RH—See Relative humidity

The WVTR through the container is determined by the container wall thickness, the permeability of the material and the difference between the external and internal relative humidity environments. Waterman et al. [99] determined the theoretical rate of water permeation through a standard 60-cc bottle when stored at 40°C/75% RH. This equated to an uptake of 1 mg of water per day. They commented that even if the product had been packed under low water vapour conditions the relative humidity conditions within the container would be equate to 50% RH within 1 day. The WVTRs (see Table 2.8) for some common packaging materials were reported by Waterman et al. [99]. 

Figure 3.25 shows the results of one set of calculations of the effects of aerosol particles whose properties were judged to be characteristic of continental or urban situations, respectively, on the transmission of UV and visible radiation to the earth s surface (Erlick and Frederick, 1998). The ratio of the transmission with particles to that without is plotted in two wavelength regions, one in the UV and one in the visible. Two different relative humidity scenarios are shown. The average summer relative humidity was 70% RH in the boundary layer and 20% RH in the free troposphere. The high relative humidity case assumes 90% RH in the boundary layer and 30% in the free troposphere. (The RH in the stratosphere was taken to be 0% in both cases see Chapter 12.)... 

The atmospheric situation is complicated by varying conditions of temperature, relative humidity, and concentrations of other gases such as NH3 which can enhance nucleation rates over those expected for a well-mixed air mass at a fixed temperature and RH (e.g., see Nilsson and Kulmala, 1998). However, there is a general consensus that the observed rates of nucleation of H2S04 often, indeed usually, exceed those expected from classical binary homogeneous nucleation theory. (Note that this is not always the case. For example, Pirjola et al. (1998) reported that the measured formation of nuclei in the Arctic boundary layer... 

Hygroscopicity reversibly picks up water at relative humidities (RH) up to 60%. Equilibration at RH equal to or above 60% will result in deliquescence and a water content of approximately 16%w/w. See Figure 2. 

Fig. 16 Degree of swelling of a 740 nm thick (dry thickness) MePVP brush covalently attached to the surface of a LaSFN9/Au/SiOx substrate as a function of the relative humidity (RH) of the environment. For more details see text...

Since the product of flow rate, time and concentration equal the input mass, a constant input concentration permits the calculation of mass from either time or retention volume. Empty columns provide an essentially constant ratio of input mass to time at constant flow rate with the concentration of water vapor fixed by the temperature of the carrier gas saturated with water vapor (100Z RH or Aw of 1 see Figure 6). This state can be achieved with substrates that do not dissolve in water when saturated (for example, starches and many proteins), or when the relative humidity is constant but insufficient to allow uptake to produce a highly multilayered or clustered water state in the substrate equivalent to a continuous water phase or solution. This condition requires a source of humidified gas as in (7.). The sorption isotherm equation is then given by... 

If the hair and its cuticle are in good condition (e.g., near the root end), a smooth break tends to occur see Figure 8-4. As the fiber becomes dryer, below 90% RH, step fractures are the most commonly observed fracture pattern. Fibrillation and splitting describe a distinct cortical fracturing pattern and tend to occur more with twisted or kinky fibers [15] or when the relative humidity is low, rather than when the fiber is wet. The reason for this effect is that the cortex is less extensible than the cuticle when the fiber is dry, below 90% RH [13]. See Chapter 5 for electron micrographs illustrating these different fracture patterns for hair fibers. 

The electrical resistances of wool and human hair have been shown to be very similar at 85% RH (see Table 8-23), and their resistances are similar from 52 to 85% RH [131], Their moisture binding-relative humidity relationships from 0 to 100% RH are virtually identical (see Table 8-16), so their resistance-relative humidity relationships from 0 to 100% RH must also be very similar. The resistance of wool hber has been shown to vary by a factor of approximately 10 from 10 to 90% RH and by a much larger factor from 0 to 100% RH [136]. 

The technology is described by Mclnerney et al. (2002, 2004). Figure 7.24 shows a trial system installed in the Unite Kingdom with horizontal wire anodes and cathodes across the leaf piers and cathodes in the ground to draw water away. The aim of the system was to reduce the relative humidity in the concrete to a level which would not sustain corrosion below say 60% RH (see Section 4.12.4 and Lambert, 1997). 

One usually has the initial air conditions specified in terms of the relative humidity and temperature. Drying calculations are carried out in terms of the humidity ratio. Atypical use of psychrometric equations may follow the following sequences use T to calculate P, use RH and P to calculate P, and use P and P to calculate the humidity ratio H. For more equations relating other properties of moist air, see American Society of Agricultural Engineers (ASAE) standards [25]. 

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