Project ForgeFluid Mechanics
Mechanical Operations
GATE 2010
Medium
The critical speed (revolutions per unit time) of a ball mill of radius R, which uses balls of radius r, is
- A(1/2π)√(g/√(Rr))
- B(1/2π)√(g/R)
- C(1/2π)√(g/r)
- (1/2π)√(g/(R−r))
Explanation
Balls travel along the inner mill surface at an effective radius of (R−r), since their centers trace a circle of that radius. Critical speed (where centrifugal force just balances gravity) is Nc=(1/2π)√(g/(R−r)).
Source: GATE CH 2010 (2010)
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