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Fitting a curve to pump data
- Thread starter skuntz
- Start date
For some very flat curved pumps it helps if you use Snorgy's above equation with an offset from flow. Substitute (Q-q) for Q. Occasionally a c4*(Q-q)^4 will also help. Try Snorgy's first. If its close enough, stay with it.
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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)
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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)
BTW, your pump is centrifugal, right?
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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)
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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)
If what you're asking for is some software to determine the coefficients of the equation, here's one that I find handy:
I was assuming that you wanted to be able to plot a curve from tabulated data, in which case excel or any equivalent is likely your simplest solution.
I was assuming that you wanted to be able to plot a curve from tabulated data, in which case excel or any equivalent is likely your simplest solution.
BigInch's approach will probably get around the issue of "droop" vs "continuous rise to shut-off" that I have often seen in pumps with flat characteristics. I don't know if that is the primary intent though. I have also had a bit of success adding a fourth term c4*[e^Q] to flatten out the curve left of BEP a bit more.
The advantage to using an equation is that it makes (in my mind) the Excel logic easier towards manipulating curves using affinity laws and determining intersections with system head curves.
Surprisingly, the best curve fitting program I have ever used is an old DOS Shareware program called XYMATH, although I use CurveExpert32 now and that seems OK for most of my needs. I haven't played with Excel's built-in curve fitting much, but based on what I've seen to date, I prefer the two mentioned above. Both are "free" off the internet.
Regards,
SNORGY.
The advantage to using an equation is that it makes (in my mind) the Excel logic easier towards manipulating curves using affinity laws and determining intersections with system head curves.
Surprisingly, the best curve fitting program I have ever used is an old DOS Shareware program called XYMATH, although I use CurveExpert32 now and that seems OK for most of my needs. I haven't played with Excel's built-in curve fitting much, but based on what I've seen to date, I prefer the two mentioned above. Both are "free" off the internet.
Regards,
SNORGY.
Yes both the q and ^4 term gives you more control over defining or eliminating a rising head characteristic for pumps with flat curves at low flowrates, which you may find difficult to manage when using only a Q^3 term.
**********************
"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)
**********************
"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)
- Thread starter
- #9
Thank you all for the information, it has been valuable. I see that excel indeed will fit data, but I'm still looking for a standalone.
BigInch: Yes it is centrifugal. The problem I have had with second order is that it typically does not go flat at the shut-off head as the curve should.
BigInch: Yes it is centrifugal. The problem I have had with second order is that it typically does not go flat at the shut-off head as the curve should.
Yup. 2nd order slopes often vary too much to be useful over short ranges. Exactly why the ^4 and q is needed.
How bad do you need a stand-alone$
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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)
How bad do you need a stand-alone$
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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)
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