Question

An oil of viscosity 9 poise is flowing through a horizontal pipe of 60 mm diameter. If the flow is laminar, the pressure drop in 100 m length of the pipe is 1800 $kN/m^2$.The average velocity of flow of the oil is

• A. 2.25 m/s
• B. 0.55 m/s
• C. 5.5 m/s
• D. 22.5 m/s

Answer 1

The correct option is A 2.25 m/s

$\text{1 poise}=0.1{\text{N-s/m}}^2$

$\therefore \mu =0.9{\text{N-s/m}}^2$

$V_{av}=\frac{1}{8\mu }\frac{dp}{dz}{R}^2$

$\frac{dp}{dz}=\frac{1800\times {10}^3}{100}=18\times {10}^{3}N/m^2/m$

$R=\frac{60}{2}=30\text{mm}=0.03m$

$\therefore V_{av}=\frac{1}{8\times 0.9}\times 18\times {10}^3\times (0.03{)}^2$

$=2.25\text{m/s}$