Does brake horsepower include volumetric efficiency? 2

[micalbrch]

Hello Everybody,

If I had to answer my question, I would say YES but I haven't found any standard where this is explicitly described. I checked Hydraulic Institute and also API 675 but couldn't find an answer. I remember that there is one power definition which does not include the volumetric efficiency of a pump (means the power calculation bases upon 100 % filling) but I cannot recall which one it is. Can anybody help and name the corresponding reference? Thank you in advance!

Michael

 

[EmmanuelTop]

You are correct - see J. Evans' article:

http://www.pumped101.com/recip.pdf

Dejan IVANOVIC
Process Engineer, MSChE

 

[micalbrch]

Thanks Dejan, but can you confirm what I read out of this article? Under section "power" it is said that the brake horsepower is only calculated with the mechanical efficiency but not with the volumetric efficiency. So, brake horsepower multiplied with the volumetric efficiency leads to the shaft horsepower? Or in other words: The brake horsepower is always calculated with 100 % filling efficiency?

 

[EmmanuelTop]

The actual GPM (which appears in the BHP equation) is a function of volumetric efficiency - see the section "Capacity".

Dejan IVANOVIC
Process Engineer, MSChE

 

[zdas04]

Pump power is a function of how much stuff you are lifting (mass flow rate) and how far you are lifting it (head increase).

Pump efficiency is a comparison of how much power you would need to lift a perfect fluid a given distance with no mechanical losses vs. actual power used for the actual fluid and the same distance. So if there were no mechanical losses, the only remaining factor is deviation from a perfect fluid (i.e., volumetric efficiency). Like Dejan says, volumeteric efficiency is included in the flow rate term.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[micalbrch]

Thanks for the fundamentals, David! But am I wrong with my memories that there is one "pump power" term which - per definition - does not count the volumetric efficiency? I could swear there is one but I do not remember its name. Or is there any API standard where all the terms are defined? What about terms like "design flow rate", "design pressure" etc.? API 674 for example says that these terms are not covered by the standard but should be defined between manufacturer and purchaser. From my understanding "design flow rate" bases upon 100 % filling efficiency. So, is the term I'm looking for perhaps "design power"?
It is not of any actual importance for me but it is thing that is on my mind for weeks now, like an actor you have seen in a movie but do not recall her/his name for days.

 

[EmmanuelTop]

The term for what you are describing is "Shaft Output Power", i.e. the (Input Power) X (Mech.Eff.), although it is commonly used for electrical motors. See

http://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html

This is the net amount of energy supplied to the fluid, including useful energy plus hydraulic/fluid losses.

Equivalent term would be Hydraulic Input Power. Karassik uses the term "BHP with zero slip" (see attached page from the pump handbook).

Dejan IVANOVIC
Process Engineer, MSChE

 

[BigInch]

You may be getting mixed up with reciprocating compressors.

 

[DubMac]

Hydraulic Horsepower