Diffusion co-efficient

Cooke and Wien have found that the NMR proton chemical shift in muscle water is similar to that in an aqueous salt solution273. The relaxation times are different. But the activation energy of the diffusion co-efficient of cellular water in muscle... 

Three mechanisms have been invoked to describe the transfer of water vapor from the feed-membrane interface to the strip-membrane interface, namely Poiseuille flow, Knudsen diffusion, and Fickian (molecular) diffusion. The operative mechanism in a particular system depends on the pore diameter and on whether or not the pores are filled with stationary air. The membrane mass transfer co-efficient (as kgm h Pa ) applicable to each of these mechanisms can be estimated using Eqs. (4), (5), and (6), respectively. Here, r is the pore radius, e is the membrane porosity, is the molar mass of water, is the mean water vapor pressure in the pores, is the membrane thickness, x is the pore tortuosity, is the viscosity of water vapor, R is the gas constant, T is the absolute temperature, is the diffusion co-efficient of water vapor in air,... 

Feed-side and strip-side concentration polarization result in a reduction in the driving force for mass transfer. There is a decrease in water activity at the feed-membrane interface and an increase at the strip-membrane interface. This results in a reduction in the water vapor pressure gradient across the membrane. The feed side and strip side mass transfer co-efficients, Kf and K, respectively, can be expressed in terms of the solute diffusion co-efficient in the boundary layer, D, ... 

The water vapor flux increases exponentially as the mean temperature of the system increases in accordance with the Antoine equation [Eq. (17)]. Here, T is the absolute temperature and A, B, and C are constants. Temperature also affects water flux through the thermal sensitivity of solution viscosity, solute dif-fusivity, and the diffusion co-efficient of water vapor in air-filled membrane pores. Elevated temperatures tend to lower feed-side, membrane, and strip-side resistances to mass transfer. However, operation at such temperatures may lead to a loss of product integrity through thermal degradation or volatiles loss. 

This equation indicates that resolution is affected by the applied potential, the molecular diffusion co-efficient, and the differences between the mobilities of the ions under both electrophoretic and electro-osmotic conditions. 

Designed a state-of-the-art new neutron imaging facility for fuel cell research. This facility will be used for critical water transport studies in the MEA and the flow channels, for the measurement of the hydrogen diffusion co-efficient across the MEA and water/vapor phase, and for evaluation of the integrity of various interfaces. The facility is expected to be operational in October, 2002. 

Slattery, J. C. and R. B. Bird. Calculation of the diffusion co-efficient of dilute gases and of the self-diffusion co-efficient of dense gases. AlChE Journal 4 137-142, 1958. 

Fuller, E. N., P. D. Schettler and J. C. Gliddings. New method for prediction of binary gas-phase diffusion co-efficients. Industrial and Engineering Chemistry 58(5) 18-27, 1966. 

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