Flowmeters are very important equipments installed for process flow measurement. The key to success is to select the right flow meter while choosing the wrong one means nothing but trouble.
There are many criteria should be considered for selecting a suitable flowmeter for each purpose, and there are enough types of flowmeters available in the market.
Following are general criteria for selecting a flowmeter:
1. Flow type:
The first phase selecting a flowmeter is to know the flow type, is that liquid or gas and the chosen flow meter should support the type of fluid been subjected to measuring.
Through measuring the flow of a fluid or gas through the tube, it is possible to determine how it operates and from there, to limit the choice of flowmeters to those best able to cope with the conditions of operation.
| Electromagnetic type | Vortex type |
Paddle wheel type |
Floating element type |
Thermal type | Diaphragm type | Ultrasonic type | Coriolis type | |
|---|---|---|---|---|---|---|---|---|
| Liquid | Available | Available | Available | Available | N/A | Available | Available | Available |
| Gas | N/A | Available | N/A | Available | Available | Available | Available | Conditional |
| Vapor | N/A | Available | N/A | Available | N/A | Available | Conditional | N/A |
| High temperature support | Available | Available | Available | Available | Available | Available | Available | Available |
| Micro flow | Conditional | N/A | Available | N/A | Available | Conditional | N/A | Available |
| Medium flow | Available | Available | Conditional | Available | Available | Available | Conditional | Available |
| Large flow | Available | Available | Conditional | Available | Available | Available | Available | Conditional |
| Viscosity | Available | N/A | N/A | Conditional | N/A | N/A | Available | Conditional |
| Slurry | Available | Conditional | N/A | Conditional | N/A | Available | Available | Available |
| Oil | N/A | N/A | Available | Available | N/A | Available | Available | Available |
| Accuracy | Available | Available | Conditional | Conditional | Available | N/A | Available | Available |
| Maintainability | Available | Available | N/A | N/A | N/A | N/A | Available | Available |
| Pressure loss | Available | Conditional | N/A | Conditional | N/A | N/A | Available | N/A |
| Air bubbles | Conditional | Conditional | Conditional | Conditional | N/A | N/A | N/A | Available |
To select the best flowmeter, it is necessary to calculate the Reynolds number of the application. Once the values of Reynolds are known, they can then be compared to the Reynolds range of a flowmeter to help pick the one that best fits the application’s requirements.
2. Accuracy of application:
Accuracy level of measurement should be the prime consideration of choosing flowmeter.
Positive displacement meters are generally the best choice for the lowest measurement uncertainty. Electromagnetic meters provide the widest range of flow, turbine meters are generally the best choice for the highest short-term reproducibility, while orifice plate meters are the most widely used metering tool. Coriolis mass flowmeters are ideal for measuring particularly viscous substances and anywhere that the measurement of mass rather than volume is required.
3. Installation:
Where are how the flowmeter should be installed is an important consideration, this can affect the accuracy, cost and efficiency.
Pipeline obstructions such as joints, bends or valves in close proximity to the meter can all cause flow distortions that affect the accuracy and repeatability of the flowmeter. Flowmeters should be mounted in positions where there are several straight pipeline lengths upstream and downstream of the meter to ensure the best performance.
4. Cost:
Of course cost is a factor in selecting flow meter, but a quality product in possible low cost.
Eventually, the most cost-effective installation will be the one where the manufacturer can offer good technical support, easily traceable test facilities, a proven track record and a reputation for highly reliable goods based on sound research and development.
Applications of Different Flowmeters:
Rotameter:
- Measuring water and gas flow in plants or labs
- Monitoring chemical lines
- Purging instrument air lines (i.e., lines that use a valved meter)
- Monitoring filtration loading
- Monitoring flow in material-blending applications (i.e., lines that use a valved meter)
- Monitoring hydraulic oils (although this may require special calibration)
- Monitor makeup water for food & beverage plants
Mass flowmeter:
-
Monitoring and controlling air flow during gas chromatography
-
Monitoring CO2 for food packaging
-
Gas supply and control of fermenters and bioreactors
-
Leak testing
-
Hydrogen flow monitoring (e.g., in the utility industry)
-
Control of methane or argon to gas burners
-
Blending of air into dairy products
-
Regulation of CO2 pumped into bottles during the manufacture of beverages.
-
Nitrogen distribution and control for tank blanketing
Coriolis flowmeter:
-
For either gas or Liquid
-
Monitoring concentration and solids content
-
Blending ingredients and additives
-
Conducting a primary check on secondary flowmeters
-
Metering natural-gas consumption
-
Used for fluids as syrups, oils, suspensions and pharmaceuticals
Differential pressure flowmeter:
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Chemical applications (ratio, metering, and additive control)
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Pharmaceutical systems (injection and batching of liquids)
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Food and beverage applications (CO2 measurements, air drying, and process control)
Turbine flowmeter:
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Rotometer replacement
-
Pilot plants
-
Research and development facilities
-
Cooling water monitoring
-
Water consumption
-
Makeup water
Bubble Flowmeter:
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Supercritical fluid extraction
-
Chromatography column, detector, and carrier-gas measurement
-
Monitoring post detector flow volumes in HPLC systems
-
Variable area and electronic flow meter configuration and flow testing
-
Calibration of air sampling pumps
-
General purpose gas flow verification
-
Precise flow calculation without recalibration of gas mixtures