Exergy analyses of criyogenic cycles

The field of cryogenics seemed to be a very difficult field to understand, however it has a great influence in today's industry and scientific field. In this study, optimum working conditions are obtained by applying exergy analysis and local optimization methods to some cycles of the Cryogenic field. The first and second laws of thermodynamics, exergy analysis and local optimization methods were applied to the most commonly used method, namely the two and three stage cascade cryogenic cycle. Undoubtedly, new cryogenic cycles can be obtained by adding new stages to these cycles and/or adding new devices to the cycles. By considering the conditions, needs and demands for this, it is possible to create new cycles from cascade vapor compression cryogenic cycle. From the findings and results of the two and three stage vapor compression cascade cryogenic cycle, the optimum operating conditions of these two cycles have been obtained. The optimum operating conditions which are minimum work, maximum COP and maximum exergetic efficiency for the two stage vapor compression cascade cryogenic cycle, are obtained at P7=2400 kPa pressure. For the three stage vapor compression cascade cryogenic cycle, it has been understood that in order to achieve high efficiency and high COP values, it is necessary to reduce the compression ratio of the compressor as much as the fluid allows, and to use a turbine instead of a throttle valve in order to transform the work losses in the throttle valve into gain. The high compression ratio of the compressor, increases the work spent on the cycle and the amount of heat losses and decreases the COP values of the cycle. The work obtained by using the turbine instead of the throttle valve is spent on the compressor work required, thus reducing the amount of work required by the outside of the cycle. For this reason, cycle efficiency and COP values can be increased.