Quiz Corner: Coriolis mass flowmeter orientation for vapor applications, part 3

Which of the following orientations can be used to install a Coriolis mass flowmeter to measure the mass flow of a condensable vapor in a vertical pipe flowing down?   

1. U-tube down
2. Inverted U-tube
3. Horizontal (parallel to grade)
4. Flag position

Coriolis mass flowmeters in vapor service must be completely full of gas to measure accurately. The U-tube down orientation (Answer A) could accumulate liquid and should not be used for vapor applications.

The inverted U-tube orientation (Answer B) and horizontal orientation (Answer C) could be acceptable but would entail modification of the upstream and downstream piping. The flag position (Answer D) would be the most practical answer. 

Additional complicating factors

Not all Coriolis mass flowmeters have U-tube geometry, and some of these geometries can allow liquid to accumulate in the flowmeter.

For example, a Coriolis mass flowmeter with delta-shaped tubes can accumulate liquid in the downstream (lower) portion of the tubes when mounted in a flag position (Answer D), so the upstream and downstream piping should be modified to mount the flowmeter with its delta-shaped tubes inverted (Answer B) or horizontal (Answer C). 

Similarly, a single-path self-filling and self-draining Coriolis mass flowmeter that forms a loop, jumps up (sideways if mounted in flag position) and then forms another loop must be installed in the horizontal plane (Answer C) to remove all liquid from the system because any other orientation can allow liquid to accumulate in the flowmeter. 

David W. Spitzer is a principal at Spitzer and Boyes, LLC, which offers engineering, focused market research, writing/editing white papers, strategic marketing consulting, distribution consulting, seminars and expert witness services for manufacturing and automation companies. Spitzer has written more than 400 technical articles and 10 books about flow measurement, instrumentation and process control. He can be reached at 845-623-1830 or via spitzerandboyes.com.