Abstract
A modified closed binary Brayton cycle model with variable isothermal pressure drop ratios is established by using finite time thermodynamics in this paper. A topping cycle, a bottoming cycle, two isothermal heating processes and variable-temperature reservoirs are included in the new model. The topping cycle is composed of a compressor, a regular combustion chamber, a converging combustion chamber, a turbine and a precooler. The bottoming cycle is composed of a compressor, an ordinary regenerator, an isothermal regenerator, a turbine and a precooler. The heat conductance distributions among the six heat exchangers are optimized with dimensionless power output as optimization objective. The results show that the double maximum dimensionless power output increases first and then tends to be unchanged while the inlet temperature ratios of the regular combustion chamber and the converging combustion chamber increase. There also exist optimal thermal capacitance rate matchings among the working fluid and heat reservoirs, leading to the optimal maximum dimensionless power output.
Highlights
Due to the characteristics of high power density (PD), small vibration, high automation, low operating pressure and easy lubrication, gas turbine plants (Brayton heat engine cycle) are extensively applied in the fields of aviation, energy, transportation, etc
The topping cycle is composed of a compressor (Com1), a regular combustion chamber (RCC), a converging combustion chamber (CCC), a turbine (Tur1) and a precooler (PC1)
The bottoming cycle is composed of a compressor (Com2), an ordinary regenerator (OR), an isothermal regenerator (IR), a turbine (Tur2) and a precooler (PC2)
Summary
Due to the characteristics of high power density (PD), small vibration, high automation, low operating pressure and easy lubrication, gas turbine plants (Brayton heat engine cycle) are extensively applied in the fields of aviation, energy, transportation, etc. Based on El-Maksoud’s classical thermodynamic model [8], Qi et al [62] established a closed endoreversible binary Brayton cycle model with two isothermal processes, without internal irreversibility, and coupled to constant-temperature reservoirs (CTRs). They derived the functional expressions of PO, TEF, PD and ecological function, respectively. The impacts of different thermodynamic parameters on the relationships among performance indexes and the pressure ratio of the topping cycle were analyzed, and the heat conductance distributions (HCDs) among heat exchangers were further optimized. The influences of different thermodynamic parameters on the optimal performance will be analyzed, and the thermal capacitance rate matchings (TCRMs) among the WF and the heat reservoirs will be discussed
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