VENTURI on a Nitrogen line 1

[mylexicon]

Gents,

Would you recommend using a Venturi type flow meter on a piping system carrying Gas? If so, what are the advantages and disadvantages? What if we are dealing with extremely high flow velocities in the pipe? Say 300 m/s. let's assume the venturi flanges to be 8". Would you still recommend installing a Venturi type flow meter on this line?

Thanks a mill,

drno

 

[zdas04]

Venturi meters are pretty expensive and not very flexible. On the other hand Square Edged Orifice Measurement is amazingly flexible (you can change the plate on a dual-chamber fitting in a couple of minutes without interupting flow), accepted by anyone you're likely to do business with (or be regulated by), and are much less expensive than Venturi meters.

Having said that, venturi meters work. The only real limitation is that for your "extremely high flow velocities in the pipe" situation you have to be very careful that the velocity in the throat of the venturi does not approach "a significant fraction of the speed of sound" (one of the explicit assumptions in Bernoulli's original derivation). The number where Bernoulli's law starts flaking out is somewhere between Mach 0.3 and 0.6. Above 0.6 density increases rapidly with increasing velocity. At 0.3 you can see an increase in density, but it is probably still within the accuracy of the rest of the calculations.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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