Partial pressure, water vapour

This step is intended to reduce residual moisture to levels allowing no microbial growth or chemical reactions of the end product. The amount of residual moisture present in a product depends on its desorption isotherms. Such isotherms in turn depend on various factors including the product temperature, pressure chamber, partial vapour pressure in the container and nature of the interaction of the water vapour with the interstitial material formed in the freezing step. The computer should be fed with information on the target sample component. For example, if the component of interest is a protein, then overdrying may alter its configuration and decrease the potency of the end product. Consequently, the computer should control not only the final product temperature but also the partial water vapour pressure and the duration of the desorption step. 

FIG. 94. Vaporization of Na20 from float glass at 1450 C in a stream of dry nitrogen, and in N2 + H2O (partial water vapour pressure 0.3, flow rate... 

Measurements in a vacuum were performed with an STA 429 thermal analyser, and those in air, with STA 429 and 449 thermal analysers. The partial water-vapour pressure in air was estimated from the relative humidity (measured with a hygrometer) and tabulated pressures of saturated water vapour at the temperatures in the room (see Appendix, Table A6). 

CZ Definition Criteria Mean annual temperature measured in the open air / Mean annual partial water vapour pressure Testing conditions [°C / % RH]... 

The same principle can be applied to other parameters like partial water vapour pressure. 

The original Wexler s equation published in 1971 [8] has been revised in 1976 [9], and updated in 1998 with coefficients computed for the International Temperature Scale of 1990 (lTS-90) [10]. This updated version of Wexler s equation has been used to calculate the saturation water vapour pressure Ps for each mean daily temperature, and also to calculate the partial water vapour pressure Pd at the same time point and place by taking the corresponding daily dewpoints instead of the temperature. 

Knowing the saturation and the partial water vapour pressure at each time point and place, the relative humidity RH can be calculated using the following equation ... 

Ps = Saturation vapour pressure Pd = Partial water vapour pressure... 

The Philippines can be characterised as tropical islands with only minor fluctuations of temperatures and partial water vapour pressure during the day or year. Mean maximum temperatures normally do not exceed 31°C, and never drop below 23°C. Pd values can be found in the range of 25.0-33.0 hPa. All of the islands belong to Koppen Group Am just a small part of the northern island Luzon is characterised by Group Aw. 

Pd = Mean partial water vapour pressure, calculated by taking the dewpoints. 

To calculate the adequate relative humidity for long-term stability testing, the mean partial water vapour pressure calculated for Sanya (27.16 hPa) is used at the standard testing temperature 30°C to get 64.0% RH. Testing at 30°C would include a safety margin of 14% added to the MKT, and testing at 65% RH would include a safety margin of 2% for Pd. Sanya, however, presents an extreme climate compared to the other parts of the country. 

Extreme low mean partial water vapour pressure values have been found near Ti-n-Zaouatene, Sahara desert, Algeria (6.04 hPa), in Khvor in the Salt Desert, Iran (6.24 hPa), in Riyadh, Saudi Arabia (6.91 hPa), and in Bou Arfa, Sahara desert, Morocco (6.96 hPa). 

The annual mean RH in Riyadh is 21.5% (annual mean partial water vapour pressure = 6.91 hPa annual mean temperature = 25.23°C). Moving the temperature... 

The most humid place is Mbandaka Group Af) values for partial water vapour pressure increase to almost 29.0 hPa in May, and decrease to a minimum of 24.9 hPa in July (see Fig. 4.14). 

The mean temperatures measured are all above 22°C and the partial water vapour pressure values are all above 15 hPa, i.e., the countries analysed are either in Climatic Zone IVA or IVB by definition (see Table 4.3). 

All countries except Nicaragua and Panama show positive safety margins Ypd for the testing condition 30°C/65% RH although some of the partial water vapour pressure values are above 27.0 hPa, the threshold for the Climatic Zone classification according to Table 4.3. 

Panamd is the only country showing partial water vapour pressure values of more than 29 hPa at three places and no place with less than 27 hPa, in other words, testing at 30°C/65% RH would not be sufficient. 

Desiccation of plant tissues presents a shift of the water from the liquid to the vapour phase (Sun, 2002). Temperature influences evaporation, as well as the partial water vapour pressure in the air and the energy status of water in plant tissue, both in dry and hydrated plant tissue. An increase in temperature results in a decrease in the equilibrium water content at a given relative humidity (water activity) or an increase in the equilibrium water activity for a given tissue water content (Fig. 1). Water activity can be described as the effective water content, which is thermodynamically available for various physiological processes in cells. The temperature dependence of the isotherm shift is described by the Clausius-Clapeyron Equation ... 

Very interesting results are obtained on zeolites using a moistened carrier gas [99]. A systematic study has been made on the chromatographic properties of a KY zeolite using a moistened carrier gas at a partial water vapour pressure (from 0 to 2.35 kPa) over a wide temperature range (40-300 °C) [99]. Plots of the specific retention volume versus the partial water pressure in the carrier... 

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