friction for laminar and turbulent flow through pipes and
TRANSCRIPT
Friction for Laminar and Turbulent Flow Through Pipes and Fittings
D. J. Courtemanche, PhD
04/04/2017
References
• Transport Phenomena • Bird, Stewart, and Lightfoot
• Transport Processes and Unit Operations • Christie J. Geankoplis
• Chemical Engineers’ Handbook • R. H. Perry and C. H. Chilton
Frictional Pressure Losses Associated with Flow Through Piping • One of the most common engineering calculations performed by a
chemical engineer
• Used to determine • Pumping requirements
• Required pipe pressure ratings
• Design of pressure relief systems
• Practicality of piping arrangements
Mechanical Energy Balance
Laminar versus Turbulent Flow
Viscosity
Viscosity
For a Newtonian fluid the viscosity, m, is independent of the shear rate
Reynolds Number Dimensionless number comparing inertial to viscous forces
Shell Momentum Balance Inside a Pipe
The sum of the forces on the Control Volume = Flux of Momentum from Control Volume Assumptions • r is constant • m is constant • No time dependence (steady state) • No entrance effects (flow is established)
Shell Momentum Balance Inside a Pipe
Shell Momentum Balance Inside a Pipe
Velocity Profiles
Note that in Mechanical Energy Balance we represent Kinetic Energy using (VAV)2 , where we really need to use (V2)av
For laminar profile (V2)av = ½ (VAV)2 For turbulent profile (V2)av = (VAV)2 approximately
Hence the term a is equal to 2 for laminar flow and equal to 1 for turbulent flow
Calculating Frictional Pressure Loss in Pipe Fanning Friction Factor
Fanning Friction Factor
Calculating Frictional Loss in Fittings
Example
Frictional Loss
Mechanical Energy Balance
Units??
Pumping Power Requirement