Thermodynamic cycles and electrical charge recovery in high-efficiency electrocaloric cooling systems

Abstract

• A linearized model provides insight into electrocaloric cooling thermodynamic cycles. • Derivations for Brayton, Carnot, and Otto cycles are provided. • Modeling results highlight the importance of efficient charge recovery. • Brayton and Otto cycles can be more efficient than Carnot cycles in practical systems. This paper introduces a linearized model of electrocaloric cooling. The model is derived for electrocaloric Brayton, Carnot, and Otto cycles, and a more practical hybrid constant voltage-charge (HCVC) variation of the Otto cycle. It is then parametrized for a benchmark terpolymer material. Model outputs are used to examine the system performance under each cycle as a function of temperature lift. The impact of electrical charge recovery efficiency on performance is then investigated to provide insight into system optimization requirements. Practical limitations of charge recovery circuits are discussed in the context of heat and work transfer in each cycle leg. Results indicate that electrical charge recovery efficiency greater than 95% is needed to achieve competitive system efficiency and that this is challenging with a Carnot cycle, despite its theoretical optimality. The Brayton and Otto cycles, in contrast, can achieve cooling efficiencies that approach the theoretical maximum.