Date post: | 15-Jan-2016 |
Category: |
Documents |
Upload: | judith-neal |
View: | 217 times |
Download: | 0 times |
ACADs (08-006) Covered
Keywords
Flow rate, total flow, differential pressure, percent flow, cotameter, Bernouli.
Description
Supporting Material
1.1.2.1 5.4.1.7
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.
Measuring Flow
Differentiate between Flow Rate and Total FlowDescribe the relationship between differential
pressure and flowGiven a percent range of DP sensed by an
orifice plate, calculate the percent flowDescribe the theory of operation of a given flow
measurement deviceDescribe the considerations for
removing/restoring a rotameter from/to service
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 minuteWe 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
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
• http://home.earthlink.net/~mmc1919/venturi.html
pressure ialDifferrent%% Flow
Pressur alDifferenti%Flow% 2
-or-
Flow Instruments
Flow
Example 1
• Pressure drop range: 0-100 in H2O• Flow: 0 to 100 GPM• Currently reading 25 in H2O• What is the flow?
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?
Discovered two centuries ago by Italian scientist GiovanniBattista Venturi (1746 - 1822).
Venturi Tube
Flow Nozzle
Elbow
Tap
Henri de Pitot (1695-1771)
Annubar
When flow exists,
there is a constant differential pressure across the float
Rotameter
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
Flow Instruments: DP Cell
Ultrasonic Flow Measurement Devices
Examples: Controlotron, UFM
Coriolis
• 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
flowWatch the Coriolis Flow video-10 min
Electromagnetic Flow Measurement
Faraday’s Law
Flowmeter Pressure LossTypical
AccuracyRequired upstream pipe
diametersRelative
cost
Orifice Medium ±2 to ±4 10 to 30 Low
Venturi tube Low ±1 of full scale 5 to 20 Medium
Flow nozzle Medium ±1 to ±2 10 to 30 Medium
Pitot tube Very low ±3 to ±5 20 to 30 Low
Elbow meter Very low ±5 to ±10 30 Low
Positive Displacement High ±0.5 of rate None Medium
Turbine High ±0.25 of rate 5 to 10 High
Vortex Medium ±1 of rate 10 to 20 High
Electromagnetic None ±0.5 of rate 5 High
Ultrasonic (Doppler) None ±5 of full scale 5 to 30 High
Ultrasonic (Time of Travel) None ±1 to ±5 5 to 30 High
Mass (Coriolis) Low ±0.4 of rate None High
Other methods of measuring flow
Rotary Vane Positive Displacement-turbineNutating Disk or pistonHot wire method, temperature methodPelton WheelVortex sheddingCalorimetric methodOpen ChannelsWeirsTarget meter
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.
On toMeasuring Temperature