Mass transfer coefficient permeability constant

The substance-specific kinetic constants, kx and k2, and partition coefficient Ksw (see Equations 3.1 and 3.2) can be determined in two ways. In theory, kinetic parameters characterizing the uptake of analytes can be estimated using semiempirical correlations employing mass transfer coefficients, physicochemical properties (mainly diffusivities and permeabilities in various media), and hydro-dynamic parameters.38 39 However, because of the complexity of the flow of water around passive sampling devices (usually nonstreamlined objects) during field exposures, it is difficult to estimate uptake parameters from first principles. In most cases, laboratory experiments are needed for the calibration of both equilibrium and kinetic samplers. 

The following symbols are used in the definitions of the dimensionless quantities mass (m), time (t), volume (V area (A density (p), speed (u), length (/), viscosity (rj), pressure (p), acceleration of free fall (p), cubic expansion coefficient (a), temperature (T surface tension (y), speed of sound (c), mean free path (X), frequency (/), thermal diffusivity (a), coefficient of heat transfer (/i), thermal conductivity (/c), specific heat capacity at constant pressure (cp), diffusion coefficient (D), mole fraction (x), mass transfer coefficient (fcd), permeability (p), electric conductivity (k and magnetic flux density ( B) ... 

Enzyme activity decay constant, T 1 Enzyme Michael is constant, M L 3 Overall mass transfer coefficient, L T 1 Reactor length, L Critical reactor length, L Membrane hydraulic permeability, L2 T M ... 

The rate of transport across the membrane in units of mass (or moles) per unit time per unit area is termed a flux J and it is found to be proportional to the difference between the concentrations on either side of the membrane. The proportionality constant is called the permeability P with intrinsic dimensions of the same as the mass transfer coefficient and the same as velocity. 

A Effective membrane area C, Concentration of metal ion in bulk feed at time t Co Initial concentration of metal ion in bulk feed Membrane thickness Thickness of aqueous boundary layer Membrane diffusion coefficient Aqueous diffusion coefficient Aqueous feed film mass transfer coefficient Organic membrane phase mass transfer coefficient Overall mass transfer coefficient Distribution ratio Two-phase extraction constant Aqueous feed mass transfer coefficient Membrane mass transfer coefficient Aqueous strip mass transfer coefficient Length of the fiber Molecular weight of the complex Number of fibers Permeability coefficient (cm/s)... 

Possible consistent units could be the same as above for the flux, the diffusivity, the thickness, and the concentration, with the pressure in cm Hg (cm mercury), Henry s constant in kmoPm cm Hg, the permeability in kmol/s.m.cm Hg, and the mass transfer coefficients and the permeance in kmol/s m cm Hg. An alternative set would have the flux in cm (STP, standard temperature and pressure)/cm2-s, Henrys constant in cm (STP)/cm cm Hg, the thickness in cm, the pressure in cm Hg, the permeability in cm (STP)/s cm cm Hg, and the mass transfer coefficients and permeance in cm (STP)/s cm cm Hg. In converting molar flow rates to volumetric flow rates it is noted that the volume of 1 kmol gas is 22.4 m3 (STP). 

Local flow rate inside the membrane separator G General driving force property H Henry s constant K Equilibrium distribution coefficient k Mass transfer coefficient L Membrane thickness M Molecular weight M Factor defined by Equation 18.26 N Flux P Total pressure Pm Permeability p Partial pressure Pm Permeance... 

Permeability According to the aforementioned, both the sorption and the diffusion of a solute determine the mass transfer across, and hence the separation characteristics of the membrane. The product of the diffusion coefficient and the sorption coefficient Sf is denoted the permeabihty of the membrane for component i and is commonly designated as Pf. In order to avoid confusing permeability and pressure, however, here it will be denoted (used commonly for the phenomenological constant)... 

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