Mixing in thermally stratified energy stores

Two important aspects of short-term thermally stratified energy storage, thermocline mixing and thermocline thickness, are studied analytically, experimentally and numerically The storage detrimental aspects are investigated for a simplified configuration, i.e. an adiabatic box containing a quasi-stationary thermocline. Numerical finite difference/volume simulations agree well with experiments. The dissipation-free 1D analytical model shows a large discrepancy. It appears that mixing inside thermally stratified stores is a two-stage process. First fluid is withdrawn from the thermocline by viscous drag. Subsequent mixing takes place by stretching and folding of fluid particles, thereby enabling diffusion to become active. Copyright (C) 1996 Elsevier Science Ltd.