generation II technologies

dehumidification systems

HDH units can be categorized into three groups [135]. The first category is based on the energy source employed, including wind, solar, geothermal, electrical energies, or hybrid devices. An attractive and promising aspect of this classification is the use of renewable and low-grade energy resources [47,136]. The second category is related to the type of heated stream (air-heated or water-heated). In HDH, hot air is used to exchange water content from seawater to air owing to its high water-carrying capacity (high absolute humidity). This hot air can be generated from the heating of seawater or air [136].

Cycle configuration is the basis of the third category. The HDH system is divided into two cycles: open-air closed-water (OACW) and closed-air open-water (CAOW) systems [47,136] (see Fig. 4.14). In the OACW cycle, the air warms, humidifies, condenses, and eventually leaves the system. In the CAOW cycle, the airflow circulation occurs in a closed cycle. In both configurations, airflow can circulate naturally or forcibly. Forced flow, however, is preferred owing to the production of more water. Fig. 4.14 shows a schematic of the two cycles, OACW and CAOW, in both air-heated and water-heated modes in the HDH system. Unlike the other three cases, where the heater is placed between the humidifier and the dehumidifier, in OAOW, the heating system is placed at the bottom of the humidifier and both water and air leave the system at the end of the process.