Adsorption-type dehumidifiers operate on the use of sorbent materials for adsorption of moisture from the air. Sorbents are substances that contain a vast amount of microscopic pores. These pores afford a great internal surface to which water adheres or is adsorbed. A typical dehumidifier based on the honeycomb desiccant wheel principle is shown schematically in Fig. 3-21. The wheel is formed from thin corrugated and laminated asbestos sheets rolled to form wheels of various desired diameters and thickness. The wheels are impregnated with a desiccant cured and reinforced with a heat-resistant binder. The corrugations in the honeycomb wheel form narrow flutes perpendicular to the wheel diameter. Approximately 75 percent of the wheel face area is available for the adsorption or dehumidifying flow circuit, and 25 percent is available for the reactivation circuit. In the smaller units, the reactivated air is heated electrically; in the larger units, it is heated by electric, steam, or gas heaters.
Figure 3-22 shows another industrial adsorbent dehumidifier of the stationary bed type. It has two sets of stationary adsorbing beds arranged so that one set is dehumidifying the air while the other set is drying. With the dampers in the position shown, air to be dried flows through one set of beds and is dehumidified while the drying air is heated and circulated through the other set. After completion of drying, the beds are cooled by shutting off the drying air heaters and allowing unheated air to circulate through them. An automatic timer controller is provided to allow the dampers to rotate to the opposite side when the beds have adsorbed moisture to a degree that begins to impair performance.
