Energy effectiveness analysis of desiccant coated heat exchanger based on numerical method

The conventional air-to-air heat pumps rely heavily on the condensation dehumidification principle to regulate air humidity, thereby severely limiting the system energy efficiency. Significant energy efficiency improvements can be realized by coating high-performing solid desiccants on both evaporator and condenser heat exchangers. Thus far, existing fundamental analysis developed to evaluate energy performance improvement and achieve accurate performance prediction of desiccant coated heat exchangers with two-phase refrigerant (DCHERs) has been impeded by the complex physical phenomena, approximations in the heat/mass transfer paths, and the severe reliance on the use of empirical correlations. Therefore, in this work, a mathematical approach has been judiciously developed based on mass, momentum, energy, and species conservation principles in order to study the flow field distribution within DCHERs and predict their performance. The model is extensively validated with experimental data obtained under various working conditions with discrepancies of +/- 10 % and +/- 9 % for outlet air temperature and humidity, respectively. The model provides essential information on local temperature and humidity distributions, and key insights on the transient heat and mass transfer phenomena. Further, a general design guideline for the performance enhancement of DCHERs is established. Key results from the study reveal that the air RH varies within 15 % along the DCHER's flow channel. Thick desiccant coating, high inlet air relative humidity, and long air-desiccant contact time markedly improve latent energy effectiveness to a maximum of 0.51. Lastly, employing the proposed guideline to design the heat exchanger with optimal tube configurations yields a 23 % enhancement of latent energy effectiveness.