What is molecular diffusion coefficient?
The molecular diffusion coefficient is caused by the random thermal motion of molecules in a gas or liquid and depends on the temperature and pressure, molecular properties, such as mass and volume, and the forces between molecules.
What is the relationship between molecular radius and diffusion coefficient?
According to the Stokes–Einstein equation, the diffusion coefficient of a molecule is expected to increase in inverse proportion to its approximate radius. Therefore, a larger molecular weight is related to a larger approximate radius, so that the diffusion coefficient is generally smaller.
What is diffusion coefficient formula?
The diffusion coefficient is often defined as the ratio of flux density to the negative of the concentration gradient in direction of diffusion, then according to Fick’s law:(2.1)Ji=−Didφdywhere J is the transfer rate (kg/m2s); From: Basic Equations of the Mass Transport through a Membrane Layer, 2012.
What is meant by molecular diffusion?
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or. gas) particles at temperatures above absolute zero. The rate of this movement is a. function of temperature, viscosity of the fluid and the size (mass) of the particles.
What is the diffusion coefficient of nacl?
The diffusion coefficient of Na+ and Cl- ions in water, extracted from relevant data in Table 2, are found to be 1.33 x 10-5 cm2/s and 2.03 x 10-5 cm2/s respectively.
What does a larger diffusion coefficient mean?
The diffusion coefficient, also known as the diffusivity, describes how fast one material can diffuse through another material. The higher the diffusion coefficient, the faster diffusion will be.
How does molecular weight affect diffusion coefficient?
Diffusion coefficients decreased with increasing molecular weight for both linear and globular molecules; and the linear molecules had further reduced diffusivity than globular molecules with comparable molecular weights.
What is the significance of diffusion coefficient?
The diffusion coefficient is an important variable in many diffusion equations that describes how quickly one material can diffuse through another material. Increasing temperature increases the diffusion coefficient, as demonstrated by the equation relating the diffusion coefficient to temperature.
What affects diffusion coefficient?
Diffusion coefficient depends on size and shape of molecule, interaction with solvent and viscosity of solvent.
What is an example of molecular diffusion?
For example, in the alveoli of mammalian lungs, due to differences in partial pressures across the alveolar-capillary membrane, oxygen diffuses into the blood and carbon dioxide diffuses out. Lungs contain a large surface area to facilitate this gas exchange process.
What is the Taylor diffusion coefficient?
The first term on the right-hand side of eq (3.2-15) accounts for the dispersion of the pulse caused by diffusion in the axial direction. The second term is known as the Taylor diffusion co.efficient, and ac counts for the dispersion of the pulse caused by the parabolic velocity profile, as modified by diffusion in the radial direction.
How to measure the diffusion coefficient of a gel sample?
In the case of the diffusion of solvents, ions, and molecules contained in a gel sample, their mobility is restrained, and their diffusion coefficients become small . If we want to measure D values of such samples, we should employ large G or long Δ in PGSE NMR imaging.
What is the self diffusion coefficient of a gas?
Here, examples of self-diffusion and interdiffusion (binary diffusion) coefficients in a gaseous and liquid media are given in Tables 1, 2, and 3 . Table 1. Self-diffusion coefficient DA of some gases at T = 273 K and p = 0.1 MPa
Is the diffusion coefficient an integral of the expansion coefficient?
The diffusion coefficient now appears as an integral of the expansion coefficient over the molecular velocities:(ref. 2, sec. 7.4 a). The expansion coefficient satisfies a linear int.egro differential equation obtained from the Boltzmann equation.