Venturi flow meter diameter selection

[TheLucifer]

Hi all,
I have a problem about a small air ventilation pipe that will be installed on an A/C. the pipe inner diameter is 8,305 mm. Pressure difference between the two ends of the pipe varies from zero to 56 kPa. We are expecting air flow rates up to 11 lt/s from this pipe.

A flight test team intends to use a venturi flow meter for the first flight test of this equipment to measure real flow rate. they request us to define a minimum venturi diameter to avoid shock waves etc.

The problem is: I'm not experienced with internal flows, venturi tubes and so on. The flow is choking near the middle of this pressure difference range, and velocity exceed 200 m/s. Reynolds number is calculated around 240000. seems like the flow is highly turbulent.

So: I want to ask experienced piping engineers:
1- isn't this reynolds number too high? am I doing something wrong?

2- Is using venturi flowmeter reliable in turbulent flows?

3- And the final question: How can I find this "critical" diameter?

Thanx in advance,

 

[dcasto]

reynolds number in the millons is normal for gases. The higher the reynolds number the more stable and defined is the flow pattern and accuracy of the meter.