Mixed convective flow and thermal stratification in hot water storage tanks during discharging mode

An analysis of transient, two dimensional, mixed convection and thermal stratification in cylindrical hot water storage tanks is presented. The governing equations together with inflow and outflow boundary conditions are written for laminar mixed convection flow using a finite volume based computational code in the dynamic discharging mode based on Boussinesq approximations and conjugate heat transfer. The equations are solved numerically and the results are obtained for aspect ratios of the tanks ranging from 1 to 4 in the Richardson number range of 105 to 108 using a finite volume based computational code. The dynamic discharging mode is considered using a conjugate heat transfer model. The transient temperature profiles in the bulk fluid reveal reduced mixing at higher Richardson numbers during discharging process. The system performance in the dynamic mode of operation is defined by a Mix Number and discharging efficiency parameter. Mixing at the bottom of the tank due to inflow of low temperature water from the load is found to have significant influence on the storage efficiency. The discharging efficiency decreases with Fourier number due to increased thermal degradation with time. © 2009 Allerton Press, Inc.