화학공학소재연구정보센터
International Journal of Heat and Mass Transfer, Vol.128, 1322-1343, 2019
A thermal non-equilibrium approach on thermo-solutal natural convection due to the lateral flux of heat and solute on enclosure walls: Multi-solutions and oscillations
In this paper, we address the influence of the thermal non-equilibrium state on double-diffusive convection in a porous enclosure, subject to constant heat and solute fluxes at the vertical walls, while other walls of the enclosure are adiabatic. For this, Darcy model has been adopted. The governing equations are solved numerically by the ADI method and analytically by using parallel flow assumption valid for the slender enclosure. A comparative study has been made in between buoyancy aiding flow(i.e., buoyancy ratio, N > 0) and buoyancy opposed flow(i.e., buoyancy ratio, N < 0). It was found that same as LTE (local thermal equilibrium) state particular oscillations and multiple solutions have also been observed on considering local thermal non-equilibrium (LTNE) state between the fluid and solid phase, for a certain range of interphase heat transfer coefficient (H) and conductivity ratio of fluid and solid (gamma), when both buoyancy forces are opposite in nature (buoyancy ratio, N < 0). The range of the interval for buoyancy ratio, I-NM, (in which multiple solutions exists) increases on increasing the value of H as well as gamma, while the range of the interval for buoyancy ratio, I-NO, (in which oscillation exits) vary in a subtle way. In general, same as LTE state, here also I-NO is found to be a subset of I-NM for most of the values of H as well as gamma considered in this study. Apart from this, in case of buoyancy aiding flow, the enhancement of aspect ratio (A) enhances the heat transfer rate for both the phases, up to a threshold value A(0) of A, beyond that threshold value the impact of the same is negligible, while Sh acts in other way. (C) 2018 Elsevier Ltd. All rights reserved.