I'm missing something...

[Craig Dotson]

> You are close, but doesn't the "flow as volume/time" definition assume
> something less compressible than air, like a liquid?  With a liquid, your
> argument holds :a glass of water at sea level has roughly the same volume
as
> a glass of water on a mountain.  So if you were drawing water through the
> air flow meter, the density wouldn't change much and the measurement would
> be pretty much the same at sea level as on a mountain.  But if you replace
> the uncompressible water with a compressible gas, doesn't something have
to
> change?  (remember that "gas law thing" from high school physics).
Drawing
> a gas at low pressure through that spring loaded door will have a
different
> effect than drawing that same gas through the same spring loaded door,
under
> a higher pressure...I think.

It depends on the velocity (Mach number) of the air flow.  In the
Turbomachinery class I'm currently taking, the professor insists that if the
Mach number (velocity of fluid divided by the speed of sound in that fluid)
is 0.3 or less that the incompressible assumption is good.

Typically air flow in internal combustion engines nears choke (Mach 1) at
the intake valve, that is if it ever does choke.  One would have to analyze
the velocity of the air in the sensor to determine if the incompressible
assumption is good or not.

Craig Dotson
crdotson at vt.edu
2002 VT FormulaSAE
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org