Transport of gases

Existing methods for monitoring the transport of gases were inadequate for studying aerosols. To solve the problem, qualitative and quantitative information were needed to determine the sources of pollutants and their net contribution to the total dry deposition at a given location. Eventually the methods developed in this study could be used to evaluate models that estimate the contributions of point sources of pollution to the level of pollution at designated locations. 

Liquid Membranes. A number of reviews summarize the considerable research effort ia the 1970s and 1980s on Hquid membranes containing carriers to faciUtate selective transport of gases or ions (58,59). Although stiU being explored ia a number of laboratories, the mote recent development of much mote selective conventional polymer membranes has diminished interest ia processes using Hquid membranes. 

Fig. 44. Schematic examples of facUitated transport of gases and metal ions. The gas-transport example shows the transport of oxygen across a membrane using hemoglobin (HEM) as the carrier agent. The ion-transport example shows the transport of copper ions across the membrane using a Uquid...

Buried steel pipelines for the transport of gases (at pressures >4 bars) and of crude oil, brine and chemical products must be cathodically protected against corrosion according to technical regulations [1-4], The cathodic protection process is also used to improve the operational safety and economics of gas distribution networks and in long-distance steel pipelines for water and heat distribution. Special measures are necessary in the region of insulated connections in pipelines that transport electrolytically conducting media. 

How would you design the architecture of a catalyst to be used under conditions where there are severe limitations on the transport of gases into the catalyst particle ... 

The thickness of the diffusion layer is directly related to the mass transport of gases and liquid within the material because it determines the length of the flow path. The electrical conductivity and resistance of the DL are also affected substantially by the thickness of the material. Therefore, to choose an optimal DL, there has to be a compromise between the thickness of the material and the properties mentioned before. 

Transport of gases through the aerenchyma may occur by diffusion and, where pressure gradients develop, by convection. Pressurized flow is important in wetland plants with root systems permitting a throughflow of gases, but is insignificant in other plants (Beckett et al., 1988 Skelton and Alloway,... 

FIGURE 5.16 Schematic of resistance model for diffusion, uptake, and reaction of gases with liquids. Tg represents the transport of gases to the surface of the particle, a the mass accommodation coefficient for transfer across the interface, rso, the solubilization and diffusion in the liquid phase, riM the bulk liquid-phase reaction, and rinlcrl.ll c the reaction of the gas at the interface. 

Saxena, V., and Stem, S.A., Concentration-Dependent Transport of Gases and Vapors in Glassy Polymers II. Organic Vapors in Ethyl Cellulose, J. Memb. Sci., 12, 65-85 (1982). 

Koros, W. J., Ph.D. Dissertation "Sorption and Transport of Gases in Glassy Polymers," The University of Texas (Austin), 1977. 

In 1879, von Wroblewski (3) showed that sorption and transport of gases in polymers followed Henry s and Fick s laws, respectively,... 

The gas-polymer-matrix model for sorption and transport of gases in polymers is consistent with the physical evidence that 1) there is only one population of sorbed gas molecules in polymers at any pressure, 2) the physical properties of polymers are perturbed by the presence of sorbed gas, and 3) the perturbation of the polymer matrix arises from gas-polymer interactions. Rather than treating the gas and polymer separately, as in previous theories, the present model treats sorption and transport as occurring through a gas-polymer matrix whose properties change with composition. Simple expressions for sorption, diffusion, permeation and time lag are developed and used to analyze carbon dioxide sorption and transport in polycarbonate. 

Nonlinear, pressure-dependent sorption and transport of gases and vapors in glassy polymers have been observed frequently. The effect of pressure on the observable variables, solubility coefficient, permeability coefficient and diffusion timelag, is well documented (1, 2). Previous attempts to explain the pressure-dependent sorption and transport properties in glassy polymers can be classified as concentration-dependent and "dual-mode models. While the former deal mainly with vapor-polymer systems (1) the latter are unique for gas-glassy polymer systems (2). 

In Section I we introduce the gas-polymer-matrix model for gas sorption and transport in polymers (10, LI), which is based on the experimental evidence that even permanent gases interact with the polymeric chains, resulting in changes in the solubility and diffusion coefficients. Just as the dynamic properties of the matrix depend on gas-polymer-matrix composition, the matrix model predicts that the solubility and diffusion coefficients depend on gas concentration in the polymer. We present a mathematical description of the sorption and transport of gases in polymers (10, 11) that is based on the thermodynamic analysis of solubility (12), on the statistical mechanical model of diffusion (13), and on the theory of corresponding states (14). In Section II we use the matrix model to analyze the sorption, permeability and time-lag data for carbon dioxide in polycarbonate, and compare this analysis with the dual-mode model analysis (15). In Section III we comment on the physical implication of the gas-polymer-matrix model. 

A model for sorption and transport of gases in polymers has to specifically account for the fact that the presence of sorbed gases in the polymer modifies the matrix (7, 9). In developing the matrix model we are guided by the physical evidence relating to the mechanism of sorption and transport. The matrix model is consistent with the following observations and assumptions ... 

B. Transport of Gases in Glassy Polymers 1. Steady-State Transport... 

A model for sorption and transport of gases in polymers should serve two purposes. First, the model should convey an understanding of the molecular interactions which are responsible for the macroscopic processes, and second, the model should... 

Chem RT, Sheu FR, Jia L, Stannett VT, Hopfenberg HB (1987) Transport of gases in unmodified and arylbrominated 2,6-dimethyl-l,4-poly (phenylene oxide). J Membr Sci 35 103-115... 

Liquid membranes containing carriers to facilitate selective transport of gases or ions were the subject of a considerable research effort in the 1970s and 1980s. 

Chamberlain, A.C. (1966) Transport of gases o and from grass and grass-like surfaces. Proceedings of the Royal Society A, 290, 236-65. 

Transport of gases to and from surfaces. Quarterly Journal of the Royal Meteorological Society, 94, 318-32. 

Chamberlain, A.C., Garland, J.A, Wells, A.C. (1984) Transport of gases and particles to surfaces with widely spaced roughness elements. Boundary-layer Meteorology, 29, 343-60. 

Fig. 6.1. Transport of gases and particles to and from flat plates and leaves by Brownian diffusion , l3lI vapour, flat plate (Chamberlain, 1953) O, 212Pb vapour, bean leaves (Chamberlain, 1974) , water vapour, bean leaves (Grace Wilson, 1976) +, x, 0.17-jum particles to pine, oak leaves (Belot, 1975) A, V, , 0.03- m particles to nettle, beech, white poplar leaves (Little Wiffen, 1977) line A, theory, laminar flow,...

Besides Knudsen diffusion, permselective transport of gases can occur by various mechanisms involving molecular scale interactions of the sorption-diffusion type. These can be broadly classified into three groups as described below and pictured in Fig. 7. 

Transport of gases or fluids may be impaired by nonflexible tubing. 

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