GATE 2020 CE (CE2) – Question 35
Two identically sized primary tanks settle Type-I discrete particles in dilute suspension under laminar flow. Their surface overflow rates are 30 and 15 m³/(m²·day). Let $d_{30},d_{15}$ be the smallest diameters completely settled respectively. Find $d_{30}/d_{15}$ to two decimals.
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Correct answer: 1.4 to 1.42
Explanation
Complete removal requires settling velocity equal to the overflow-rate threshold. Stokes settling has $v_s\propto d^2$. Hence $d_{30}/d_{15}=\sqrt{30/15}=\mathbf{1.41}$.