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Measurement of Low Flow Liquids

  • Ultrasonic flow meters for low flow liquids are extremely useful as they operate independent of liquid type, thus they do not require recalibration between liquids.
  • The Bronkhorst ES-FLOW Series relies on Ultrasonic Wave Technology, instead of Doppler Effect or Transit Time measurement, to allow ultrasonic sensing of low flow liquids.
  • The design of the ES-FLOW allows easy cleaning and features an on-board PID controller for driving any control valve or pump, and can also be used as a standalone dosing unit.

More and more companies in varying industries are trying to make the transition to low flow liquids solutions. For manufacturers in the chemical, food and beverage, and pharmaceutical industries, there is a shift towards continuous manufacturing in efforts to reduce waste, lower downtime, and add flexibility.

Liquid flow meters play an important role here. But with so many liquid flow instruments on the market, it’s hard to decide the best liquid flow meter for your application.

Ultrasonic Instruments for Low Flow Liquids Measurement

The availability in the market of ultrasonic flow meters for liquids suitable for > 1” pipe lines are enormous. However, finding one for smaller line sizes can be a real challenge. Many ultrasonic flow meters rely on the Doppler Effect or Transit Time for measurement. But these techniques are most suitable for large bore sizes. So what should be used for low flow rates <1,500 ml/min or even down to 2 ml/min?

Measuring Low Flow Rates of Liquids

The complexity of Doppler and Transit Time measurement technology causes difficulties when trying to use the same technology in the “low flow” range. The challenge for ultrasonic flow meters is finding a solution that can apply ultrasonic measurement in tubes with very small diameters.

Operating principle of the ultrasonic ES-FLOW flow meter

In close collaboration with TNO (Netherlands organization for applied scientific research) our partners at Bronkhorst developed an innovative instrument that uses Ultrasonic Wave Technology. And this technology is applied in the ES-FLOW Series for measuring low liquid flow rates.

Using Ultrasonic Wave Technology in Liquid Flow Meters

The ES-FLOW relies on ultrasonic wave technology. Here, measurement is done in a straight stainless steel tube with a very small internal diameter and without obstructions or dead spaces. Multiple transducer discs are located at the outer surface of the sensor tube, which create ultrasonic waves by radially oscillation. Every transducer can send and receive. Therefore, all upstream and downstream 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.

Transducer discs and sensor tube

Knowing these parameters and the exact tube cross section, the ES-FLOW flow instrument is able to measure low flow liquids volumetrically. Thus, the unique properties of this flow meter enable it to measure the actual speed of sound. So, this technology is liquid independent and calibration per fluid is not necessary. Additionally, the speed of sound can be used as an indicator of the type of fluid present in the flow meter.

Considerations For Applications with Low Flow Liquids Flow Rate Requirements

The ES-FLOW is a versatile liquid flow meter that can be used for all liquids.

Do you have changing process conditions or do you make use of various liquids like additives or solvents? Since the ES-FLOW Series technology is fluid independent, recalibration is not needed when the liquid changes. Even non-conductive liquids such as demi water or oil can be measured.

Bronkhorst ES-FLOW features a compact intrinsic hygienic design.

Cleaning processes can be time consuming. Due to the straight sensor tube design, no dead volume, and small internal volume. And particles have a reduced chance of clogging the instrument. So this design results in an easy and quick cleaning procedure, which can help reduce downtime.

The ES-FLOW Series offers an 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. Additionally, the ES-FLOW can also operate as a stand-alone dosing unit.

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