Measurement of air permeability
Air permeability tester
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| Air permeability tester |
Air per permeability tester is measured by the air permeability of fabric according to the British Standard.
In this tester, the flow of air is passed through a specific area of fabric which is measured at a certain pressure drop throughout are of the specimen. This pressure is set at 10mm head of water.
A test sample of fabric is prepared by a fabric sample cutter of 25.4 mm diameter. For accurate results of testing, generally, five samples are prepared.
The specimen is then clamped over the air inlet of the instrument with the help of rubber gaskets.
To obtain accurate results in the test, edge leakage around the specimen needs to be prevented by using a guard ring or a similar device like a clamping ring.
In this instrument, the air is sucked through a pump and passed through the fabric specimen.
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| Air permeability principle |
The air valve of this instrument is adjusted for specific pressure drops by inserting data. This specific pressure across the fabric is 10mm head of water.
The airflow is measured by using a flowmeter.
(The pressure drop across the guard ring is measured by a separate pressure gauge because the Air that is drawn through the guard ring does not pass through the flowmeter.)
The mean value of airflow in ml per second (ml/sec) is calculated from the five testing results. (This air permeability can be calculated in ml per 100 mm∧2 per second.)
The reciprocal value for this specific method of air passage or the air resistance is described as the time in seconds taken for the passing of 1 ml air through 100s mm∧2 of fabric which is under 10mm of water pressure head.
Hot calendaring can be used to flatten fabric components, thus reducing air permeability.
Fabrics with different surface textures on either side can have different air permeability depending upon the direction of airflow.
(The advantage of using air resistance over air permeability is to define the fabric in the manner of its assembly of several layers of threads or coatings. In other words, the total air resistance of the fabric is the sum of the individual air resistances of all layers.)
Generally, this kind of instrument has some lefty features like a clamping device for securing the test specimen in a flat tensionless state, a device to prevent air leaking from the edges of the test area, usually called a guard ring, a pressure gauge, or manometer to measure the pressure drop from one side of the specimen to the other, an air pump to draw a steady flow of air through the clamped specimen, a means of adjusting the rate of airflow to achieve and hold the specified pressure drop from one side of the specimens to the other and a flow meter to measure the actual rate of airflow through the specimen.
In this instrument, The pressure drop caused by the resistance of the specimen is measured by a differential pressure gauge.
For pressure difference P1 and P2 for this test, The output is the air resistance R, measured in kilopascal times seconds per meter (kPa ⋅ s/m).
R = P1-P2/V = 𝚫P/V
According to the fluid flow, the specimen has small holes, therefore the pressure drop is due to frictional loss is depends on air velocity V.
ΔP = VK
where ΔP is the pressure difference, and K is the constant for the specimen.
K = 𝚫P / V
Here, R = K
where R is resistance and is linear concerning velocity for the specimen. A material with this response can be considered a ‘linear resistor’.
- How does an air permeability tester work?
- Explain the principle on which air permeability is measured.
- What is the process to measure the air permeability of fabric?
References
Booth, J. E. :. (n.d.). Principles of textile testing an introduction to physical methods of testing textile fibres, yarns, and fabrics. London: National Trade Press Ltd,1961. from https://www.abebooks.co.uk/Principles-Textile-Testing-Introduction-Physical-Methods/19989810376/bd
Cenote, M. (2015). Google Books. In The SAGE Guide to Key Issues in Mass Media Ethics and Law (pp. 847–858). SAGE Publications, Inc.
Ferreiro López-Riobóo, J. I. (2015). Long-term (2001–2012) study of a proficiency testing scheme for textiles. Accreditation and Quality Assurance, 20(4), 239–245. https://doi.org/10.1007/s00769-015-1128-1
Babu, S. (n.d.). Textile Adviser. Textileadvisor.com. from https://www.textileadvisor.com/2020/05/testing-of-air-permeability-of-fabric.html
Ding, X. (2008). Fabric permeability testing. In J. Hu (Ed.), Fabric Testing (pp. 189–227). Elsevier.
Hakoo, A. (2019, April 29). Importance of Air Permeability/Fabric porous structure in the production of technical textile fabrics. Textile School. https://www.textileschool.com/5194/importance-of-air-permeability-fabric-porous-structure-in-production-of-technical-textile-fabrics/
- Further reading
Writer - DSPAT Team
