This paper presents results for the thermal mixing which occurs during the stably-stratified filling of a tall tank by a single, horizontal jet of cold liquid. Since the overall efficiency of a stratified storage device relates directly to the fraction of the stored volume lost to thermal mixing, minimizing thermal mixing is the key to increased efficiency. Accurate models of the thermal mixing processes are necessary for effective design and simulation of stratified storage devices. In this investigation, the two-dimensional Navier-Stokes equations and heat equation were used to compute the evolution of thermal mixing during a buoyant, laminar filling process. Perturbations from the one-dimensional evolution of the horizontally-averaged temperature field are computed directly and compared to transients in the entropy generation rate due to heat transfer. The entropy generation rate shows a smooth decay in time but the temperature perturbation field indicates the mixing is a complex function of space and time. This complexity results from interaction of the jet vortex with the thermocline and from the effects of persistent internal wave motion within the thermal gradient layer.
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