devarshi-dt-logo

Question:

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

10^6

10^3

10^2

10^4

Solution:

Correct option is C. 10^4
Reynolds Number = ρ vd/η
Volume flow rate = v × π r^2
v = 100 × 10^-3 / 60 × 1 × π × 25 × 10^-4
v = 2/3π m/s
Reynolds Number = 10^3 × 2 × 10 × 10^2 / 10^-3 × 3π ≈ 2 × 10^4
order 10^4.