|David W. Spitzer|
What piping orientations are acceptable for the flowmeter to measure water that may contain non-condensable gas in volumes up to (say) one-half percent?
A. Flow up
B. Flow down
C. Flow horizontal
D. All of the above
If the gases were miscible in water to form a homogeneous liquid, any orientation within the limits of the flowmeter technology would be possible, so Answer D would be correct.
However the non-condensable gas and water are not miscible, so separation of the gas and water could occur in the horizontal piping upstream of the flowmeter. This can affect flowmeter performance because the fluid entering the flowmeter would not be homogeneous—the bottom would be water while the top would be non-condensable gas. Answer C is not necessarily correct.
Locating the flowmeter in a vertical pipe flowing upward mitigates the potential separation problem encountered in horizontal pipe. However, it does not ensure that the flow is homogeneous because the non-condensable gas and water may have already separated upstream causing more gas bubbles on one side of the vertical pipe. Answer A is not necessarily correct.
Locating the flowmeter in a vertical pipe flowing downward will generally result in a homogenous fluid entering the flowmeter because the bubbles are generally free to uniformly disperse in the water, so Answer B appears to be correct.
Additional Complicating Factors
Notwithstanding the above, the presence of non-condensable gas can and usually does affect the performance of most flowmeters. Such applications should be engineering carefully on an individual basis.
David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC offering engineering, seminars, strategic marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. He has more than 35 years of experience and has written over 10 books and 250 articles about flow measurement, instrumentation and process control.