Energy and exergy analysis of a multi-stage cooling cycle of scramjet to produce electricity and hydrogen

Abstract

A multi-stage open cooling cycle of scramjet for electricity and hydrogen co-production is proposed in which the fuel of scramjet is used as coolant of cooling cycle.Thermodynamic and exergetic examinations of the advanced system have been conducted to appraise the performance of the cycle, electricity and hydrogen production. In this integral system, the waste heat of scramjet drives the power sub-cycle whilst the PEM electrolyzer input electricity is supplied by a portion of net electricity output of the cycle. It is figured out that the multi-expansion process reveals more advantages in comparison to the single-expansion process in terms of more cooling capacity, electricity and H_2 production.For the fuel mass flow rate of 0.4 kg/s, the cooling capacity of the new proposed cycle is computed 9.16 MW, the net electricity output is calculated about 3.38 MW and the hydrogen production rate is attained 42.16 kg/h. On the other hand, the exergetic analysis results have proved the fact that PEM electrolyzer has the highest exergy destruction ratio by 48% among all components of the cycle. In this case, the energy and exergy efficiency of the overall set-up are acquired by 12.95% and 22.16%, correspondingly.The outcomes of parametric evaluation demonstrated that the electricity and hydrogen production are directly proportional to the back pressure of pump accordingly, more electricity and hydrogen are generated by higher back pressure. But, increasing the mass flow rate of fuel does not have any tangible impact on energy and exergy efficiency of whole set-up thus both remain approximately constant.