Question

Consider flow of an oil with Reynolds number 1500 in a pipe of diameter 5 cm, The kinematic viscosity of the oil, v = 0.75 cm²/s. The value of average velocity in m/s is
1. 0.75
2. 1.50
3. 2.25
4. 4.50

Answer 1

Correct Answer - Option 3 : 2.25

Concepts:

Reynold number,

\(Re =\frac{VD}{ν }\)

Where V = average velocity of the fluid(m/s), D = diameter of the pipe(m), ν = kinematic viscosity of the fluid(m²/s)

The SI unit of kinematic viscosity is m2/s and the CGS unit of kinematic viscosity is cm2/s or 'stoke'.

1 cm2/s (stoke) = 10-4 m2/s.

Calculation:

Given:

Re = 1500, D = 5 cm = 0.05 m, ν = 0.75 cm²/s = 0.75 × 10^-4 m²/s

\(1500 =\frac{V\ \times\ 0.05}{0.75\ \times\ 10^{-4}}\)

∴ V = 2.25 m/s.