Question

During the measurement of cotton fibre fineness (micronaire) by air flow method, a higher quantity of cotton fibre is taken by mistake than specified. The reading of micronaire value from the instrument will be:

• A. Higher for any fibre fineness
• B. Lower for any fibre fineness
• C. Lower for only coarser fibres
• D. Lower for only finer fibres

Hint:

- The micronaire value is inversely proportional to the air flow resistance. More cotton fibre leads to lower air flow resistance, thus a lower micronaire value.

Answer 1

The Correct Option is B

The micronaire value is a measure of the fineness and maturity of cotton fibres, typically determined by an air flow method. The principle behind the micronaire test is that the finer the cotton fibres, the more they restrict air flow through them. This restriction is measured and converted to a micronaire value, which gives an estimate of the fibre's fineness and maturity.
Now, let's consider what happens if more fibre is taken by mistake than specified. This will result in the following:
1) Effect of adding more fibre: When a higher quantity of cotton fibre is used, the volume of fibre in the test chamber increases. This causes a larger space for the air to pass through.
2) Impact on air flow: As the amount of fibre increases, the air has more space to flow through, meaning it encounters less resistance due to fewer fibres in contact with the air stream. This leads to a lower air flow restriction.
3) Conclusion on Micronaire Reading: Since the micronaire value is inversely proportional to the resistance to air flow, a lower resistance (due to more fibre) results in a lower micronaire value.
Therefore, the micronaire reading will be lower for any fibre fineness when a higher quantity of cotton fibre is used by mistake.