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Anonymous Poster #1

Water Hammer or Impulse Calculation

08/03/2011 10:18 AM

Sir,

Could you tell me how to take into account the effect of different pipe diameters presented between the reservoir and the valve which is closed rapidly and generated the shock wave? because the diameter plays a role in deciding the velocity of flow which in turn decides the kinetic energy of flow which gets converted into potential energy (pressure rise) of fluid when getting stopped by the valve closure and this energy doing some work on pipe wall and liquid.

take a case of pipe diameter at reservoir end is 50mm and keep reducing and at valve inlet it is 30mm. will it play any role in deciding the peak pressure rise during impulse or not?
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Ace Boeringa
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United States - Member - New Member Engineering Fields - Control Engineering - New Member

Join Date: Mar 2006
Location: Washington USA
Posts: 566
Good Answers: 53
#1

Re: water hammer or impulse calculation

08/03/2011 7:40 PM

yes.

Shorter, straighter, larger diameter piping runs are less restrictive than longer, crooked, smaller dia pipe runs.

Impulse is proportional to the square of velocity. Restriction is the enemy of velocity.

Good luck Petecat,

Ace
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Anonymous Poster #1
#2
In reply to #1

Re: water hammer or impulse calculation

08/04/2011 5:12 AM

I've seen a derivation for the pressure rise because of the water hammer effect. in that, total kinetic energy of the liquid [which is in between the reservoir and the valve (which is closed)] is equated to a) strain energy stored in the pipe of radius R because of the elastic deformation of pipe in radial direction and b) energy stored in the liquid by compressing it. here the deformation energy and the compression energy is because of the pressure rise, delta P (raised by stopping the liquid flow). from this energy balance, the delta P is found.

So can i use the same energy balance for my case of, two different diameter pipes in between the reservoir and valve. if so i'l have two kinetic energy terms in left hand side of my equation and 2 deformation and 2 compression energy terms (totally 4 terms) in R.H. side.

Or any other approach can be used? please correct me.
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Ace Boeringa
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United States - Member - New Member Engineering Fields - Control Engineering - New Member

Join Date: Mar 2006
Location: Washington USA
Posts: 566
Good Answers: 53
#3
In reply to #2

Re: water hammer or impulse calculation

08/04/2011 8:47 AM

Certainly the greater the elasticity of the pipeline, the more the shock effect will be dampened.
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Noudge79
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#4

Re: Water Hammer or Impulse Calculation

08/04/2011 9:20 PM

Pressure Head + Velocity Head + elevation = total energy at the valve point, you just play with the equation, I believe you'll find your working solution for your problem right there.

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