# Mass Diffusivity

on . Posted in Classical Mechanics

Mass diffusivity, abbreviated as $$D$$ or $$D_m$$, also called diffusivity, is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration of the species.  Diffusion is the spread of gases, liquids, or solids from areas of high concentration to areas of low concentration.  It is the rate one material can disperse through another material.  The higher the diffusion coefficient, the faster the diffusion will be.  The diffusion coefficient for solids tends to be much lower than the diffusion coefficient for liquids and gasses.

Mass diffusivity is influenced by several factors, including temperature, pressure, and the properties of the diffusing substance and the medium.  It is commonly determined experimentally or estimated using theoretical models and correlations.

Mass diffusivity plays a crucial role in various scientific and engineering applications, particularly in areas involving mass transfer and diffusion processes, such as chemical reactions, heat and mass transfer in fluids, and the movement of substances through porous media.  It is an essential parameter for analyzing and predicting the rates of diffusion and transport of species in different systems and understanding how they mix or disperse over time.

## Lewis Number Mass Diffusivity formula

$$\large{ D = \frac{ \alpha }{ Le } }$$     (Lewis Number Mass Diffusivity)

$$\large{ \alpha = D \; Le }$$

$$\large{ Le = \frac{ \alpha }{ D } }$$

### Solve for D

 thermal diffusivity, α Lewis number, Le

### Solve for α

 mass diffusivity, D Lewis number, Le

### Solve for Le

 thermal diffusivity, α mass diffusivity, D

Symbol English Metric
$$\large{ D }$$ = mass diffusivity  $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$
$$\large{ \alpha }$$  (Greek symbol alpha) = thermal diffusivity $$\large{\frac{ft^2}{sec}}$$ $$\large{\frac{m^2}{s}}$$
$$\large{ Le }$$ = Lewis number $$\large{dimensionless}$$

## Schmidt Number Mass Diffusivity formula

$$\large{ D = \frac{ \nu }{ Sc } }$$     (Schmidt Number Mass Diffusivity)

$$\large{ \nu = D \; Sc }$$

$$\large{ Sc = \frac{ \nu }{ D } }$$

### Solve for D

 kinematic viscosity, ν Schmidt number, Sc

### Solve for ν

 mass diffusivity, D Schmidt number, Sc

### Solve for Sc

 kinematic viscosity, ν mass diffusivity, D

Symbol English Metric
$$\large{ D }$$ = mass diffusivity  $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$
$$\large{ \nu }$$  (Greek symbol nu) = kinematic viscosity $$\large{\frac{ft^2}{sec}}$$ $$\large{\frac{m^2}{s}}$$
$$\large{ Sc }$$ = Schmidt number $$\large{dimensionless}$$

## Sherwood Number Mass Diffusivity formula

$$\large{ D = \frac{ K \; l_c}{Sh} }$$     (Sherwood Number Mass Diffusivity)

$$\large{ K = \frac{ D \; Sh}{l_c} }$$

$$\large{ l_c = \frac{ D \; Sh}{K} }$$

$$\large{ Sh = \frac{ K \; l_c}{D} }$$

### Solve for D

 mass transfer coefficient, K characteristic length, lc Sherwood number, Sh

### Solve for K

 mass diffusivity, D Sherwood number, Sh characteristic length, lc

### Solve for lc

 mass diffusivity, D Sherwood number, Sh mass transfer coefficient, K

### Solve for Sh

 mass transfer coefficient, K characteristic length. lc mass diffusivity, D

Symbol English Metric
$$\large{ D }$$ = mass diffusivity  $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$
$$\large{ K }$$ = mass transfer coefficient $$\large{dimensionless}$$
$$\large{ l_c }$$ = characteristic length $$\large{in}$$ $$\large{mm}$$
$$\large{ Sh }$$ = Sherwood number $$\large{dimensionless}$$

Tags: Diffusion