Pump Cavitation
Pump Cavitation
(OP)
How does air injection in high velocity pumps help reduce cavitation?
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RE: Pump Cavitation
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
Why? Not sure about this either, maybe it reduces pump flowrate or maybe the air which expands in the impeller eye softens the cavitation noise or maybe a combination of both - but as stated in most cases it works - so if it works why worry. Of course the downside of this is you need a source of compressed air plus a metering valve and then you may have the added problem of getting rid of the air further down the process.
RE: Pump Cavitation
David
RE: Pump Cavitation
In high value product appliations, the lost revenue from reduced flowrate, or the shutdown/hot tap to install the air release valves, would be enough by themselves to convince the managers a proper fix would be a super-high priority item.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
The paper attached is interesting.
RE: Pump Cavitation
The more oxygenated your water the faster your pipes will corrode.
Ione: Exactly where is this mine of useful information you have access to? That's got to be at least the fourth useful paper you have posted.
Always remember, free advice is worth exactly what you pay for it!
RE: Pump Cavitation
Just download, save, download, save , download, save ...
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
Air introduction does not prevent bubbles. It prevents damage from bubbles that collapse and cause damage to surfaces, because of liquid impacting it with such force. A significant amount of air in a bubble will prevent the bubble from collapsing to nothing and will act as a cushion between the liquid and the solid surface. Most cavitation noise (but not all) is caused by liquid hammering a solid surface.
RE: Pump Cavitation
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
Seems the introduction of air into a pump inlet can in some cases be of benefit whereas in others it needs to be avoided at all costs.
RE: Pump Cavitation
Regards,
SNORGY.
RE: Pump Cavitation
RE: Pump Cavitation
This was my point (maybe my not perfect command of English has distorted the message): a cushion effect on vapour bubbles impact is what you get with air injection. If you cannot exploit other possibilities to avoid cavitation, this could be a method to mitigate effects of cavitation.
ColonelSanders83,
I've appreciated you've found useful the papers previously posted. No secret, to quote BigInch: ""Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities." and so it is important to stay updated in this matter.
RE: Pump Cavitation
I wonder whether a colligative property, such as the lowering of vapor pressure by the addition of a nonvolatile solute, has been tried out to mitigate cavitation in those cases where corrosion, erosion or other unwanted effects aren't felt.
At 35oC water has a VP = 43.4 Torr that drops to 41.9 Torr upon addition of 1 mol/kg NaCl (common salt).
On cold water the addition of 0.1 mol fraction of sucrose dropped the VP of water from 4.6 to 3.8 Torr.
Artisi, BigInch, and many others.. can you enlighten me on this subject ?
Something that is not always mentioned in these forums is that even without active participation, one can learn a lot from reading the experts' contributions.
RE: Pump Cavitation
I've never heard about the approach you've described to increase NPSHa.
If I wanted to increase NPSHa by lowering the fluid vapour pressure I'd firstly try to cool the fluid. Looking at a chart, which shows the pressure vapour vs temperature (for water) I think (but I am far from an expert) that this method is much more effective.
RE: Pump Cavitation
RE: Pump Cavitation
Compositepro, I'd say 1.5 Torr = 0.065 ft of water. Indeed, still low, but I didn't insinuate eliminating cavitation, I just referred to mitigating cavitation.
Ione, at ambient temperatures a VP reduction of 1.5 Torr for water is equivalent to about 2oC cooling.
RE: Pump Cavitation
Using Wagner and Pruss correlation I got 2.2 Torr (from 22°C to 20 °C), but I also got 9.3 Torr (from 52 °C to 50 °C). The deltaT is the same, but the effect is quite different.
RE: Pump Cavitation
Correct, that is why I said at ambient temperatures.
RE: Pump Cavitation
I'm sorry of having used such a non-technical term as ambient temperature (room temperature).
BTW, the VP lowering of water by salts is tabulated in the CRC Handbook of Chemistry (Ed 77) page 5-109, as a function of moles per liter water at 100oC; the VP of pure water at this temperature would be 760 mm Hg.
A few examples:
VP drop
mol/L mm Hg
CaCl2 5 319.5
MgCl2 5 377.0
CaBr2 5 368.5
AlCl3 3 318.0
LiBr 10 438.0 (more than 50% !)
Regretfully I'don't have a source for the VP reduction at other temperatures, but the general trend is clear.
RE: Pump Cavitation
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
RE: Pump Cavitation
Thanks to all contributors for their explanations.
I found this link on NPSH that may interest readers.
The attached link implies that, in some pumps, too much of a difference between NPSHA and NPSHR in water systems below 150oF can be detrimental from the viewpoint of cavitation.
h
RE: Pump Cavitation
RE: Pump Cavitation
I wrote to them and asked them to explain.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
Take a look the link below.
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RE: Pump Cavitation
ione. That link appears broken. Can you attach the doc?
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
I'm no expert on the subject but it appears to me that a "simple" example
When the liquid level in the suction tank is high, the NPSHA is at its maximum, but since the differential head to overcome becomes smaller, the flowrate increases rising the NPSHR to cavitating conditions.
In this case a lowering of the suction tank level, with a concomitant reduction in NPSHA can suppress cavitation.
Am I wrong ?
RE: Pump Cavitation
The link sometimes works and sometimes doesn't.
Better to save a copy on my database too (it is quite interesting)
RE: Pump Cavitation
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
The article reported an approach quite unusual to fight cavitation in a specific region.
The article noticed that, in a region where cavitation is absolutely not unusual, an increase of NPSHa, if not enough adequate, can produce a detrimental effect by emphasizing damages produced by cavitation erosion.
RE: Pump Cavitation
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Cavitation
RE: Pump Cavitation
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/