The Viscosity of Liquids and Gases

Pipe Flow Rate (Q) :

• is the rate (ie: volume per unit time) at which a fluid flows through a pipe.  

Equation for calculating Pipe Flow Rate (Q) :

Q = uA = u(πR²) = u((πD²)/4)

  

where: 

•  u is the flow average velocity (m/s)
• A is the cross sectional area of the pipe (m²)
• R is the radius of the pipe (m)
• D is the diameter of the pipe (m) 

Reynold's Number (Re):  

• is a number (dimensionless) which can be used to determine the flow regime within a pipe.

Equation for calculating Reynold's Number (Re) :

 Re = ρuD/μ

where:

•  ρ is the density of the fluid (kg/m³)
•  μ is the viscosity of the fluid (kg / m*s)
• D is the diameter of the pipe (m)
• u is the average velocity in the pipe (m/s)