Flow Measurement Flashcards
What are three considerations when selecting a flow meter?
- Cost
- Accuracy requirement
- Range of flow rates
- Head loss
- Adaptability to site condition
- Operating requiements
- Ability to pass sediment and debris
- Longevity of device for operating conditions
- Maintenance requirements
- Construction and installation requirements
- Device standardisation and calibration
- Resilience i.e., vandalism.
- Impact on the environment
What is a differential head meter? Name three tyoes.
A meter based on Bernoulli’s Theorem.
- Nozzle meter - Do not use with fuel
- Orrifice plates - do not use with fuel
- Venturi meter
What are the advantages of a differential head meter?
- Accurate
- Easy to use
- Can be field manufactured
What are the disadvantages of a differential head meter?
- Can be expensive to machine
- Careful selection required
What is the meter theory equation for actual flow rate?
What are the parts of a venturi meter?
How many pressure tappings are there in a Venturi meter?
2
How close should the nearest fitting be to the venturi meter?
15 x the diameter from the divergence.
What is the minimum differential pressure required in a venturi meter?
80mm H20
What is the minimum throat pressure required in a Venturi Meter?
2.5m H20
What is the minimum velocity required for a Venturi Meter?
0.3 m/s H20
What is the calulation for the coefficient of discharge (Cd)?
What is the equation for the coefficient of velocity (Cv)?
What is the eqaution for the coefficient of contraction?
Draw a basic weir, inluding:
- Nappe
- Air vent
- Measuring staff
- Crest
- H
- h1
- Distance of staff from crest
What are the three types of open channel flows?
- Contracted weir
- Supressed weir
- Compound weir
What rule do all open channel flow weirs follow?
Qa = Cd x Qt
What are the characteristics of a contracted weir?
- No guide at outlet
- Bell mouth exit
- Sides contract (come in) 2h1 from edges of approach.
- Crest is a minimum of 2h1 high.
- Aerated holes in contraction plates.
What are the characteristics of a supressed weir?
- Horizontal crest across full width
- Crest at least 3h1 high
- vertical approaches continue at least 0.3h1
- Aerated by vent pipes at sides
What is the calulation for the theoretical flow of a rectangular weir?
What is a compound weir?
A combination of more than one tyoe of weir.
What is the calulation for the theoretical flow of a vee notch weir?
What are 4 different types of measuring flow?
- Turbine flow meter
- Accoustic flow meter (Doppler effect)
- Variable area flow meter
- Vortex Shedding
What is the equation for water power?
