There are so many different flow measurement solutions on the market today that discussing all the possible options is an impossible task. However, as with all technologies, some designs of flowmeter are more widely used than others.
• Paddlewheel flowmeters
• Mass flowmeters
• Coriolis flowmeters
• Oval-gear flowmeters
The choice for a specific application depends upon a number of parameters, including medium type (gas or liquid - viscous, free-flowing or aggressive), operating temperature and pressure, pressure drop, accuracy repeatability and cost.
Paddlewheel technology is widely established, and these flowmeters are among the lower cost devices. They can be used on fluids – including viscous and corrosive liquids. However their susceptibility to variances in viscosity, which often causes error, means that they are unsuited to highly precise measurement applications.
Typical applications include: monitoring chemical lines, filtration loading and flow in material blending applications, measuring water flow in process plants or laboratory facilities, and monitoring supplementary water for food and beverage plants.
With a wide variety of flow ranges and models for liquids, the paddlewheel meter is one of the most versatile designs on the market. They are generally reserved for use with clean liquids because of the possibility of minute particulates becoming lodged in their moving parts.
Mass flowmeters are a popular gas measurement technology. Until recently they could only be used with clean gases, but new sensor technology now allows some models to be used with aggressive gases.
A key benefit of mass flowmeters is that, because they measure mass flow rather than volumetric flow, their operation is generally unaffected by fluctuations in line pressures and temperatures.
This is important for users because, when piping expensive gases, it is certainly more cost effective to keep track of the amount of gas used based on mass, rather than volumetric flow.
Flowmeters employing the Coriolis effect are among the most accurate available, which is reflected in their high price.
Like mass flowmeters, Coriolis-based devices measure mass flow instead of volumetric flow. However, unlike mass flowmeters, Coriolis units work with both liquids and gases – including corrosive gases and viscous liquids.
Because mass is unaffected by changes in pressure, temperature, viscosity and density, reasonable fluctuations of these parameters in the fluid line have no affect on the accuracy of the meter, which can approach 0.05% of mass flow.
Typical applications are blending ingredients and additives, monitoring concentration and solids content in liquids, general-purpose gas or liquid flow, performing primary checks on secondary flowmeters, metering natural gas, and monitoring fluids such as syrups, oils, suspensions.
Care must be taken when using Coriolis meters with viscous substances, because pressure drop can increase and become unacceptably large as fluid viscosity increases.
Oval gear flowmeters are designed specifically for use at high viscosities, with some models providing precise and reliable flow measurement of high viscosity fluids (such as glue, honey or oil) at up to 1- million centipoise.
Oval gear flowmeters are often designed with a pair of meshed (geared) oval rotors that rotate under fluid pressure in an engineered measuring chamber. This arrangement is characterised by its high levels of reliability, its ability to be used on horizontal, vertical and gravity applications, and its accuracy, which is better than 0.5% of reading on larger models.