Turbulent double-diffusive convection and implementation of entropy production rate due to the mean and the fluctuating flow field

Abstract

The present study performs a CFD-based analysis of entropy production due to conjugate turbulent heat and mass transfer. For the turbulent regime, the instantaneous temperature, concentration, and velocity fields are resolved into time-averaged mean and fluctuating parts. Thus, six different terms of entropy production arise due to this mode of temperature and species transfer. Unfortunately, such a model does not exist and a new approach is therefore needed which makes this problem more challenging. Hence, the overall aim of this paper is twofold: First, is to develop a new approach to cope with the entropy production that takes into account all the six different terms due to temperature and species transport. Second, is to carry out a numerical simulation of double-diffusive free convection inside a square cavity. On the basis of asymptotic considerations, a new formula that expresses entropy production due to fluctuating concentration gradients was derived. Depending on the Rayleigh number and the buoyancy ratio, the total entropy increased significantly when the fluctuating terms were accounted for. Total entropy was found to increase by up 27% for N = +5.0 and Rayleigh number of 109. However, it increased by 38% when N = +1.0 and Ra = 1010.