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.

Hannover Messe

Marcel Katerberg
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Working in flow, specifically low flow solutions, brings you into contact with applications and challenges that can be quite surprising. This week we discuss an opportunity for new calibration techniques to prove infusion pump performance.

Infusion pumps are well-known in medical applications. They come in multiple operating principles for pumping various fluids. • Volumetric pumps are usually used for food and hydration at higher flow rates up to 1L/h. • Syringe pumps are mostly used for accurately dosing low flow rates of down to 1ml/h or even lower.

We learned from users that the readout of a syringe pump shows the set point flow but it gives no feedback on the actual flow. Because of this lack of feedback on the actual flow being delivered, it is an area that should require regular accuracy checks. A regular programme of checks at a pre-determined flow rate or range is essential for ensuring that the delivery of fluid from the pump matches the expectations of the user. This is also an excellent opportunity to data log the performance of the pump for future reference and assists management purposes.

Moreover, we learned from medical engineering groups that there are currently two main calibrating techniques available for infusion pumps;

Volumetric measuring principle

The first uses volumetric measuring principles. This method usually needs a significant flow rate and minimum volume for achieving a reasonable accuracy within an acceptable period of time. This limits the ability to quickly check syringe pumps at the lowest flow rates and in critical applications. This creates a potentially inaccurate and time consuming calibration process.

Distance measuring principle

The second technique is to measure distance that the plunger travels over a pre-determined period of time and use that figure to extrapolate a figure for accept/reject. This technique is usually determined by the manufacturers of the instruments and carries with it a high degree of inaccuracy when adding together the manual method of measuring, the inaccuracy of the ruler, stopwatch and pump.

Improving response time and accuracy of infusion pump calibrations

Recognizing some of the flaws in the techniques above, and having talked to several professional working groups that use syringe pump calibration systems, we were excited to begin new research In these studies we test new sensor technology and techniques that could benefit the response time and accuracy of infusion pump calibrations.

To define the value of this study we identified together with the working groups potential applications in which accurate dosing is a critical process parameter. Below you will find the applications as identified: • The use in pediatrics where patients are extra sensitive and vulnerable for wrong medicine dosage. • Medication dosage at low rates where it is difficult to obtain a relative accurate and stable flow. • Medication with a small therapeutic band in which a high accuracy is even more important. • Multi infusion systems where multiple pumps are connected to a single cannula. In these systems the compliance of the used syringes and tubing can cause major errors in the actual dosage.

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Low flow Coriolis sensor

We defined the hypothesis that the characteristics of a low flow Coriolis sensor could support the scope to improve the accuracy and response time of calibration systems used to calibrate syringe pumps. We demonstrated the validity of this hypothesis during an in-house study and at a hospital in the Netherlands. The Coriolis principle was chosen due to its proven accuracy and long term stability. Furthermore, due to their small internal volume and little pressure drop these instruments can be used in line to test complex multi infusion systems.

Surpassing the accuracy and response time

We bench marked the Coriolis sensor technique against an electronic analytical balance in house. The set-up of this experiment was approved by the Dutch Accreditation Council. Furthermore, we performed a bench mark study against an infusion calibration system at a hospital in the Netherlands.

The results of this study confirmed that the Coriolis sensor techniques can surpass the accuracy and response time of the incumbent measurement principles used in calibration systems.

Read about how Mandy Westhoff explains a typical day at Bronkhorst’s flow meter Calibration Centre (BCC)

Learn more about (mini) CORI-FLOW™ instruments combined with a valve or pump and watch the principle of operation of the mini CORI-FLOW Coriolis mass flow meter

Graham Todd
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When you install a mass flow meter or mass flow controller it is important that you get the best performance from the moment you install and turn it on. To help you, I have listed a few simple things you can check focusing on thermal mass flow meters and controllers for gases.

1) Mounting position of flow meter

The mounting position is important. For flow meters the preferred position is horizontal, and at high pressures ( > 10 bar for by-pass instruments) all meters should be mounted in this position. Avoid installation in close proximity to mechanic vibration and heat sources.

2) Avoid interruptions

Avoid abrupt angles – or any objects in the flow path which can cause turbulence - directly on inlet and outlet of your flow instrument, especially for high flow rates. We recommend at least 10x the pipe diameter as the distance between the angle and the inlet of the flow instrument. If you are interested in why the choice of piping is important for thermal mass flow meters, please read our previous blog for more tips.

3) Name plate (serial number label)

Read the instrument’s name plate before installation and check the electrical connection, flow range, media to be measured, inlet and outlet pressure, operating temperature, ATEX classification (when applicable), as well as input and output signals. Also check the sealing material for compatibility with the process gas.

4) Electrostatic discharge (ESD)

The flow instrument contains electronic components which are sensitive to electrostatic discharges (ESD) – a sudden flow of electricity between two electrically charged objects caused by contact. Contact with electronically charged persons or objects could possibly endanger these components or even result in their failure.

5) Pressure

Do not apply pressure until electrical connections are made. When applying pressure to the system, take care to avoid pressure shocks and increase pressure gradually.

6) Check the piping

Ensure that the piping of the system is clean (before installing the instrument). For absolute cleanliness always install filters to ensure a moisture and oil-free gas stream. It is recommended to install an in-line filter upstream of the mass flow meter or controller, and if back flow can occur, a downstream filter or check valve is recommended too.

7) In line installing

Install the mass flow meter or controller in the line and tighten the fittings according to the instructions of the supplier of the fittings.

8) Piping diameter

Avoid small diameter piping on high flow rates, because the inlet jet flow will affect the accuracy and may cause too high pressure drops over the piping and adaptors. Choosing the right piping diameter is also of importance to minimize the effect of turbulence as much as possible. Our previous blog describes the effect of turbulent flow and what to do about this.

9) Leak testing

Always check your system for leaks, before applying fluid pressure. Especially if toxic, explosive or other dangerous fluids are used.

10) Power up

Apply power to the flow meter or controller and allow for approx. 30 minutes to warm-up and stabilize. This may be done with or without fluid pressure, applied to the system.

I hope that this list is of use. Please feel free to use it as a reference for the next time you need to install a mass flow meter or controller. If you have further questions or if you think I have left anything out then please let me know. At Bronkhorst, we are happy to learn from your experience.

Check the frequently asked questions (FAQs) on our website.

Or download the manual or quick installation guide of the flow instrument.

Jeroen van Hal
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Many people have a traditional inkjet or laser printer in their homes, to print '2D' texts and images on paper. In an extension to this, 3D-printers already show up in our homes, to make gadgets, jewellery and other products. 3D printing is becoming increasingly popular and nowadays large online platforms are being set up where open source designs are accessible to everyone, like Pinshape. 3D-printing, also known as additive manufacturing is a novel production technique where 'real 3-dimensional' products are built layer by layer, made from scratch. This is the opposite of traditional machining operations such as drilling, milling or cutting, where pieces of material are removed to yield the product.

3D printing as ‘rapid prototyping’

3D printing today is often associated with a process called ‘rapid prototyping’ – which is used by research and development (R&D) teams to create a physical representation of a new invention (prototype) so that it can be tested and validated.

On a professional level, 3D-printing is already becoming a popular solution to manufacture products in small series, fast and custom-made. 3D-printing of polymers and metals already occurs on an advanced scale, alongside this 3D-printing of ceramics is rising.

3D-printing at Bronkhorst

3D-printers are very useful within the production environment. This is demonstrated by their use here at Bronkhorst - for product as well as process development. It really has become a new and very accessible way of manufacturing.

We use several 3D-printers mainly for visualisation purposes - 'the rapid prototyping way' - and to print useful tooling to facilitate the production of mass flow controllers and meters. Prior to using 3D-printing, a prototype of a component had to be manufactured at an external tool shop, which took some time - and investment - before it was ready. The use of 3D-printing has allowed us to increase our productivity: it is much faster to print a component or a tool ourselves.

Within a few hours, we can evaluate the design of a component: will it really work in the way we expected it, does it really fit? Moreover, for small quantities, no investment is required for manufacturing a mould.

In addition to its speed, 3D-printing has some convincing advantages. It is much more powerful to deal with a real component - a plastic model, with some real look & feel - than a 3D-rendered image which may look fantastic but isn't in real life. In addition, the communication between R&D, engineering and production works that much better having a component in your hand to talk about. Which are the key problems we will encounter, what can be the risks of a new design? In the R&D department, 3D-printing is mainly used to test the functionality of a design. The engineering department goes one step beyond, in making the design feasible and realisable.

3D printer Kaak

3D printer Kaak

Cooperation with external partners

K3D, part of Kaak Group in Terborg, acquired the first real industrial 3D-printer for metal. Since September 2016, the printer is fully operational. The MetalFab1 machine is based on selective laser melting (SLM), a 3D-printing technique where a layer of metal powder is deposited, after which a part of these powder particles is selectively melted together by means of laser heat. It is the first local step in real production of metal parts with a 3D-printer.

Want to learn more about Mass Flow Controllers in 3D-printers? Read the blog of Jens Kiene about how a MASS-STREAM mass flow controller is used for selective laser melting.

Kaak approached seven companies in the region to experiment with the 3D-technique together, with the aim to turn the eastern part of the Netherlands into a 'print valley'. Each week, Bronkhorst has access to the printer for several hours. Bronkhorst is constantly looking for possibilities to improve the production process of flow meters, e .g. whether it’s possible to integrate more functions in the modules without interfering with the modular design. Moreover, local educational institutes are invited to get access to the machine, in order for their students to become acquainted with this technology.

Mass flow controllers for 3D-printers

Besides the fact that we use 3D-printing for our own product and process development, it also goes the other way around: mass flow controllers are used inside 3D-printers for metals. In selective laser melting, it is essential to have an inert gas atmosphere around the to-be-melted metal powder particles inside the 3D-printer, to prevent the metal from oxidation during the laser melting with oxygen from the surrounding air. To that end, an inert shielding gas has to be applied: argon gas for steel and titanium, and nitrogen gas for aluminium. Bronkhorst helps 3D-printer manufacturers with a system that generates and controls the flows of these inert shielding gases.

3D-printing is a way of additive manufacturing, a novel production technique essential for Bronkhorst to keep up with all new trends in the market for product- as well as process development.

Read more about this application using 3D-printing of metal products.

Check out the mass flow controller MASS-STREAM D-6300 that is used for 3D-printing

Watch the video

Egbert van der Wouden
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Customers over the world are searching for simplication and integration of their gas, liquid or vapour flow processes. They prefer integrated platforms that are compact, robust and reliable, and even containing different type of sensors.

In this blog I provide a sneak-preview of the ‘toolbox’ which is under development at Bronkhorst High-Tech B.V. One of the components which we are working on, a micro Coriolis mass flow sensor, is already shared with you in our previous blog ‘Miniaturization to the extreme’.

Why do we develop a next-generation toolbox?

On a daily base, our customers tell us their need for miniaturization and the need to control a complex set of different parameters to meet the stringent demands of their customers. These types of customers include the life-science market, analytical device manufactures but also markets in which online gas-concentration levels are measured.

MEMS based technology

These types of requests triggered us to work on the next level of sensor development which can support the future need of our customers. This new development includes MEMS based technology (Micro Electro Mechanical System) which gives you the possibility to measure more than just flow alone on one customized system that can consist of one or a combination of sensors.


For instance, a measured physical property can be used to identify the type of medium, if that property is unique for that medium. Or, in case the medium consist of a mixture of 2 gasses, a property can be used to analyse the fraction of this binairy mixture.

Other parameters which can be thought of are the sugar content of a fluid, also referred to as the Brix number, or heat capacity that can be used to measure oil/water mixtures.

In short, these new concepts are under development to support our customers to solve their next generation technology challenges.

Multi-parameter sensor chip

An example of how a program was started to minimize the footprint; Bronkhorst received the request to measure fysical gas properties in combination with several partners. The fysical properties included the: • heat capacity (cp) • density (ρ) • thermal conductivity (λ) and • viscosity (η)

To analyze these properties several individual sensors like a Coriolis-, Thermal-, Pressure- and Density sensor were needed. To proof that the combination of several sensors in combination with electronics could meet the needs of the customer, a demonstation model was developed. This demonstration model contained commercially available products which where combined in one system.

Demonstration model

The learnings from the demonstration model support the project team to define the exact scope for the multiparameter chip alternative.

One important aspect of sensor performance is the stability, espacially when multiple sensors are combined to determine information about the medium in the system. In figure below it's shown that we can measure the viscosity with a combination of the massflow, density and differential pressure. With the demonstration model shown above we have tested if the viscosity of a medium can be measured accurately over longer periods independent of room temperature changes. The measurement of viscosity can be interesting for some applications, for instance with natural gas where viscicosity and calorific value are strongly correlated. The test results are shown bellow for a test period of 84 hours, the histogram shows that all measurements values for the viscosity fall within a band of 0.5 %.

Test results

The next level will be to combine the same functionalities on a much smaller footprint. The concept below shows the possibities to combine the required parameter on chip level.


Bronkhorst® Flow Solutions

For machine builders all over the world who are searching for simplification and integration of their gas, liquid or vapour flow processes, Bronkhorst can already help in developing and supplying 100% customized flow solutions that fully meet the customer’s needs.

For information about our future toolbox concepts please contact our office [email protected]

In several earlier blogs the results of this co-creation process has been addressed:

Miniaturization to the extreme: micro-Coriolis mass flow sensor.

• Bronkhorst, its share of a clean – solar – energy future: a collaboration between Tempress’ engineers and Bronkhorst

Customized low flow measurement skids and the four reasons why customized skids are popular

Allard Overmeen
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Thermal flow instruments behave best using a laminar flow, at least if we look at the thermal mass flow meters and controllers with a bypass sensor. To conduct a precise measurement with this flow instrument, laminar flow is preferred.

However, in practice you will encounter a turbulent flow quite often. A turbulent flow can be caused by restrictions in an installation, such as valves or adapters, in combination with a high velocity of the used fluid. This effect is known as ‘turbulence effect’. A turbulent flow can affect the accuracy of your measurement, something you would like to prevent.

“Turbulence is a dangerous topic which is often at the origin of serious fights in the scientific meetings devoted to it since it represents extremely different points of view, all of which have in common their complexity, as well as an inability to solve the problem”. Marcel Lesieur, 1987

How can you prevent this turbulence effect? Let’s start with explaining what turbulent flow is:

Turbulent flow versus laminar flow

In general it can be said that there are two types of flows: a laminar flow and a turbulent flow. In picture 1 laminar flow has been visualized by an experiment using ink in a cylindrical tube. The ink has been injected into the middle of a glass tube through which water flows. When the speed of the water is still low, the ink does not appear to mix with water, the stream lines are parallel; this is called laminar flow.

laminar flow profile

If the speed of the water increases, a sudden change will occur at a certain speed. The flow completely disrupts and the water turns homogeneous through the ink. The stream lines are chaotic, not linear anymore, which is called turbulent flow.

In theory the flow pattern depends on four variables:

  • Diameter of the tube
  • Speed of the fluid
  • Density of the fluid
  • Dynamic viscosity of the fluid

The factors combined provide the so called Reynolds number (Re), an important parameter that describes whether flow conditions lead to laminar flow or turbulent flow. In general it can be said that a laminar flow occurs at a low Reynolds number (≤ ca. 2300) and a turbulent flow occurs at a high Reynolds number (≥ ca. 3000). In between these two numbers (Re 2300-3000) you have a ‘transitional flow’, meaning the flow can be laminar or turbulent (numbers mentioned are for a cylindrical tube).

When can turbulence effect occur?

As mentioned before, turbulence effect is a common effect which can occur in installations using (too many) restrictions, such as valves or adapters, in combination with a high velocity of the used fluid. In every restriction, the flow has been disrupted and the speed of the gas will change (as visualized in picture 2). Besides the usage of restrictions, the pipe length is something to take into account. As it takes some time for a turbulent flow to get laminar again, it is important to use the right pipe length.

A turbulent flow is something you would like to prevent at the inlet of your flow measurement instrument, as it can affect the accuracy of your measurement. It is preferable to have a laminar flow just before your flow instrument. However, the instrument itself used as flow controller, with a valve behind the meter, can cause a turbulent flow again. Not all kinds of flow meters experience this as disadvantageous. Mainly thermal flow meters using the bypass principle are sensitive for this effect. Flow meters based on the Coriolis, CTA (Constant Temperature Anemometry) or Ultrasonic principle are independent of turbulence.

Why are thermal flow meters with bypass sensor more sensitive?

Instruments with a bypass sensor work based on a main flow going through a restriction and a small part of the flow going through the actual sensor. The ratio between these two flows is determined by the pressure drop over the sensor and the restriction in laminar flow. The turbulence effect will disturb this ratio. As the instruments with bypass sensor are often used for very precise measurements, the turbulence effect can have a huge effect on the measurement results.

What can you do to minimize the disadvantageous effects of turbulent flow?

When using thermal mass flow meters with the bypass sensor, we advise it is advised to do the following:

1) Try to prevent restrictions in your process, such as valves, adapters and elbow couplings:

  • Do not mount the flow meter directly behind a restriction, such as a valve. However, if this cannot be arranged differently, than you could use a turbulence filter between the valve and flow meter or use a flow meter with integrated turbulence filter.
  • Using an elbow coupling close to a flow meter should be limited as much as possible.

2) Limit the speed of your flow by using the right pipe length. Generally it is advised to use a minimal pipe length of:

  • 10x the pipe diameter, at the inlet of the instrument
  • 4x the pipe diameter, at the outlet of the instrument (flow meters only)
  • For gas flow rates > 100 l/min it is common to use as a minimum a 12mm or ½” pipe.

laminar flow element lfe

Laminar flow element (LFE)

3) Use a ‘turbulence’ filter in your flow process. The turbulence filter will filter the flow before it reaches the sensor and makes it laminar again. Nowadays, flow meters often have such a filter integrated in the flow meter (for example Bronkhorst EL-FLOW series) or have an extended flow path inside the flow meter (for example the Bronkhorst Low delta P flow meters).

Extended flow path inside a flow meter

Extended flow path inside a flow meter


It depends very much on the application what the consequences are of turbulences. As an example in semicon processes, particularly in coating processes such as layer deposition, turbulent flow is out of the question. A stable process is essential here. However, in other coating processes, such as flame spray techniques, the impact of turbulences will be less due the high pressure in the flow.

It all depends on the process and application.

If you need any assistance for installation of your flow meter, contact our Customer Service Department by submitting the contact form.

For more information about the working principle of the Bronkhorst flow devices, have a look at the various working principles of flow instruments as applied by Bronkhorst.

Have a look at the related blog articles:

Why is the choice of piping important for thermal mass flow meters?

Why use thermal mass flow meters and mass flow controllers?

Thermal mass flow sensor: Bypass versus CTA