Numerical study of transient and steady-state natural convection and surface thermal radiation in a horizontal square open cavity

This article reports a numerical study of the transient and steady-state heat transfer and air flow in a horizontal square open cavity. This study has importance in several thermal engineering problems, for example, in the design of electronic devices and thermal receivers for solar concentrators. The most important assumptions in the mathematical formulation of the horizontal square open cavity are three: The flow is laminar, the fluid is radiatively nonparticipating, and the Boussinesq approximation is valid. The conservation equations in primitive variables are solved for a range of Rayleigh number, Ra, from 10³ to 10⁷ using the finite-volume method and the SIMPLEC algorithm. The results show that the radiative exchange between the walls and the aperture increases considerably the total average Nusselt number, from around 94% to 125%, versus the one with no radiative exchange between walls. Also, for Ra = 10⁷, the numerical model predicts periodic formation of thermal plumes in the bottom wall of the cavity, and their further movements explain the oscillation behavior of the Nusselt number with time.