Concentration of water vapor

One procedure makes use of a box on whose silk screen bottom powdered desiccant has been placed, usually lithium chloride. The box is positioned 1-2 mm above the surface, and the rate of gain in weight is measured for the film-free and the film-covered surface. The rate of water uptake is reported as u = m/fA, or in g/sec cm. This is taken to be proportional to - Cd)/R, where Ch, and Cd are the concentrations of water vapor in equilibrium with water and with the desiccant, respectively, and R is the diffusional resistance across the gap between the surface and the screen. Qualitatively, R can be regarded as actually being the sum of a series of resistances corresponding to the various diffusion gradients present ... 

A closer look at the Lewis relation requires an examination of the heat- and mass-transfer mechanisms active in the entire path from the hquid—vapor interface into the bulk of the vapor phase. Such an examination yields the conclusion that, in order for the Lewis relation to hold, eddy diffusivities for heat- and mass-transfer must be equal, as must the thermal and mass diffusivities themselves. This equahty may be expected for simple monatomic and diatomic gases and vapors. Air having small concentrations of water vapor fits these criteria closely. 

Thermal Decomposition of GIO2. Chloiine dioxide decomposition in the gas phase is chaiacteiized by a slow induction period followed by a rapid autocatalytic phase that may be explosive if the initial concentration is above a partial pressure of 10.1 kPa (76 mm Hg) (27). Mechanistic investigations indicate that the intermediates formed include the unstable chlorine oxide, CI2O2. The presence of water vapor tends to extend the duration of the induction period, presumably by reaction with this intermediate. When water vapor concentration and temperature are both high, the decomposition of chlorine dioxide can proceed smoothly rather than explosively. Apparently under these conditions, all decomposition takes place in the induction period, and water vapor inhibits the autocatalytic phase altogether. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, HCl, HCIO, and HCIO. The ratios of products formed during decomposition depend on the concentration of water vapor and temperature (27). 

The alumina column was moderated by a constant concentration of water vapor in the carrier gas. As the temperature of the distribution system was increased, less of the water moderator was adsorbed on the surface. As a consequence, the alumina became... 

Figure 9-3 shows this schematically. If the partial pressure of the vapor is less than the equilibrium value (as in Figure 9-3A), the rate of evaporation exceeds the rate of condensation until the partial pressure of the vapor equals the equilibrium vapor pressure. If we inject an excess of vapor into the bottle (as in Figure 9-3Q, condensation will proceed faster than evaporation until the excess of vapor has condensed. The equilibrium vapor pressure corresponds to that concentration of water vapor at which condensation and evaporation occur at exactly the same rate (as in Figure 9-3B). At equilibrium, microscopic processes continue but in a balance that yields no macroscopic changes.

The composition of the earth s atmosphere differs from day to day, from altitude to altitude, and from place to place. The largest variation is in the concentration of water vapor. Water evaporates continually from the hydrosphere, from the soil, from leaves, from clothes drying, etc. At intervals, parts of the atmosphere become chilled until the dew point or frost point is reached and then any vapor in excess of the saturation amount is precipitated as rain or snow. 

Effects of Cold Gas Recycle and Approach to Equilibrium. Product gases resulting from various CGR ratios were analyzed (Table XI). For the experiments tabulated, a decrease in the cold recycle ratio resulted consistently in increases in the product gas concentrations of water vapor, hydrogen, and carbon dioxide and a decrease in methane concentration. These trends may be noted in experiment HGR-12 as the CGR ratio decreased from 8.7 1 to 1.2 1, in experiment HGR-13 as it increased from 1.0 1 to 9.1 1, and in experiment HGR-14 as it decreased from 3.0 1 to 1.0 1. These trends indicate that the water-gas shift reaction (CO + H20 —> C02 + H2) was sustained to some degree. Except for the 462-hr period in experiment HGR-14, the apparent mass action constants for the water-gas shift reaction (based on the product gas compositions in Table XI) remained fairly constant at 0.57-1.6. These values are much lower than the value of 11.7 for equilibrium conversion at 400°C. In... 

With increasing the concentration of water vapor, NO and N02 removal efficiencies increased [26,27,29,30] as a result of generation of more OH and H02 radicals by electron impact dissociation of H20 molecules. 

Figure 7.7(a) shows the Is photoemission spectra of MgO(lOO) following reaction with different concentrations of water vapor. Liu et al. [143] interpreted these spectra as indicating that water vapor reacts primarily with defect sites on the Mg(100) surface at p(H20) < 10 4 torr and with terrace sites at p(H20) > 10-4 torr. 

In this expression Ac describes the difference between the concentration of water vapor at the water surface and that at the desiccant surface Ac = cw - cdes. Since cdes < cw, Ac may be replaced by cw, which in turn equals pM/RT, where p and M are the vapor pressure and molecular weight, respectively, of water. With this substitution the expression for dQldt becomes A(DIAx)(pMIRT). The ratio DlAx has units length time 1, so we identify it as the reciprocal of the transport resistance. Note that r increases as the effective value of Ax increases and the effective value of D decreases. Thus l/r is the only unknown in the expression dQldt = A(Mr) pMIRT) and can be calculated from the measured rate of weight increase with different monolayers present. ... 

The quasi-steady-state theory has been applied particularly where a condensed phase exists whose volume changes slowly with time. This is true, for example, in the sublimation of ice or the condensation of water vapor from air on liquid droplets (M3, M4). In the condensation of water vapor onto a spherical drop of radius R(t), the concentration of water vapor in the surrounding atmosphere may be approximated by the well-known spherically symmetric solution of the Laplace equation ... 

The concentration of water vapor in the atmosphere is thought to have remained steady over time, but concentrations of some other greenhouse gases are rising. From the year 1000 or earlier until about 1750, the C02 concentration in the atmosphere remained fairly stable at about 280 10 parts per million by volume (ppmv). Since then, the C02 concentration has increased by 28% to 360 ppmv. The concentration of methane, CH4, has more than doubled during this time and is now at its highest level in 160000 years. Studies of air pockets in ice cores... 

Although the troposphere has the characteristic of containing a high relative concentration of water vapor (10 5-10-2), the stratosphere is dry and the water vapor concentration is only a few parts in a million. However, the oxidation of methane by hydroxyl radical must be intro-... 

The effect of water vapor on the device hydrogen sensitivity however, is the same for both C-I-S diode and C-I-S capacitor structures that is, high concentrations of water vapor speed up the response but significantly reduce the sensitivities. 

In the case of the counter-flow/sweep membrane module illustrated in Figure 4.18(c) a portion of the dried residue gas stream is expanded across a valve and used as the permeate-side sweep gas. The separation obtained depends on how much gas is used as a sweep. In the calculation illustrated, 5 % of the residue gas is used as a sweep even so the result is dramatic. The concentration of water vapor in the permeate gas is 13 000 ppm, almost the same as the perfect counter-flow module shown in Figure 4.18(b), but the membrane area required to perform the separation is one-third of the counter-flow case. Mixing separated residue gas with the permeate gas improves the separation The cause of this paradoxical result is illustrated in Figure 4.19 and discussed in a number of papers by Cussler et al. [16]. 

Figure 4.19(a) shows the concentration of water vapor on the feed and permeate sides of the membrane module in the case of a simple counter-flow module. On the high-pressure side of the module, the water vapor concentration in the feed gas drops from 1000 ppm to about 310 ppm halfway through the module and to 100 ppm at the residue end. The graph directly below the module drawing shows the theoretical maximum concentration of water vapor on the permeate side of the membrane. This maximum is determined by the feed-to-permeate pressure ratio of 20 as described in the footnote to page 186. The actual calculated permeate-side concentration is also shown. The difference between these two lines is a measure of the driving force for water vapor transport across the membrane. At the feed end of the module, this difference is about 1000 ppm, but at the permeate end the difference is only about 100 ppm. 

The author supports the view of Latchinov and co-workers that all conditions tending to increase the concentration of water vapor in the gas during the reduction diminish the activity of the catalysts, thus high space velocity and low temperature and low pressure yield the most active catalysts. Water vapor influences areas of the catalyst already reduced in the same way as water vapor influences a totally reduced catalyst, which means that it inflicts it with a progressive permanent deterioration. 

When utilizing circulating gas for the reduction, as is the case in most industrial installations, it is very important that when reduction has started, the circulating gas is cooled almost down to zero centigrade, as otherwise a gas with a high concentration of water vapor reenters the catalyst bed. In this connection it should be emphasized that the saturation concentration of water vapor in the gas is much higher than... 

As soon as some formation of ammonia has started, this permits the cooling down of the circulating gas even below zero, and as the liquid ammonia extracts water from the gas, the concentration of water vapor is reduced to an innocuous level. 

The temperature to which the turbulent air must be reduced at constant pressure for it to become saturated with water vapor is known as the dew point temperature, or dew point, r few point. When T4 3 is less than T few point, the turbulent air contains a higher concentration of water vapor (cj ) than the air at the leaf surface can hold Water vapor then diffuses toward... 

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