Effect Of Altitude On Pump Performance

GA PW, can you spare an O₂ tank I can borrow while I do the tests? Sounds like a straight up HW question

Why 10 km? There is not such a place on Earth 10 km above sea level.

Testing almost impossible unless you create the same environment in a test chamber. But what for? Are you working in the aviation industry?

Sorry I am short of an answer, but this might be of interest for somebody else on the forum.

Dear Friend,

Your understanding is correct.

As for as the altitude is concerned, it plays a role for EFFECTIVE SUCTION HEAD, WHICH WILL REDUCE. This is to be taken care. Of course, ambient temp. will be less and viscosity will vary or increase, mobility will be affected, when compared to sea level.

DHAYANANDHAN.S

Thank you sir for the reply.

My apologies for asking such a question. But i want to understand the effect of atmosphere pressure alone for the following conditions,(Comparison of conditions between sea level and 10km altitude). And this for the aviation industry only.

1. Liquid temperature is same (vapor pressure, friction losses same) and Pump RPM is same

2. Volume flow rate through the pump is same (incident angle of flow on impeller blade is same (impact loss same))

3. Pump is immersed in liquid and assuming the Liquid column above pump is neglected or same

4. Gauge pressure at the pump discharge line is measured at same point.

5. the whole test setup (tank with pump and pressure gauge at discharge line) is in a controlled room and room absolute pressure is measured

6. In case 1: room absolute pressure is 101kPa and in case 2: room absolute pressure is 23kPa

for this condition, is my pump performance curve will vary if it is drawn between Volume flow rate Vs Gauge pressure?

Continuation of above replied message:

And also with the above mentioned conditions, the available pressure value is well above cavitation limits and boiling limits

From my understanding the curves will not change for above mentioned two cases sing the gauge pressure is with respect to room ambient condition and the same is acting on the pump suction side.

Kindly correct me.

There cannot be a room at 10km above sea level as there is no land at that altitude to build it on, as explained above; the concept is folly.

The pump needs to "see" a positive suction head, otherwise the fluid will cavitate and boil, and the impeller will be short-lived. Without full fluid details, lacking more often than not in Mechanical Engineering threads on CR4, the question is unanswerable.

"In case 1: room absolute pressure is 101kPa and in case 2: room absolute pressure is 23kPa"Yes pump performance in these two cases will be different and can be given by any pump manufacturer because NPSH will be different.

Is this pump trying to transfer a media from an area in one pressure zone (inlet) to another pressure zone (outlet). Or is the pump working within one pressure zone.

The magic word... "Aviation"

You must be a student or a Boeing Engineer working on a 787 problem.

I suggest you contact a specialist pump company that makes those tiny aviation fuel pumps, and get their pump curves.

The boiling point of the fluid being pumped needs to be considered also. For a pressure of 265mBara, the boiling temperature of water is around 66degC (source: Mayhew & Rogers, "Thermodynamic and Transport Properties of Fluids", Oxford Basil Blackwell, 1976).

You need to study Net Positive Suction Head. One of its components is atmospheric pressure; if the atmospheric pressure reduces (as from altitude), so does the NPSH_A.

I'm coming at this from a firefighting stance, not an industrial stance. Terms like NPSH are therefore "foreign." I qualitatively think of it like this. It's much easier to say the pump sucks the liquid from the source, but that is not what actually happens. The pump (or priming pump) create a vacuum, and the atmospheric pressure on the liquid pushes the liquid into the pump. So, at a higher elevation there is less atmospheric pressure to push the liquid into the pump, so the flow rate will be less because of the reduced inlet pressure. Clear as mud??

Do the pump manufacturers provide graphs or charts for derating pump performance according to altitude?.

I would hope so, but I don't know so.

No, because the GPM doesn't change on account of altitude, unless NPSH_A becomes insufficient and cavitation occurs.

Unfortunately, there are by now many incorrect responses, irrelevant questions, and unsuitable votes in this thread.

got to agree, it's a ridiculous question, badly worded and open to all sort of interpretation, and with most of the much needed info missing in the first post.

These Dreamliner engineers must learn to write proper like what I does!

The pump does not need to be derated. It is the pipework that needs consideration, as altitude affects the net positive suction head that the pump "sees".

There still isn't any land at +10km on which to mount the pump, though if there were a brick wall at that altitude, one might be tempted to bang one's head against it (or someone else's).

Like inlet pressure will the pressure at discharge point too decrease?.

I am curious as how the lower gravity at that altitude would affect the operation of the pump?

Stay curious.

first.. I think this is homework! As no-one in their right mind would ask such an impractical question, as previously stated.... there is no land mass at 10Km high.

As you are asking the question, you must look at "pump delta P", which... if you are asking question about C/F pumps, you know all about. Intake pressure plus 'pump delta P' will affect the discharge pressure.

You must also consider that the majority of C/F pumps are usually submerged in a fluid, hence the pump curve at 'sea level', and while you are correct about the rpm, you don't mention if you are asking about a single stage or multi-stage pump or mention the required rpm/Hz.

One other thing.. Have you ever seen a pump test bench?

I would say, many people are having similar doubt of mine.

See the below discussion.

http://www.eng-tips.com/viewthread.cfm?qid=253163

i would like to ask you people again the same question, is my point correct?

It says "power requirements are increased at high altitudes",if flow and (P1-p2) are same and density/viscosity changes,how will it vary?.

I understood now that the performance curve of Q Vs P (gauge pressure) will not vary for a particular pump with constant Speed, Fuel temperature, Impeller diameter and with varying pressure at suction side(Altitude) provided the NPSHa is well above the NPSHr. The below equation shows that,

.

μ- No. of blade coefficient,

u - Impeller tangential velocity

V2u- tangential component of flow along the blade

And the reason for the manufacturer to mention tested altitude (SL) is to tell the parameter which decides the maximum flow through pump without having cavitation.

And as altitude increases, the maximum flow limit will come down as NPSHa decreases.

One point i would like to mention here, To understand the real physics of the practical problem we need to understand the text book problems first. Please don't mention that as a reason for not explaining the physics.

This is a prime example why we should not entertain home work questions in this forum. I do hope you got a passing score on your home work assignment? Or at least your Professor/Instructor has enough sense to see where your answers came from!! Being involved in Aviation, there is reasons why they're Hydraulics are pressurized Oh yeah, there are several women on this forum that pretty sharp too.

Thank you for the reply. But i do know that, the hydraulics reservoir are pressurized in aviation to avoid

1. Evaporation of fluid and Boiling of fluid at high altitude
2. Avoid the air evolution from oil because of ambient pressure reduction above oil surface which increases the altitude limit of aircraft
   
3. To give positive NPSHa at pump inlet to avoid cavitation

But my assumption in the question is, no oil boiling and air evolution and so no change in oil density (which is a theoretical assumption to understand the effect of inlet pressure alone on the pump performance) and no cavitation in pump

Thank you.

"theoretical assumption" should be your first clue. Theories are like opinions and a** holes, everyone has one. Either take your pump up to altitude or setup a test bench and test your " theory". If you are in school, you should seek your own answer. If your an Engineer....We may all be in trouble!

#3 is the correct answer as to why hyd. reservoirs are pressurized

wait a minute..... you now say you are working on a hydraulic system, Yes?

someone correct me if I'm wrong.. but I've never seen C/F pump on a hydraulic system, the ones I've seen are positive displacement...

This thread is a total waste of our time, as the others on airplane fuel systems this person has posted.

OP/AP, go read a book.

Totally agree!