Water from a pipe is coming out at the 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 mPa s)

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(2) 10⁴. Given: Q=100 L min⁻¹=(0.1)/(60)=1.67×10⁻³ m³ s⁻¹, r=5×10⁻² m, ρ=10³ kg m⁻³, η=10⁻³ Pa s. Mean speed: v=Q/(π r²)=(1.67×10⁻³)/(7.85×10⁻³)=0.212 m s⁻¹. The Reynolds number uses the diameter as the length scale, Rₑ=(ρ vD)/η with D=2r=0.1 m. Rₑ=(10³×0.212×0.1)/(10⁻³)=2.1×10⁴. So the Reynolds number is of the order of 10⁴ — well past the turbulent threshold.

Water from a pipe is coming out at the 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 mPa s)

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