In a sedimentation tank of length L, width B, and depth D handling discharge Q, what is the particle settling velocity____________________?
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Answer: D. Q/(B × L)
Explanation
Surface overflow rate in a rectangular sedimentation tank equals discharge Q divided by the horizontal surface area given by length L times width B. This hydraulic loading parameter directly determines the theoretical particle settling velocity that a sedimentation basin can successfully capture. Particles possessing settling velocities greater than or equal to the surface overflow rate will settle completely before reaching the basin outlet. Ideal sedimentation tank theory assumes uniform horizontal velocity and complete mixing within vertical fluid cross-sections. Surface overflow rate is expressed in units of cubic meters per square meter per day, representing vertical settling velocity. Designing basins with lower overflow rates increases particle removal efficiency for fine suspended solids in wastewater treatment.
Option A divides discharge by width and depth, which calculates vertical cross-sectional velocity rather than surface overflow rate. Option B divides discharge by length and depth, representing side-area velocity rather than the horizontal surface settling area. Option C divides discharge by length alone, failing to incorporate the necessary tank width dimension required for surface area calculation.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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