In screening operations, how does increasing the feed capacity (throughput per unit area) generally affect the overall screen effectiveness (sharpness of separation and undersize recovery)?

Introduction / Context:
Screening performance depends on loading, particle size distribution, moisture, and vibration parameters. This question focuses on the impact of capacity on effectiveness—vital for balancing throughput and product quality.

Given Data / Assumptions:

• “Capacity” refers to feed rate per unit screen area.
• “Effectiveness” refers to separation sharpness and correct placement of undersize/oversize.
• Operating within typical industrial regimes.

Concept / Approach:
As capacity increases, bed depth grows, particle stratification worsens, and the probability of undersize contacting and passing apertures declines. Residence time also drops. Consequently, misplacement errors increase and effectiveness falls.

Step-by-Step Solution:
Relate feed rate to bed depth and residence time.Infer reduced probability of passage for near-size particles.Conclude that effectiveness decreases with increasing capacity.

Verification / Alternative check:
Empirical capacity-effectiveness curves in screen design references show inverse relationships at higher loadings.

Why Other Options Are Wrong:
Increases/Does not affect: contradicts industrial experience.Unpredictable: trends are well established.

Common Pitfalls:
Ignoring moisture and pegging, which can further worsen performance at high loadings.

Final Answer:
Decreases