Question

Screen efficiency in size separation depends on:

• A. Feed rate and screen aperture only
• B. Aperture size, feed rate, and particle shape
• C. Density of particles only
• D. Moisture content only

Hint:

The efficiency of a screen is typically calculated as the product of the recovery of the desired undersize in the underflow and the rejection of oversize in the overflow.
Always optimize the feed rate to prevent screen overloading and blinding.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the key factors that influence the efficiency of a screening operation in solid-solid size separation.
Screening is a mechanical separation process used to separate mixture of particles into fractions based on their size.

Step 2: Key Formula or Approach:
Screen efficiency (\( \eta \)) is a measure of how successfully a screen separates undersized material from oversized material.
It is defined based on the mass fractions of materials in the feed, overflow, and underflow streams.
This industrial efficiency is influenced by both the equipment geometry and material properties.

Step 3: Detailed Explanation:

• Aperture Size: The dimensions of the screen openings determine the cut point of the separation.
If the aperture size is close to the average particle size, particles can easily wedge in the openings, causing blinding and reducing separation efficiency.

• Feed Rate: The rate at which material is introduced onto the screen surface is a critical operating variable.
At low feed rates, particles have ample opportunity to contact the screen openings, leading to high efficiency.
At high feed rates, a thick bed of material forms on the screen, preventing undersized particles from reaching the apertures and reducing efficiency.

• Particle Shape: Spherical or cubical particles pass through screen openings easily.
Elongated, needle-like, or irregular particles may only pass through if they align vertically with the openings.
This makes shape a key factor in screening performance.

• Other Factors: While moisture content and density play a role, the combination of aperture size, feed rate, and particle shape represents the primary design and operational parameters.


Step 4: Final Answer:
Screen efficiency depends on the aperture size, the feed rate, and the shape of the particles.