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Based on the exergetic analysis the paper analyses the conduct of a simple Linde cryogenic refrigeration cycle looking for its weaknesses and trying to find ways for operating or structural improvements. The exergetic analysis reveals that a major exergy destruction is due to heat transfer across a finite temperature difference in the recuperative heat exchanger. The optimization procedure points out that this exergy destruction reaches a minimum if the temperature difference between the high (hot) and low pressure (cold) streams decreases with temperature. To achieve this desiderate structural changes in the architecture of the Linde cryogenic refrigeration system should be done. Two schematics are proposed – one with external precooling of the forward gas stream and the second one with an expansion machine. The analysis shows substantial improvement of the performance of the simple Linde cycle when using external precooling of the forward gas stream or an expansion machine. These results validate the model according to which the minimization of the input power of the cryogenic system takes place under conditions in which the temperature difference between the forward and return gas streams in the recuperative heat exchangers decreases proportionally with temperature. [ABSTRACT FROM AUTHOR]

The energy consumes for district or industrial heating and electrical energy are in most of cases concomitant. The paper analyses from the point of view of the First and Second Laws of Thermodynamics the advantages of producing heat and mechanical power each one individually or through cogeneration. It is clearly pointed out that the energy balance induces the idea that the most efficient conversion process is to produce heat in an individual boiler while the mechanical power production in a steam turbine system is much less efficient. The energetic analysis accounts only for the interactions with the external medium considering any heat loss as depending only on its magnitude and neglecting its temperature level as quality factor. The large energy loss in the condenser of the steam turbine system decreases dramatically the energetic efficiency of the overall system even if this heat transferred to the environment is useless due to its low temperature level. The exergetic analysis that accounts for both the quantity and quality of a heat carrier shows the real level of efficiency for each process advocating for the production of both heat and mechanical power by cogeneration. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of the behaviour of an air-water vapour compression heat pump at the variation of some of the decisional parameters as the state of the fluid at the compressor intake. Different refrigerants as CO2, NH3 and R600a, and different schematics are considered. The large use of rotary compressors in the industrial and domestic heat pump area has determined the investigation of the influence of the wet compression. The analysis is based on the exergy concept that enables to point out the location and magnitude of any malfunction. The exergy analysis gives solutions for improving the performance and design of the heat pump system. The exergetic analysis helps to improve the constructive structure of the heat pump schematic. The exergetic analysis points out that the largest exergy destruction in the CO2 cycle is due to the throttling process and offers solutions to diminish it. [ABSTRACT FROM AUTHOR]