Test 3 Flashcards
What is an integral orifice meter?
Small orifice plate mounted internally in a dp transmitter or externally on transmitter
What are integral flow meters typically used for?
- Air flow
- Gas flow
- Small gas flows
- Chemical additions
Requirements for fluid running through an integral orifice meter?
- Clean
- Free of suspended solids
- At moderate temperature
What is a venturi tube?
- Convergent/Divergent shape
- Dif pres comes from smallest and largest sections
Advantages of a venturi tube?
- Very small process pressure loss
- Available for large pipe diameters
- Accurate
Disadvantages of a venturi tube?
- Expensive
- Requires long section of straight pipe
What is a (conventional) pitot tube?
A tube with a hole pointing upstream to measure the impact pressure
If the pitot tube is used in a pipe under pressure…
- Second hole
- Downstream
- Static pressure
- Differential pressure
A second hole will point downstream to measure the static pressure so that a differential pressure can be taken
Uses of (conventional) pitot tube?
- Large water lines
- Open channel measurement (OCM)
- Air speed
- Water speed
Advantages of (conventional) pitot tube?
- Convenient insertion in flow lines
- Measurement of large flows
- Little to no restriction in process line
Disadvantages of (conventional) pitot tube?
- Plugs easily
- Accuracy issues
What is an annubar pitot tube?
Same principle as conventional but has holes across flow to give an average -> more accurate output
When are area averaging pitot tubes used?
- In large duct work/where there are large flows with low pressure gasses
Principle of operation of flow meter?
- Nozzle -> Restriction -> Dif Pres prop to flow rate
What are flow nozzles mainly used for?
- Steam flow applications
Advantages of flow nozzle?
- Less pressure loss than an orifice plate
- Can be used on high pressure/high temperature applications
- Very little wear caused by erosion
Disadvantages of flow nozzle?
- Difficult to install/remove (wider than opening it goes in)
- Expensive
Difference between segmental wedge and orifice applications?
A segmental wedge is more gradual than orifice applications
Primary use for segmental wedge?
Slurry applications
Advantage of segmental wedge?
Can measure low velocity/high viscous fluid
Disadvantage of segmental wedge?
Low accuracy
Variable area type rotameter principle of operation?
- As flow increases, the displacer moves up the tube -> allowing more area for the flow
- Differential pressure remains constant and the orifice size changes
- Can be used to measure flow by installing directly in the line
Main parts of a variable area type rotameter?
- Tapered
- Displacer (float)
- Scale for reading
Principle of operation of a bypass meter?
- Can be mounted across a restriction -> allows a small rotameter to measure a large flow in a large pipe
- Can have a remote displacer for an external indication or be connected to some device to produce an output
Displacer notes:
- Sometimes called “floats”
- Various designs (shapes) for a wide range of flow rates
- Gas/air flow typically uses a ball-shape
Rotameter disadvantages?
- Must use clean liquid (unless using remote displacer -> still should be, but doesn’t have to be)
- Fragile
- Cannot freeze
What type of meter is a nutating disk?
Positive displacement type meter
What type of meter is a diaphragm meter?
Positive displacement type meter
What WAS a common use for nutating disks?
Residential water use
Nutating disk principle of operation?
- Disk wobbles (not spins) as flow passes through meter
- Disk is connected to a gear train that turns an integrator or counter
Disadvantage of nutating disk?
Cannot be used with:
- Corrosive chemicals
- Suspended solids
- High pressure (applications)
- High temperature (applications)
Diaphragm meter principle of operation?
Works on the principle of diaphragm expansion and sliding disks
Diaphragm meters are used for…
Gas flow applications only
Diaphragm meter advantages?
- Very little maintenance
- Accurate
Diaphragm meter common use?
Residential natural gas
Turbine meter principle of operation?
Flow drives a turbine that can be connected to an integrator or electronic speed pickup
Turbine meter disadvantages?
Can be expensive
Turbine meter advantages?
- Can be used for high-pressure application
- Specially designed units can be used to measure mass flow
Target flow meter principle of operation?
- Process fluid hits disk. Impact force is transmitted through the force bar to the sensor
Target flow meters are often used as…
A flow switch for alarm purposes
Target flow meter advantages?
- Can be electric or pneumatic
- Compact
- Easily installed
Target flow meter disadvantage?
- Mechanical parts
Paddle wheel principle of operation?
Rotation of the paddle wheel can be detected magnetically or optically
Paddle wheel advantages?
- Cheap
Paddle wheel disadvantages?
- Low accuracy
Sight flow indicator…
Provides a window into a pipe system when visualization of the process is necessary
A flow switch…
Is used to determine if the flow rate is above or below a certain value
A magnetic flow meter is…
an instrument that measures flow based on the principles of Faraday’s law (electromagnetic induction)
Magnetic flow meter principle of operation 1?
- A magnetic coil sets up a magnetic field. This field is powered either by an AC voltage or pulsating DC voltage (more common due to the ability to eliminate static nouse continually)
Induced voltage formula?
E=kBD*V
A magmeter contains:
- Magnetic coils
- Electrodes (must contact the fluid to measure induced voltage)
- Straight length of non-magnetic stainless-steel pipe
- Insulated inside with a non-conductive material (Teflon, ceramic, rubber, etc.)
In a magmeter, fluid must be…
A suitable conductor
Magmeters are used to measure…
- Slurries
- Corrosive chemicals
- Water
- etc.
Magmeters CANNOT measure…
- Gas/steamm
- High temp
- High pres
Vortex flowmeter principle of operation 1:
- Fluid vortices or eddies are formed as flowing fluid passes a bluff body (wedge shaped obstruction) located in the stream
Vortex flowmeter can be…
Very accurate
Vortex flowmeters are not affected by…
- Viscosity
- Density
- Pressure
- Temperature
Vortex flowmeters can measure the flow of…
- Liquids
- Gases
- Steams
Vortex swirlmeter principle of operation 1:
- Blades at the inlet to the meter cause the process to swirl
Ultrasonic flow meter (transit time type) principle of operation 1:
- This type of flowmeter has two transmitter-receiver (they do both) units mounted on an angle to the flow
Ultrasonic flow meter (doppler type) principle of operation 1:
- Doppler effect
Ultrasonic flow meter (doppler type) disadvantages?
- Accuracy varies
- Calibration is difficult
- Must have suspended solids in the flow
Ultrasonic flow meter (doppler type) is often used as a…
portable unit for flow verification
Mass flow measurement is…
a measure of the weight of solution rather than just the volume. Measurement is given in pounds or kilograms rather than liters or gallons
Mass flow measurement can be made by measuring the…
density and flow separately and computing the mass flow from these values
Mass flow of slurry will go to…
a math unit
Mass flow of slurry uses…
flow and density
The mass flow of a slurry would use a….to measure flow
Magnetic flow meter
The mass flow of a slurry would use a….to measure density
Radiation type transmitter
Mass flow of air is measured with…
- Venturi Tube
- Orifiace plate
- Etc.
What all is measured to get the mass flow of air?
- Pressure
- Flow
- Temperature
What changes the volume/density of air?
- Temperature
- Pressure
What dpe is best for duct work?
Pitot tubes
What element, despite being the best for duct work, should not be used on mass-flow?
Pitot tubes
Principle of operation for coriolis mass flow meter 1?
- A C-Shaped tube is vibrated at its resonant
What is the phase shift?
The difference in time/location sensors pick up during oscillations
Coriolis mass flow meter: the oscillating frequency is a direct measure of…
density
Magnetic flow meter principle of operation 2?
- The fluid in the pipe, running between the magnets, acts as a conductor, cutting the lines of force of the magnetic field
Magnetic flow meter principle of operation 3?
- As the lines of force are cut, a voltage is induced. This voltage is picked up by electrodes embedded in the walls of the pipe
Magnetic flow meter principle of operation 4?
- The induced voltage picked up by the electrodes is proportional to the strength of the magnetic field and the velocity of the conductor
Principle of operation for coriolis mass flow meter 2?
- A driving mechanism is used to cause the tubes to oscillate
Principle of operation for coriolis mass flow meter 3?
- The material passing through the interior of the pipe will cause the pipe to twist
Principle of operation for coriolis mass flow meter 4?
- This twisting is proportional to the value of the mass-flow
Principle of operation for coriolis mass flow meter 5?
- The twisting can be measured with optical or magnetic sensors
Principle of operation for coriolis mass flow meter 6?
- Mass-flow is determined by measuring the phase shift between the two sensor positions
Vortex flowmeter principle of operation 2:
- The frequency of the shedding of these vortices is proportional to the fluid velocity
Vortex flowmeter principle of operation 3:
- The frequency is picked up by sensitive sensors located in the bluff body
Vortex flowmeter principle of operation 5:
- Various types of detector technologies can be used (E.g. strain gauge, piezoelectric, capacitance)
Vortex swirlmeter principle of operation 2:
- The body or bore of the meter body contracts -> fluid accelerates
Vortex swirlmeter principle of operation 3:
- As the swirl enters the throat of the meter, it takes on a helical motion that increases as the body enlarges
Vortex swirlmeter principle of operation 4:
- The velocity of the fluid in the vortex is faster than the surrounding fluid
Vortex swirlmeter principle of operation 5:
- As each vortex passes the sensor, there is a change in fluid velocity
Vortex swirlmeter principle of operation 6:
- The frequency at which the velocity change occurs is proportional to the volumetric flow rate
Ultrasonic flow meter (doppler type) principle of operation 2:
- A transmitter reciever unit is placed on the outside of a pipe and a sound wave is transmitted into the flow
Ultrasonic flow meter (doppler type) principle of operation 3:
- The sound wave is reflected off air bubble and/or particles within the flow back to the receiver
Ultrasonic flow meter (doppler type) principle of operation 4:
- A frequency shift is measured that is proportional to the velocity -> the volumetric flow rate
Ultrasonic flow meter (transit time type) principle of operation 2:
- Sound waves are sent from one transmitter-receiver unit to the other and back again
Ultrasonic flow meter (transit time type) principle of operation 3:
- In one direction, the process flow will aid the sound waves and the other direction will oppose the sound waves
Ultrasonic flow meter (transit time type) principle of operation 4:
- The difference in time between upstream and downstream signals is directly proportional to the velocity of the flow therefore the flow rate
Rotameter advantages?
- Simple
- Inexpensive
- Can measure low flow rates accurately
- Can be used to measure corrosive, clear liquids and gases
- Can be supplied with a needle valve to adjust the flow rate
