Question

If a fluid having viscosity $0.6{\text{Ns/m}}^2$ and density of $900{\text{kg/m}}^3$, flows through a pipe of diameter $40\text{mm}$, then find the maximum velocity of fluid (in $\text{m/s}$) inside the pipe for laminar flow. (Critical Reynold's number $=2100$)

• A. $35$
• B. $90$
• C. $46.6$
• D. $31.5$

Answer 1

The correct option is A $35$

Reynolds number = $\frac{Dv\rho }{\mu }$
For the flow to be laminar,
$\frac{0.04\times v\times 900}{0.6}<2100$
$\Rightarrow \frac{0.04\times v_{max}\times 900}{0.6}=2100$
$\Rightarrow v_{max}=35\text{m/s}$