Question

The Reynolds number and nature of flow of water flowing with a velocity of $10~\text{cm s}^{-1}$ through a pipe of diameter $1.8~\text{cm}$ is (Coefficient of viscosity of water $=10^{-3}~\text{Pa s}$)

• A. 900 and laminar
• B. 1800 and laminar
• C. 1800 and unsteady
• D. 1800 and turbulent

Hint:

Laminar flow if $Re<2000$, turbulent if $Re>4000$.

Answer 1

The Correct Option is B

1. Reynolds number: $Re = \frac{\rho v D}{\mu}$, $\rho = 1000~\text{kg/m}^3$, $v = 0.1~\text{m/s}$, $D = 0.018~\text{m}$, $\mu = 10^{-3}~\text{Pa s}$
2. $Re = \frac{1000 \cdot 0.1 \cdot 0.018}{10^{-3}} = 1800$
3. Since $Re<2000$, the flow is laminar