PUMP NPSHA

[tomato5]

A PUMP HAS ITS NPSHA DEFINED. IT IS DECIDED TO USE THE SAME PUMP WITH A DIFFERENT LIQUID.

THE TWO FACTORS THAT WOULD AFFECT THE NPSHA WOULD BE THE NEW VAPOR PRESSURE AND THE NEW SP GR.

IS THERE A RULE OF THUMB TO EVALUATE THE NPSHA WITHOUT HAVING TO DO MORE DETAILED CALCULATIONS?

THANK YOU VERY MUCH

WOULD YOU ALSO KNOW HOW ONE CAN SEND A MESSAGE OR QUESTION DIRECTLY TO A MVP, THIS SITE SEEMS TO BE SO CLOSE-FISTED THAT I HAVE NOT BEEN ABLE TO FIND OUT


WOULD SOMEONE AUTHORITATIVE RESPOND BY THIS AFTERNOON?

 

[LittleInch]

FIRST, please don't write in CAPITALS - it is interpreted as shouting.

The pump has it's NPSHR defined. The NPSHA is calculated for the specific liquid and as well as vapour pressure, specific gravity it is also affected by the pressure losses in the incoming system which are affected by the viscosity of the fluid. So no, there is no really simple way to determine the NPSHA of a fluid which has changed from the one originally calculated.

There is no way I know of to directly contact an MVP outside of the forum and that's the way most MVPs like it as it avoids spam and lots of direct (free) advice being sought.

Is this a real question or theory / student work? If you give some numbers and details you might get a better answer....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

tomato5,

A person should be able to verify the process conditions and determine the NPSH in 2-3 hours.

 

[tomato5]

Yes, I understand!

This is a cryogenic in-pot centrifugal pump designed for ethylene service, but tested on propane

Ethylene VP 282 psia SG 0.44 Viscosity 0.074 cp Npsha 9.7 ft to inducer c'l Pumping temp -23 F Flow 2160 gpm Npshr 5.2 ft to same datum


Propane VP higher than that of ethylene Npsha less than 9.7 ft because of higher vapor pressure of propane Testing temp = - 47 C = - 53 F Flow 2160 gpm

Required: To calculate Npsha for propane to same datum. Point is to calculate this from the 9.7 ft for ethylene, with somewhat minimal calculations, rather than from scratch

thank you

 

[Artisi]

tomato5:
WOULD YOU ALSO KNOW HOW ONE CAN SEND A MESSAGE OR QUESTION DIRECTLY TO A MVP, THIS SITE SEEMS TO BE SO CLOSE-FISTED THAT I HAVE NOT BEEN ABLE TO FIND OUT

WOULD SOMEONE AUTHORITATIVE RESPOND BY THIS AFTERNOON?


Of course a polite request would never go amiss instead of demanding answers.



It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[TD2K]

I'm having a hard time following the information. For a given flow, the NPSHR from the pump curve is in feet of liquid and it's the same feet of liquid be it feet of of ethylene or feet of propane or feet of water.

So, assuming with ethylene you need 5.2 ft of NPSHR at 2160 gpm, you need 5.2 ft when pumping 2160 gpm of propane.

Since it's likely that the ethylene and propane are both saturated liquids, then the NPSHA is the vertical head of liquid from the centerline of the pump to the liquid level minus the suction piping line losses in feet of liquid.

 

[georgeverghese]

If you take a look at fig 10-25 in Perry 7th edn, it indicates that NPSHr for a given pump not only changes with the fluid being pumped, but also with its operating temp. It has curves for the reduction in NPSHr for many pure hydrocarbon liquids including C3, but not for C2=, so we should ask the pump vendor for new NPSHr curve for C3. Also it doesnt go down to these low temps you are looking at.

The graph shown in this figure is abstracted from the Hydraulics Institute standards, which may perhaps have more information.

 

[tomato5]

Gentlemen, thank you but the question was for Npsha, not Npshr, if you read above

Required: To calculate Npsha for propane to same datum. Point is to calculate this from the 9.7 ft for ethylene, with somewhat minimal calculations, rather than from scratch (in other words, consider the fairly large difference in vapor pressure of the two liquids, propane higher than ethylene)

And ARTISI and BIMR Please just stay at home, enough folks in the world quoting from Aesop's fables thank you

 

[LittleInch]

Ah yes, that well known way to get free help and assistance, insult two of the most knowlegable posters on this forum.....



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Aesop also said, "change not friends for foe's", something probably worth considering.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[tomato5]

littleinch and artisi sirs, we have a question here regarding npsha please do that, do not spend time in idle talk what, does that relieve some unwanted feelings in your sytem?

no more correspondence with you two!

 

[micalbrch]

tomato5: You know the formular to calculate NPSHA? If you look at it you will see where the SG and the vapor pressure are integrated. If one value changes, it will be easy to find out how that affects the result (NPSHA). If two values change, it will not be that much more difficult. It is pure mathematics. Look at the formular for NPSHA calculation. I think that answers your question.

Keep in mind that nobody here is paid for the help he/she provides. Everybody does that for free. You can ask for help but you have no claim to it. And your initial request to get a respond the same day and to tell you how to contact somebody directly without is/her approval was anything else than polite.

 

[bimr]

 

[Artisi]

Looks like it might increase to three in the sin-bin.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

tomato5,

I looked up your posting history and you've been around long enough and asked enough question to surely understand how this site works.

Your question might be about NPSHA, but people with experience are also noting that the NPSHR might also change.

Your question seems to ignore the initial pressure on top of the liquid and unless your piping system is short and easy to measure, the impact of different fluid viscosity on the friction drop.

your data is all over the place as presented here and I can't see what the difference is between your VP between liquids at whatever temperature you're working at.

Basic answer to your first question - Is there a rule of thumb - No

Last question you posed - Yes it does.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DubMac]

Mr/s Tomato, I think everyone would be better off if you put us all in your penalty box and take your questions to Google.

You might check into a stint in Charm School as well.

 

[Artisi]

Now that is being very mean

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[georgeverghese]

Think we've zeroed in on where D Trump gets his lessons in public speaking from.