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# Post Water Hammer Jet Kinetic Energy

10/15/2006 11:14 AM

Textbook formula for a closed pipe water hammer pressure is P= mass density x vel x celerity. There were recordings of water hammer pressure incidents that not only ruptured the penstock but also blasted the surrounding structures. This must be a very strong force. Is there any studies or researches to harness this destructive force and turn it into something that is constructive?

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#1

### Re: Post Water Hammer Jet Kinetic Energy

10/15/2006 11:46 PM

Look up Hydraulic ram.

This is the analog of inductive kick back when you open an inductive circuit instantaneously and the stored charge in the inductor at low voltage and high current turns into high voltage and low cirrent. you can do the same with water. A long column of water is flowing down under gravity. You drop a marble into the flow that will seal the exit end of the tube perfectly. As the water stops in a millisecond or less you will get a large peak pressure in the pipe. This peak can be tapped off to pump some water uphill to a greater height than the original flow.

You can buy these to run on stream flows over 5 feet of rock to pump water up 100 feet. The higher you pump = the less the flow, but people usually fill a tank at the high point and leave the ram running 24/7

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#2

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 12:02 AM

Blasts may be associated with tribo-electricity which can generate up to 100000V and can explode the zone due to high electric discharge. This has been often seen in water jets used for cleaning or cutting. Perhaps a nozel jet is responsible for greater friction and other frinction sources are air friction and hitting on the matter with energy. Tribo electricity can do lot more damage and is hard to predict the event. You need static electricity metter to scan the zone to see what is developing there that may be a balst accident thereafter.

This may be of some use.

www.jci.co.uk/Papers/TankWashingRisks.pdf

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#3

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 2:38 AM

Shyam wrote: "Blasts may be associated with tribo-electricity which can generate up to 100000V and can explode the zone due to high electric discharge."

This may be interesting in it's own right, but the topic here is about water hammer systems, which has nothing to do with electricity. The explosions referred to (as far as I can tell) is metalwork failing under enormous water hammer pressure.

Jorrie

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#4

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 8:26 AM

Dear Jorrie,

You are right. If explosion takes place within the nozel then it is more structural failure. Microstatic discharge in the pipe can also do the damage as there will be lots of local heat and expansion of the medium but does not look like the cause here. I can only think such thing in jet engines where velocities are real high.

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#6

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 1:50 PM

Hi Shyam,

I think we must try and get our terminology straight - you are apparently referring to a water hammer as something with a nozzle that has enormous fluid velocities going through it. It's not.

Water hammer effects are indeed caused by water with velocity, but it is actually about that water being abruptly stopped inside the system. You have heard the 'knocking' in the pipes when you close a tap in some domestic water system? That's a mild form of water hammer effect! It is not a "water hammer" that drills holes in a rock!

The explosions happen due to extreme spikes in water pressure that cause structural failures in the system.

Jorrie

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#7

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 4:11 PM

Hola Jorrie and Shyam

The explosions are actually catastrophic structural component failure of penstocks and valves (steel or concrete fracture) due to pressure spikes (waves) traveling along steel or concrete penstocks, the longer the penstock the worse the effect of the water hammer. There is another condition also destructive, where negative pressure, developed by opening flow control valves, may go below the vapor pressure of water, then the water will vaporize similar to water boiling or cavitating. This vaporized water is called column separation. The extreme vacuum may colapse the penstocks and other conveyance facilities, then when presure returns to normal values the water vapor will return to liquid state and a colunm of water will rush upstream creating a powerfull wave with devastating consecuences.

On the other hand cavitation is the formation of the vapor phase in a liquid flow when the hydrodinamic pressure falls below the vapor pressure of the liquid for that temperature. Water will boil out but not for the addition of heat but because the pressure drops below this value. As vapor bubbles travel downstream the pressure rises and the bubbles transform back into liquid water then they colapse causing an implosion wich produce shock waves with pressures as high as 200,000 psi. This rapid formation and colapsing of bubles produce craks near the surface of the turbine or nozzle producing an erosion which will increase as more bubbles are produced. To avoid the cavitation you have to avoid shapes or obstructions in water or liquid passages that will acelerate the flow of water/liquid because this in turn will drop its hydrodinamic pressure creating the cavitation.

There are pumps that use the water hammer for pumping water, you only need a stream of water an the pump wich will take the water up several meters. These pumps have low efficiency but do not need a motor.

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#5

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 1:28 PM

Good morning gentlemen. Water hammer is common on all hydraulic systems. Water hammer is the pressure wave wich ocurs with a sudden change in water velocity inside a penstock due to a valve closure or load rejection. In small systems as tap water it may produce noice and vibration on pipes. On big systems as in hydro power plants, where you have penstocks full of water driving the hydraulic turbines/generators for electricity, having a hydraulic ram (water hammer) could be extremely dangerous. In these power plants water flows in 4 to 20 feet dia. penstocks (depending on size/output of turbine/generator). If you have a sudden load rejection (a unit trips because and electrical problem or major mechanical breakdown) the valves controling the water flow, will close to avoid generator overspeed and further damage to mechanical components. In this conditiong the water flow will be stoped in a very short time (3-10 sec.). Due to the high inerta and volumen of water, its kinetic energy is transfered to the penstocks walls and upstream trough the water column inside the penstocks. In order to control this events (which ocurs severals times each year mainly due to ligthing and storms) you have to design a safe closing time on the water control valves and hydraulic governors and servo motors. The penstocks are design acordingly to withstand the huge energy surges and in addition, energy disipators are installed upstreams in the penstocks. These could be breathing pipes or air acumulators/disipators (surge tanks and pressure-regulating valves). These conditions are very dangerous and have produced fatal accidents where seccions of power plants have been severely damaged. There are other instances where high energy shock waves are produced in hydraulic systems as cavitation, that may produce extensive localized erotion. This cavitation fenomena is used for achieving high velocity torpedoes and for cleaning painted surfaces, but that is another subject. For further assitance check Hydropower Engineering Hanbook, J.S. Gulliver and R.E.A. Arndt. Regards. Luis

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#8

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 9:38 PM

Most of the pipes are cylindrical and hence inward pressure due to vacuum may be less effective than outward pressure due to sudden stopage of the water. There were water supply pipe bursts and perhaps this may be the cause.

Most of the pipe system in critical area carry a rupture disk mounted on a flenge and this usually puctures out for safety.

In 1976 I was part of the experiment to see the effect of sudden pressure on pipe walls. We placed different amount of RDX in steel pipes that were filled with water and has rupture disks at ends. Pressure pulses were only few microseconds and we could see that pipes were enlarged in explosion area and some time bursed out if rupture disks failed due to extra thickness. Perhaps similar thing can happen if water flow is stopped.

Earlier I have mistaken it for water hammering on the external material. Which is not the discussion here. Thanks Jorrie.

I think this discussion is a good one and has pointed out clearly that maximum breaking velocity and length of the pipe or the total mass and its total kinetic energy in the pipe is to be considered and perhaps it will be nice to do some experiments on it. Explosion as we did, gives multi-directional pressure from explosion point and differs from breaking energy of water hammer idea.

Can some one explain on how vibration will be produced in such systems? Water is not that much compressable liquid. It can't act as spring. Does it move like a bouncing ball or how does it happen? If it is tunning fork effect on pipes then I can understand it.

It is very interesting to have few more details on this subject. Thank you all. Keep pulling ideas.

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#9

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 9:55 PM

The repetitive hammering is the pressure pulse propagating inside a sealed system (or one with a long path to the ourside world. The pulse goes up and down the various lengths of the water system and bangs and reflects at dead end pipes.

This is what I surmise, I have not done experiments.

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#10

### Re: Post Water Hammer Jet Kinetic Energy

10/16/2006 10:29 PM

Dear Aurizon,

Looks to me that all kinetic energy is supplied by the pump and there can not be an extra source and perhaps accumulated energy may be the problem.

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#11

### Re: Post Water Hammer Jet Kinetic Energy

12/13/2006 3:21 PM

Hallo,

blasting the surrounding structures happened on water jet cleaning the interior of crude oil tankers.

The droplets of the water jet carry some charge (as in generating lightnings from droplets in thunderstorms).

If the charge builds up on the walls of the tanks and reaches sufficient charge and voltage then this will arc.

If the concentration of hydrocarbons in air is sufficient this will trigger an explosion.

Remember that 1 kg of fuel carries the same energy as 10kg of TNT.

I am convinced that the TWA800 flight that exploded some years ago above New York had the same mechanism. The fuel tanks if near empty are not vented with inert gas but with air. And the fuel tanks of that machine were more or less empty and any spray of kerosene has generated and transported some charge!

I had a phone conversation with NTSB members and Lufthansa safety pilot, they were interested but nothing resulted. But: new airplanes are now built with nitrogen inside the fuel tanks.

Regards

RHABE