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Unformatted text preview: 57:020 Mechanics of Fluids and Transport
December 8, 2010 AME
Quiz 12. Small water droplets ( = 9800 N/m3) of d = 0.06 m (6 10-8 m)
diameter fall through air. The drops reached to a terminal falling velocity V
and the drag force D acting on the droplet is in balance with its weight W =
V, where the volume V = d3/6. The drag force is known that D = 3dV if
the flow Reynolds number is small such that Re << 1. (a) Find the falling
velocity V if the air is under standard sea-level condition ( = 1.23 kg/m3 and = 1.789 10-5 Ns/m2) and (b) calculate the Re and justify the validity of
the use of the low Re drag equation. Note that the buoyancy force acting on
the droplet is negligibly small and the drops do not evaporate. Solution:
(a) Since D = W, or
Solve for V:
(+3 points) (b) Reynolds number:
(+2 points) ...
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This note was uploaded on 12/08/2011 for the course MECHANICS 57:020 taught by Professor Fredrickstern during the Fall '10 term at University of Iowa.
- Fall '10