Turbulent mixed convection of air in a cavity with a heat-conducting inner solid: Effect of surface radiation and thermal diffusivity on heat transfer and exergy destruction

The study of natural and forced turbulent convection of heat has been essential to improving the design pa-rameters of several engineering applications. However, few works have described the simultaneous effect of turbulence and thermal radiation phenomena on heat transfer and exergy destruction in cavities with inner solid bodies. This work investigates the turbulent mixed heat convection of air and the surface thermal radiation in a cavity with a heat-conducting square solid at its center through computational modeling. A turbulent k-epsilon model with damping functions and temperature-variable thermal properties are used for the air, while the local exergy destruction is computed by a direct method for turbulent flows. The effects of turbulence and surface thermal radiation are analyzed through the variation of the Grashof (10(8) <= Gr <= 10(10)) and Richardson (0.1 <= Ri <= 10) numbers, the emissivity of the surfaces (0 <= is an element of <= 0.9) and the thermal diffusivity ratio between solid and fluid (1 <= R <= 10(3)). The main results indicate that the increment of Ri notably changes the magnitude and distribution of velocities and temperatures, increasing from 30% to 300% the maximum dimensionless velocity. The maximum temperatures in the cavity are reduced by 30% when thermal radiation is considered, resulting in weaker buoyancy-driven flows. The increment of the emissivity increases up to 5 times the value of the dimensionless heat transfer at the inner-solid surfaces, Nusselt number Nu, and decreases from 45% to 75% the total exergy destroyed (Xd(T)) in the cavity. On the contrary, the increment of R only produces variations lower than 8% of the Nu and the XdT for all the cases investigated.

Automated summary

This study investigates the combined effects of turbulent mixed heat convection and surface thermal radiation on heat transfer and exergy destruction in a cavity with a heat-conducting square solid at its center. The results show that turbulence and thermal radiation significantly affect velocity, temperature, and exergy destruction, while the variation of the thermal diffusivity ratio has a smaller impact.