Textile Structure
how cloth is put together
Concept

Kozeny carman — where it appears

A fitted relation giving the permeability of a packed bed from its porosity and the size of its obstacles. It goes as the square of the size and as the cube of the porosity, and its constant varies from about one to five between sources and the permeability goes as its reciprocal, so every number computed from it carries a fivefold bracket.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

What a muslin passes, against how closely it is set. A muslin's air permeability at 100 Pa as the sett is closed from 6.9 to 34.2 threads per centimetre, with the two paths separated. The channels between the threads carry 8285 mm/s at the open end and 1330 at the close one, and they go to zero when the cloth jams. The threads themselves carry 1.7 to 6.4 mm/s and never go to zero at all, because a thread is sixty per cent fibre whatever the sett is. Extended to a cloth with no channel left, that path is 8.1 mm/s — a floor set by the yarn rather than by the construction, and a specification asking for less has asked for a fabric that cannot be woven from this yarn at any sett.

A cloth stops having holes before it stops passing air

Close a woven cloth up and the channels between its threads shut. What passes through it does not go to zero, because a thread is sixty per cent fibre and forty per cent air and stays that way whatever is done to the construction. So a fabric's permeability has a floor, the floor belongs to the yarn rather than to the weaver, and no sett on any loom reaches it.

applied · Permeability Four ways of closing a muslin, and the floor under all of them. The same muslin at four states: as woven, calendered to 3:1, wetted so its fibres swell by 20 per cent, and with the channel between its threads gone altogether. Air permeability at 100 Pa falls from 3505 mm/s to 8.1 — a factor of 434 — and stops there. The last figure is not a cloth with no holes in it: it is a cloth whose only remaining path is through the threads, which are sixty per cent fibre whatever is done to the construction. That number is the floor, it is a property of the yarn, and no sett reaches it. Note that the two middle routes are not in a fixed order: a 3:1 calender closes more than this swelling and a 2:1 calender closes less, so which is the stronger depends on how far each is taken.

A windproof cloth is at its yarn's limit

Windproof is a threshold on air permeability, and it is the only fabric specification on this site that the construction cannot settle. No weavable sett of an ordinary shirting yarn gets within two hundred times of it, layering the cloth barely helps because the resistance is inertial rather than viscous, and the floor set by the yarn's own porosity lands on the same order as the threshold with a fivefold bracket around it.

applied · Permeability

Named alongside it

The objects these essays reach for when they reach for this one.

Air permeabilityClear openingCover factorPacking factorCoatingDarcy lawFibre volume fractionInertial lossJammingTwo pore systems

All concepts