Effect of asymmetric opening characteristics on coupled natural convection and surface radiation heat transfer in a semi-enclosed cavity

In a semi-enclosed cavity with asymmetric openings, natural convection and surface radiation exhibit nonlinear coupling and competition. The effect of opening characteristic topology evolution on this convection–radiation coupling remains unclear. A coupled heat transfer model of surface radiation and natural convection is developed for a confined space with asymmetric openings and non-uniform thermal boundary conditions. The effects of opening position and opening size on the coupled heat transfer inside the cavity are analyzed. The results show that natural convection and surface radiation have very different sensitivities to opening characteristics. As the opening ratio increases, the removal of geometric shielding causes a sharp increase in radiative view factors. The fourth-power dependence on absolute temperature is then strongly amplified at high temperature differences. The average enhancement of radiative heat transfer reaches 59.3%, which is higher than that of natural convection (39.6%), and radiation becomes the dominant heat dissipation mode at large openings. In contrast, changing the opening position aligns the heat removal path with the buoyancy-driven thermal accumulation region near the cavity top. This compresses the near-wall thermal boundary layer. This process is dominated by convection, and the average enhancement of convective heat transfer reaches 59.0%. A comparison between co-side and counter-side opening configurations shows that the radial height of the opening is the primary factor controlling the overall heat transfer intensity, while the opening direction is a secondary factor. The counter-side opening configuration further increases convective heat transfer by 4.5% compared with the co-side configuration. The radiative heat-transfer fraction increases with temperature difference, with values ranging from 38.1% to 59.7%.