Accurate SRT-BGK model evaluation of heatlines visualization and entropy generation of convective heat transfer inside an inclined U cavity receiver as application of solar thermal energy systems

The present study analyzes thermal and dynamic fields, heatlines visualization and entropy generation as well as flow energy, flow rate and heat transfer through a natural convection flow inside a top-open cavity receiver. For the case of a horizontal cavity, lower walls are heated at a uniform temperature while vertical walls are treated as adiabatic. The lattice Boltzmann method (LBM) is applied to solve governing equations of the problem. Effects of Rayleigh number (103 ≤ Ra ≤ 105), cavity orientation (0° ≤ θ ≤ 75) and cavity aspect ratio (1 ≤ A ≤ 1.75) on thermo-fluid characteristics of the flow are performed. It was found that current findings computed by LBM are in line with existing literature. Findings reveal that flow patterns and heat transfer are strongly affected by variations of Ra, θ and A. The rise of Ra leads to a change in the orientation of heatlines trajectories with a growth of the stratification degree of entropy generation within the horizontal square cavity. Additionally, an enhancement of the convective heat transfer is detected as increasing Ra accompanied with more energy absorbed by the flow and an intensification of the entrainment phenomenon of fresh air by thermal plumes. For Ra = 5×104, the optimization of heat transfer and total entropy generation demonstrate the existence of a critical angle of the square cavity receiver corresponding to the cavity orientation of θ = 45°.Increasingthe angle θ reduces the stratification degree of heatlines and entropy generation as well as the flow rate. The rise of the geometrical parameter A entrains an increase of thermal gradients with a deceleration of the flow circulation. A decrease of flow rate and convective heat transfer with the growth of the aspect ratio of a horizontal cavity is detected for Ra = 5×104.