Humidity humid volume

The calculations of absolute humidity, relative humidity, wet-bulb temperature, dew-point temperature, humid volume, humid heat, and humid enthalpy are based on information found in Pakowski and Mujumdar (2006) and Moyers and Baldwin (1997). 

Electrical, electronic, and technical appHcations use polycarbonates for a variety of purposes. The woddwide market is about 156,000 t aimuaHy. Because of exceHent electrical properties (dielectric strength, volume resistivity), and resistance to heat and humidity, polycarbonate is used for electrical connectors (qv), telephone network devices, oudet boxes, etc. Polycarbonate had been popular for use in computer and business machine housings, but the use of neat resin has been largely supplanted by blends of polycarbonate with ABS. OveraH, however, the total use of polycarbonate continues to increase. 

The humidity term and such derivatives as relative humidity and molal humid volume were developed for the air—water system. Use is generally restricted to that system. These terms have also been used for other vapor—noncondensable gas phases. 

At equihbrium with relative humidity below 100%, the moisture ia wood is present primarily ia the cell wads. The moisture content at which the ceU wads would be saturated and the ced cavities empty is caded the fiber saturation poiat. Actuady, such distribution is impossible. Beginning at - 90% relative humidity, some condensation may occur ia smad capidaries. The determination of the fiber saturation poiat is based on the fact that certain properties of wood (eg, strength and volume) change uniformly at first with increasing moisture content and then become iadependent of the moisture content (Fig. 2). The equdibrium moisture content (usuady determined by extrapolation), at which the property becomes constant at 25 to 30% moisture, is represented by the fiber saturation poiat. 

Phenohc resins (qv), once a popular matrix material for composite materials, have in recent years been superseded by polyesters and epoxies. Nevertheless, phenohc resins stiU find considerable use in appHcations where high temperature stabiHty and fire resistance are of paramount importance. Typical examples of the use of phenoHc resins in the marine industry include internal bulkheads, decks, and certain finishings. The curing process involves significant production of water, often resulting in the formation of voids within the volume of the material. Further, the fact that phenoHcs are prone to absorb water in humid or aqueous conditions somewhat limits their widespread appHcation. PhenoHc resins are also used as the adhesive in plywood, and phenohc molding compounds have wide use in household appliances and in the automotive, aerospace, and electrical industries (12). 

The water removal mechanism is adsorption, which is the mechanism for ad Class 4 drying agents. The capacity of such materials is often shown in the form of adsorption isotherms as depicted in Figures 9a and 9b. The initial adsorption mechanism at low concentrations of water is beheved to occur by monolayer coverage of water on the adsorption sites. As more water is adsorbed, successive layers are added until condensation or capidary action takes place at water saturation levels greater than about 70% relative humidity. At saturation, ad the pores are fided and the total amount of water adsorbed, expressed as a Hquid, represents the pore volume of the adsorbent. 

In Figure 2 the lines, volume, m /kg dry air, indicate humid volume, which includes the volume of 1.0 kg of dry gas plus the volume of vapor it carries. Enthalpy at saturation data are accurate only at the saturation temperature and humidity however, for air—water vapor mixtures, the diagonal wet bulb temperature lines are approximately the same as constant-enthalpy adiabatic cooling lines. The latter are based on the relationship ... 

Humid volume is the volume in cubic feet of 1 lb of dry air and the water vapor it contains. 

Saturated volume is the humid volume when the air is saturated. 

Example 8 Determination of Air Properties For a barometric pressure of 25.92 inHg (Ap = —4), a dry-bulb temperature of 90 F, and a wet-bulb temperature of 70 F determine the following absolute humidity, enthalpy, dew point, relative humidity, and specific volume. 

Humid volumes are given by the curves entitled Volume mVkg diy air. The volumes are plotted as func tions of absolute humidity and temperature. The difference between dry-air specific volume and humid-air volume at a given temperature is the volume of water vapor. 

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