Analyses of entransy dissipation, entropy generation and entransy–dissipation-based thermal resistance on heat exchanger optimization

Heat exchangers are widely used in industries and daily life. The optimization design of heat exchangers is of great significance to the consumption reduction of energy. This paper analyzes and discusses two-/three-stream heat exchangers based on the concepts of the entransy dissipation, the entropy generation and the entransy–dissipation-based thermal resistance of multi-stream heat exchangers. It is found that the minimum thermal resistance based on entransy dissipation always corresponds to the best performance of heat exchangers, while the minimum entropy generation and the extreme entransy dissipation do not always correspond to the best performance of heat exchangers. The relationship between the thermal resistance and uniformity factor of temperature difference field, the relationship between the thermal resistance and the effectiveness of heat exchangers are derived for the two-stream heat exchangers. The results indicate that the uniformity factor of temperature difference field and the effectiveness of heat exchangers would both increase with the decrease of the thermal resistance. In addition, it is found that a larger uniformity factor always leads to a higher effectiveness of heat exchangers. The physical meaning of the phenomenological principle of the uniformity of temperature difference field is discussed for the two-stream heat exchangers, and the uniformity principle of temperature difference field is proved directly.

► Minimum thermal resistance corresponds to best effectiveness.
► Entropy generation is not always appropriate to optimize heat exchangers.
► Application of entransy dissipation to heat exchanger optimization is conditional.
► The uniformity principle of temperature difference field is proved.