EXERGETIC ANALYSIS OF PLATE HEAT-EXCHANGER IN PRESENCE OF AXIAL-DISPERSION IN FLUID

This paper presents an exergetic analysis of a single pass counterflow plate type heat exchanger for cryogenic applications. The special focus of the analysis is the study of the effect of axial dispersion which takes the flow maldistribution into consideration. It is found that with unutilized exergy fraction as the figure of demerit the exergetic performance of the heat exchanger can be consistently presented without the 'paradox' which has been observed by many investigators. The axial dispersion is found to reduce the exergetic performance and so does the frictional pressure drop of the fluids. This makes it possible to identify a minimum irreversibility corresponding to a given level of dispersion. It has been observed that over a relatively broad zone near the optimum NTU the change in exergy loss is small, providing more flexibility for the designer of the heat exchanger to alleviate the penalty for exergy loss, which is particularly severe in the cryogenic regime.