1. Measuring Flow
ACADs (08-006) Covered
Keywords
Flow rate, total flow, differential pressure, percent flow, cotameter, Bernouli.
Description
Supporting Material

2. Measuring Flow
What are we really measuring? Volume? Mass? Instantaneous flow or how much flow has passed by in an second? Minute? Hour?
Flow rate is the instantaneous flow but is expressed in the time domain, as in gallons per second or pounds-mass per hour, assuming flow remains constant for that time period.
Total flow is how much flow HAS PASSED in the last second, minute, hour or other time period. It is an integration of flow over time.
The gas pump is a total flow device. Who cares how many gallons per second pass as long as you get the right amount of gas.
Difference between volumetric and mass flow rate:
Gallons are a unit of volume
Pounds are a unit of mass
Terminal Objective: Given the appropriate equipment and procedures the I&C Technician will calibrate and maintain flow instrumentation. Mastery will be demonstrated by successful completion of a Lab Performance Exercises and written Exam.

3. Differentiate between Flow Rate and Total Flow
Describe the relationship between differential pressure and flow
Given a percent range of DP sensed by an orifice plate, calculate the percent flow
Describe the theory of operation of a given flow measurement device
Describe the considerations for removing/restoring a rotameter from/to service
Read the objectives

4. Flow Rate vs. Total Flow
Flow Rate is the amount of fluid, either in mass or volume that passes a point in a given time. Examples: Pounds mass per hour, gallons per minute
We measure flow rate using ultrasonics, venturi, orifice plates, etc.
Total Flow is the flow rate multiplied by an amount of time. It is the accumulated or ‘totalized flow. Result will be in either mass or volume.
Gas pumps and water meters measure total flow

5. Daniel Bernouli
Discovered the square root relationship between DP and flow
Bernoulli's Principle states that as the speed of the fluid increases the pressure in the fluid decreases
Therefore, across a restriction in flow, as the fluid velocity increases, pressure decreases
9/venturi.html
Daniel Bernouli, , Dutch scientist

6. -or-
If we put the output of a differential pressure transmitter directly to an indicator, then vary flow it would look like this
For 0% flow we have zero dp
For 10% we only get 1% dp
For 50% flow we’re up to 25%dp
For 75% flow we have 56.25%dp
and for full flow we get full dp
Talk about square root extractors
Or simply marking the face plate
Show the high inherent amplification of square root extractors on their low end and talk about noise in the process
Differential pressure flow measurement stinks on the low end

7. Flow Instruments
The downside: measuring flow with differential pressure requires and obstruction in the pipe, typically an orifice plate.
The problem with obstructions in your pipe: They rob energy by creating a permanent pressure drop. Your process never gets back up to pressure after the orifice.
At 10¢/kWh and continuous operation, a 1.65 psi pressure drop in a 1000 gpm flow will cost $1000 per year in electrical costs
Also discuss turbulence caused by the obstruction

8. Example 1 Pressure drop range: 0-100 in H2O Flow: 0 to 100 GPM
Currently reading 25 in H2O
What is the flow?

9. Example 2 Pressure drop range: 0-100 in H2O Flow: 0 to 1000 GPM
Currently flow is 80 GPM
What is the differential pressure?
What devices may be used for the square root function?

10. Different orifice plates for different uses.
What do you want to pass? Is your process dirty? Sludge?
Which direction should an orifice plate face? Draw a cross section.

11. Manometer / U-tube flow indicator

12. Discovered two centuries ago by Italian scientist Giovanni
Giovannin Battista Venturi, 1746 to 1822
Discovered two centuries ago by Italian scientist Giovanni
Battista Venturi ( ).

13. Venturi tube reduces total head loss but still does not bring it to zero
Costs lots more than an orifice plate
Venturi Tube

14. Flow tube or Flow Nozzle

15. Elbow
Tap
Used in the circ water system

16. Henri de Pitot (1695-1771) Used in the condensate system
Tell story of the bent pitot tubes in the condensate lines
Henri de Pitot ( )

17. Annubar Good on air systems, HVAC
Generates low differential pressures, inches of water or fractions of an inch
Annubar

18. there is a constant differential pressure across the float
Rotameter
Rotameters and the various floats
When flow exists,
there is a constant differential pressure across the float

19. Replacing a Rotameter
Isolate the instrument
Drain
Verify correct replacement part
Install
Verify pressure tight
Un-isolate slowly to prevent slamming the float
In service leak check

20. Flow Instruments: DP Cell
Notice the faceplate and how it is marked. The marking does it’s own square root extraction.
Note the distance between 0 and 10, then the spacing between 20 and 30
Flow Instruments: DP Cell

23. Ultrasonic Flow Measurement Devices Examples: Controlotron, UFM
Two methods of ultrasonic flow measurement:
Doppler - good on dirty fluids and slurries, not terribly accurate
Time of travel - best on clean fluids with not obstructions for the sound, fairly accurate
Ultrasonic Flow Measurement Devices
Examples: Controlotron, UFM

24. Watch the Coriolis Flow video-10 min
Offer direct mass flow, volume flow, density, and temperature measurement of liquids, gases, and slurries
No moving parts
Mass flow rate causes the vibrating tubes to twist
The twist of the tubes is proportional to mass flow
Watch the Coriolis Flow video-10 min
Watch the Coriolis Flow video-10 min

25. Electromagnetic Flow Measurement Faraday’s Law

26. Turbine Flow Meter
Used in Radwaste control on slurry mixtures of resin
Tell story of John Cole and I getting crapped up
Signal generated by the rotating turbine is proportional to flow rate
Pulses
no square root conversion
Magnetic pickup
No ‘hole’ in the process piping

27. Tradeoffs

28. Other methods of measuring flow
Rotary Vane Positive Displacement-turbine
Nutating Disk or piston
Hot wire method, temperature method
Pelton Wheel
Vortex shedding
Calorimetric method
Open Channels
Weirs
Target meter

29. Read OE18368 at end of ‘Flow’ section in handout.
Discuss: What happened?
Could it happen here? What can we do to mitigate it?
Discuss control of test leads.

30. On to Measuring Temperature