pump curves for different temperatures

[Cheetos]

Hi, i'm fairly new at the pump curve stuff. I just started looking at a PD pump curve for my working fluid at 60C. If my fluid goes down to 40C, will the curve stay the same or shift toward left? PD pump should have a predictable flow rate at given pressure/speed, so even though colder fluid has higher density, the curve should stay the same?

 

[MJCronin]

Post your question in the "Pump Engineering" forum ....

MJCronin
Sr. Process Engineer

 

[Latexman]

Yes, to the left. But how much? What’s the fluid? Does the viscosity change a lot for the 60^oC to 40^oC change?

Good Luck,
Latexman

 

[LittleInch]

Can you post the curve?

PD pumps are essentially constant volume devices.

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

 

[Cheetos]

@MJCronin: Sorry about that. Thanks for point that out.

The fluid is R134a. The density at 65C/40C is 1025.3 / 1146.1 kg/m3

I wasn't sure if there's a simple correlation (like the fan laws) that I can do to shift the pump curve or do I need to retest this at 40C?

 

[Cheetos]

Here is the attachment of the pump curve.

Link

 

[Latexman]

You sure about that? More flow = less pressure drop!



Good Luck,
Latexman

 

[LittleInch]

It's not pressure drop it's pump differential pressure and this is a typical PD curve with a "lean" to the left.

The density hasn't got much to do with it, but viscosity changes can impact the extent of the "lean".

But each pump type is different as to how much change there is. I wouldn't anticipate more than 5% myself.

The actual pressure the system sees will be dependent on the system curve which could be significant, but the flow rate will be somewhere around 4 gpm if you maintain the same pump speed.

At a lower temp / higher viscosity, the normal expectation is that the line at higher pressures will move a little to the right, but the lower end will stay much the same (i.e. it will pivot about the low pressure end. Basically there is less "slip" of the fluid.

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

 

[Latexman]

Discharge pressure - suction pressure? I don't think so. The discharge pressure = the backpressure. Suction pressure is usually pretty constant, because low suction pressure drop is desireable. I would expect the mirror image about the midpoint of the curve shown.

The more flow, the more backpressure, the more discharge pressure. If suction pressure is more constant (typically), yep, the mirror image. Attached graph is wrong even for pump differential pressure.

Now, available pressure from some maximum, I'd believe that, but have never seen it plotted.

Good Luck,
Latexman

 

[LittleInch]

Well it matches just about all the curves I found when I searched "PD pump curves" and has the right feel about it.

The discharge pressure does equal back pressure, but if the suction pressure increased then the differential goes down and the power input to the pump at the same speed also goes down.

This is the pump curve we're looking at not the system curve.

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

 

[Latexman]

You are right, I've been describing the system curve. Sorry about that.

Good Luck,
Latexman