Thermodynamic optimization of a stratified thermal storage device

Thermodynamic optimization combines exergy analysis with dynamical modeling to determine optimal design parameters. In this work we apply exergy analysis to an analytically solvable model of a single-medium stratified thermal storage device. We consider a simple one-dimensional model that includes conductive losses to the environment. Competition between mixing and conductive losses gives rise to a thermodynamically optimum charging time for the system. The model can treat the full range of stratification from the fully-mixed limit to perfect stratification and we are therefore able to determine the effect of stratification on the thermodynamic optimum. We show that stratification increases the overall efficiency and shortens the thermodynamically optimum charging time.