Multiple choice

The following data are given for a channel-type grit chamber of length 7.5 m.

  1. Flow-through velocity = 0.3 m/s
  2. The depth of wastewater at peak flow in the channel = 0.9 m
  3. Specific gravity of inorganic particles = 2.5
  4. g = 9.80 m/s2, m = 1.002 x 10-3 N-s/m2 at 20 oC, $\rho w$ = 1000 kg/m3 Assuming that the Stokes is valid, the largest diameter particle that would be removed with 100 percent efficiency is

  1. 0.04 mm

  2. 0.21 mm

  3. 1.92 mm

  4. 6.64 mm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using Stokes' law, settling velocity vs = g(G-1)d^2 / (18*nu). The removal efficiency is 100% if vs >= depth / (length / velocity). Solving for d gives approximately 0.21 mm.

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