Four Quadrant Data and Moment of Inertia

[stanier]

I model waterhammer using AFT's Impulse. The new version 3.0 has a database of four quadrant data taken from various references that provides four quadrant data based upon the specific speed of the pump.

My question relates to when one adds a flywheel to a pump to mitigate the affects of pressure transients. If the MOI is changed does this affect the four quadrant data for a particular pump? The specific speed would remain the same as calculated as flywheel effects are not taken into account.

Would one have to test the pump and flywheel and determine 4Q data four that set?

Are there any technical publications for such relationships.

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[Kawartha]

stanier,

I have been involved with a few transient analysis studies using Windows based software. This program also has 4 quadrant data included in the software for a range of specific speeds. This program also allows entry of MOI (liquid filled pump and motor). Without entry of this information, I don't understand how a transient analysis can be performed. MOI is a major factor in the calculations.

You may want to call AFT to discuss how they planned to account for differences in MOI. When we were using our Transient Analysis Program (first windows based conversion from the DOS version), we were in contact with the program developers on regular basis.

Separate subject. Several months ago you (as I recall)posted that the NPSHr changes with different materials of construction. I had never heard this statement before, and was interested in further details. One of your explanations was based on the surface finish of different materials - the smoother the finish - the lower the NPSHr. Do you have any details regarding this theory? If surface finish is the governing factor - wouldn't polishing to equal surface finish negate the impact of different materials? Sorry if I add confusion to your current thread.

 

[stanier]

KAwartha,

AFT Impulse allows the definition of MOI for a drive. The 4Q data is also added based upon pump specific speed. This data is from tests carried out by researchers for a range of pumps in industry.

My question relates to the relationship of 4Q data to specific speed being affected by MOI. ie If the researchers had tested pumps with flywheels (raising the MOI) would they have got different 4Q data?

In respect of your question I dont recall making that statement. I do recall others commenting that the affinity laws do not hold true in all cases but as I recall I wasnt part of that discussion. Perhaps you can point me to the thread so I can refresh my memory.

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[Kawartha]

stanier,

Yes, you are right about the NPSHr comment. I remember that the comment was made by an other member of this site.

I'm sorry not to get back to you regarding the transient analysis problem. Just haven't had time to study your question in detail. The answer just doesn't pop up. My expectation would be that MOI should be considered in the program. I would guess that it is not included in the 4-Q data.

 

[eljauzy]

I would like to add abt the NPSHr effect on polish material. It is indeed true that well polish or buff finish inducer ( as being termed widely in this industries ) as an example would reduce the NPSHr further as compared to normal finishing. It is related to friction factor. The fluid need to reach the impeller eye and roughness will surely causes it to be restricted.