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Centrifugal pump test

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petertha:
I mentioned previously that the outside of pump body was rough looking cosmetically. That's because I orientated the print to favor a smoother inside flow surface - where it counts. Therefore the exterior surface shows stringy artifacts of slicer tree support. The filament is PLA using 0.4mm nozzle on Bambu A1.

MJM460:
Congratulations on getting your pump working. Always a satisfying achievement.

I tend to agree with you that the shiny coupling is possibly confusing the tacho by providing extra reflections that make a definitive count more difficult.  I would suggest some black tape right around the coupling first, then put your reflector spot on top of the black tape.

It’s not easy to infer the power drawn by a pump in a circulating system from a single operating point test in an open system.

First, the power estimated by measurement of the input electrical power includes the efficiency of the motor as well as the efficiency of the pump.  It is difficult to separate these two.

Second, the pump drive power required is proportional to the head times volume divided by efficiency.  The efficiency ranges from zero at zero flow to a maximum then back to zero at the maximum flow with an open discharge.  Of course, there is power absorbed by friction in seals and bearings, and some hydraulic issues.  This is additional to the hydraulic power requirement.

  The maximum efficiency is usually at a flow a bit over 50% of the maximum.  Your little pump efficiency is probably less than 50% but even so, that provides a large range for error when you know neither head nor flow in your engine cooling circuit.

With a few more tests to determine the range of input power at a suitable range of speed, you could at least estimate a likely maximum.  I don’t really know the motor efficiency, but  someone else may be able to suggest an appropriate number to use.

MJM460

Charles Lamont:
In my pump tests I never tried to measure the power requirement. The maximum power output I calculated was about 23mW, at 25cm head and 9.5ml/sec flow rate. That was with a 1/2" diameter impeller at 4000rpm.

The impeller diameter is one of the prime dimensions of a centrifugal pump, and with a cursory check back through the thread I don't think we know how big yours is, if that is not an impertinent question.

Scaling up linear dimensions increases the power output as the 4th power (unless I am having an off day). Power output is also proportional to the cube of the speed.

Using a really rather inadequate motor, I was very conscious that the mechanical friction was very variable, and absorbed much more power than actual pumping did. 

petertha:
Charles, here are some dimensions of my pump. It wasn't sized to any particular task, more or less TLAR to get started & something that would reasonably print. My CAD file is somewhat parametric, so if I start with a different rotor diameter & volute rise (=throat height, is that the right word? maximum dimension above rotor at throat) then much of the body self-updates. Not quite that simple but that was the general idea.

Rotor diameter = 27mm. Inlet pipe ID = 6mm. Inlet eye diameter = 7.8mm (what the inlet pipe trumpets outward to and the open circle at center of vanes). Throat height = 4mm. Throat width = 6mm = width of vanes which are constant width in this version. Throat rectangular sectional area = 24mm2. Vane to opposing pump face clearance ~ 0.2mm. Radial gap at cutwater ~1mm. Outlet pipe ID = 6mm.

Sheesh I should just make you a dimensioned drawing but hopefully this helps. I'm sure I've misinterpreted some design parameters along the way. I think the only meaningful way I can attempt to correlate to your pump curves is to measure flow

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