Thermodynamic Mechanism of Self-Heat Recuperative Heat Circulation System with Non-Isentropic Compression and Expansion for a Continuous Heating and Cooling Gas Cycle Process

Abstract

Self-heat recuperation drastically reduces the energy consumption of thermal processes by adding work to circulate the whole process heat without heat addition. However, its theoretical foundations have not been fully established yet. This paper aims to elucidate the thermodynamic mechanism of self-heat recuperation with non-isentropic compression and expansion for a thermal gas cycle in terms of exergy analysis. The exergy analysis was performed with a modularization method using the module expression flow, the temperature–entropy, and the energy conversion diagram. The exergy analysis led to the significant conclusions that self-heat recuperation minimizes the energy consumption of gas thermal processes and that key information can be easily obtained by simply focusing on the exergy destruction without using complex process simulations. Heat circulation is driven by adding the work input to provide the minimum work required for heat transfer using the compressor, and theoretically all the excess work can be recovered to offset part of the work input using the expander. In practice, the irreversibility of adiabatic compression and expansion destroys part of the excess work, leading to a decrease in the excess work and an equivalent increase in the waste heat. The net work input is equal to the minimum work required for heat circulation and is converted into waste heat, whose anergy is transformed from the exergy destruction due to heat transfer, non-isentropic compression, and non-isentropic expansion. The minimum work required for heat circulation can be quantified by calculating the waste heat via the total exergy destruction. Thus, self-heat recuperation is the most energy-efficient solution to the design and retrofit of energy-saving gas thermal processes and is promising for process intensification. A case demonstration with numerical results on the heat circulation of air is presented to facilitate an intuitive understanding of the thermodynamic mechanism.