reynolds, Rayleigh and Hartmann numbers, slip coefficient, nanoparticle volume fraction and axial distance on forced convection heat transfer in MATLAB. The ranges of studied Reynolds number, Rayleigh number, magnetic field strength, nanoparticle volume concentration and slip coefficient include 200 ≤ Re ≤ 4000; 103 ≤ Ra ≤ 106; 0 ≤ Ha 90; 0 ≤ φ ≤ 2%; 0.005 ≤ B ≤ 0.02, respectively. The results show that increasing Reynolds number and nanoparticle volume fractions improve heat transfer in the 2D microtube under laminar, turbulent, slip and temperature jump boundary conditions. Decreasing the values of slip coefficient decreases the temperature jump and enhances the Nusselt number. A critical value for the Rayleigh number (105) and magnetic field strength (Ha 10) exists, at which the impacts of the solid volume fraction and slip coefficient effects are the most pronounced. The pressure drop shows a similar type of enhancement in magnitude, as observed in the case of the Nusselt number. However, application of nanofluids for low Reynolds numbers is more beneficial, and the effect of volume fractions are more pronounced in comparison to slip coefficient, though the effects are marginal.

The forced convective heat transfer with 3D, triangular, porous pin fins as bundle of MWCNTs at the bottom of rectangular mini channels made of silicon. Overall heat transfer performances in porous pin fins are much better than those in traditional solid pin fins. As nanofluid volume concentration increases, pressure drops and heat fluxes in porous pin fin channels increase and maximal overall heat transfer are obtained at 0.01% concentration. Enhancement in Nu were 6% with respect to porosity and 88 % with respect to 0.01% Al₂O₃/H₂O. With the same physical parameters, the Nu in the staggered triangular porous pin fin channels of CNTs with fin height of 0.75 mm, smaller fin width of 0.5 mm and spacing double the fin width using 0.01% CuO/H₂O nanofluid showed the highest enhancement of 91% at higher Re with a corresponding decrease in pressure drop of 25%. DOI: http://dx.doi.org/10.5755/j01.mech.24.1.17284

Heat transfer enhancement could be realized using magnetohydrodynamics together with nanofluids specifically in flow micro-convection in a microtube, flow past a vertical porous plate, and square duct flow with discrete heat sources numerically. A critical value for the Rayleigh number, a maximum value for the magnetic field strength, a low Reynolds number, and volume concentrations exists for thermal enhancement to simulate nanofluid flow in a microtube. Heat transfer enhancement is observed with a reduction in the magnetic field strength in a flow past a heated porous vertical plate. Alumina nanofluid subjected to Hartmann number 10 can boost 81% enhancement in Nusselt number in a square duct at lower Reynolds number using three discrete heat sources under the impact of thermal and solutal buoyancy. A 4% increase in the cooling effect near the center of the last heat source in a nanofluid flow is of practical use in hot spot cooling.