To understand the flow and transport characteristics in the entrance region of Poiseuille-Rayleigh-Benard (P-R-B) double diffusive convection within horizontal channel, a series of three-dimensional numerical simulations are conducted to assess the impact of aspect ratio (B), Reynolds number (Re), buoyancy ratio (N), and Rayleigh number (Ra), with the following ranges: 1 <= B <= 10, 0 <= Re <= 25, - 0.3 <= N <= 0.3, and 40 <= Ra <= 1.2 x 105. The results indicate that the vertical velocity exhibits periodic sinusoidal fluctuations in both space and time as transverse rolls (TRs) develop. The amplitude of these fluctuations increases with Ra and N, while the fundamental frequency decreases as N rises. In the presence of longitudinal rolls (LRs), the vertical velocity is symmetrically distributed in the spanwise direction. If LRs do not fully develop in the entrance region, the vertical velocity will not form regular periodic fluctuations. When stable TRs occupy the entrance region, both temperature and concentration fields fluctuate sinusoidally over time with identical fundamental frequency. Correspondingly, Nusselt (Nu) and Sherwood (Sh) numbers show sinusoidal variations in the streamwise direction, and their amplitudes increase with Ra and N. Moreover, for LRs, the entrance lengths for the onset of secondary flow (L1) and for its full development (L2) decrease with Ra and N, but increase with Re and B. Meanwhile, at high Ra or large positive N, the reductions of L1 and L2 become less pronounced. In addition, the overall transport performance is not improved monotonically with increasing B. Based on simulation data, correlations for L1 and L2 were proposed. Ultimately, the thermal and solute transport correlations including the entrance region were also derived. These findings provide a theoretical foundation for the dimensional design of chemical reactors, heat and mass transfer equipment, and other systems involving P-R-B double diffusive convection.
更多
原文链接
分享
引用
