Question

Find the Reynolds number if a fluid of viscosity 0.4 Ns/m2 and relative density of 900 kg/m3 through a 20 mm pipe with a velocity of 2.5 m/s. Is the flow Laminar or Turbulent?

Note: If Reynolds < 2000 the flow is laminar
If Reynolds > 4000 the flow is turbulent
If 2000 < Re < 4000 it is transitional flow
Re = ρVL/η < 10^3 shows viscous force dominate. That is, viscous forces keep streamlines
constant so they flow steadily over each other in predictable path.
Re = Reynolds

Answer 1

Answer:

Find the Reynolds number if a fluid of viscosity 0.4 Ns/m2 and relative density of 900 kg/m3 through a 20 mm pipe with a velocity of 2.5 m/s. Is the flow Laminar or Turbulent?

Note: If Reynolds 2000 the flow is laminar

If Reynolds 4000 the flow is turbulent

If 2000 Re 4000 it is transitional flow

Re = shows viscous force dominate. That is, viscous forces keep streamlines

constant so they flow steadily over each other in predictable path.

Re = Reynold

Answer 2

Given: viscosity is 0.4 Ns/m^2 , relative density is 900 kg/ m^3 , 20 mm pipe , velocity is 2.5 m/s.

To find:  The Reynolds number ?

Solution:

• So we have given the values as:

              viscosity = 0.4 Ns/m^2

              relative density = 900 kg/ m^3

              pipe dimension = 20 mm

              velocity = 2.5 m/s.

• Now we know the formula for Reynolds number which is:

              Reynolds number N = relative density X velocity X dimension / viscosity

• So putting the values in Reynolds number N, we get:

              Reynolds number N = 900 x 2.5 x 0.020 / 0.4

              Reynolds number N = 900 x 2.5 / 2

              Reynolds number N = 450 x 2.5

              Reynolds number N = 112.5

Answer:

              So the Reynolds number is 112.5