Humidity chart construction

The use of these relationships in constructing and applying humidity charts is best illustrated by examining a simplified case, that of adiabatic cooling or humidification. Figure 5.4 illustrates this process between air and water that is recycled through the cooling tower. In this operation air is both cooled and... 

You can find further details regarding the construction of humidity charts in the references at the end of the chapter. Tables are also available listing all the ther-... 

HUMIDITY CHARTS FOR SYSTEMS OTHER THAN AIR-WATER. A humidity chart may be constructed for any system at any desired total pressure. The data required are the vapor pressure and latent heat of vaporization of the condensable component as a function of temperature, the specific heats of pure gas and vapor, and the molecular weights of both components. If a chart on a mole basis is desired, all equations can easily be modified to the use of molal units. If a chart at a pressure other than 1 atm is wanted, obvious modificatioi in the above equations may be made. Charts for several common systems besides air-water have been published. ... 

Construction of psychrometric charts by computer methods is common. Three types of charts are most popular Grosvenor chart, Grosvenor (1907) (or the psychrometric chart), Mollier chart, Mollier (1923) (or enthalpy-humidity chart), and Salin chart (or deformed enthalpy-humidity chart) these are shown schematically in Figure 3.3. 

Before addressing the properties and construction of the humidity charts, we consider a small variation on the simple contact of water with flowing air, which led to the wet-bulb conditions, hi this modified arrangement, shown in Figure 9.2, a stream of air is hmnidified in contact with constantly recirculated water. Both the water and the exiting gas stream attain adiabahc saturation temperature, which is lower than the dry-bulb temperature of the entering air because of evaporative cooling. 

The basis for the construction of the psychrometnc chart is the Gibbs phase rule (Section 6.3a). which states that specifying a certain number of the intensive variables (temperature, pressure, specific volume, specific enthalpy, component mass or mole fractions, etc.) of a system automatically fixes the value of the remaining intensive variables. Humid air contains one phase and two components, so that from Equation 6.2-1 the number of degrees of freedom is... 

A special psychrometric chart would need to be constructed for the acetone-nitrogen system to get first estimates (this can be done using PSYCHIC, as shown in Fig. 12-7). A humidity of 0.025 kg/kg at F = 60 C lies just below the adiabatic saturation line for — 40°C. The wet-bulb temperature will not be the same as Fas for this system as the psychrometric ratio p is less than 1, Fwb should be significantly above F. However, let us assume no good first estimate is available and simply take F b to be 0°C initially. 

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