Meltblown Pore Size & Filtration Pressure Drop Modeler

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 6 inputs are read from the form on every keystroke: Mean Fibre Diameter, Basis Weight, Web Thickness, Polymer Density, Face Velocity and Air Viscosity.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Mean Pore Size together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Web Solidity, Pressure Drop, Davies (1953), Pressure Drop, Recalibrated on N95 Media, Specific Surface Area, Fibre Length, Porosity and Resistance Constant, Recalibrated — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

The tool loads with this case already solved — the Mean Pore Size shown above is its answer. Change one value and the difference from this baseline is the sensitivity of the result to that variable.

How to use it

1. Work through the input groups in order — Web and Test Condition. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Mean Pore Size in the dark results panel — that is the headline figure, expressed in µm.
4. Check the supporting rows underneath (Web Solidity, Pressure Drop, Davies (1953), Pressure Drop, Recalibrated on N95 Media, Specific Surface Area, Fibre Length, Porosity and Resistance Constant, Recalibrated) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Mean Pore Size before a trial is booked, so machine time and material in Nonwovens & Technical Textiles are committed against a calculated figure rather than an estimate.
• Costing and quotation — Mean Pore Size is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Mean Fibre Diameter) shows how much of the gap in Mean Pore Size each variable explains.
• Teaching and study — the accepted ranges bracket normal Nonwovens & Technical Textiles practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Assumptions and limits

• Pressure drop is given two ways. The Davies figure is his 1953 correlation as published, computed from the solidity and fibre diameter above with no fitted constant; he built it on media with fibres far coarser than meltblown. Refitted to six N95 filtering layers with fibres of about 2.5 µm, the same correlation needed its leading constant cut from 64 to 8.3 (O Shaughnessy and others, Journal of Occupational and Environmental Hygiene, 2023), so the recalibrated figure is the closer guide for fine meltblown and the Davies figure an upper estimate. The recalibrated resistance constant is that figure in the form the Filter Media Efficiency, Resistance and Quality Factor tool takes, so the two tools agree when it is carried across. Pressure drop is mechanical only; it says nothing about the electret charge that carries most of the efficiency in respirator media, and charge decays. Respiratory protection is decision-support only — certification requires testing to the applicable standard.
• Every input is bounded to the range normal practice occupies (Mean Fibre Diameter 0.1 to 50 µm, Basis Weight 1 to 500 g/m² and Web Thickness 0.01 to 20 mm, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Questions people ask