Change in Pipe Section
Pressure head loss due to change in pipe size or shape
Key FactsGyroscopic Couple: The rate of change of angular momentum () = (In the limit).
- = Moment of Inertia.
- = Angular velocity
- = Angular velocity of precession.
OverviewThe sudden changes or the introduction of bends or valves disturbs the flow pattern along the pipe. The result is an increase in turbulence and this increases the frictional losses.
Note: The pressure just inside the larger pipe is the same as that in the small pipe!Momentum at section (1) = Mass Velocity = Momentum at section (2) =
Drop in momentum
for this to happen there must be a force opposing motion The magnitude of the force =
Sudden ContractionThe coefficient of Contraction is defined as :
where aC is the area of the choke and a is the area of the pipe
The head lost is given by:
Head Loss At An Obstruction (e.g. A Valve)The general equation for the head loss due to an obstruction, including bends, elbows, gate values, etc, is
- k is the constant associated with the obstruction
- v is velocity
|Fitting or Obstruction||Value for K|
|Standard 45 degree Elbow||0.5|
|Standard 90 degree Elbow||1.0|
|Globe Value - fully open||10.0|
|Gate Valve - fully open||0.2|