A Comparative Analysis of Solar Parabolic Dish Driven Recompression S-CO2 Brayton Cycles with and without Reheat

The current study presents a thermodynamic comparison between two different supercritical carbon dioxide (S-CO2) Brayton cycles integrated with parabolic dish solar system. Recompression S-CO2 Brayton cycles with reheat and without reheat are examined for their net power output, cycle efficiencies as well as integrated system efficiencies. The analyses are conducted by developing a comprehensive mathematical code in Engineering Equation Solver (EES). Parabolic dish system is assessed and optimized on the basis of yearly available data and by using the optimization results, a thorough comparative study based on thermal efficiencies, integrated system efficiencies and work output is carried out. The system comprises of indirect heated Brayton cycle in which fresh water is utilized as a heat transfer fluid in solar collector, whereas, Brayton cycle comprised of S-CO2. The dish system is designed by taking the average annual direct normal irradiance (DNI) 1000 W/m2 approximately and such system is effective for southern part of Pakistan, Cyprus and Spain and many other countries where sun shines almost nine to eleven hours daily and DNI varies from 700 to 1000 W/m2 The outcomes of the research state that the recompression with reheat S-CO2 Brayton cycle has achieved thermal efficiency almost 47.70%, while the other system has nearly 45.02%. The recompression with reheat cycle has an overall energy efficiency of almost 30.37 % however the recompression without reheat system has almost 27.5%. Furthermore, second law integrated efficiency of recompression without reheat system is almost 29.6%, whereas, reheating system has 32.7% overall exergetic efficiency. Reheating has improved efficiency almost 10.5 %. The effect of increase iv in minimum cycle temperature is positive for reheat system and the efficiency tends to be reduced due to the increase in main compressor work for without reheat system. Moreover, the effect of rise in pressure ratio on integrated system performance is similar to that of minimum cycle temperature influence. Exergy destruction rate of collector receiver is approximately 40% which reduces with increase in the inlet temperature of the compressor, whereas, recuperators and pre cooler has more exergy losses than other components. Keywords: Parabolic dish system, S-CO2, Brayton cycle, Energy and Exergy efficiency, Pressure ratio, Net power output, minimum cycle temperature