STRUCTURAL OPTIMIZATION OF CRYOGENIC CYCLES BASED ON EXERGETIC ANALYSIS.

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]