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Designing new and efficient heat engines and increasing the efficiency of previous ones is one of the researchers’ interests in the field of thermodynamics. In this regard, what is mainly concerned is to design a cycle with the positive features of previous cycles, such as less pollution, and higher power‐to‐weight ratio and efficiency. One of these cycles is the supercritical carbon dioxide cycle (SCDC). The main goal of this research is designing a highly efficient SCDC with pessimistic and relatively optimistic efficiencies of 45% and 47%. This paper includes the complete first law analysis of the designed cycle, designing and discussion of efficiency improvement methods and comparison of SCDC with other power cycles. The sensitivity of the cycle efficiency to some important parameters has also been studied.

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In conventional ejector refrigeration cycles, the ejector mostly operates at fixed pressure points in the secondary stream and outlet. Studying the sensitivity of the system to the pressure alternation of the mentioned points has not been investigated. To cover this gap, an extra turboexpander, compressor, and gas cooler were introduced to the conventional ejector layout. It was found that pressurizing the secondary entrance of the ejector could be beneficial to COP if it is not warmer than the gas coolers. Also using the expansion process right after the ejector has the potential to increase the efficiency of the system if the discharge pressure of the ejector reaches supercritical or superheat condition.

Nuclear energy has been considered as clean and environmentally friendly method of power production. With the emergence of Generation IV reactor, a new horizon was opened in nuclear technology. The invention of new materials and production processes and magnetic bearings, the new ideas for increasing the efficiency of nuclear power plants are being considered more feasible. In this paper the thermodynamic analysis of a Helium pseudo-isothermal expansion and compression power cycle which can be utilized to couple with a Very High-temperature Gas Reactor (VHTR) was performed. A novel thermodynamic modelling of estimating the isothermal process based on the irreversibility during the compression or expansion was done. The results show that isothermal process is not so far from the reality and the power cycle can exceed other designs in terms of efficiency.