Abstract
Hot water heat stores (HWHS) are generally used to overcome the diurnal or seasonal mismatch in the availability and demand of thermal energy. To enhance the system efficiency, good thermal stratification of the HWHS is required. In order to simulate different flow processes in stratified HWHS the effects of stratification on the turbulence are to be considered. Benchmark experiments have been conducted on turbulent flows into a continuously stratified HWHS. Based on these benchmark experiments, different two-equation turbulence transport models namely the RNG (ReNormalizable Group) and the realizable k-epsilon turbulence models have been calibrated. The major improvement is provided to the epsilon-equation by introducing the effects of the buoyancy field on the turbulence dissipation rate. It is achieved by calibrating the coefficient of the dissipation term (C-epsilon 2 in the RNG and C-2 in the realizable k-epsilon model) based on the benchmark experiments. A re-definition of the turbulent Prandtl number (Pr-t) incorporating the effects of stratification on turbulent thermal diffusivity improved the calibration further. The calibrated computational fluid dynamic models are found to predict the charging, discharging and storing processes of typical HWHS with good accuracy. Copyright (C) 2008 John Wiley & Sons, Ltd.