Thermodynamic analysis and the recuperator's effects on two cycle systems aiming for hypersonic vehicles

For potential applications of hypersonic vehicles, two cycle systems integrated engine cooling and power generation based on the closed Brayton cycle is analyzed and compared. The investigated two systems are named simple recuperated layout (SRL) and recompressing recuperated layout (RRL) respectively. Thermal performance of the two systems and the required mass flow rate of the working fluid at the given heat source power are explored. The characteristics of the recuperators at the maximum cycle efficiency and the effects of the recuperators on the cycle efficiency are analyzed in detail. The results show that the maximum cycle efficiency of the SRL and RRL are 38.80% and 45.24% respectively. At the given heat source power, the required mass flow rate of the SRL and RRL are 4.85 kg/s and 6.67 kg/s respectively. Compared to the SRL, the RRL has an absolute increment rate of 16.60% for the cycle efficiency and 37.53% for the required mass flow rate. At the given heat source power, heat transfer in the recuperators of the RRL is 726.81 kW higher than that of the SRL, which is beneficial to the improvement of the cycle efficiency. The effectiveness and the pressure drop of the recuperators have significant influence on the performance of both cycle systems. The cycle system performances are affected more by the pressure drop in the hot side of recuperators than that in the cold side. This study provides a reference for the design of recuperators in an onboard power cycle system and for the researches on engine cooling and power generation of hypersonic vehicles.