Pressure Drop

Pressure drop. Laminar flow, horizontal pipe  
Flow Rate, Q (m3/s): 
Pipe Inside Diameter, D (m): 
Pipe Length, L (m): 
Density, ρ (kg/m3): 
Dynamic Viscosity, μ (N-s/m2): 
Pressure Drop, P1-P2 (N/m2): 
Velocity, V(m/s): 
Reynolds Number, Re: 

Pressure Drop Drawing and Equation:

Pressure drop drawing

Pressure drop equation

Pressure Drop Equation Derivation

For steady flow of an incompressible fluid in a constant diameter horizontal pipe using the Darcy-Weisbach friction loss equation, the energy equation from location 1 to 2 is expressed in terms of pressure drop as:

Pressure drop energy equation


Area, velocity, Reynolds number for pressure drop derivation

When Re < 2100, flow is laminar and:

Friction factor for pressure drop derivation

Then pressure drop is:

Equation 1 for pressure drop   Equation 2 for pressure drop

The final pressure drop equation is often called Poiseuille's law after the original researcher (Munson et al., 1998, p. 468).

Unit abbreviations, symbols: kg=kilogram, m=meter, N=Newton, s=second. A=Pipe area, f=Moody friction factor.

Reference for pressure drop: Munson, B. R. Young, D. F. and Okiishi, T. H. 1998. Fundamentals of Fluid Mechanics. John Wiley and Sons. Inc. 3ed.


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