Effects of altitude changes on venturi flow meters


Thread Starter

Scott Owen

Does anybody know any references on the effects of altitude changes on venturi flow meters when measuring air flow at ambient conditions?
How about converting to standardized flow?

Thanks in advance

James Fountas

Assuming you are using the equation for compressible fluids in a venturi meter the pressure changes are taken into account so long as the expansion factor is corrected for the actual two pressures.

Unit Operations of Chemical Engineering has the equations. I assume Perry's Chemical Engineering Handbook would also have the equations.
The basic law for venturi flow meters is Bernoulli's. A rigorous analysis includes the altitude term. Practically speaking, if you follow ASME MFC-3M- 1985 you should be able make the required compensations. On our website
(http://inflowinc.com) is a technical paper which may give you some additional insite.

John Catch
[email protected]
From practical experience, if you desire to know your true flow you will need to monitor airstream temperature as well as absolute pressure, in conjunction with the process signal that you will measure from your venturi. Knowing your process pressure, in either psiA or "Hg, will allow you to "standardize" your flow conditions.

Check "Flow Measurement Methods and Applications", JE Hardy, et al, Wiley &
Sons (Scientific) , 1999; section 6.3.1, Venturi Meters.

This section describes all parameters which need to be monitored to be able to properly use a venturi meter. There are about a dozen variables, or so, but there is no reference to altitude effects. I doubt that altitude is a concern, unless you are discharging from your venturi DIRECTLY into the atmosphere - but this is very unlikely.

Feel free to contact me for more information.

thank you,
thomas main
[email protected]
650-462-7290, ext 105