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HW #4

Solutions

2. Calculate the drag force on a spherical particle moving at 0.25 m/s. Consider particle diameters of: a) 100 μm and b) 1 μm.

The drag force is given by :

[pic]

The drag coefficient, CD, depends on Reynolds number

[pic]

Since density and temperature are not specified, we use typical values of 1.2 kg/m3 for density and 1.8x10-5 kg/(m s)for dynamic viscosity. Re = 1.8 and 0.018 for problems (a) and (b), respectively.

For (a), (9.32) tells us to use

[pic]

and FD = 4.0 x 10-9 N.

For (b) Re ................
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