Humidification and Dehumidification

HUMIDIFICATION AND DEHUMIDIFICATION

Most commonly, air is humidified by passage through a spray of water. Three methods are illustrated by the humidity diagrams drawn in Figure 6.2. In the first, air at a temperature T₁ is heated to T₂ (Fig. 6.2(A)). The latter temperature is chosen so that adiabatic cooling and saturation followed by heating to T₄ will give a humidity rise from H₁ to H₂. The humidification stage is performed by passing the air through water sprays at the adiabatic saturation temperature, T₃. Alternatively, the incoming air could be heated to T₅, air of the correct humidity

FIGURE 6.2 The humidification and dehumidification of air.

emerging when it is adiabatically cooled to T₄ with water (Figure 6.2(B)). In neither of these methods is control of the water temperature necessary. In the third method, air of humidity, H₁, and temperature, T₁, is passed through and saturated by a water spray maintained at T₃ (Figure 6.2(C)). On leaving the chamber, it is heated to T₄.

For small quantities of air, dehumidification is most easily accomplished by adsorbing water vapor with alumina or silica gel arranged in columns. These are mounted in pairs so that one can be regenerated while the other is in use. Alternatively, the air can be cooled below the dew point. Excess water vapor condenses and the cold, saturated air is then reheated. For well-mixed gases, the process is described in Figure 6.2D.