Experimental performance evaluation of desiccant coated heat exchangers from a combined first and second law of thermodynamics perspective

The electricity-driven vapor-compression air-conditioning system registers around 3-10% second law efficiency under tropical climates due to the coupling between sensible and latent cooling loads. Desiccant coated heat exchangers (DCHEs) are the next-generation technologies that can improve the efficiency of the air-conditioning process by decoupling sensible and latent loads. Existing literature on DCHEs is primarily directed towards material development and performance evaluation from the first law of thermodynamics standpoint. However, to have an insight into the operation of DCHEs concerning its process irreversibility, performing the second law of thermodynamics analysis is necessary. This analysis will pinpoint the causes of irreversibility in the DCHE system and evaluate the useful work destroyed during its cyclic operation. In this paper, we have developed a general steady-state thermodynamic framework to study the performance of DCHEs from a combined first and second law perspective. Experiments were carried out to obtain the thermodynamic state properties of air, water, and desiccant that are necessary to perform energy and exergy analyses. Further, fundamental parametric studies were conducted to understand the influence of different desiccant type, varying operating parameters, and ambient conditions. Key results revealed that the regeneration process contributed to significant entropy generation rates and by reducing the hot water temperature by 10 degrees C, the second law efficiency illustrates improvement of almost two times. Additionally, by selecting to coat the heat exchanger with a composite polymer material instead of silica gel, the second law efficiency of DCHEs is enhanced by around 2.6 times. Lastly, a hybrid air-conditioning system comprising vapor-compression chiller and DCHE records 50% savings in energy consumption and yields two-times higher second law efficiency.