Water hammer
Water hammer
(OP)
Hi,
Im looking into water hammer at the moment. I am trying to figure out whether or not my lines are at risk from water hammer stresses.
I have found a design guide which tells me that if t>3L/Vsound then water hammer is not a problem.
t = valve closing time
L = length of column of fluid (pipe length)
Vsound = velocity of sound in fluid
then Vsound is given as sqrt(k/rho) where rho is fluid density, and k is the bulk modulus of the fluid where the bulk modulus is given by k = -V dP/dV.
This is pretty much where I get lost.
If my fluid is an oil, with density 840 kg/m3 and is essentially incompressible (=> Zl=0) haw do I calculate k and thus Vsound to find out if I have a water hammer problem?
Any and all help appreciated!!
Thanks
Niall
Im looking into water hammer at the moment. I am trying to figure out whether or not my lines are at risk from water hammer stresses.
I have found a design guide which tells me that if t>3L/Vsound then water hammer is not a problem.
t = valve closing time
L = length of column of fluid (pipe length)
Vsound = velocity of sound in fluid
then Vsound is given as sqrt(k/rho) where rho is fluid density, and k is the bulk modulus of the fluid where the bulk modulus is given by k = -V dP/dV.
This is pretty much where I get lost.
If my fluid is an oil, with density 840 kg/m3 and is essentially incompressible (=> Zl=0) haw do I calculate k and thus Vsound to find out if I have a water hammer problem?
Any and all help appreciated!!
Thanks
Niall





RE: Water hammer
RE: Water hammer
The modulus of elasticity being typically about 14,000 kg/cm2 at ambient temperature, the celerity of the pressure wave (sound) in your oil would be, approximately:
(14,000 kg/cm2×10,000 cm2/m2×9.8 m/s2÷840 kg/m3)0.5 = 1280 m/s.
RE: Water hammer
Remember F=MA
What is the flowing velocity of the fluid in the pipe? V
How long does it take for the valve to close? T
What is the density of the fluid? G
What is the cross sectional area of the pipe? A
How long is the pipe? L
So you have a MASS of fluid coming at the valve ADL
And it will be accelerated at V/T
So it will take a force AGLV/T to do that.
Force is Pressure times area, so pressure is Force divided by Area P=GLV/T
Since this disregards compressibility or elasticity, it is not absolutely correct, but it will put you in the ball park to estimate the pressures. It also assumes the valve has a linear characteristic and closes at a continuous rate. Therefore it might be prudent to double the force and pressure numbers.
RE: Water hammer
Please have a look on my webpage... Surge "Blog" for when you sould do a waterhammer analysis. Note, if it is a code design, a "waterhammer" analysis is required... not optional.
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RE: Water hammer
"Then Vsound is given as sqrt(k/rho) where rho is fluid density, and k is the bulk modulus of the fluid where the bulk modulus is given by k = -V dP/dV".... UNDER ISENTROPIC CONDITIONS.
MORE LATER
RE: Water hammer
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RE: Water hammer
OFFICE OF ELECTRICTIY DELIVERY AND ENERGY RELIABILITY
ENERGY ASSURANCE DAILY
Wednesday, August 16, 2006
http:/
Update: BP Prudhoe Pipeline Shutdown
Pressure Surge Forces BP to Shut Point McIntyre Field in Alaska
On August 11 a pressure surge during a repressurizing of the pipeline serving the Point McIntyre field in Alaska led to BP shutting down the 20,000 b/d field. The surge caused the pipeline to shift from some of its supports.
BP will inspect the line for damage and remount it on the supports before restarting the system. No oil was spilled
as a result of the surge.
Reuters, 10:51 August 16, 2006
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RE: Water hammer
read the whole article here,
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RE: Water hammer
The referenced equation is for frictionless one dimensional flow of a highly incompressible fluid. The referenced equation should have a + or - between the two terms and in reality is therefore two equations. Along with these equations are two additional ones
Dv/dt=u+/- a,
where a is the sound velocity and u local veloity.
Solution of these 4 equations and not one equation is required for the most basic problem.
Of course other factors, such as friction, elevation should be included in more sophistacted analyses.
Misuse or misunderstanding of the basic equations leads to errors in practical applications.
GITGO or garbage in=garbage out is the result of using programs in which the user is not knowledgable about the basic formulations in a program.
The Joukowsky equation or water hammer equation came about in the early 1900s. Integration of the equation was really solved in the mid 1800s by the mathematican Reimann.
Regards
RE: Water hammer
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RE: Water hammer
Dv/dt=u+/- a,
where a is the sound velocity and u local veloity.
SHOULD READ
Dx/dt= u+/- a where x is distance.
regards
RE: Water hammer
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RE: Water hammer
or ........ relates to with regard to the original post.
Regards
RE: Water hammer
Why must I restrict myself to the OP, when you yourself don't?
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RE: Water hammer
http://
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