A steady laminar two-dimensional magneto-hydrodynamics mixed convection flow in a square inclined cavity filled with Cu–water nanofluid is investigated numerically by using the finite difference method. The left and right vertical sidewalls of the cavity are considered adiabatic and move upward, while a partial slip flow condition is imposed on these walls. The horizontal top wall is considered cold and stationary, while a part of the stationary bottom wall is subjected to a uniform heat source and the remaining parts of it are considered adiabatic. An adiabatic obstacle is located in the center of the cavity and an external magnetic field is applied parallel to the horizontal x-axis. Parametric studies of the influence of various parameters such as Hartmann number, inclination angle of the cavity, dimensionless heat generation/absorption coefficient, obstacle aspect ratio, dimensionless length and location of the heat source, and solid volume fraction on the fluid flow and heat transfer have been performed. Comparisons with previously published numerical work are performed, and good agreements between the results are observed. It is found that the nanofluid was better than water to enhance the heat transfer when the effect of the magnetic field is weak, while the water is better than the nanofluid when its effect is strong. Moreover, the results indicated that the partial slip has a significant effect on the above-mentioned parameters.

Hybrid photovoltaic-thermal heat pump (PV/T-HP) solar energy systems are promising since they can achieve a system total efficiency greater than 80%. By maximizing the output of a PV/T system for simultaneous heating and cooling, this strategy can meet over 60% of urban households’ heating needs and around 40% of their cooling needs. In this work, a novel PV/T evaporator was designed, fabricated, and an aluminium foil encapsulated hydrated salt (HS36) PCM was integrated with the PV/T evaporator of the PV/T direct expansion heat pump system (PV/T-DXHP). Energy analysis was carried out on the PV/T-DXHP system with PCM in tropical climate regions of India for achieving net zero energy buildings. The experimental study revealed that the average PV electricity efficiency was 14.17%, which is near the PV panel’s STC value. The average thermal efficiency of the system was 104.38%, and the PV/T system’s average overall efficiency was 117.58%. The heating and cooling COPs of the system were 5.73 and 4.62, respectively. It was concluded that net-zero energy buildings are possible with the help of photovoltaic heat pump systems that use PCM and solar energy to make electricity, cool spaces, and heat water.

In this paper, a 2D numerical study of natural convection heat transfer in a W-shaped inclined enclosure with a variable aspect ratio was performed. The enclosure contained a porous medium saturated with Ag/Al₂O₃ hybrid nanofluid in the presence of uniform heat generation or absorption under the effect of a uniform magnetic field. The vertical walls of the enclosure were heated differentially; however, the top and bottom walls were kept insulated. The governing equations were solved with numerical simulation software COMSOL Multiphysics which is based on the finite element method. The results showed that the convection heat transfer was improved with the increase of the aspect ratio; the average Nusselt number reached a maximum for an aspect ratio (AR) = 0.7 and the effect of the inclination was practically negligible for an aspect ratio of AR = 0.7. The maximum heat transfer performance was obtained for an inclination of $\omega =15$ and the minimum is obtained for $\omega =30$ . The addition of composite nanoparticles ameliorated the convection heat transfer performance. This effect was proportional to the increase of Rayleigh and Darcy numbers, the aspect ratio and the fraction of Ag in the volumetric fraction of nanoparticles.

The mixed convection in a cubical cavity with active lateral walls and filled with a graphene–platinum hybrid nanofluid was investigated numerically and exclusively in the present paper. The lateral left and back sidewalls were kept at a hot temperature (Th), while the lateral right and front sidewalls were kept at a cold temperature (Tc). Both the top and bottom walls were assumed thermally insulated. The top wall of the cavity was considered moving with two different directions. The first one is in the x-direction (case I), while the second case is in the z-direction (case II). Also, the case of the fixed top wall was studied just for comparison. The solid volume fractions have been varied as 0 ≤ φ ≤ 0.1%, while the Richardson number is varied in the range of 0.01 ≤Ri ≤ 10. It was found that the maximum average Nusselt number corresponds to the case when the top wall moving in the negative x-direction. Also, the results indicated that the average Nusselt number increases with the increase in the Richardson number and the solid volume fraction.