Flow meters work by measuring the amount of gas, liquid, steam, or other material that passes through or around their sensors. While they all serve the same function, there are many ways to do it – hence the many flow meter types to choose from.
This article will help you choose the flow meter that will deliver accurate and repeatable measurements for specific applications, whether for general research, process control, or monitoring.
Flow meter types
Volumetric vs mass flow meter
Flow meters measure either mass or volume. In a volumetric flow meter, the flow (Q) equals the cross section of the pipe (A) times the velocity of the fluid (v): Q = A * v
For things like chemical reactions, combustion, or buying and selling gases, you need the mass flow rate. In a mass flow meter, the mass flow (ṁ) equals the volumetric flow rate (Q) times the fluid density (ρ): ṁ = Q ∗ ρ
And for things like chemical reactions, combustion, or buying and selling gases, we need the mass flow rate. So in a mass flow meter, the mass flow (ṁ) equals the volumetric flow rate (Q) times the fluid density (ρ): ṁ = Q ∗ ρ
Electromagnetic flow meter
Electromagnetic flow meters require the measured liquid to be a water-based or conductive. This makes the electromagnetic flow meter an excellent choice for wastewater or process water or other kinds of dirty water.
To read more about Picomag, you can check out the Visaya Product Review
Capillary thermal mass flow meter
A capillary thermal mass flow meter relies on heat transfer between gas in a very small tube (the capillary) and a set of sensors that indicate the gas mass flow.
Immersible thermal mass flow meter
An immersible thermal mass flow meter also relies on heat transfer, but in a different way. The heat is transferred from a heated sensor immersed in the flow.
Vortex shedding flow meter
Vortex shedding flow meters are also immersed in the flow of material, but they use vortices and a computed fluid density to measure both volumetric and mass flow.
Transit-time ultrasonic flow meter
Transit-time ultrasonic flow meters can measure flow speed from outside the pipe using ultrasound. Consequently, they don’t need to be immersed in the measured material.
Applications for various flow meter types
There are a number of applications where a flow meter can work, and they call for different devices depending on the measured material, the amount of flow, and other conditions:
- Gas, liquid or steam?
- Very large flows or only small flows?
- High or low temperature or pressure conditions?
- Simple or complicated pipe layouts?
- Costly products that need precise measurement?
Selecting the right flow meter for your process
Type of fluid
We have to know the characteristics of a product. In many cases, providing the name of the product will help the vendor identify the required needs. However, we should still know the product’s conductivity, density, and viscosity in case the vendor doesn’t have those details.
The minimum, maximum, and operating temperatures of the process will eliminate some principles from our list. The ways they affect the product can also influence our selection process.
Flow measurement goals
Calculating the minimum, maximum, and operating flow range can help to pinpoint the right size meter for your application. In some cases, the meter can be smaller than the pipe, but we must know the pressure drop limit of these processes.
The pressure can limit the model and material of the meter. Again, we should know the minimum, maximum, and nominal pressure here as well. High-pressure processes sometimes need a special version of a certain flow meter too.
Knowing the size of the pipe along with other information will help us decide whether a flow meter of the same size will work or if we would need a smaller one.
To know more about Coriolis flow meters, you can read the Visaya Article on Coriolis
Measuring principle recommendations
- Thermal mass flow meters: These flow meters can precisely measure mass flow of gases from low to high flows.
- Vortex flow meters: These flow meters are ideal for measuring liquid and steam flows at high temperatures and pressures.
- Ultrasonic flow meters: These flow meters work well in liquids when we want to avoid pipe cutting or shutdown
- Older technologies such as differential pressure, positive displacement, and turbine meters also have their places.
To know more about flow meters or for advice on choosing the right device for your application, get in touch with our engineers!