Question

Problem:
A sample of powdered zinc oxide, density 5.60 g/
cm3, is allowed to settle under the acceleration of
gravity, 981 cm/sec2, at 25°C. The rate of settling, v,
is 7.30 x 10-3 cm/sec; the density of the medium is
1.01 g/cm3, and its viscosity is 1 centipoise = 0.01
poise or 0.01 g/cm sec. Calculate the Stokes
diameter of the zinc oxide powder.​

Answer 1

The Stokes diameter of the zinc oxide powder is 5.3*10⁻⁴ cm.

Given,

Density of zinc oxideρ = 5.60 g/cm3

The density of the medium ρ=1.01 g/cm3

The rate of settling (v)= 7.30 x 10-3 cm/sec

Viscosity(μ) =0.01 g/cm sec.

To find,

Stokes diameter of zinc oxide powder.

Solution,

We can simply solve this numerical problem, by the following process:

v = gD² (ρ₁ - ρ₂) / 18μ

(where D is diameter and ρ₁ = Density of the particle and ρ₂ is the density of the fluid)

7.30 * 10⁻³ = 981 * D² (5.60 - 1.01) / 18* 0.01)

D= 5.3*10⁻⁴ cm.

Hence, the Stokes diameter of the zinc oxide powder is 5.3*10⁻⁴ cm.

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