<VV> Custom Fans (Perfect Example)

[RoboMan91324 at aol.com]

The statement of a certain contributor is exactly wrong but it  is stated 
in a way to give the impression that the person making the statement  has 
authority and knowledge on the subject.  Someone  without their own knowledge 
on the subject or the willingness to fact-check  might trust this 
mis-information.
 
Ignoring such factors as turbulence, vena contracta, changes  in density, 
friction, etc. flow through an orifice goes up by the SQUARE  ROOT of the 
delta pressure, not the SQUARE of the pressure.  Big, HUGE  difference.
 
If it were by the square of the pressure, doubling the  pressure gives 4 
times the flow, 10 times the pressure gives 100 times the flow,  etc.  There 
are better sources but I don't want to waste time .... doing a  quick search 
on the internet you have _http://engineersedge.com/pipe_flow_capacity.htm_ 
(http://engineersedge.com/pipe_flow_capacity.htm)  which  shows a 1 Inch pipe 
with 13 CFM of flow at 5 PSI.  According to the WRONG  formula 10 PSI would 
get 169 CFM and 20 PSI would get 28,561 CFM.   That's a comma between the 8 
and the 5 folks, not a decimal point.  Wow, I  do believe our humble fans 
could make flying machines of our Corvairs with  the pressure they would 
generate with the wrong formula.  As you can see,  the figures in the chart show 
21 and 35 CFM for those stated pressure  increases.  These approximate 
square root increases when real world factors  are included.
 
If you look at the air flow curve at 
_http://www.genpore.com/pdf/air_flow.pdf_ (http://www.genpore.com/pdf/air_flow.pdf)  (Again, not the  best example 
but good enough.) you will see the chart breaks to the right as  pressure 
increases.  Imagine the curve continuing its trajectory as  pressure 
increases more and more.  Eventually, air flow INCREASES (not just  air flow) 
diminish to nothing with incremental increases in pressure.  Flow  reaches a 
steady state no matter what the pressure increases are.  As I  said in my 
previous post, increases in delta pressure eventually result in no  flow increases 
and if you include the factors I said I ignored at the  beginning of this 
post, you could very well see decreases in flow.  If flow  increase by the 
square of pressure increases, the curve would curve upward  instead of over to 
the right and we would soon approach infinite flow with minor  incremental 
increases in pressure.  Hmmmm, someone wants to reinvent the  laws of Physics.
 
Well, I guess some alleged facts can be disputed  when someone has the REAL 
facts.
 
Doc
 
1960 Corvette, 1961 Rampside, 1962 Rampside, 1964 Spyder  coupe, 1965 
Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS, 1968  Camaro ragtop

~~~~~~~~~~~~~~~~~~~
 
In a message dated 5/23/2012 4:05:20 P.M. Pacific Daylight  Time, 
jvhroberts at aol.com writes:

No knee jerk here. Flow through an orifice goes up with the  square of the 
pressure. So, yes, a big jump in air pressure gets you a jump in  air flow. 
It's that simple, and by the square of the pressure.  

Snarkyness aside, this is a fact and it's not in dispute.  



John  Roberts