Dehumidification

Overview

Engineering reference data for Dehumidification in air psychrometrics.

Key Formulas

Humidity Ratio

$\omega = 0.622 \frac{P_v}{P_a}$

Mass of water vapor per mass of dry air.

Relative Humidity

$\phi = \frac{P_v}{P_{vs}} \times 100\%$

Ratio of actual to saturation vapor pressure.

Wet Bulb Temperature

$T_{wb} = T_{db} - \frac{P_{vs} - P_v}{\gamma}$

Temperature measured by wet-bulb thermometer.

Enthalpy of Moist Air

$h = c_p T + \omega h_g$

Sensible + latent heat per unit mass of dry air.

Variables

Methods of Dehumidification

1. Cooling (Condensation)

In a cooling system, humidity is reduced by cooling the air below its dew point. A portion of the moisture in the air condenses and is drained away. This process can be visualized on a Mollier diagram, showing the simultaneous cooling and dehumidification of air.

2. Adsorption

This method uses an adsorbent material (e.g., silica gel, activated alumina) to physically remove moisture from the air. The water vapor condenses on the material's surface without altering its chemical structure.

Key Adsorbent Properties:

Reactivation: The saturated adsorbent can be regenerated using heat.

• Temperature: 160 - 170 °C
• Heat Required: 4800 kJ per kg of water removed

3. Absorption

This method uses a liquid absorbent material (e.g., a calcium chloride solution) to chemically remove moisture. Unlike adsorption, this process involves a change in the chemical structure of the absorbent material. The material is generally difficult to reactivate.

Interactive Charts

References

• Original Source