Question

Water from a pipe is coming at a rate of $100litres$ per minute. If the radius of the pipe is $5cm$, the Reynolds number for the flow is of the order of (density of water $=1000kg/m^3$, coefficient of viscosity of water $=1mPa$).

• A. ${10}^6$
• B. ${10}^3$
• C. ${10}^4$
• D. ${10}^2$

Answer 1

The correct option is C ${10}^4$

Reynolds Number $=\frac{\rho vd}{\eta }$
Volume flow rate $=v\times \pi r^2$
$v=\frac{100\times {10}^{-3}}{60}\times \frac{1}{\pi \times 25\times {10}^{-4}}$
$⟹v=\frac{2}{3\pi }m/s$
Reynolds Number $=\frac{{10}^3\times 2\times 10\times {10}^{-2}}{{10}^{-3}\times 3\pi }$
$\simeq 2\times {10}^4$ $(\because 3\pi \approx 10)$
of the order of ${10}^4$.