Calculator inputs
This tool applies one-dimensional steady diffusion using Fick’s first law, with optional porosity, tortuosity, and partition adjustments.
Formula used
J = -D × (dC/dx)
J = -D × (C2 - C1) / Δx = D × (C1 - C2) / Δx
Dadj = D × (ε/τ) × K when effective correction is enabled.Dadj = D × K when effective correction is off.
Rate = J × AAmount = Rate × t
This page assumes one-dimensional, steady-state diffusion across a uniform thickness. The concentration profile is taken as linear between side 1 and side 2.
How to use this calculator
- Enter the diffusion coefficient and choose its unit.
- Provide concentration values on side 1 and side 2.
- Enter barrier thickness, diffusion area, and elapsed time.
- Enable effective correction when porosity and tortuosity matter.
- Set a partition factor if interfacial partitioning is relevant.
- Click Calculate diffusion to see flux, rate, transferred amount, and graphs.
- Use the CSV and PDF buttons to export the result summary.
Example data table
| Parameter | Example value | Unit | Meaning |
|---|---|---|---|
| Diffusion coefficient, D | 1.50 × 10-9 | m²/s | Base molecular diffusivity in the medium. |
| Concentration at side 1, C1 | 2.50 | mol/m³ | Higher concentration boundary. |
| Concentration at side 2, C2 | 0.50 | mol/m³ | Lower concentration boundary. |
| Thickness, Δx | 0.002 | m | Path length for diffusion. |
| Area, A | 0.015 | m² | Cross-sectional area normal to diffusion. |
| Time, t | 3600 | s | Observation duration. |
| Flux, J | 1.50 × 10-6 | mol/(m²·s) | Predicted steady diffusive flux. |
| Transferred amount | 8.10 × 10-5 | mol | Total amount crossing during the chosen time. |
Frequently asked questions
1) What does this calculator compute?
It computes concentration gradient, diffusive flux, transfer rate through an area, and total transported amount during the entered time using steady one-dimensional diffusion assumptions.
2) Which Fick law is used here?
This page uses Fick’s first law. That means it assumes steady-state diffusion and a linear concentration drop across a uniform thickness.
3) Why can flux be negative?
The sign shows direction. Positive flux means transport from side 1 to side 2. Negative flux means the opposite direction because side 2 has the higher concentration.
4) When should I enable porosity and tortuosity?
Enable them for porous or tortuous materials where the actual diffusion pathway is longer and more restricted than a straight line through a dense slab.
5) What is the partition factor used for?
It scales transport when interfacial partitioning matters. A value above one increases the adjusted coefficient, while a value below one reduces it.
6) Do the concentration units have to be mass based?
No. You can use molar or mass-based concentration options. The calculator keeps the output amount consistent with the chosen concentration basis.
7) What happens when C1 equals C2?
The concentration gradient becomes zero, so the calculated steady diffusive flux and transferred amount also become zero.
8) Does this handle transient diffusion?
No. Transient diffusion needs Fick’s second law and a time-dependent concentration field. This calculator is intended for steady, linear-gradient cases.