Diffusion of Gases in Water

Oxygen deprivation in soil is caused by an imbalance between the 10" times slower diffusion of gases in water as compared with air, and the oxygen rate consumption by plant roots and microorganisms. To reduce the oxygen deprivation stress impact, plants have evolved a... 

Diffusion of gases in the air surrounding and within leaves is necessary for both photosynthesis and transpiration. For instance, water vapor evaporating from the cell walls of mesophyll cells diffuses across the intercellular air spaces (Fig. 1-2) to reach the stomata and from there diffuses across an air boundary layer into the atmosphere (considered in detail in Chapter 8,... 

Non-celluloslc Membranes. While the development of CA gas permeation membranes can be directly attributed to the development of water desalination membranes, the Invention of modified silicone membranes and polysulfone membranes was more Influenced by the extension of knowledge of transport, sorption and diffusion of gases In polymers (24-27). In principle, rubbery polymers exhibit the highest gas permeabilities at the lowest selectlvitles, and. 

Silicalite is a microporous crystalline silica molecular sieve with remarkable hydrophobic properties ( 1) and has been considered to offer practical applications in the clean-up of water contaminated with hydrocarbons and the separation of ethanol from dilute fermentation aqueous solutions (2 ii> 2) Many studies have been reported on the properties of adsorption and diffusion of gases in silicalite (e.g., 6, 8, , HI) However, despite the many potential applica-... 

Diffusion of gases through water is 10,000 times slower than in air where oxidized forms act as electron acceptors. Wetland plants pump oxygen to the roots to assist in respiration. 

For low wind speeds, one might ask, at what characteristic depth or distance from the interface is the rate of advective transfer of normal dissolved gases away from the interface equal to diffusive transfer To answer this question, we can use the dimensionless Peclet number, (dV/D), which expresses the relative importance of mass transfer by advection to transfer by diffusion. In the Peclet number, d can be taken as the thickness of the diffusive layer, V the velocity and D as the gas diffusivity in the water phase. If we take V as the piston velocity with an appropriately low value of about 1 cm h, and a typical diffusivity for gases in water of about 10" cm s the thickness of the boundary layer can be determined for a Peclet number, Pe= 1, i.e. at a distance from the interface where advective and diffusive transport are comparable. Under these conditions, d is... 

Sovova, 1976 (10) proposed a correlation for predicting the diffusivity coefficient of gases in water and in two groups of organic liquids. The general form of the correlation is... 

Tammann G, lessen V. Diffusion coefficients of gases in water and their dependence on temperature. Z Anorg AHg Chem 1929 179(1/3) 125—44. 

A diffusion mechanism is also used in dialysis as a means of separating colloids from crystalloids. The rate of diffusion of molecules in gels is practically the same as in water, indicating the continuous nature of the aqueous phase. The diffusion of gases into a stream of vapour is of considerable importance in diffusion pumps. 

The major weakness is the requirement of nonreactivity of gases in the mucous layer. Very weakly reactive gases may be treated as nonreactive. However, the uptake of ozone, which is known to decompose in water and is expected to react rapidly with biopolymers and other organic molecules in the mucus layer, is probably underestimated in the upper airways and overestimated in the terminal airways of their model. Thus, their model represents a worst-case estimate of dosage of ozone to the terminal airways, which are unprotected by mucous. Too little is known of the chemical and physical properties of the mucus layer, and there is great uncertainty in the values of the diffusivity of ozone or other gases to be used in the liquid phase of gas uptake models. 

Jahne B., Heinz G., and Dietrich W.E. (1987) Measurement of the diffusion coefficients of sparingly soluble gases in water. /. Geophys. Res. 92, 10767-10776. 

Table 1.10 Diffusion coefficient of inorganic gases in water at 20 °C (Pavlov et al., 1979) ...

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