Investigation of Thermal Adiabatic Boundary Condition on Semitransparent Wall in Combined Radiation and Natural Convection

TL;DR

This study investigates how different thermal adiabatic boundary conditions on a semitransparent window affect natural convection and radiation heat transfer in a cavity, revealing significant changes in vortex dynamics, temperature, and heat transfer rates.

Contribution

It introduces a comparative analysis of conductively adiabatic versus combined conductively and radiatively adiabatic boundary conditions on semitransparent windows in natural convection problems.

Findings

Temperature and Nusselt number increase significantly under combined boundary conditions.

Vortex dynamics inside the cavity are highly sensitive to irradiation and boundary conditions.

Radiative effects drastically alter heat transfer characteristics in the cavity.

Abstract

Two thermal adiabatic boundary conditions arise on the semitransparent window owing to the fact that whether semitransparent window allows the energy to leave the system by radiation mode of heat transfer. It is assumed that being low conductivity of semitransparent material, energy does not leave by conduction mode of heat transfer. This does mean that the semitransparent window may behave as only conductively adiabatic (qc = 0) or combinedly conductively and radiatively adiabatic (qc + qr = 0). In the present work, the above two thermal adiabatic boundary conditions have been investigated in natural convection problem for the Rayleigh number (Ra) 10^5 and Prandtl number(Pr) 0.71 in a cavity, whose left vertical wall has been divided into upper and lower parts in the ratio of 4:6. The upper section is semitransparent window, while lower section is isothermal wall at a temperature of 296K. A collimated beam is irradiated with different value (0, 100, 500 and 1000 W/m2) on the semitransparent window at an angle of 45^0 . The cavity is heated from the bottom by convective heating with free stream temperature of 305K and heat transfer coefficient of 50 W/m2K while right wall is also isothermal at same temperature as of lower left wall and upper wall is adiabatic. All walls are opaque for radiation except semitransparent window. The results reveal that the dynamics of both the vortices inside the cavity change drastically with irradiation value and also with the boundary conditions on the semitransparent window. The temperature and Nusselt number increase inside the cavity multifold for combinedly conductively and radiatively adiabatic condition than the only conductively adiabatic condition on the semitransparent window.