Humidification and Dehumidification

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Chapter: Pharmaceutical Engineering: Air Conditioning and Humidification

Most commonly, air is humidified by passage through a spray of water.


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.

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