EN Thermodynamic analyses of heat exchangers in cryogenic systems

Abstract

The problems of thermodynamic analysis associated with the heat exchangers that used in cryogenic technology are discussed. Heat exchangers of high and medium pressure air separation and fluidizing plants operating at different temperature levels were selected for modelling. There are many features according to which the classification of heat exchangers is made. These features include such facts as the number of flows of the working fluid, the relative direction of the flows of working substances, the purpose of the apparatus, and others. These features are also associated with the design of heat exchangers and the software for the design, which contains thermodynamic calculations. The general thermodynamic approach is based on the equation for the values of the thermodynamic efficiency characteristics and the restrictions imposed on them At the exergy method of analysis, the corresponding balance is based on the energy balance equation. On the basis of this balance, the losses from irreversibility of the selected object and its exergy (thermodynamic) efficiency can be directly determined In a heat exchanger, both types of losses exist, but it is not possible to reveal the contribution of each type to total losses using only the exergy balance. This is due to the fact that this balance is drawn up for a closed control surface that reflects a physical object and not logical reasons associated with this object. Meanwhile, the determination of technical losses is an urgent tasks since the change in the thermodynamic parameters that regulate these losses are the basis for increasing the coefficient of the thermodynamic efficiency of the analyzed system A method and an algorithm for calculating the components of losses from irreversibility in these heat exchangers are proposed. The exergy method of thermodynamic analysis was used to calculate the components of these losses for some two-flow heat exchangers. The investigation of the obtained calculation results is presented