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How to measure low flow rates of liquids?

June 21, 2022 Ferdinand Luimes

Ultrasonic instruments for liquid flow measurement

More and more companies in varying industries are trying to make the transition to low flow solutions. In the chemical industry and food & pharma market, you see a shift towards continuous manufacturing, to reduce waste, lower downtime and more flexibility.

Liquid flow meters play an important role here. There are multiple liquid flow instruments available on the market. In our e-book ‘How to handle low liquid flows’ you can read all about the kinds of instruments and how to select the best one for your process.  

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ES-FLOW Ultrasonic Flow Meter

Ultrasonic instruments for liquid flow measurement

In this blog we focus on the ultrasonic flow instruments. The availability in the market of ultrasonic flow meters for liquids suitable for > 1” pipe lines are enormous. Finding one for smaller line sizes is a real challenge. The major part of the ultrasonic flow meters on the market use either the Doppler Effect or Transit Time measurement. These techniques are most suitable for large bore sizes.
But… what to do with low flow rates <1500 ml/min or even down to 2 ml/min?

Measuring low flow rates of liquid

Due to the complexity of physics and technology there are not many measurement techniques in the ‘low flow’ range. In particular when looking at ultrasonic flow meters. The challenge was to find a solution to use ultrasound in tubes with very small diameters. 
In close collaboration with TNO (Netherlands organization for applied scientific research) we succeeded to develop an innovative instrument using Ultrasonic Wave Technology. This technology is applied in the ES-FLOW series for measuring low liquid volume flows.

Principle of operation ultrasonic ES-FLOW flow meter

Transducer discs and sensor tube
Transducer discs and sensor tube

How does Ultrasonic Wave Technology work?

The ES-FLOW  is based on ultrasonic wave technology. Measuring is done in a straight stainless steel tube with a very small internal diameter, without obstructions or dead spaces. At the outer surface of the sensor tube multiple transducer discs are located which create ultrasonic waves by radially oscillation. Every transducer can send and receive, therefore all up- and down-stream combinations are recorded and processed. By accurately measuring the time difference between the recordings (nanosecond range) the flow velocity and speed of sound is calculated.

Knowing these parameters and the exact tube crosssection, the ES-FLOW flow instrument is able to measure liquid volume flows. The distinctive character of this flow meter is that it’s capable to measure the actual speed of sound, meaning that the technology is liquid independent and calibration per fluid is not necessary. Next to that the speed of sound can be used as an indicator of the type of fluid present in the flow meter.

afbeelding

How can you benefit from ES-FLOW Ultrasonic flow meter?

  1. A versatile flow meter for all liquids: Do you have changing process conditions or do you make use of various liquids like additives or solvents? The ES-FLOW technology is fluid independent, therefore recalibration is not needed when the liquid changes. Even non-conductive liquids as demi water or oil can be measured.
  2. Compact intrinsic hygienic design: Cleaning processes can be pretty time consuming. But due to the straight sensor tube design with no dead volume and small internal volume, particles have reduced chance of clogging the instrument. This design results in a easy and quick cleaning procedure, consequently the process down time is limited.
  3. Advanced signal processing: The on-board PID controller is the perfect choice for driving any control valve or pump. This enables you to establish a complete, compact control loop with fast response time. ES-FLOW can also operate as a stand-alone dosing unit.

Would you like to learn more about utrasonic flow meter for low flow?

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