Percent relative humidity

Percent saturation is the ratio of the partial pressure of a condensable vapor ia a gas to the vapor pressure of the Hquid at the same temperature, expressed as a percentage. For water vapor ia air this is called percent relative humidity. 

Example 3 Air Heating Air is heated by a steam coil from 30 F dry-bulb temperature and 80 percent relative humidity to 75 F dry-bulb temperature. Find the relative humidity, wet-bulb temperature, and dew point of the heated air. Determine the quantity of heat added per pound of dry air. 

In diying solids it is important to distinguish between hygroscopic and nonhygroscopic materials. If a hygroscopic material is maintained in contact with air at constant temperature and humidity until equilibrium is reached, the material will attain a definite moisture content. This moisture is termed the equilibrium moisture content for the specified conditions. Equilibrium moisture may be adsorbed as a surface film or condensed in the fine capillaries of the solid at reduced pressure, and its concentration will vaiy with the temperature and humidity of the surrounding air. However, at low temperatures, e.g., 15 to 50°C, a plot of equilibrium moisture content versus percent relative humidity is essentially independent of temperature. At zero humidity the equilibrium moisture content of all materials is zero. 

The percent relative humidity is defined as lOOp/P, where p is the actual partial pressure of the water vapor and P is the vapor pressure of water at the same temperature. The total pressure is taken as normal barometric, unless otherwise stated. Note that since the per cent relative humidity is defined as 100(p/Pj) and the per cent absolute humidity equals 100[p/(760-p) -h P,/(760-Pj)], the factor by which the former must be multiplied to convert it to the latter is (760 -P ) / (760-p), where p and Pj can be expressed in units of millimeters of mercury. 

How much water is present and what is the corresponding water activity (approximated by relative pressure or percent relative humidity/100) ... 

The insulation was 3.5-in.- (90-mm-) thick, unfaced, glass-fiber insulation (friction-fit). Walls with insulation also had a 4-mil clear polyethylene vapor barrier on their interior side. All wood and gypsum materials were conditioned at 23°C and 50 percent relative humidity, resulting in moisture content of 9 to 10 percent in wood materials. Figure 1 is a diagram of the wall frame construction. The hardboard siding was on the exterior side of the 5/8-in. (16-mm) plywood (not shown). 

Although bromocriptine mesilate is sensitive to heat and light, it is stable for up to 3 years at ambient temperature (20) when stored in sealed polyethylene bags contained in twist-off amber glass bottles. In warm and tropical climate (30 °C/75 percent relative humidity) and under identical package conditions, it is stable for 1 year, however only for 3 months at 50 °C. 

Cytotoxicity can also be determined post-treatment as follows T25 flasks are set up after treatment containing 0.75 x 105 cells per ml in 5 ml CM10. Flasks are incubated with loose lids at 37°C with 5 percent CO2 in 95 3 percent relative humidity. Two days later the cell titre of each culture is determined with a Coulter counter. 

Table I shows the equilibrium moisture content (EMC) of several lignocellulosic materials at 65 percent relative humidity (RH). Reduction in EMC at 65 percent RH of acetylated fiber referenced to unacetylated fiber plotted as a function of the bonded acetyl content is a straight line (Fig. 2). Although the points shown in Figure 2 come from many different lignocellulosic materials, they...

Figure 5—Changes in ovendry (OD) thickness at 30 percent and 90 percent relative humidity of aspen flakeboard made from acetylated flakes (27°C). 0= control + = 7 3 WPG ...

For storage stability tests, a sufficient number of badges were exposed to an exposure dose level of approximately one-half the charcoal capacity at 80 percent relative humidity. Half the samples were refrigerated (40-45°F) and half were left at ambient temperatures (75-80°F). Badges were then analyzed at intervals ranging from one day to three weeks. 

Percent Relative Humidity Percent Weight Lost... 

Percent relative humidity is the best known ami perhaps the most widely used method for expressing the water vapor content of air. Percent relative humidity is defined as the ratio of the prevailing water vapor pressure c . to the water vapor pressure if the air were saturated, t, multiplied by 100 ... 

Determine the percent relative humidity and the wet-bulb temperature before and after for each of the following conditions ... 

ASTM D-1412. Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30°C. 

The increase in equilibrium moisture content is negligible at 27°C and 30 to 50 percent relative humidity. A 2 to 8 percent increase in moisture content occurs in the treated wood at 27°C and 65 percent relative humidity, and at 80 percent relative humidity the moisture content may increase 5 to 15 percent and cause exudation of the chemical solution from the wood. 

In an unpublished study at the U.S. Forest Products Laboratory, the moisture content of wood treated with two commercial formulations reached 48 to 58 percent (based on ovendry weight of treated sample) in 4 weeks1 exposure at 27°C and 90 percent relative humidity. Continuous exposure of wood treated with water-soluble salts to conditions above 80 percent relative humidity can result in loss of chemicals and in adverse effects on dimensional stability and paint coatings. Corrosion of some metals in contact with the wood will also occur. 

Zinc chloride will add considerably to the equilibrium moisture content of wood in the range of 30 to 80 percent relative humidity (8). Ammonium sulfate will add at relative humidities exceeding 65 percent, and borax and boric acid will attract water at lower humidities. Phosphate salts affect hygroscopicity mostly when relative humidity exceeds 80 percent (58). 

Most commercial treatment formulations are developed for use under conditions not greater than 80 percent relative humidity. 

At 60 and 90 percent relative humidities, the effects of moisture laden air upon sample retention were tested by introducing moist diluent air into a known concentration of... 

Internal degradation within the bulk adhesive or sealant occurs primarily by absorption of water molecules into the polymer structure. All polymers will absorb water to some extent. Moisture can also enter by wicking along the adhesive-adherend interface or by wicking along the interfaces caused by reinforcing fibers and the resin. Deterioration may occur more quickly in a 100 percent relative humidity (RH) environment than in liquid water because of more rapid permeation of the vapor. 

The time between surface preparation and application of adhesive and the environmental conditions present during this period. This includes the temperature and percent of relative humidity. Usually standard atmospheric conditions are specified (25°C and 50 + 4 percent relative humidity). 

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