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 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

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Controlled Evaporation System

Chris King
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The National Aeronautics and Space Administration (NASA) recently redesigned the system used to test the new space suit Portable Life Support System (PLSS) that is under development. In order to test the PLSS a simulated human metabolic load must be applied to the various sub-systems and so NASA needed to simulate the human production of CO2 and water vapor with its associated heat load.

Working closely with NASA engineers to fully understand the application requirements, Bronkhorst learned that accurate, stable control of water vapor was critical to efficient and repeatable testing and therefore successful development of the PLSS.

The recommended Bronkhorst solution was a CEM (Controlled Evaporatorion and Mixing) system to properly control the mass of water being vaporized as well as the amount of CO2 in the vapor. NASA has three CEM systems connected to an outlet manifold. Each CEM system consists of a liquid mass flow controller (H2O), a gas mass flow controller (CO2), a Controlled Evaporator Mixer, and a readout/control unit. The three connected CEM systems are collectively referred to as the Human Metabolic Simulator (HMS).

NASA CEM System

The Bronkhorst HMS equipment is controlled via analog (0-5 Vdc) signals through the Bronkhorst readout/control units (1 per CEM system) which in turn are connected to the NASA main test system running NASA’s customized LabVIEW software.

This setup allows NASA to simulate those aspects of human metabolic output up to a rate of ~3500 BTU/hr, or a bit over 1000 Watts, by injecting the CO2/water vapor mix into a simulated spacesuit volume containing a manikin (“Manny”) which is wearing a Liquid Cooling and Ventilation Garment (LCVG). The LCVG removes sensible heat to keep the human core temp in nominal range, and also provides some latent heat removal via condensation of human-generated water vapor on the surface of the cooling tubes.

To complete the human metabolic load simulation, NASA has placed controllable heaters on the CO2/H2O vapor deliver lines to prevent condensation and to add super-heat as needed. Additionally, they have controllable electric heaters on the manikin body to simulate sensible heat generation by a human being working at various levels of effort. There is also a Bronkhorst Mass Flow Controller to remove gas from the suit at rates that simulate metabolic consumption of suit gas as well as suit leakage.

Learn more about Bronkhorst's Controlled Evaporation Mixing 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’.

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