Surface Flux Calculator
Enter consistent units. Concentrations should match each other, and molar mass should be in g/mol.
Example Data Table
| Scenario | Effective D (m²/s) | ΔC (mol/m³) | Δx (m) | Area (m²) | Time (s) | |J| (mol/m²/s) | |n| (mol) |
|---|---|---|---|---|---|---|---|
| Membrane A | 1.20E-9 | 1.50 | 0.0020 | 0.80 | 3600 | 9.00E-7 | 2.592E-3 |
| Film B | 7.20E-10 | 0.90 | 0.0015 | 1.20 | 1800 | 4.32E-7 | 9.331E-4 |
| Coating C | 2.75E-9 | 3.00 | 0.0030 | 0.50 | 5400 | 2.75E-6 | 7.425E-3 |
Formula Used
1) Effective Diffusivity
Deff = D × correction factor
This adjusts the base diffusivity for membrane effects, porosity, tortuosity, or empirical calibration.
2) Concentration Gradient
dC/dx ≈ (C₁ - C₂) / Δx
The calculator uses a finite concentration difference across the diffusion path thickness.
3) Surface Flux Density
J = -Deff × (C₁ - C₂) / Δx
This is Fick’s First Law. The negative sign indicates movement from higher concentration toward lower concentration.
4) Total Transfer Rate
N = J × A
Multiply flux density by available surface area to estimate total molar transfer rate.
5) Transferred Amount and Mass
n = N × t
mass = |n| × molar mass
This converts the transfer rate into cumulative moles and estimated mass moved over the selected time.
How to Use This Calculator
- Enter diffusivity for the species and medium.
- Provide the concentrations on both sides of the surface.
- Enter the diffusion path thickness and surface area.
- Add exposure time for cumulative transfer estimation.
- Use the correction factor if your system needs calibration.
- Enter molar mass when you also want the transferred mass in grams.
- Click the calculate button to display results above the form.
- Use the CSV and PDF buttons to export the finished result summary.
FAQs
1) What does surface flux mean in chemistry?
Surface flux is the amount of material moving through a unit area in a unit time. It is commonly used for diffusion, membrane transport, evaporation, and mass transfer studies.
2) Why is there a negative sign in Fick’s law?
The negative sign shows that diffusion naturally moves down the concentration gradient. Material flows from a region of higher concentration toward a region of lower concentration.
3) Which concentration units should I use?
Use any consistent concentration unit pair, but both sides must match. This layout assumes mol/m³, which is common for diffusion calculations in chemistry and engineering.
4) What is the correction factor for?
It lets you scale diffusivity for real systems. You can use it for porosity, tortuosity, membrane efficiency, calibration, or empirical transport adjustments.
5) Can this calculator estimate transferred mass too?
Yes. If you enter molar mass, the calculator multiplies the transferred moles by that value and reports the estimated mass in grams.
6) What happens if both concentrations are equal?
The concentration gradient becomes zero, so ideal net diffusive flux is zero. In that case, no directional mass transfer is predicted by the model.
7) Is this suitable for membranes and coatings?
Yes. It works well for membranes, films, coatings, barriers, and lab diffusion setups, as long as the assumptions behind one-dimensional steady diffusion are acceptable.
8) Does the graph show instantaneous or cumulative behavior?
The graph shows cumulative transferred amount over time using the computed transfer rate. It helps you visualize how total transport builds during the selected exposure period.