Question

11. Oil is being pumped into a 10.0 mm diameter pipe with a Reynolds number of 2100.

The oil density is 855 kg / m3 and its viscosity is 2.1 x 10 -2 Pa. S

A) What is your speed in the pipeline? B) You want to keep the same Reynolds number of 2100 and the same speed that in part (a) using a second fluid with a density of 925 kg / m³ and a viscosity of 1.5 x 10-2 Pa. s. What should be the diameter of the pipe that is used?

Answer 1

diameter = 10 mm x 1m/1000mm = 0.010 m

Oil density = 855 kg/m3

viscosity = 2.1 x 10^-2 Pa-s

Reynolds number = 2100

Part a

Reynolds number = 2100

Diameter x speed x density / viscosity = 2100

speed = (2100 x viscosity) / (Diameter x density)

= (2100 x 2.1 x 10^-2 Pa-s) / (0.010 m x 855 kg/m3)

= 5.158 m/s

Part b

Speed = 5.158 m/s

density = 925 kg/m3

viscosity = 1.5 x 10^-2 Pa-s

Reynolds number = 2100

Diameter x speed x density / viscosity = 2100

Diameter = (2100 x viscosity) / (speed x density)

= (2100 x 1.5 x 10^-2 Pa-s) / (5.158 m/s x 925 kg/m3)

= 0.00660 m x 1000mm/m

= 6.60 mm