L.7 - Flow Measurement Flashcards
List seven flow measurement systems:
1) Head type flowmeters
2) Variable area flowmeter (rotameter)
3) Turbine flowmeter
4) Vortex shedding flowmeter
5) Magnetic flowmeter
6) Coriolis flowmeter
7) Ultrasonic flowmeter
List some Head Type flowmeters:
1) Orifice Plate
2) Venturi
3) Pitot tube
List some Ultrasonic flowmeters:
1) Transit time
2) Doppler
List the different factors that affect the selection of a flowmeter, w/ examples.
- Hardware factors
- accuracy
- size
- cost - Application factors
- material compatibility
- flow rates - Installation and maintenance factors
- installation complexity
- maintenace requirements
Define Flow:
rate at which a fluid (liquid or gas) moves through a conduit
When is flow considered laminar?
when Reynolds number is less than 2000
When is flow considered turbulent?
when Reynolds number is greater than 4000
What is the region between laminar and turbulent flow called?
transitional flow region
How do head type flowmeters work?
by inserting a restriction in flow path and measuring resulting differential pressure
What are orifice plate requirements?
1) turbulent flow
2) straight pipe runs
3) maintain sharp edge
What are some adv. and disadv. of an orifice plate?
Adv.:
1) inexpensive
2) simple to install
3) no moving parts
Disadv.:
1) straight pipe runs
2) constant pressure loss
3) not ideal for viscous fluids (gets plugged up) (using eccentric or segmental can help)
How do Orifice Plates and Venturi flowmeters work?
fluid passes through a restricted cross-sectional area causing an increase in fluid velocity and a decrease in static pressure
What are some adv. and disadv. for venturi flowmeter?
Adv.:
- constant pressure loss not as large as orifice plate
Disadv.:
- more expensive
- longer axial length
What are some adv. and disadv. for pitot tube?
Adv.:
- negligible pressure loss
- economical
Disadv.:
- not extremely accurate
- delta p is very small
List some applications for pitot tube:
- measure airspeed (planes)
- HVAC systems
- formula one cars
What are some adv. and disadv. for a rotameter?
Adv.:
- direct indication of flow
- low cost
- low pressure drop
- no power required
Disadv.:
- must be mounted vertically
- easily breaks
- fluid must be clean
- sensitive to fluid density
What are some adv. and disadv. for turbine flowmeter?
Adv.:
- high accuracy
- repeatable measurement
Disadv.:
- high cost
- moving parts
- not good for low flow
What is an application example for turbine flowmeters?
oil & has blending
What are some adv. and disadv. for vortex shedding flowmeter?
Adv.:
- no moving parts
- good accuracy
Disadv.:
- not suitable for dirty, abrasive fluids
- not suitable for laminar flow
- midrange, expensive
What are some adv. and disadv. for magnetic flowmeter?
Adv.:
- no restriction of flow
- very accurate
Disadv.:
- only works for conductive fluids
What are some adv. and disadv. for coriolis flowmeter?
Adv.:
- highest accuracy
Disadv.:
- not good for slurries
- expensive
What are some adv. and disadv. for ultrasonic flowmeters?
Adv.:
- simple construction
- easy to install
- can handle corrosive fluid
Disadv.:
- disturbed by electrical noise easily
- build up on pipe wall affects the reading
