Ric Besseling
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In different kinds of applications like aging processes, validation testing and/or in research on plant growth, often a specified flow of moist air is needed to achieve specific ambient conditions in a test chamber. Nowadays, we have multiple solutions for these kinds of applications, one of them with the help of controlled evaporation and mixing systems. Let me explain what the benefits are of these systems in comparison with the more conventional bubbler systems.

How does a Bubbler System work?

Small concentrations of moist air can be created using a bubbler system. This conventional method requires optimal pressure and temperature control of the bubbler system. A complete bubbler level measurement system therefore consists of a source of compressed air, an air flow restrictor, sensing tube, and pressure controller. The latter converts the back pressure to provide output to a controller, which calculates the liquid level. The quality of the moist air fully depends on the theoretical calculation of the degree of saturation of the air flowing through the liquid and the accuracy of pressure and temperature control. With this conventional approach it is difficult to achieve a specific air moisture content.

Set-up Conventional Bubbler System

Figure 1. Set-up Conventional Bubbler System

Bronkhorst evaporation systems

In addition to this approach, Bronkhorst developed a CEM-system, based on Controlled Evaporation and Mixing, which can be used for moist air applications. This CEM-system is an innovative vapor delivery solution, based on a liquid flow controller (LIQUI-FLOW or mini CORI-FLOW), a gas flow controller and a temperature controlled mixing and evaporating device.

Compared to the more conventional bubbler system, a CEM-system offers a more direct approach. The method is very straightforward, and theoretically any concentration can be made in a matter of seconds with high accuracy and repeatability. Moreover, it’s possible to adjust a relative humidity between 5 and 95 percent.

Set-up Bronkhorst CEM System

Figure 2. Set-up Bronkhorst CEM System

The moisture content is accurately controlled by the liquid flow controller and the amount of air flow can be adjusted by the gas flow controller. On top of the CEM a mixing valve allows for a correct atomization of water in the air flow. Because of the relatively low pressure ratio of the water mist in the air flow, the water can be evaporated at a low temperature in the spiralized heater tube at the outlet of the mixing valve.

CEM insights

The set-up of a CEM-system basically consists of:

  1. A Mass Flow Controller for gases for measurement and control of the carrier gas flow (e.g. EL-FLOW Select series).
  2. Mass Flow Meter for Liquids for measurement of the liquid source flow (e.g. LIQUI-FLOW series, mini CORI-FLOW series).
  3. Temperature controlled mixing and evaporating device (CEM) for control of the liquid source flow and mixing the liquid with the carrier gas flow resulting in total evaporation; complete with the Temperature Controlled Heat-Exchanger to add heat to the mixture; Basic Bronkhorst CEM-systems are available as a complete solution, including control electronics, offering total flexibility in realizing a vaporizing solution in virtually any situation.

Do you want to learn more about CEM technology? Visit the Bronkhorst Vapour Flow Control section on our website and read all about our different products and applications in vapour control.

James Walton
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Why Generating Vapour is easier, quicker and more accurate

Generating vapour is a perfect example of how technology development in one area can benefit multiple industries, as can be read in our blog ‘A new trend in vapour generation’. By combining the accuracy and digital performance of modern mass flow metering and control technology, alongside temperature control, you can control the properties of vapour as never before.

Vapour production has always been a necessary, yet complex and expensive process. There have been multiple methods employed to achieve the dispersion of liquid into a gas phase. The variety of methods used is a reflection of the bespoke approach taken by many to compensate for the lack of awareness of a commercially viable solution.

Some of the examples that we have come across;

  • Dew-point generator (bubbler)
  • Mixed-flow Generator
  • Static method of humidity generation
  • Two-Pressure process
  • Two-temperature process
  • Saturated salt solutions
  • Each of these methods has been developed to control the concentration (volume per volume) of liquid in gas to achieve the desired end result.

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What is the end goal?

There are many industries that need, or would benefit from vapour generation to achieve their end goal, we have been talking to biomedical researches, technical fabric manufacturers, glass coating companies, catalysis research & development, graphene research & development and bulk food packaging machine manufacturers.

As always there are a few common themes amongst each of the people that we speak to. In application development the drive is always to increase or decrease something, it could be: cost, waste, yield or raw materials. Almost anything associated with an application will either have an increase or decrease requirement.

How do we achieve the goal of increase and decrease?

Multiple factors can be improved by installing a Bronkhorst® Controlled Evaporating Mixing system (CEM) or Vapour Delivery Module (VDM) in your installation, these include:

  • Speed of response to process changes
  • Reduced raw materials costs
  • Accurate temperature control
  • Quick turnaround on substrate
  • Choice of Parts per Million, Parts Per Billion, Mole or concentration output conditions.

How does the Bronkhorst® Controlled Evaporating Mixing sytem (CEM) or Vapour Delivery Module (VDM) system achieve these things?

Vapour is generated through the addition of a liquid into a gaseous stream, usually under temperature. We add control to each of the inputs, thereby acquiring control of the output. If we take the first example from the list at the beginning of this blog, Dew-point generation, then we can see;

  • Evaporation of the fluid can cause concentration changes in vapour
  • Differences in back pressure created by changing fluid levels
  • Flow rate changes with fluid level resulting in changing process conditions
  • Variations in thermostat accuracy can add temperature variations to the fluid
  • High energy consumption from heating a fluid bed

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By removing those sources of variation from the input, combining liquid flow control with a Coriolis mass flow meter (MFM) and gas flow control with thermal bypass mass flow controller (MFC) with a temperature controlled flow path you can predict the conditions of the resultant vapour more accurately. Once an output has been achieved with a known input combination, it can be replicated repeatably.

For example, in the picture below we know that the input conditions entered will achieve the desired process conditions, that level of control is not available in the other process.

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With direct control of the liquid and gas flows into a temperature controlled flow path it is easy to change the input conditions and predict consistent process conditions. The Coriolis liquid mass flow meter and thermal bypass gas flow controller are directly linked to a 3-way mixing valve on top of a temperature controlled flow path. By passing the liquid and gas through the valve orifice the combined flow is aerosolized before being heated and this ensures complete vaporisation of the liquid in the gas stream.

Taking this a stage further, if you have a specific composition in mind then check out our online free to use database called Fluidat, go to www.fluidat.com register and you can check out yourself what is possible.

Looking at the 6 old ways and 1 new, the innovation and thought that has gone into the original and still used old methods of vapour generation is clear.

However the beauty of society is that we can learn from one another, another technology is available.

Henk Wassink
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Smaller, faster, smarter - three keywords that summarise the trends in the high-tech machine building industry well. This holds for various industries:

  • Complex machines in the semiconductor industry, that manufacture integrated circuits or 'chips' for devices like tablets, smartphones and notebooks.
  • Machines in the solar industry, that manufacture solar panels to convert sunlight into electrical energy as a decentral replacement of traditional power plants.
  • Analytical equipment within and outside chemical laboratories, that analyses or diagnoses the chemical composition or other physical properties of samples taken from a process flow.
  • Machines in food and beverage industry where several nutritional compounds or flavourings are added, mixed and processed to obtain the desired food.

Measurement and control of gas and liquid flows

The common part where Bronkhorst and machine builders operate is that part of the machine where gas and liquid flows have to be measured or controlled. Machines for chips or solar panel manufacturing make use of chemical vapour deposition steps for coating application or diffusion doping, where organometallic vapours have to be generated and supplied to (silicon) supports onto which a solid deposition has to take place.

Read more in our blog about the solar energy future in which one of our project leaders shares his experience with Boron and Phosphor doping for solar panels.

In analytical devices such as various chromatography equipment (e.g. GC or HPLC) and mass spectrometers (MS), very low gas or liquid flows carry the to-be-analysed chemical compounds along with them.

In his blog ‘A closer ion them’ our analytical industry specialist shares his ideas about mass spectrometry and mass flow control.

In food machines, liquid additives such as colours, aromas and flavours have to be supplied accurately, to control the exact food composition.

For dosing flavours to your sweets the ultrasonic waves technology could be a solution. Read about it in our previous blog ‘Ultrasonic waves technology’.

Miniaturisation of high-tech machines

The miniaturisation trend is observed in many places. Small components need fewer quantities of raw materials, in production as well as in (chemicals) use. Customers of high-tech machines would like to have their equipment as compact as possible. Machines have to be smaller in size, as floor area is expensive, especially in cleanrooms - the 'natural' habitat of machines that manufacture solar panels and chips.

Compactness is also needed for online on-site analysis and monitoring - so outside the lab. Under those conditions, test equipment is preferably handy-sized. One would like to know on-site and in real-time what is going on - in order to react proactively instead of reactively, and to reduce the time to bring measuring samples to the lab. It is part of the online quality control: as a safeguard, but also to save on raw materials.

Removing the housings of standard products, and putting the components on a manifold gives a desired saving of space. Placing the input and output lines and connections on positions that are suitable for the customer often leads to a unique and compact solution. Compact devices with a combination of several analyses on a small surface area increase speed and reduce costs.


Read more about miniaturization in flow control in our blog The trend towards miniaturization in flow solutions. The latest technology is MEMS (micro electro mechanical system) technology, a micro-Coriolis mass flow sensor. Read about this new development of our R&D department.

Customized measurement systems

To stay ahead of competition, and to cope with fast evolving technological demands, the time-to-market is getting shorter and shorter. This asks for a new and flexible approach, where machine builders increasingly need to subcontract parts of their machine in a smart and efficient way.

Such a subcontractor is fully responsible for his part of the machine, and he takes away the worries of the machine builder in the field where he is 'king' - by supplying a total solution, preferably a compact unit. This 'subsystem' is a reliable combination of components that works as a whole, contrary to components that operate independently of each other. Moreover, the subsystem requires no more than one I/O connection.

The scrum methodology - known from software development - is ideal for this approach, in order to guide the process in a flexible way, using multidisciplinary teams that co-operate in short runs to anticipate evolving conditions and product demands.

Bronkhorst Customized Solutions

Smarter solutions

'Smarter' deals with the process to manufacture such a machine - as mentioned above - but also with the way the machine itself is being managed. Of course, each subsystem needs to be compatible with the rest of the machine, but it also needs to be well integrated - for example to be suitably controlled by the main control system of the machine. Preferably it should work instantly, tested and 'plug & perform' delivered to the machine builder.

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 help in developing and supplying customised flow solutions.

Watch our video about Bronkhorst Customized Flow Solutions and the Co-creating Process

Sandra Wassink
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It happens to all of us…. You want to go out for a jog, a walk or a bike ride and it rains! Luckily waterproof clothing or raincoats do exist. What interests me is how this type of clothing is manufactured, how does a fabric become waterproof or water -repellent and yet breathable? In other words, what is responsible for this anti-wetting behaviour? An answer to this question can be hydrophobic coating.

In today’s blog I would like to share a successful application with you regarding hydrophobic coating using a Controlled Evaporation and Mixing system (CEM).

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Hydrophobic coating Waterproof yet breathable clothing prevents rainwater drops from penetrating, and at the same time allows perspiration vapour to pass – a very desirable feature when going out exercising in the rain.

How can you make fabrics and textiles hydrophobic or add other functionalities to them without affecting the bulk properties of their fibers?

Empa, the Swiss Federal Laboratories for Materials Science and Technology Empa, a research institute of the ETH Domain and devoted to materials science and technology development, investigates and applies plasma polymerisation to deposit thin, nanoscale layers on top of fabrics and fibers, in order to functionalise their surface - and more specific: to make them water-repellent.

A Controlled Evaporation and Mixing system, also called CEM system, played an important role in this process, especially in the controlled supply of polymer precursors. A CEM system is an innovative Liquid Delivery System (LDS) that can be applied for atmospheric or vacuum processes. The vapor generation system consists of a (thermal or Coriolis) liquid flow controller, an MFC for carrier gas and a temperature controlled mixing and evaporation device. In one of our previous blogs ‘A new trend in vapour generation’ you can read about this technology.

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Plasma polymerisation process In this laboratory scale setup of a low-pressure (0.1 mbar) plasma polymerisation process, the liquid polymer precursor hexamethyldisiloxane (HMDSO) is evaporated and successively activated by the plasma with the aim to be polymerised and deposited onto the fiber surface as a hydrophobic coating. In order to obtain a stable and repeatable polymer precursor vapour flow, the liquid HMDSO flow as well as a carrier gas flow have to be controlled accurately.

A CEM system is used to evaporate the HMDSO. In this setup, liquid HMDSO is drawn from a container at room temperature and measured by a Coriolis flow meter. Then the liquid HMDSO is mixed with argon carrier gas from a thermal mass flow controller and vaporised inside a heat exchanger for controlled heating. The vapour flow is introduced into the plasma reaction chamber operated at 0.1 mbar absolute pressure. All controlled by a PLC system and visualised by LabView software.

HMDSO allows the deposition of polysiloxane coatings at low temperatures, which makes it feasible to coat textile fibres that cannot withstand high temperatures. Empa’s attempts to conduct the plasma polymerisation at low pressure aim at increasing the production yield by promoting heterogeneous deposition on the fiber surface, and by reducing the amount of chemicals.

After a successful experimental setup and test it’s Empa’s aim to upscale the process from laboratory scale to industrial scale.

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James Walton
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Why using a Controlled Evaporation and Mixing system can decrease food waste

We are all aware that the current level of food waste cannot be sustained if we have a hope of reducing food poverty across the world. This is not just a Western issue; globally food is lost or wasted at different points in the supply chain. Today’s technologies, such as sterilization, can help reduce this spoilage. However, the strict compliance requirements will ask for continuous improvement of this technology. An analysis from the Food and Agriculture organization of the United Nations highlights some discrepancies;

• In developing countries food waste and losses occur mainly at early stages of the food value chain and can be traced back to financial, managerial and technical constraints in harvesting techniques as well as storage and cooling facilities.

• In medium- and high-income countries food is wasted and lost mainly at later stages in the supply chain. Differing from the situation in developing countries, the behavior of consumers plays an important role in industrialized countries.

So, where can we make a difference?

Looking at the graph of food losses below, and the statements above, we can see that it is worthwhile to invest in production techniques, potentially to increase the shelf life of packaged food. This would have a positive impact on the waste of food in developed countries.

Food losses

[source: http://www.fao.org/save-food/resources/keyfindings/en/]

One of the ways to improve these figures is to improve the sterilization of the packaging that food is placed in, to reduce spoilage and increase shelf life. This is the point where Controlled Evaporation Mixing (CEM) systems come in the picture.

Bronkhorst share in extension of the shelf life

Sterilisation of packaging to extend shelf life is not something new, it already has been done for years. I believe the first aseptic filling plant for milk was already presented in 1961. However, it is a technology which has been improved tremendously throughout the years and still is improving. Bronkhorst has an extended range of instruments which can support you in this process. An ingenious development in this area is a Controlled Evaporation and Mixing system (also called a CEM), as one compact solution for industrial processes such as sterilization. The compact solutions consist of various type of instruments, such as liquid and gas flow meters and an evaporator.

Using Controlled Evaporation Mixing (CEM) systems for sterilisation

The challenge given to Bronkhorst via a customer that was using a Hydrogen Peroxide (H2O2) mix (containing 35% of H2O2 and water) to decontaminate carton and plastic packaging for liquid and cream filling. Using a mix of H2O2 is an excellent way to do this, because it is great at killing bacteria and can be easily evaporated. Bronkhorst is an experienced supplier of this kind of solutions.

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To get the best production with minimal waste you need to:

  1. Dose the correct amount of H2O2 mixture
    • Too much and the final product is spoiled
    • Too little and the residual bacteria is too high
  2. Avoid de-gassing of the H2O2 mix
  3. Have a controlled flow that condenses on the inside of the package
  4. Limit the flow. If it’s too high it will increase drying time at the end of sterilisation

The best result for this application was given by vapour generation combined with a Coriolis mass flow meter. Because H2O2 mixtures are not particularly stable this results in changing physical properties. Adding a Coriolis mass flow meter to the CEM made the measurement of mass flow medium properties independent. Furthermore as the Coriolis instrument is capable of measuring medium density, it can be used to monitor the concentration and thus watch over quality of H2O2.

Using a CEM system has some real advantages:

  • Stable temperature of vapour
  • Stable concentration of condensation because of a controlled dew point of the mixture
  • All of the above is possible because the gas, liquid and mixing temperature are controlled

Benefits as perceived by the customer

  • Stable liquid mass flow, even if physical properties vary
  • Monitoring the concentration and quality of the H2O2
  • Monitoring and traceability of the sterilisation process
  • Mass flow control of liquid
  • Mass flow control of gas
  • Direct control of dew point through control of gas and air mixture
  • Increased use-by-date
  • Longer life of fresh food


Controlled Evaporation System

Rob Giesen
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CO2 reduction is one of the major trends worldwide in the energy market. Nowadays alternative clean energy sources are more and more used to reduce the carbon emissions. One of these alternative energy sources is solar.

The global focus on CO2 reductions matches perfectly within the Bronkhorst principles regarding respect for nature and environment. Therefore contributing to the supply chain of a future energy source, in this case solar, is for Bronkhorst an interesting project.

Solar energy panels Solar panels will convert sunlight into electrical energy and can easily be placed in various locations as a decentral replacement of traditional power plants. A solar panel contains multiple wafers. Manufacturer Tempress Systems is involved in the diffusion doping process of the wafers and apply an anti-reflection coating.

The Tempress equipment contains Bronkhorst technology within the subsystem devolved for the generation of chemical vapour required for the diffusion doping process. Together with Tempress, Bronkhorst designed a custom made solution for this application

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Fit for purpose Due to the intensive collaboration between Tempress’ engineers and Bronkhorst, it was possible to design a ‘fit for purpose’ subsystem that is completely integrated in the Tempress system. The design was extremely compact. Furthermore the fully digital control of the custom made subsystem has been a huge advantage.

The power behind a successful solution One of the reasons for a successful low flow fluidic handling solutions development is the collaboration between Bronkhorst and her customer. The win-win situation is a motivation for both parties. Thinking of a compact ‘plug and play’ custom made solution which offers the logistic advantages of less suppliers, reduction in lead times and less inventory.
The new technologies which are developed on the road will help Bronkhorst to keep up with new possibilities for future projects.

I believe the success factor for the Bronkhorst Solutions team is the close cooperation with the customer working towards a joint objective. It’s like a good marriage; the subsystem does not work without the control system in the main system and the main system needs the intelligence from the subsystem in order to continue the innovative equipment status.

These are some thoughts about how a low flow fluidic handling subsystem can be part of a clean – solar based – energy future. I am proud, that I am a member of the team that realized this solution.

For more information about this solution, please read our application note ‘Boron and phosphor doping for solar panels’.