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What does diffusion coefficient tell you?

What does diffusion coefficient tell you?

Definition of diffusion coefficient : the quantity of a substance that in diffusing from one region to another passes through each unit of cross section per unit of time when the volume-concentration gradient is unity.

How are diffusion coefficients measured?

Direct methods evaluate the diffusion coefficient by measuring concentration of the diffusing species (solvent) as a function of depth of penetration.

What is diffusion coefficient in mass transfer?

The diffusion coefficient (or diffusivity) is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration of the species (or the driving force for diffusion).

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 factors affect the diffusion coefficient?

The diffusion coefficient is a function of the fluid, size of the diffusing molecule (larger molecules diffuse more slowly), temperature, obstruction of diffusion by pore structure in sediments or other materials, and the rate of mixing of water.

On what factors the diffusion coefficient depends?

Diffusion coefficient depends on size and shape of molecule, interaction with solvent and viscosity of solvent.

What does a high diffusion coefficient mean?

The higher the diffusivity (of one substance with respect to another), the faster they diffuse into each other. Typically, a compound’s diffusion coefficient is ~10,000× as great in air as in water.

Why is the diffusion coefficient important?

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 increases the diffusion coefficient?

Diffusion – useful equations. The value for f calculated for a sphere is a minimal value; asymmetric shape of molecule or non-elastic interaction with solvent (e.g. hydration) will increase f. Diffusion coefficient depends on size and shape of molecule, interaction with solvent and viscosity of solvent.

How does diffusion coefficient change with temperature?

The coefficient of diffusion increases gradually as the temperature of the air increases.

What does a low diffusion coefficient mean?

The number density of molecules in liquid is also very much higher and their mobility is lower, which implies a much lower diffusion coefficient In solids, diffusion is still slower. If experimental data are lacking, the diffusion coefficient can be calculated.

What is the diffusion coefficient?

The diffusion coefficient is a physical constant dependent on molecule size and other properties of the diffusing substance as well as on temperature and pressure. Diffusion coefficients of one substance into the other are commonly determined experimentally and presented in reference tables.

How do you measure diffusion coefficient in NMR?

Diffusion coefficients in a sample are measured by NMR spectroscopy using the pulsed-field-gradient spin-echo (PGSE) pulse sequence [41, 42, 89]. The magnetic field gradient is applied in a single direction to encode the location of spins in this method.

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 [90]. If we want to measure D values of such samples, we should employ large G or long Δ in PGSE NMR imaging.

Who wrote diffusion coefficient measurements?

Title Diffusion Coefficient Measurements Author Jiann Yang Created Date 7/3/2013 4:56:32 PM