Question

The oil with specific gravity 0.8, dynamic viscosity of 8 × 10^–3 Ns/m² flows through a smooth pipe of 100 mm diameter and with Reynolds number 2100. The average velocity in the pipe is: 

(a) 0.21 m/s 

(b) 0.42 m/s 

(c) 0.168 m/s 

(d) 0.105 m/s

Answer 1

(a) 0.21 m/s 

Answer 2

Re= rho V avg D mu

Where, p is the density of the fluid and V avg is the average velocity of the fluid in the pipe and D is the diameter of the pipe and µ is the dynamic viscosity of the fluid

Calculation:

Given,

Specific gravity of oil = 0.8 , thus density =0.8* 1000 = 800kg / (m ^ 3)

Reynolds number =2100 , Dynamic viscosity =8 *10^ -3 Ns/m^ 2

Diameter =100 mm=100*10^ -3 m

Re= rho V avg D mu

V avg = mu Re rho D

V avg = 8*10^ -3 *2100 80*100*10^ -3 =0.21 m/s