Talk:Affinity laws

message: in support of the comments raised below for a centrifugal pump (or fan) the velocity of the fluid exiting the impeller is proportional to Diameter, whereas the flow (assuming geometrically similar impellers) is proportional to the cube of diameter, as not only the flow velocity increases but the flow passage in the impeller has increased in proportion to the square of the diameter increase hence:
Q1/Q2 = N1/N2*D1^3/D2^3
 
meaning the wiki article is factually wrong in presenting:
Q1/Q2 = N1/N2*D1/D2
This is stated in any good text on the subject and needs corrected as anyone using the formula presented could make some really bad mistakes in selecting a pump size   — Preceding unsigned comment added by 90.255.214.32 (talk) 12:48, 11 June 2020 (UTC)
thread_title: Affinity Law

message: Hi There,
I Apologize in advance for the formatting and posting mistakes made here. I have no idea how this site works but I also picked up the issue regarding to the relationship between head, flow and power to diameter. I would like to offer my 2nd year fluid mechanics textbook Fluid Mechanics (J. Douglas, M.Gasiorek & J.Swaffield) as a reference to support what this relationship should be.
Q ∝ N*D^3               (equation 23.27)
gH ∝ N*D^2              (equation 23.28)
P ∝ ρ*N^3*D^5           (equation 23.29)
Where
Q = Flow
H = Height height
P = Power
g = Gravitational acceleration constant
ρ = Density
N = Speed
D = Machine wheel diameter
Would love to re-open this discussion because. Many people use the internet to quickly check engineering equations. These pump affinity laws are used too frequently and a mistakes could be very costly in real world applications.
Braam Daniels (talk) 07:44, 18 February 2018 (UTC)
thread_title: Affinity Law Reference

message: I suggest
# nondimensionalize the variables, e.g. replace rpm with speed N, replace cfm with volumetric flowrate V dot
# make sure that it is clear that the affinity laws assume the pump efficiencies remain constant and the system performance curve also remains constant. In addition, they don't apply as well to open-loop geodetic situations.
# add the rest of the affinity laws, such as changing the diameter of the pump blades
Any comments?   Chrike 16:21, 24 October 2007 (UTC)
thread_title: Comments

message: I am not sure that the affinity laws apply to all pump types. The literature confirms that they apply to all types of Centrifugal pumps, including radial, mixed flow and axial flow pumps. --GILDog (talk) 12:34, 21 June 2009 (UTC)
replies: text: { Q \over {N^2 D^3}} = constant        and      { h \over {N^2 D^2}} = constant   
However, I now realise that the version on the main page is more accurate for changing the impeller diameter without altering any other pump dimensions (e.g. the volute)--GILDog (talk) 11:41, 29 April 2010 (UTC)
thread_title: Application to pumps

message: Indication on Swedish side (Affinitetslagarna) that D is actually not 
the impeller/fan diameter, but more of a "size".  No refererence though.  — Preceding unsigned comment added by WikyHicky (talk • contribs) 14:27, 9 June 2011 (UTC)
thread_title:  D not diamater 

message: There seem to be two camps: Some say Power is proportional to the cube of the diameter and some say it's proportional to the fifth power of the diameter. In the history of this article, this has been changed several times. When googling for other sources, no improvement :( Is there any source for ()^3 vs ()^5? What are the assumptions? I consulted several books about fan design, but didn't find any affinity relations for the fan diameter. ()^3 seems plausible as Pressure*Flow is equal to Power, ()^5 might come from pressure drop in duct resistances? Kelaodisi (talk) 14:57, 17 January 2012 (UTC)
thread_title:  Proportionality of power and impeller diameter 

message: I have noticed that despite multiple contributors on the talk page and appropriate references and engineering analysis demonstrating the case that the Affinity laws have been again adjusted to the wrong values in relation to geometrically similar pump and scaling with pump diameter. Again this could lead to large errors the correct power laws are stated in the talk but the article is factually wrong 217.33.165.88 (talk) 13:37, 20 December 2023 (UTC)
thread_title:  Affinity Law update