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Ultrasonic Flowmeters (Part 2 of 4) by David W Spitzer and Walt Boyes
In Doppler ultrasonic flowmeters, ultrasonic energy is transmitted into the pipe. Some of this energy is reflected by particles, bubbles, and eddies in the flow stream. The frequency difference between the transmitted energy and its reflected ultrasonic signal is used to determine the flow in the pipe.
At no flow conditions, the frequencies of the transmitted energy and its reflected signal are the same. However, under flowing conditions, the frequency of the reflected signal will be different than that of the transmitted energy. This is due to the Doppler effect that relates how sound is perceived when reflected from objects in motion. For example, the horn of a moving car has a higher pitch moving towards a listener than it does moving away from the listener. The frequency difference between the transmitted energy and the reflected ultrasonic signal increases linearly as flow increases. The transmitter processes signals representing the transmitted energy and its reflections to determine the flow rate where the fluid velocity is proportional to the difference in their frequencies.
Excepted from The Consumer Guide to Ultrasonic and Correlation Flowmeters.
Calculating Billing Costs for Sewage Districts by David W Spitzer
Previous columns described the sewage collection systems for two adjacent sewage districts where sewage from the first sewage district and the combined sewage (sewage plus drainage water) from the second sewage district are treated in a sewage treatment plant owned and operated by the second sewage district.
If the billing rate is $3 per 1,000 gallons and the surcharge is $10 for flow in excess of 500,000 gallons during a given day, the cost associated with a dry weather flow of (say) 300,000 gallons on a given day would be $900 (3 x 300).
However, wet weather events, such as rain and snow melts, can significantly increase the amount of liquid that needs to be treated by the water treatment plant. For example, the cost associated with a daily flow of 700,000 gallons on a given day would be $2100 (3 x 700) plus a surcharge of $2000 (10 x 200) or $4100, which is more than four times the amount billed on a typical dry day.
This would not be an issue in desert locations such as Las Vegas where few wet weather events occur. However, this did present a significant issue in the northeastern U.S. where these flowmeters were located.
Read more next month about how the first sewage district discovered a high sewage flow.
This article originally appeared in P. I. Process Instrumentation magazine.
Coriolis Mass Flowmeter Orientation for Gas Applications (Part 1 of 3) by David W Spitzer
Which of the following orientations can be used to install a Coriolis mass flowmeter to measure the mass flow of a gas in a horizontal pipe?
A. U-tube down
B. Inverted U-tube
C. U-tube horizontal (parallel to grade)
Coriolis mass flowmeters in gas 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 gas applications.
Few Coriolis mass flowmeters are mounted in the horizontal plane (Answer C), so mounting the flowmeter with an inverted U-tube orientation (Answer A) that hydraulically removes liquid from the flowmeter would be practical.
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 single path self-filling and self-draining Coriolis mass flowmeter that forms a loop, jumps up 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.
This article originally appeared in P. I. Process Instrumentation magazine.
ABOUT SPITZER AND BOYES, LLC
In addition to over 40 years of experience as an instrument user, consultant and expert witness, David W Spitzer has written over 10 books and 500 articles about flow measurement, level measurement, instrumentation and process control. David teaches his flow measurement seminars in both English and Portuguese.
Spitzer and Boyes, LLC provides engineering, technical writing, training seminars, strategic marketing consulting and expert witness services worldwide.
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