Abstract
Electrothermal energy storage (ETES) provides bulk electricity storage based on heat pump and heat engine technologies. A subcritical ETES is described in this paper. Based on the extremum principle of entransy dissipation, a geometry model is developed for heat transfer optimization for subcritical ETES. The exergy during the heat transfer process is deduced in terms of entropy production. The geometry model is validated by the extremum principle of entropy production. The theoretical analysis results show that the extremum principle of entransy dissipation is an effective criterion for the optimization, and the optimum heat transfer for different cases with the same mass flux or pressure has been discussed. The optimum heat transfer can be achieved by adjusting the mass flux and pressure of the working fluid. It also reveals that with the increase of mass flux, there is a minimum exergy in the range under consideration, and the exergy decreases with the increase of the pressure.
Highlights
Energy storage plays an important role in energy utilization and conversion systems
It is found that Thermal energy storage (TES) has been employed to contribute electrothermal energy storage (ETES), which is a type of bulk electricity storage technology to balance power demand and supply
As for the theoretical analysis, it is well known that the entropy production of a thermal system at steady-state should be the minimum, so many researchers have developed the concept of entropy production to deal with heat transfer optimization
Summary
Energy storage plays an important role in energy utilization and conversion systems. The different forms of energy that can be stored include mechanical, electrical and thermal energy [1]. Some researchers have proposed a combination of a heat pump and a heat engine to store energy [10,11], and some studies have been carried out on the optimizations for ETES. Morandin [18,19] used pinch analysis tools to optimize various forms of transcritical CO2 cycle based ETES They showed that the thermal energy available from the heat pump condenser at high temperatures can be stored and further used in a more efficient way, and the heat transfer feasibility must be required in the optimization. Desrues [8] presented a thermal energy storage process for large scale electric applications based on a high temperature heat pump cycle and a heat engine cycle.
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