Factors in Boost Venturi Calibration Boost Venturi probes can be used with either
liquids or gasses.
With liquids the gain ration is
more constant as it depends only
on Reynolds
Numbers (Nr = VpD/u = velocity x density x
diameter
/ viscosity). With gases, it depends on
both Reynolds Number and
Mach Number (NM =
V/a = velocity / speed of sound).
The effect
of friction causes the gain to become
smaller as the Reynolds Number becomes
smaller,
similar to the drop in flow coefficient of nozzles at
Reynolds Numbers. |
The effects of compressibility cause the gain to
become smaller as the Mach
Number becomes
larger. This can be seen by noting that with
increasing velocity and M1 approaching the probe,
PT1-PS1 would increase,
but PT2-PS2 at the throat
would approach a limit as choking was approached.
With
probes designed for high gain, i.e. a large
increase
in velocity at the throat, greater
compressibility effects are observed at
lower
approach velocities than with probes designed for
less gain.
Typical variations are shown in Fig. 1. |
