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is the gradient, i.e., rate of change with position, of the logarithm of the salt concentration, which is equivalent to the rate of change of the salt concentration, divided by the salt concentration – it is effectively one over the distance over which the concentration decreases by a factor of e. The above equation is approximate, and ...
Fick's first law relates the diffusive flux to the gradient of the concentration. It postulates that the flux goes from regions of high concentration to regions of low concentration, with a magnitude that is proportional to the concentration gradient (spatial derivative), or in simplistic terms the concept that a solute will move from a region of high concentration to a region of low ...
As mentioned above, chemical molar flux of a component A in an isothermal, isobaric system is defined in Fick's law of diffusion as: = where the nabla symbol ∇ denotes the gradient operator, D AB is the diffusion coefficient (m 2 ·s −1) of component A diffusing through component B, c A is the concentration (mol/m 3) of component A. [9]
The mole fraction, the molar concentration, and the partial pressure of both gases involved in equimolar counterdiffusion vary linearly. These relationships can be found in the following equations expressing the molar flow rates for each species, A and B, for a one-dimensional flow through a channel with no homogeneous chemical reactions:
In physics and engineering, permeation (also called imbuing) is the penetration of a permeate (a fluid such as a liquid, gas, or vapor) through a solid.It is directly related to the concentration gradient of the permeate, a material's intrinsic permeability, and the materials' mass diffusivity. [1]
Figure 3. Model of six adatoms diffusing across a square surface lattice. The adatoms block each other from moving to adjacent sites. As per Fick’s law, flux is in the opposite direction of the concentration gradient, a purely statistical effect. The model is not intended to show repulsion or attraction, and is not to scale on a spatial or ...
Dependence on a total concentration n for a given temperature has always the same character, 1/n. In applications to gas dynamics, the diffusion flux and the bulk flow should be joined in one system of transport equations. The bulk flow describes the mass transfer. Its velocity V is the mass average velocity. It is defined through the momentum ...
Diffusivity, mass diffusivity or diffusion coefficient is usually written as the proportionality constant between the molar flux due to molecular diffusion and the negative value of the gradient in the concentration of the species. More accurately, the diffusion coefficient times the local concentration is the proportionality constant between ...