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Since87 · 11-13-2002, 10:55 PM

Ok, I hope you guys will bear with me. I'm a mere EE. In my work, motion is something to be avoided. It is much more often an annoying aspect of the product's environment, than a desired goal.

I guess the main thing that was throwing me, was that in the case of a heavily loaded or stalled electric motor, the power consumption is high compared to an unloaded motor. My initial assumption was that restricting a centrifigual pump's output would have an effect on the impeller equivalent to loading the shaft of an electrical motor. That's obviously wrong as indicated by my test results.

myv65 a lot of what you wrote is over my head, but thinking about what you wrote, I've developed the following mental model/paraphrase.

I'm picturing the power delivered by the impeller being used to do two distinct things.

1. The impeller is maintaining the rotation of a cylinder of water the shape of the impeller chamber. Sort of a flywheel, albeit one with fairly lousy bearings, so it takes a fair amount of power to maintain its rotation. (And that power is dissipated in the lousy bearings.) This "water flywheel" component is capable of storing potential energy and that stored energy is effectively the same as pressure.

2. The impeller is also tossing water out the pump outlet. Obviously kinetic energy.

At zero flow, all the energy imparted by the impeller is being used to overcome the "bearing friction" of this "water flywheel". This is the state of lowest power consumption once this flywheel is up to speed. It is also the state in which the impeller chamber is heated the most, because all of the power dissipation is occuring inside the impeller chamber, and most of the heat is staying there.

At max flow, none of the impeller power is going into maintaining the rotation of the water-flywheel. All of the power is going into tossing water out the outlet. However, even though no energy is being stored, the "bearing friction" associated with the "water flywheel" must still be overcome, because the bearing friction is a function of the the impeller and the impeller chamber chacteristics. The power required to toss water out the outlet is added to the power required to overcome the "bearing friction". This is the state of highest power consumption, but most of the heat is moving out of the impeller chamber with the water.

This is undoubtedly a gross oversimplification, but it explains the data as I understand it.

Are there major factors I'm missing here?

11-13-2002, 10:55 PM	#10
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	Ok, I hope you guys will bear with me. I'm a mere EE. In my work, motion is something to be avoided. It is much more often an annoying aspect of the product's environment, than a desired goal. I guess the main thing that was throwing me, was that in the case of a heavily loaded or stalled electric motor, the power consumption is high compared to an unloaded motor. My initial assumption was that restricting a centrifigual pump's output would have an effect on the impeller equivalent to loading the shaft of an electrical motor. That's obviously wrong as indicated by my test results. myv65 a lot of what you wrote is over my head, but thinking about what you wrote, I've developed the following mental model/paraphrase. I'm picturing the power delivered by the impeller being used to do two distinct things. 1. The impeller is maintaining the rotation of a cylinder of water the shape of the impeller chamber. Sort of a flywheel, albeit one with fairly lousy bearings, so it takes a fair amount of power to maintain its rotation. (And that power is dissipated in the lousy bearings.) This "water flywheel" component is capable of storing potential energy and that stored energy is effectively the same as pressure. 2. The impeller is also tossing water out the pump outlet. Obviously kinetic energy. At zero flow, all the energy imparted by the impeller is being used to overcome the "bearing friction" of this "water flywheel". This is the state of lowest power consumption once this flywheel is up to speed. It is also the state in which the impeller chamber is heated the most, because all of the power dissipation is occuring inside the impeller chamber, and most of the heat is staying there. At max flow, none of the impeller power is going into maintaining the rotation of the water-flywheel. All of the power is going into tossing water out the outlet. However, even though no energy is being stored, the "bearing friction" associated with the "water flywheel" must still be overcome, because the bearing friction is a function of the the impeller and the impeller chamber chacteristics. The power required to toss water out the outlet is added to the power required to overcome the "bearing friction". This is the state of highest power consumption, but most of the heat is moving out of the impeller chamber with the water. This is undoubtedly a gross oversimplification, but it explains the data as I understand it. Are there major factors I'm missing here?