Optimization of a natural convection vertical channel with a heated ribbed wall

Heat transfer and mass flow rate in a natural convection vertical channel was investigated using a CFD code coupled with anoptimization dedicated software. The channel was considered bidimensional and set in vertical position, immersed in air, witha heated wall at uniform temperature condition, the other wall being adiabatic. The channel was open at the bottom and at thetop to allow the natural circulation of the ambient air. The heated wall was filled with ribs whose height, width, pitch, thermal conductivity and side wall inclination were variable. The analysis proceeded through the following steps: a) results validation versus schlieren experiments [1]; b) performance comparison: ribbed versus smooth configuration; c) smooth channel sensitivity analysis; d) ribbed channel sensitivity analysis; e) ribbed channel DOE sampling; f) ribbed channel optimization through genetic and simplex algorithms, aiming at average heat transfer and mass flow maximization. In the first steps the existence of an optimal channel width was investigated; the results coming from the latter steps clearly show the importance of the rib height: higher ribs strongly disturb the air stream leading to a performance drop.