Guus Witvoet
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Let me start with explaining what demineralised water is. Demineralised water, also known as demi water, is purified water and is often used in laboratory applications for industrial and scientific purposes. However, also in your everyday life you will encounter applications with demi water.

For example for ironing your clothes with a steam iron, demi water can be used to avoid lime scale in your iron. But it is also used in car wash installations. A thin layer of demi water is sprayed over the car at the end of the car wash program to avoid dried up drops on your car. At the end of this document a few examples of the use of suitable Bronkhorst instruments are given.

Demineralised water versus distilled water

Demineralised water is water that has been purified in such a way that (most of) its mineral- and salt ions are removed. You can think for example of Calcium, Chloride, Sulphate, Magnesium and Sodium. Demineralised water is also known as demi water or deionised water. Demineralised water is generally considered different from distilled water. Distilled water is purified by boiling and re-condensing. In this way salt ions are being removed.

The major difference between demineralised water and distilled water is that distilled water usually has less organic contaminants; deionisation does not remove uncharged molecules such as viruses or bacteria. Demineralised water most times has less mineral ions; this is dependent on the way it is produced. Deionisation has a cleaner production and it leaves behind less scale in the installations it is used in. A point of attention when using this demineralised water is the material of your instruments. Not all material is suited to serve as a piping material for demi-water; this also depends on temperatures that are used.

How is it made?

Demineralised water is produced via three main routes:

  1. Via Ion-exchange process using Ion exchange resins: Positive ions are replaced by hydrogen ions and negative ions are replaced by hydroxide ions.
  2. Via Electro-Deionisation also an Ion-exchange process takes place: An electric current is sent through the resins to keep them regenerated. The unwanted ions move away from the reaction surface to the electrodes.
  3. Via Membrane filtration: most times in multiple steps

To get the right quality of demi-water several stages of demineralization are necessary. The use of membrane filtration in this case has the advantage that in general no chemicals are needed to produce the demi-water (except perhaps for cleaning); the disadvantage is the amount of (electrical) energy consumed by the process.

Demineralised water – common uses

Demineralised water is used for industrial and scientific purposes. You can think of the following applications:

  • Laboratory applications and testing
  • Carwash
  • Wash water for computer chip manufacture
  • Automotive uses eg. lead-acid batteries and cooling systems
  • Boiler feed
  • Laser cutting
  • Optimisation of fuel cells
  • Steam irons and steam raising applications
  • Pharmaceutical manufacturing
  • Cosmetics
  • Aquariums
  • Fire extinguishers

Car wash

Health Risks of demineralized water

Demineralised water, which is completely filtered of minerals via (electro) ion-exchange, distillation, membrane filtration or other production methods, you would think that it could be used as drinking water. However, as with all things, there are advantages and disadvantages to drinking demineralised water. The advantage is that the minerals that are bad for us have been taken out. There is a lot of documentation available about bad influences of certain minerals on our bodies. The big disadvantage of drinking demineralised water, however, is that demi water takes out also the good minerals from our body and causes a shortage so our health system cannot function properly anymore. Summarised: demi-water should not be used for drinking water as it removes minerals that are needed for a good health.

Some examples of instruments which can be used for demi water

  1. Coriolis flow meters, series mini CORI-FLOW

  2. Ultrasonic flow meters, series ES-FLOW

  3. Thermal mass flow meters, series LIQUI-FLOW

Products that can be used for demi water

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Erwin Eekelder
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More and more companies in varying industries are trying to make the transition to low flow solutions. Especially in the chemical industry and food & pharma market the trend is to focus on continuous manufacturing, waste reduction, lower downtime and more flexibility. In these industries the availability of ultrasonic flow meters for liquids suitable for 1” pipe lines or larger are enormous, but it is much harder finding solutions for smaller line sizes. Conventional ultrasonic flow meters use either the Doppler Effect or Transit Time measurement. These techniques are practically suitable for large bore sizes.

But what about ultrasonic flow meters for flow rates lower than 1500 ml/min or even 200 ml/min?

Due to the complexity of physics and technology there are not many measurement principles present in this particular flow area, especially ultrasonic flow meters. Therefore the big 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) Bronkhorst managed to develop an innovative instrument using Ultrasonic Wave Technology. This technology is applied in the new ES-FLOW™ series for measuring liquid volume flows between 4 to 1500 ml/min independent of liquid density, temperature and viscosity with an accuracy of 1% of rate ± 1 ml/min.

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 an inner diameter of 1.3 mm, 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™ is able to measure liquid volume flows. The distinctive character of this flowmeter 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 flowmeter.

transducer discs and sensor tube picture1: transducer discs and sensor tube  

Four reasons why to use the ES-FLOW™ Ultrasonic flow meter:

1. One sensor for multiple liquids

Many companies have changing process conditions and make use of various liquids like additives or solvents. As the ES-FLOW™ technology is fluid independent, recalibration is not needed with liquid changes. Also non-conductive liquids as demi water can be measured.

2. Easy to clean and reduced risk of clogging

Cleaning processes are often time consuming. Due to the straight sensor tube design with no dead volume, particles have reduced chance of clogging the instrument. Cleaning can be done in a few minutes therefore the amount of down time will be limited.

3.Vibration insensitive

Ultrasonic measurement is not sensitive for vibrations as it doesn’t rely on frequencies or rotations. It is also irrelevant if the flow is laminar or turbulent.

4. Integrated PID controller and fast response

The on-board PID controller can be used to drive a control valve or pump, enabling users to establish a complete, compact control loop with fast response time.

Erwin Eekelder
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As the demand for natural and healthier ingredients (such as sweets with vitamins) increases, manufacturers of chocolate and sweets often decide to change the existing artificial flavours, aromas and colours, into more natural additives. Because these additives are more expensive and have changing fluid properties (e.g. density and viscosity), traceability and an accurate process are desired.

The desired flow solution should provide detailed process information, more efficient production lines, better product consistency and higher quality of the overall process. For this we have developed an ultrasonic flow meter for small liquid volume flows called the ES-FLOW.

Confectionery market

Worldwide the confectionery industry is expected to grow towards 275 billion dollar in 2025, an enormous market. Looking into that, America is number 1 in terms of candy retail volume, but if you measure the consumption per capita, it seems the European countries win the battle. Germany has the highest consumption per capita (according to market data and estimates from Euromonitor in 2016).

Market suppliers continuously learn from the market to keep adding value to the daily life of their customers. A sustainable supply chain, improvement of the well-being of consumers and continuous product innovation are required to support the long term needs of this market.

Chocolate production

Continuous production process

At the same time, trends have been observed in recent years towards a continuous production process, prevention of waste, shorter downtimes and higher flexibility, not only in the food sector but also in the chemical industry.

The use of additives – flavours, aromas and colours - requires that small flow rates are measured and controlled. For this, not many solutions can be found. Nowadays many confectioners use dosing pumps and rely on positive displacement. But how to be sure that the desired volume was actually displaced? Was the pump head completely filled with liquid? Or did (partly) dry-running occur?

Dosing pumps are often calibrated or programmed for a set fluid and flow rate. For changing process conditions or production changeovers this usually needs to happen again, which could lead to long down times. The ES-FLOW ultrasonic volume flow meter has an integrated PID controller that can be used to operate pumps and valves. This allows the user to build a complete automated control circuit with fast response times.

Real time flow measurement and control for flow rates lower than 1500 ml/min or even 200 ml/min?

In close collaboration with TNO (a Dutch organization for applied scientific research) we managed to develop an instrument using Ultrasonic Wave Technology. This technology is applied in the ES-FLOW ultrasonic flow meter series for measuring and controlling liquid volume flows between 4 to 1500 ml/min independent of liquid density, temperature and viscosity with an accuracy of 1% of rate ± 1 ml/min.

“Want to know how this Ultrasonic Wave Technology works? Read all about it in our blog How to measure low flow rates of liquids using ultrasonic wave?”

ES-FLOW ultrasonic flow meter

Recalibration is unnecessary

Many companies have changing process conditions and often use a variety of additives and solvents. The ES-FLOW ultrasonic volume flow meter is liquid-independent, therefore recalibration is not needed. Also non-conductive liquids, such as distilled and demineralised water or solvents can be measured. In addition to this, the sensor is insensitive to surrounding vibrations.

Hygienic Design

The instrument is designed according to hygienic standards with a self-drainable straight sensor tube, surface roughness ≤ 0.8 µm and no dead volume. Therefore particles or bacteria cannot accumulate easily and contaminate the sensor tube. As a result the cleaning process only takes a few minutes, which minimises downtimes.

Find out the working principle of the for very low liquid flow rates:

Read more about the Pilot Series Process for the ES-FLOW ultrasonic volume flow meter