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Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and
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Fluid Pressure Drop Along Pipe Length of Uniform DiameterFluid
Flow Table of Contents
Hydraulic and Pneumatic KnowledgeFluid Power Equipment
Pressure drop in pipes is caused by:
FrictionVertical pipe difference or elevationChanges of kinetic
energyCalculation of pressure drop caused by friction in circular
pipes
To determine the fluid (liquid or gas) pressure drop along a
pipe or pipe component, the following calculations, in the
following order.
Equation Reynolds Number:
Where:
Re = Reynolds Number
= Velocity of Flow
D = Diameter of Pipe
v = Kinematic Viscosity
Kinematic Viscosity Table Chart of Liquids
If the Reynolds number < 2320, than you have laminar
flow.
Laminar flow is characterized by the gliding of concentric
cylindrical layers past one another in orderly fashion. The
velocity of the fluid is at its maximum at the pipe axis and
decreases sharply to zero at the wall. The pressure drop caused by
friction of laminar flow does not depend of the roughness of
pipe.
If the Reynolds number > 2320, you have turbulent flow.
There is an irregular motion of fluid particles in directions
transverse to the direction of the main flow. The velocity
distribution of turbulent flow is more uniform across the pipe
diameter than in laminar flow. The pressure drop caused by friction
of turbulent flow depends on the roughness of pipe.
Select pipe friction Coefficient:
The pipe friction coefficient is a dimensionless number. The
friction factor for laminar flow condition is a function of
Reynolds number only, for turbulent flow it is also a function of
the characteristics of the pipe wall.
Determine Pipe friction coefficient at laminar flow:
Where:
= Pipe Friction Coefficient
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Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and
Pneumatic, Engineers Edge
http://www.engineersedge.com/fluid_flow/pressure_drop/pressure_drop.htm[4/13/2015
11:20:41 AM]
Re = Reynolds number
Note: Perfectly smooth pipes will have a roughness of zero.
Determine Pipe friction coefficient at turbulent flow (in the
most cases):
Where:
= Pipe Friction Coefficient
g = Acceleration of Gravity
Re = Reynolds Number
k = Absolute Roughness
D = Diameter of Pipe
lg = Log
The solutions to this calculation is plotted vs. the Reynolds
number to create a Moody Chart.
Determine Pressure drop in circular pipes:
Where:
= Pressure Drop
= Pipe Friction Coefficient
L = Length of Pipe
D = Pipe Diameter
p = Density
= Flow Velocity
If you have valves, elbows and other elements along your pipe
then you calculate the pressure drop with resistance coefficients
specifically for the element. The resistance coefficients are in
most cases found through practical tests and through vendor
specification documents. If the resistance coefficient is known,
than we can calculate the pressure drop for the element.
Where:
= Pressure Drop
= Resistance Coefficient (determined by test or vendor
specification)
-
Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and
Pneumatic, Engineers Edge
http://www.engineersedge.com/fluid_flow/pressure_drop/pressure_drop.htm[4/13/2015
11:20:41 AM]
p = Density
= Flow Velocity
Pressure drop by gravity or vertical elevation
Where:
= Pressure Drop
p = Density
g = Acceleration of Gravity
= Vertical Elevation or Drop
Pressure drop of gasses and vapor
Compressible fluids expands caused by pressure drops (friction)
and the velocity will increase. Therefore is the pressure drop
along the pipe not constant.
Where:
p1 = Pressure incoming
T1 = Temperature incoming
p2 = Pressure leaving
T2 = Temperature leaving
We set the pipe friction number as a constant and calculate it
with the input-data. The temperature, which is used in the
equation, is the average of entrance and exit of pipe.
Note: You can calculate gases as liquids, if the relative change
of density is low (change of density/density = 0.02).
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Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and
Pneumatic, Engineers Edge
http://www.engineersedge.com/fluid_flow/pressure_drop/pressure_drop.htm[4/13/2015
11:20:41 AM]
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