Fan and Pump Curves vs. Affinity Laws
Fan and Pump Curves vs. Affinity Laws
(OP)
I have always wondered why fan curves don't appear to be consistent with the affinity laws that we are taught. For example. We are taught that:
P2/P1 = (RPM2/RPM1)^2 = (CFM2/CFM1)^2
This would mean that fan curves should be perfect quadratic squares and all look like parabolas. However, we know this is not the case. They are often very flat at low CFM or even have a dip.
For example: http://www.fumetech.com.au/images/300perfcurve.gif
or
http://www.viconequip.com/Content/Governair%20Mult...
or
http://www.greenheck.com/images/articles/rpm_curve...
Does this mean the affinity laws are not correct or are an approximation? What is the explanation for the discrepancy between the curves and the laws? Do the laws not apply under certain conditions? Does this have to do with laminar/turbulent flow?
Thanks!
P2/P1 = (RPM2/RPM1)^2 = (CFM2/CFM1)^2
This would mean that fan curves should be perfect quadratic squares and all look like parabolas. However, we know this is not the case. They are often very flat at low CFM or even have a dip.
For example: http://www.fumetech.com.au/images/300perfcurve.gif
or
http://www.viconequip.com/Content/Governair%20Mult...
or
http://www.greenheck.com/images/articles/rpm_curve...
Does this mean the affinity laws are not correct or are an approximation? What is the explanation for the discrepancy between the curves and the laws? Do the laws not apply under certain conditions? Does this have to do with laminar/turbulent flow?
Thanks!





RE: Fan and Pump Curves vs. Affinity Laws
RE: Fan and Pump Curves vs. Affinity Laws
RE: Fan and Pump Curves vs. Affinity Laws
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Fan and Pump Curves vs. Affinity Laws
RE: Fan and Pump Curves vs. Affinity Laws
RE: Fan and Pump Curves vs. Affinity Laws
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Fan and Pump Curves vs. Affinity Laws
RE: Fan and Pump Curves vs. Affinity Laws
The page has some good images on it you may find helpful. There are many other great webpages and books available as well though. That was just my first hit.
http://www.greenheck.com/library/articles/10
RE: Fan and Pump Curves vs. Affinity Laws
RE: Fan and Pump Curves vs. Affinity Laws