Performance of Desiccant Heat Exchangers with Aluminum Foam Coated or Packed with Silica Gel

Performance of two types of desiccant silica gel aluminum foam heat exchangers - desiccant coated heat exchanger (DCHE) and desiccant packed heat exchanger (DPHE) are evaluated experimentally and numerically. The DCHE is fabricated by coating silica gel over the ligaments of an aluminum foam, while the DPHE is built by packing an aluminum foam with silica particles. Equilibrium isotherms of the two heat exchangers are measured using the gravimetric approach. An open flow loop test rig is designed and built to measure the dry bulb temperature and humidity ratio of air upstream and downstream of the desiccant heat exchangers during the humidification and dehumidification process. In addition, a mathematical model is developed to investigate the heat and mass transfer process in the two desiccant heat exchangers. The experimental data obtained are used to validate the numerical results, and good agreement is established. The effects of heat exchanger length and inlet operating conditions on the performance of DPHE and DCHE are investigated. Experimental and numerical results indicate that the DPHE outperforms the DCHE in terms of cooling capacity and moisture removal capacity. It is observed that the performance of the DPHE is close to that of the DCHE in handling sensible heat loads but exceeds the latter in removing latent heat loads. The DPHE can provide dehumidified air for a longer time due to its higher moisture removal ability and higher density of the desiccant material compared to the DCHE.