Pipe Sizing Calculation – Part 6: Determining Reynolds Number

In this part we will calculate Reynolds number for the pipe sizing calculation example. Refer Part-1 for understanding the problem statement and the solution steps.

From the concept of Reynolds number, it can be written that

Reynolds number (Re) = ρ*s*L/μ ………………………eq.1


ρ – Density of the fluid

s – Velocity of the fluid

L – Characteristic length

μ – Dynamic viscosity


For our water pipe sizing calculation example, we have the following inputs (refer Part-1):

Fluid used = water

So, density of fluid (ρ) = 1000 kg/m3

Dynamic viscosity of fluid (μ) = 0.000894 Pa-S

Assumed flow rate = 0.5 Liter/sec = 0.0005 cubic-meter/sec

Assumed pipe diameter = 20 mm = 0.02 m

So, velocity of the fluid (s) = 0.0005/(π*0.25*0.02*0.02) = 1.591 m/sec

Characteristic length (L) = 0.02 m

By putting all the input values in the eq.1, we get

Re = 35592.84

As, the Reynolds number is greater than 4000, so, the flow in our case is of turbulent type.

The next part (Part-7) will deal with the selection of  correct moody friction factor.

Shibashis Ghosh

Hi, I am Shibashis, a blogger by passion and engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies.
Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.

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