Entropy and exergy analysis of a hollow fiber membrane humidifier

Abstract

Entropy and exergy analysis methods can be used to evaluate availability losses during heat and mass transfer, which facilitates targeted measures to reduce entropy generation and exergy destruction. In this paper, an entropy generation and exergy destruction model of the hollow fiber membrane humidifier is developed to calculate the entropy generation and exergy destruction in the heat and mass transfer process. The effects of operating conditions, geometry structures, and membrane properties on heat and mass transfer performance, entropy generation, and exergy destruction are investigated. Further, the internal relationships between them are analyzed and disclosed. The results show that increasing the heat and mass transfer driving force can improve the heat and mass transfer performance of the humidifier under different operating conditions. However, the energy grade between air and water stream increases, which results in entropy generation and exergy destruction increases. The effects of the air stream on the performance are more significant than that of the water stream. In addition, the humidifier performance can be improved by 8.4%-11% by increasing the packing fraction and width-height ratio, while the exergy destruction and entropy generation rate are decreased by about 5.9%-11.9%. It is worth noting that when the width-height ratio is larger than 1.5, the effect of increasing the width-height ratio on the entropy generation rate and exergy destruction gradually diminishes. The width-height ratio between 1.5 and 1.75 may be a better choice. Employing a membrane with a larger diffusivity can enhance the water vapor transfer performance by approximately 63.7%, which results in the mass transfer entropy generation rate and chemical exergy destruction increase by 61%-86.8%.