npsh(r)??
npsh(r)??
(OP)
hi friends:
i have got manufacturing recomendation that npsh (r)=1.5m.
so when i install the pump from where i must measure at suction line to provide this no. ????
please clarify me this .if there is article clarify this point i will be appressiate.
best regrds
i have got manufacturing recomendation that npsh (r)=1.5m.
so when i install the pump from where i must measure at suction line to provide this no. ????
please clarify me this .if there is article clarify this point i will be appressiate.
best regrds





RE: npsh(r)??
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Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: npsh(r)??
Most pump manufacturers test with water, so I assume the 1.5m of NPSHr is water based.
You may want to confirm.
Have you done a search of Eng-Tips fora? This topic has been discussed in many threads already.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: npsh(r)??
In any case NPSH available should exceed NPSH required by an adequate margin to avoid erosive cavitation. A margin that varies as function of rotating speed, cavitation-resistant metallurgy, fluid corrosivity, operating conditions, dissolved gases, and thermo-physical properties of the fluid.
Sulzer Brothers Ltd say:
RE: npsh(r)??
Sulzer is correct. The effect of cavitation between water and HC is different. For whatever reason (my chemistry is not so good), I have been told that HC cavitation effect is less troublesome than that of water.
I think it has either something to do with HC bubbles forming or collapsing that is the difference.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: npsh(r)??
You state: "1.5 m NPSHr probably means you need 1.5 m of water column of pressure at your suction to the impeller." I believe the unit of head height is that of the flowing fluid being handled - not that of water (unless, of course, the flowing fluid is water). I don't think the fluid has been identified as water - yet.
RE: npsh(r)??
RE: npsh(r)??
Yes, you are correct. I am assuming.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: npsh(r)??
bingopin,
I've heard the same thing and it makes sense. Any crude is a complex mix of stuff with a wide range of boiling points and when the light ends flash, the latent heat of vaporization lowers the temperature slighly and it can be a while (miliseconds sometimes) before the next constiuent flashes. The impact tends to be less.
David
RE: npsh(r)??
Cavitation damage is the result of high-velocity liquid jets impinging on solid surfaces as a result of bubbles' implosion.
Since impact forces are proportional to velocity, density and flow rate, I assume hydrocarbons (pure or mixed) would probably be less devastating than water also because of the following:
a. a smaller bubble volume for equal pressure reductions (at saturation) resulting in decreased jet flow rates
b. lower densities
c. probably attenuated velocities due to higher viscosities
Any comment ?
RE: npsh(r)??
I think this is probably a large part of the reason. For the non-chemical engineers amongst us - the reason for the small bubbles is that hydrocarbons have higher molecular weights than water (in general) and this results in higher vapor densities. On the other hand, hydrocarbons have lower latent heats of vaporisation which would result in more vapor being generated i.e. resulting in bigger bubbles.
I believe David has highlighted the major reason for hydrocarbons being less prone to cavitation i.e. because the liquid contains more than one component the collapse of the bubble does not occur all at once at a single temperature or pressure - it will contract relatively slowly over a range of tremperature or pressure.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: npsh(r)??
For what it's worth, the speed of sound waves in liquid hydrocarbons drops with increasing temperatures. In water it increases. Wonder whether this also applies to shock waves.
RE: npsh(r)??
http://www.engineeringpage.com
choose pumps > pump condition
Wim
RE: npsh(r)??
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
www.waterhammer.bigblog.com.au