What does the diffusion coefficient represent?
The diffusion coefficient is the proportionality between flux and concentration gradient. The electrode area can be determined electrochemically with equations equivalent to an equation and by using a redox couple having a known diffusion coefficient.
How do you calculate effective diffusion coefficient?
Diffusion Coefficient: Effective Diffusion Coefficient Deff = Effective Diffusion Coefficient, D = Molecular Bulk Diffusion Coefficient. Here 0.707 is a correction for the actual diffusion process length. Where, φ is the porosity.
What is the unit of coefficient of diffusion?
square metres per second
The SI units for the diffusion coefficient are square metres per second (m2/s).
What is effective moisture diffusion coefficient?
Effective Moisture Diffusivity. The term effective diffusivity ( ) is defined to describe the rate of moisture movement, no matter which mechanism is involved. A complete drying profile consists of the first stage of drying, a constant-rate period, and a falling-rate period.
What is effective coefficient?
The effective coefficient of friction for a multiple cable pull is a function of the basic coefficient of friction KQ and the weight correction factor Wc. In effect, this means that when the cable is pulled around bends, initially use the higher coefficient of friction to calculate the SWBP.
Can a diffusion coefficient be negative?
In general, negative diffusion coefficient would denote process of “concentration” as opposed to diffusion. That means, it’s not a random walk problem but additional forces are acting opposing to diffusion process resulting in concentration.
What is Fick’s Law equation?
It states that ‘the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane’. Fick’s law can be written as: Rate of diffusion ∝ surface area × concentration difference thickness of membrane.
Does diffusion work better in dry or moist conditions?
Thus the diffusion coefficient does not depend on the moisture concentration itself and there is no difference in diffusion speed between absorption and desorption.
Does diffusion work better at high or low temperatures?
When temperature increases, the kinetic energy of the particles has increased. The increased motion of the particles causes them to diffuse faster. Therefore, at higher temperatures, the rate at which fluid particles will diffuse is faster than at lower temperatures.
What is the ratio of the diffusion coefficient?
Carman proposed the following ratio between the bulk and effective diffusion coefficients: Where, Deff= Effective Diffusion Coefficient, D= Molecular Bulk Diffusion Coefficient. Here 0.707 is a correction for the actual diffusion process length.
Is the diffusion coefficient the same for straight capillary tubes?
For a bundle of straight capillary tubes, the effective diffusion coefficient and the bulk diffusion coefficient are the same. However, the straight capillary model is not a very good representation of a porous rock. A lot of work has been done to predict the apparent diffusion coefficient in porous media.
What does Deff stand for in fluid flow?
Deff = Effective Diffusion Coefficient, D = Molecular Bulk Diffusion Coefficient. Here 0.707 is a correction for the actual diffusion process length. On the other hand in the porous medium the cross section area available for diffusion is not the total cross section of the medium.
Is the diffusion coefficient of a porous media anisotropic?
In some types of porous media, the (effective) diffusion coefficient may also be anisotropic, so that the rate of diffusion depends on the direction of the concentration gradient. In this case, the diffusivity is a tensor.