Section 4: Soil and Water Conservation Engineering
Fluid Mechanics
Subtopic: Laminar and turbulent flow in pipes, Darcy–Weisbach and Hazen–Williams equations
Question Statement:
Milk and rapeseed oil are flowing in pipes of 5 cm diameter with the same flow velocity of 3 m s⁻¹. The densities of milk and rapeseed oil are 1030 and 900 kg m⁻³, respectively. The viscosity of milk is 2.1×10⁻³ N s m⁻² and that of rapeseed oil is 118×10⁻³ N s m⁻². The values of Reynolds' number for milk and rapeseed oil will be respectively
Options:
(A) 73571 and 1144
(B) 1144 and 73571
(C) 73175 and 1144
(D) 1414 and 73571
Official Answer Key:
A
Step-by-Step Solution & Explanation
Re = ρVD/μ. Milk: Re = 1030×3×0.05/(2.1×10⁻³) = 154.5/0.0021 = 73,571. Rapeseed oil: Re = 900×3×0.05/(118×10⁻³) = 135/0.118 = 1144.
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