Absorption by water vapour

Fig. 5.47 Spectral transmissivities ta,w and ta,g as a result of absorption by water vapour, O2 and CO2 respectively, for mrjL = 1...

Fig. 2. Ozone effect on solar radiation (left) and dependence of ozone concentration on atmospheric altitute (right). In the left part the dotted curve represents the photon distribution of solar energy outside the atmosphere (based on the assumption of black body radiation at T = 5773 K). The full curve gives the photon distribution of solar radiation reaching earth surface (see Ref.8. The ozone effect is shown by shadowed area, the dicline above 800 nm is mainly due to absorption by water vapour. On the right side the full curve represents qualitatively a typical ozone profile, the real ozone distribution significantly depends on the local situation (geography), see Ref.15)...

To study the Far Infrared wavelength range there is a need for space observatories due to one main reason the Earth s atmosphere. The atmosphere presents a high attenuation of the signal due to the absorption by water vapour, and the level of atmospheric attenuation is a function of the line-of-sight water vapour concentration. For this reason most of the ground based observatories are located at high altitude sites. However, the only way to eliminate the atmosphere effect is to go to space. 

Note the total absorptions by water vapour bands in the single channel spectrum (left) and the discontinuity in the resulting absorption spectrum (right panel). See text and captions of Figures 6.1 and 6.2 for further details. 

Wilson and Miles [12] have measured the absorption of nitric acid by treating with it nitrocotton of 13.8% N. Under a pressure of 4 mm Hg as much as 15% of HN03, was absorbed by this nitrocotton. Nitric acid is absorbed better by a lowernitrated substance, just as the absorption of water vapour is easier in the case of lower-nitrated nitrocellulose. The maximum absorption has been established with nitrocellulose of 7% N. The amount of nitric acid absorbed by cellulose depends on its type. For native cellulose it amounts to about 25% by weight of the cellulose, and approaches 50% for mercerized cellulose. Such differences in the behaviour of different kinds of nitrocellulose indicates that swelling has an appreciable influence on absorption. Mercerized cotton which is more liable to swell simultaneously shows stronger absorption. 

The reaction is autocatalytic, resembling in this respect the situation already encountered with uncoated quartz or glass vessels. However, in contrast with the results of Lewis and von Elbe [23] for a quartz vessel, Baldwin and Mayor [45] found little or no effect of addition of up to 22 torr added water on either the induction period or the maximum rate, irrespective of whether the water was added a short time before, or together with, the reactants themselves. They concluded that the autocatalytic effect cannot be due to poisoning (by absorption of water vapour produced in the reaction) of the ability of the surface to destroy chain centres, as had previously been suggested. 

In spite of its capacity to absorb moisture in the form of vapour, it is extremely diffieult to wet wool out in cold water. This is because the vapour ean penetrate to the cortex where it is retained, but in the liquid phase water must pass through the epithelial scales which offer considerable re-sistanee. In order to wet wool out the temperature of the water must be raised to 60°C (HOT) or, alternatively, a wetting agent must be used. The absorption of water vapour is accompanied by the liberation of considerable quantities of heat as illustrated by the following figures (AiEsaNDER AND Hudson, Wool, its Chemistry and Physics, 1st edn.), see Table 5.3. 

Material Chemical attack by Water vapour absorption ... 

In order to clarify the process of dissolution of water vapour (or hydrogen) to generate protons in SrCeOg-based oxides at high temperature, the evolution and the absorption of water vapour and/or oxygen were studied by changing the temperature or partial pressure in a flow of wet or dry gases °. 

A heat exchanger preheats the dilute solution by exchanging heat with hot strong LiBr solution (which is reused for absotbing water vapours) which, in turn, is cooled before absorption of water vapours. 

Attempts to conduct the photochemical conversion of methane in water vapour at temperatures below 100 °C and atmospheric pressure were made in [203]. Since the first absorption band of paraffinic hydrocarbons is located in the Schumann ultraviolet region, starting from 144 nm for methane, it was assumed that the conversion of methane is initiated by hydroxyl radicals formed by water vapour photolysis. The main products were methanol (with a selectivity of 70% at 90 °C), formic add (11%), ethanol (5%), formaldehyde (5%), acetone (4%), and acetic add (3%). The photolysis was carried out with a 20-W low-pressure mercury lamp. Given that the absorption of UV radiation by water vapour starts at 185 nm, which is the lower boimdary of mercury lamp radiation transmitted by a quartz bulb, the photochemical conversion of methane in these conditions is unlikely to be sufficiently efficient. 

Dehydration can be performed by a number of methods cooling, absorption and adsorption. Water removal by cooling is simply a condensation process at lower temperatures the gas can hold less water vapour. This method of dehydration is often used when gas has to be cooled to recover heavy hydrocarbons. Inhibitors such as glycol may have to be injected upstream of the chillers to prevent hydrate formation. 

In the far-infrared region strong absorption by the water vapour normally present in air necessitates either continuously flushing the whole optical line with dry nitrogen or, preferably, evacuation. 

Certain copolymers of this type have been found to have excellent gas barrier properties, with the dry polymer having an oxygen permeability only about 1/lOth that of polyvinylidene chloride. Unsurprisingly, the copolymer has a high moisture absorption and a high moisture vapour transmission rate. Where the material is swollen by water, gas permeability is also higher. 

In a typical process, the conversion of isobutene in the reactor stage is 97 per cent. The product is separated from the unreacted methanol and any C4 s by distillation. The essentially pure, liquid, MTBE leaves the base of the distillation column and is sent to storage. The methanol and C4 s leave the top of the column as vapour and pass to a column where the methanol is separated by absorption in water. The C4 s leave the top of the absorption column, saturated with water, and are used as a fuel gas. The methanol is separated from the water solvent by distillation and recycled to the reactor stage. The water, which leaves the base of the column, is... 

Figure 261 shows the absorption and the regeneration process schematically. During Absorption the concentrated salt solution is distributed over an exchange surface, which is in contact with an air stream. The air will be dehumidified and the salt solution will be diluted by the absorbed water vapour. During regeneration the diluted solution becomes concentrated again by desorption from a hot air stream. 

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