Rotating Wheel

The desiccant wheel functions much like the rotating bed. The difference is that the rotating bed type uses a wheel of granular desiccant in a packed bed and the wheel type uses a wheel of corrugated heat exchanger type surface. This results in different heat and mass transfer and pressure drop characteristics. The rotating desiccant wheel structure is lightweight and porous and can use several kinds of solid desiccants. The corrugated design combines high surface area with low total mass and presents minimal air pressure resistance, resulting in good efficiency. The surface can also be loaded with more than one type of desiccant in order to match very specific air treatment requirements.

Figure 39-13 provides an illustration and equilibrium diagram of a rotating desiccant wheel. In the sorption process (1-2), the desiccant picks up moisture as the process air flows through the flutes formed by the corrugations, becomes saturated, and its surface vapor pressure is elevated. As the wheel rotates into the reactivation airstream (2-3), the hot reactivation air causes its surface vapor pressure to rise farther, causing the desiccant to release its moisture in the desorption process. As the hot desiccant rotates into the process air (3-1), a small portion of the process air cools the desiccant, allowing it to collect more moisture from the rest of the process airstream.

Process Air. Entering

Process Air. Entering

Multiple vertical beds

Moisture Content of the Desiccant

Multiple vertical beds

Moisture Content of the Desiccant

Fig. 39-12 Illustration of Multiple Vertical Bed System. Source: Munters Cargocaire and Mason Grant Company

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