Question

In the fineness measurement by Sheffield micronaire instrument, the flow of air through a plug of fibers is related to \(\underline{\hspace{2cm}}\) of fiber.

• A. Area of cross section
• B. Perimeter
• C. Weight per unit length
• D. Specific surface

Hint:

The Micronaire principle is based on air resistance: - Fine Fibers = High Surface Area = High Air Resistance = Low Airflow. - Coarse Fibers = Low Surface Area = Low Air Resistance = High Airflow. The property that combines surface area and mass is the specific surface.

Answer 1

The Correct Option is D

Step 1: Understand the principle of the Micronaire instrument. The Micronaire test measures the fineness of cotton fibers. It works by forcing a constant volume of air at a set pressure through a "plug" of a known weight of cotton fibers compressed to a fixed volume. The instrument measures the rate of airflow (or the resistance to airflow). 
 

Step 2: Relate airflow to fiber properties. The resistance to the flow of air depends on the total surface area of the fibers within the plug. - If the fibers are coarse (thick), for a given weight, there will be fewer fibers, and their total surface area will be lower. This creates larger channels for the air to flow through, resulting in low resistance and high airflow. - If the fibers are fine (thin), for the same weight, there will be many more fibers, and their total surface area will be much higher. This creates a denser plug with smaller air channels, resulting in high resistance and low airflow. 
 

Step 3: Define "Specific Surface." Specific surface area is the total surface area per unit of mass (e.g., cm\(^2\)/g). Fine fibers have a much higher specific surface than coarse fibers. The airflow resistance measured by the Micronaire is directly related to this property. 

Conclusion: The airflow through the fiber plug is a function of the specific surface area of the fibers.