Computational study of natural convection and entropy generation in 3-D cavity with active lateral walls

Numerical simulation of the natural convection and entropy generation in an air-filled cubical cavity with active lateral walls is performed in this work. Both the lateral front and right sidewalls are maintained at an isothermal cold temperature. While an isothermal hot temperature is applied for both the lateral back and left sidewalls. The upper and lower walls are kept adiabatic. Entropy generation rates due to the fluid friction and the heat transfer are simulated by using the Second law of thermodynamics. Results are illustrated for Rayleigh numbers varied from (10³ ≤ Ra ≤ 10⁶). It was shown that the increase in the Rayleigh number leads to increase the average Nusselt number and to decrease the Bejan number. Also, it was found that both, Sth, and Stot, increase slightly with the increase in Rayleigh number until they reach (Ra = 10⁵) and then begin to jump after this value. After (Ra = 10⁵), the increase in both, S_tot, and S_fr, is greater than S_th. Moreover, it was observed that iso-surfaces of S_tot are similar to Sth at (10³ ≤ Ra ≤ 10⁵), while they are similar to Sfr at high Rayleigh number.