Aspect ratio effect on natural convection in water near its density maximum temperature

The effect of the aspect ratio on natural convection in water subjected to density inversion has been investigated in this study. Numerical simulation s of the two-dimensional, steady state, incompressible flow in a rectangula r enclosure with a variety of aspect ratios, ranging from 0.125 to 100, hav e been accomplished using a finite element model. Computations cover Raylei gh numbers from 10(3) to 10(6). Results reveal that the aspect ratio, A, th e Rayleigh number, Ra, and the density distribution parameter, R, are the k ey parameters to determine the heat transfer and fluid flow characteristics for density inversion fluids in an enclosure. A new correlation for predic ting the maximum mean Nusselt number is proposed in the form of <(Nu)over b ar>(max) = a - b log(A), with the constants a and b depending on density di stribution number R. It is demonstrated that the aspect ratio has a strong impact on flow patterns and temperature distributions in rectangular enclos ures. The stream function ratio Psi(inv)/\Psi(reg)\ is introduced to descri be quantitatively the interaction between inversional and regular convectio n. For R = 0.33, the density inversion enhancement is observed in the regim e near A = 3. (C) 1999 Elsevier Science Inc. All rights reserved.