Question

The efficiency of a screen cleaner can be increased by
A. Reducing the screen size
B. Increasing the feed rate keeping all other factors constant
C. Uniformly spreading the material over the full width of screen
D. Keeping grain depth equal to twice that of particle size
E. Increasing the screen size
Choose the correct answer from the options given below:

• A. E only
• B. A and B only
• C. C and E only
• D. B and D only

Hint:

To maximize screening efficiency:
- Utilize the entire screen width (uniform spreading).
- Provide sufficient screen length/area (larger screen size).
- Maintain a thin bed depth (avoid high feed rates).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A screen cleaner is a machine used to separate grains or seeds of different sizes using perforated screens.
The efficiency of a screen cleaner depends on the probability that a smaller particle will encounter a screen opening and fall through it.

Step 2: Detailed Explanation:
Let us analyze how each parameter affects cleaning efficiency:
- A. Reducing the screen size: This restricts the passage of smaller particles, which reduces the separation efficiency.
- B. Increasing the feed rate: If the feed rate is too high, a thick layer of grain forms on the screen. This prevents smaller particles from contacting the screen surface, causing them to slide off with the larger particles, which reduces efficiency.
- C. Uniformly spreading the material over the full width of the screen: This is correct. Spreading the grain evenly utilizes the entire surface area of the screen, preventing crowding and allowing smaller particles to contact the screen openings more easily, which increases efficiency.
- D. Keeping grain depth equal to twice that of particle size: A thin, single-particle layer is ideal for screening. A depth of twice the particle size is too thick and can reduce efficiency.
- E. Increasing the screen size: This is correct. Increasing the length or width of the screen increases the total screen area and the residence time of the grains on the screen, giving smaller particles more opportunities to fall through the openings and increasing separation efficiency.
Therefore, statements C and E are correct.

Step 3: Final Answer:
The correct option is (C).