Ron Tietge
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The Christmas holidays are coming! And just like in everyday life, Bronkhorst products are important for many applications being used during the Christmas season. Whether it’s decorations or dinner, it stands to reason that flow meters have been used in their production. In this blog I will briefly explain different Christmas related flow applications, and how flow measurement and control is involved.

Adding fragrances in candles

Most of us light up a few candles to create a bit of ambiance during Christmas. But besides that extra light you get, they often also have something else to offer. Candles can make a room smell like literally anything. Candle manufacturers work closely with fragrance companies to develop scented formulas that are not only pleasing, but will also burn safely and properly. The addition of fragrance to a candle should be carefully monitored to ensure the candle burns cleanly and safely. For dosing the fragrances in a candle, Bronkhorst CORI-FILL dosing technology would be a very good option to use.

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Mass flow control at your Christmas dinner

In most households, Christmas is usually celebrated with a sumptuous dinner. Such a dinner is partly made possible by mass flow meters. These instruments are used for the production of multiple foods and beverages, like:

Bronkhorst instruments are also often used for sealing, coating and sterilisation the packaging of such things as juices or dairy products. Want to learn more about mass flow measurement for the production of foods and beverages? Read all about the different applications in this industry.

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Dosing Teflon on baking trays

During Christmas dinner my family and I always enjoy using a table grill. But isn’t it frustrating when food sticks to your grill grates? Luckily, the baking tray of a table grill often has a Teflon coating to prevent food from sticking to it. Here mass flow control comes into the picture. Mass flow meters are used to evenly spray Teflon during the production of baking trays for optimal accuracy and consistency.

Christmas LED lights

Christmas and lighting are inextricably linked, for instance when it comes to the sparkling lights that light up your Christmas tree. All those tiny LED lights sparkling away have been produced with the help of a mass flow meter. After all, the working principle of LED is via a two-lead semiconductor light source. The semiconducting material used in LEDs is basically aluminium-gallium-arsenide (AlGaAs), which is accurately applied with mass flow meters. Different wavelengths involved in the process determine the various colours produced by the LEDs. Hence, light emitted by the device depends on the type of semiconductor material used.

The applications explained in this Christmas story are just a fraction of the possibilities that Bronkhorst instruments have to offer. Flow instruments can be used in numerous applications and industries. To find the right flow meter for your application, please visit

And finally, I would like to wish you all a very Merry Christmas and a Happy New Year!

Egbert van der Wouden
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Natural gas has been an important source of energy for domestic and industrial use worldwide. Recent trends in energy supply have led to changes in the composition of the supplied gas in many countries. Due to these changes, it becomes even more important to measure the composition of this gas. Especially in small-scale applications a need for in-line measurement technology was detected.

For instance, in the Netherlands in the 1950’s a large natural gas reservoir was discovered near Slochteren which supplied a steady and constant source for many decades. However, production from the Slochteren field is declining and will be stopped in 2030. Therefore, the gas grid has to be fed with gas from different sources.

Natural gas

What natural gas from all sources has in common is that it is composed of methane, usually 75…95%. The rest of the mix typically consists of higher alkanes, like ethane and propane and fractions of nitrogen and carbon dioxide. The exact composition depends on the source of the gas, so when a grid is supplied with a variety of gases the composition will change. Furthermore, other recent trends contribute to the fluctuations in composition.

Trends in gas compositions

Natural gas is very suitable to facilitate in the increasing use of renewable energies. Biogas produced from renewable energy sources in biogas plants can, after proper treatment, be fed into the grid. However, biogas composition will depend on the feedstock, which is not always constant in time.

  • For more information about adsorption processes used for purification of bio- or natural gas, read our blog about Biogas Purification Testing.

Another important trend is power to gas or P2G; here electricity, produced from renewable sources like solar or wind, is used to produce a gas as an energy carrier. This can be hydrogen produced with electrolysis, or synthetic methane by combining carbon dioxide and hydrogen produced from electrolysis.

A major factor in renewable energy is the mismatch between supply and demand. As you can imagine solar energy is only being produced during daytime. Transferring electrical energy into chemical energy by producing combustible gases and feeding this in the national grid can help to balance this mismatch by utilizing the large buffer capacity of the available gas networks. Recent research, by for instance Kiwa, has shown that the current gas grid in the Netherlands can handle several tens of percent of hydrogen with limited modifications.

All these factors are leading to increasing changes to the gas composition in the network. Composition and quality are strongly correlated; increasing amounts of inert gases, like nitrogen or carbon dioxide, reduce the amount of energy produced when burned, also known as the calorific value. The presence of hydrogen in natural gas can change flame characteristics, such as temperature and flame speed.

Measuring the composition

With changing chemical compositions it becomes increasingly important to measure calorific value and components. With only a single point of entry, one measurement sufficed to analyse the composition in the downstream network. In the present day grid, networks are more intertwined and have multiple points where gases are blended. At every point of entry, it is necessary to measure the composition, not only for quality control but also for fiscal purposes. In this way, the suppliers can make sure consumers receive the quality they need and are charged for the heating value of the gas rather than the volume they receive.

The current standard for determining gas quality is gas chromatography; this method is very accurate but also slow and expensive. Alternative methods like calorimetry are similarly expensive and have a large footprint, making it hard to implement in small-scale applications.

All these future trends lead to a need for measurement technology that can be used in-line and in small-scale applications. This requires sensors that are compact, cost-effective and preferably measure composition.

New solution for gas property measurement In collaboration with:

  • TNO (the Netherlands Organisation for Applied Scientific Research),
  • Venne Electronics (a Dutch supplier of electronic products) and
  • Dutch gas grid operators Alliander and Gasunie

Bronkhorst is developing a solution for gas property measurement that can be installed in many installations for a wide range of applications.


Probe sensor concept with protective cover removed.

The operational principle of the concept is based on the preferential absorption of gas components on coatings that are applied to interdigitated electrode structures. The absorption is proportional to component concentration and results in a change in electrical properties that can be detected as a variation in capacitance of the coating.


DIE sensor (sensor with a small silicon circuit) with interdigitated electrodes and coatings.

Currently, the concept is being tested in the natural gas network of the Netherlands in close collaboration with grid operators and project partners, Alliander and Gasunie.


Methane concentration in the Dutch national grid measured with the concept and gas chromatograph.

Based on the measured components detected at the different coatings, the calorific value can be calculated, based on the concentration of the measured components. In combination with the integrated pressure and temperature sensor, other key parameters for the characterization of natural gas like; Wobbe Index, Propane Equivalent or combustion air requirement can be determined.

By using these parameters as input for a control system, users can optimize their processes to increase efficiency, reduce pollutants, or manage load. For instance in processes such as:

  • Monitoring of gas quality in the national grid
  • Process control in the production of biogas/synthetic gas
  • Motor management for gas engines and burners

Would you like to learn more about odorization of natural gas? Have a look at our blog ‘How Mass Flow Controllers make our gas smell’

  • Want to stay up to date on new flow solutions? Would you like to receive every month the latest tips in your inbox?

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.

Chris King
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Selecting the right flow meter is the key to success while selecting the wrong one means nothing but trouble. Flow meter technology has significantly increased the available choices for every kind of application. The right flow meter is essential for crucial data collection and the wrong one can lead to grief in the budget and costly lost production time. In this blog I will discuss some of the important elements that go into the decision-making process of a flow meter.

Price versus popularity, Most common criteria to select the flow meter

Beware of relying on two of the most common criteria that people tend to use in the selection process: cost and popularity. If you place price at the top of your criteria, it will be easy to get the wrong flow meter for the application or one that does not hold up physically or performance-wise. That bargain will quickly turn into a budget nightmare. If the measuring device and its ancillary equipment need frequent and expensive maintenance, what you saved on that flow meter will quickly dissipate. Moreover, a flow meter that has a higher initial investment can also make up for it by costing less to maintain and operate. Coriolis mass flow meters are more expensive in purchase initially than many other types of flow meters, but can save a great deal of money over time because they are easier to maintain, translating into less downtime.

A Set-up of Coriolis Mass Flow Meters (mini CORI-FLOW) A Set-up of Coriolis Mass Flow Meters (mini CORI-FLOW)

While it is important to research what type of flow meter is most commonly used in your industry, just selecting what is popular can also lead to disaster. If the flow meter is not appropriate for the application, measurements can be under or over which means valuable material can be lost and revenue negatively impacted.

New flow technologies offer new solutions

Advances in technology can also put instruments on the market that may not be as well-known, but provide a better solution. For instance, in the past, inline ultrasound flow meters had to be re-calibrated when a new fluid was introduced and could not be used in applications where hygiene was important. Nowadays new ultrasonic flow meters have solved those concerns and opened up the use of inline ultrasound flow meters to those types of applications. A flow meter is a highly technical device that is influenced by lots of variables. We’ll breakout the most important ones, but realize that every application is unique.

Ultrasonic volume flow meter (ES-FLOW) Ultrasonic volume flow meter (ES-FLOW)

Volume or Mass flow measurement

There are two basic measurements of fluids, volume and mass flow measurement, so a flow meter is either a volumetric flow meter or a mass flow meter. However, you can calculate volume from mass and mass from volume if you know the density and agreed upon variables. Whether a volumetric flow meter or mass flow meter is the best depends on the application, its components and the purpose of the measurement.

Flow meter categories

Some flow meters can be easily eliminated because they simply will not work with the application. For instance, electromagnetic flow meters will not work with hydrocarbons and require a conductive liquid to function. Many flow meters cannot measure gases or slurries. Listed below are some of the main flow meter categories paired with the fluid type the meters can handle.

  • Gas – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Area, Variable Differential Pressure, Positive Displacement, Turbine
  • Liquid – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Differential Pressure, Positive Displacement, Turbine, Electromagnetic
  • Slurry – Coriolis Mass, some subsets of Variable Differential Pressure, Electromagnetic, Ultrasonic
  • Vapour – Vortex, Ultrasonic, Diaphragm, Floating Element

Fluid properties

It is crucial to know the properties of the fluid being measured, below are some of the primary components:

  • Type of fluid – liquid, gas, slurry, vapour
  • Density
  • Viscosity
  • Temperature
  • Pressure
  • Condition of the fluid – foreign objects in it, suspended particles, air bubbles,
  • Other contaminants
  • Flow consistency – consistent or breaks, fill the pipe or partially fill or varies
  • Flow range – the minimum and maximum of the flow
  • Corrosive nature of the material – corrosive liquid or gas can deteriorate inline sensors

Physical properties

It is also important to know about the physical dynamics of the application site. Some of the physical properties of the site to consider are:

  • Configuration of the pipe before and after the flow meter and the length of straight pipe at the inlet and outlet of the flow meter.
  • The size of the pipe. Some flow meters have a poor performance with very small pipes and some cannot measure fluids in larger pipes
  • The material the pipe is made from
  • The surrounding environment and whether it is stable or variable
  • Will the flow meter work at a certain angle? This can seriously affect a flow meter’s performance Read in our previous blog why the choice of piping is important for thermal mass flow meters

Flow meter specifications

Last but not least, also the specifications itself have to be taken into consideration when selecting the right flow meter.

Accuracy – Naturally, an important factor of a flow meter is accuracy. To even suggest that accuracy is a variable seems ridiculous. Who would want an inaccurate meter? However, not all flow meters possess the same accuracy; some applications do not even require precision.

Thermal mass flow meters for gas (EL-FLOW Prestige) Thermal mass flow meters for gas (EL-FLOW Prestige)

Repeatability – Repeatability means the number of times (%) you get the same results running the same test or measurement under the same conditions. Accuracy requires repeatability, but repeatability does not require accuracy. It just needs consistency. Therefore, it can be said that repeatability of a flow meter is often considered even more important than accuracy.

Turndown Ratio or Rangeability – This implies the range that a flow meter can accurately measure the fluid. Usually, it’s best to choose a flow meter with the greatest range available without compromising other components that are more critical.

Hygiene requirements – Flow meters for food, pharmaceuticals, and the medical industry especially demand sterile environments.

Cost – As stated above, this should include installation, maintenance and repairs over time. How much the meter costs to operate, like its electrical demands, can also increase the overall cost of the flow meter.

As you can see, there are a lot of variables to finding the right flow meter and the ones we have listed are only the basics. This does not even touch on the various options in different models. The best way to get the right meter is to get help with your search and team up with experts in the field. Experience matters.

It is important to get your information from people who know these complex and important devices. To let Bronkhorst help in the search for the right flow meter for your needs, please contact us.

• When you have selected the right flow meter, the next step is installing this instrument. Graham Todd gives some useful tips when installing a mass flow meter.

Gerhard Bauhuis
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The so-called ‘Graphene Flagship’ originitated from the European Commission. This initiative has set a goal to concretise the development of Graphene before the start of 2020, from laboratory level to the consumer market.

What is graphene?

Graphene can be subdivided in three different types: single-layered, double-layered and multi-layered graphene:

  • Single-layered graphene is the purest form available with with unique characteristics. These characteristics make (single-layered) graphene an attractive product for a large number of applications.
  • Double-layered as well as multi-layered graphene have other (less qualitative) characteristics.

As the number of layers increases, it also becomes increasingly cheaper to produce.

In this blog I limit myself to only single-layered graphene, because as of today this type still gives the best result in various research.

Graphene is the world’s first 2D material that consists of only a single atomic layer of carbon; the same material that’s used in diamonds and penciltips. The carbon atoms in graphene are ranked in a hexagon structure. Single-layered graphene is characterized by the following properties

  • 200 times stronger than steel
  • 1.000.000 times thinner than a single human hair
  • The world’s lightest material (1 m² weighs about 0,77 milligram)
  • Flexible
  • Transparent
  • Impenetrable for molecules
  • Excellent electrical and heat conduction

Graphene can also be combined with other materials, such as gases and metals, to produce new materials with the abovementioned properties or to improve existing materials.

Graphene production

At this point there isn’t a method available yet to produce graphene on a larger scale against acceptable costs. However, this is still being researched.

Plasma Enhanced Chemical Vapour Deposition (PE-CVD)

There are a couple of different methods to produce graphene. One of the most common methods in single-layered graphene production is Plasma Enhanced Chemical Vapour Deposition (PE-CVD). In this method, a mixture of gases - in which at least one gas contains carbon – is heated until a plasma has formed. Mass flow meters and controllers are used in CVD processes to dose gases and liquids accurately.

In PE-CVD the plasma forms a graphene layer on a nickel or copper substrate. Heating takes place in a vacuum, but a more ‘green’ CVD process can be used as well, in which heating takes place under atmospheric pressure. By using Chemical Vapour Deposition large sheets of graphene can be produced.

Some of the precursors are liquids that need to be evaporated first, to be used in the CVD process in its gaseous form. It’s very important that the plasma is created with the right proportions and precision. This can be achieved by using highly accurate flow instruments. A deviation in the plasma can cause defects in the graphene layer. Defects can be impurities in the 2D structure that can change the unique properties of the material.

3D-Model structure of graphene

3D-Model structure of graphene

Research for high quality graphene by using atmospheric pressure plasma-based techniques

Our Spanish distributor, Iberfluid Instruments S.A, recently cooperated with the University of Cordoba in a research to investigate the opportunities regarding graphene production on a large scale by using a plasma based technique under atmospheric pressure. In this research ethanol was evaporated with the use of Bronkhorst evaporation system, the so-called Controlled Evaporation and Mixing (CEM) system, to form a plasma. With the use of an evaporation system liquids are being evaporated directly to create the right gas for the plasma. A possible setup of such an evaporation system can consist of a CEM system with an additional liquid flow meter (i.e. a Coriolis mass flow meter, from the mini CORI-FLOW series) for ethanol, a gas flow controller (i.e. an EL-FLOW mass flow controller) for argon, which functions as a carrier gas and finally a temperature-controlled control valve or mixing valve.

An evaporation system like the Bronkhorst CEM system can deliver excellent performance in terms of stability and accuracy. These properties guarantee a reliable creation of plasma, which eventually leads to higher quality graphene.

Bronkhorst CEM system for research at the University of Cordoba

Bronkhorst CEM system for research at the University of Cordoba

In the research document ‘Scalable graphene production from ethanol decomposition by microwave argon plasma torch’ is described why the University of Cordoba (ES) uses the Bronkhorst Controlled Evaporation and Mixing system in the PE-CVD graphene production process.

Areas of application for graphene

Due to a large amount of unique properties research takes place in numerous areas of application. The main focus is on single-layered and double-layered graphene. For now it seems that single-layered graphene still gives the best results. At the same time the use of so-called flakes has been taken into account. These flakes are tiny pieces of graphene which can be mixed with another material, such as polymers. The properties of these materials can be improved by adding graphene flakes, which makes graphene widely applicable in different industries. A couple of examples based on single-layered graphene:

  • Water purification: Scientists are currently developing an advanced filtration system based one graphene oxide that is being used to make polluted water drinkable.
  • Medical industry: Since graphene isn’t poisonous for the human body, research is being done to the possibilities to use graphene in medicine transport in the body, by attaching the medicine to the graphene. Graphene also has the properties to prevent bacteria formation, which makes it ideal to use as a coating for implants.
  • Energy industry: Because of the large surface and excellent electrical conduction, graphene could be used in energy storage. The goal is to make graphene batteries more compact than they are now, while increasing the capacity to make it possible to charge batteries within seconds.
  • Textile industry: Graphene could be used to process electronics in textiles, such as effective, efficient and highly accurate sensors. Furthermore, graphene anti-corrosion coatings and conductive inks can be made.
  • Semiconductor industry: Thanks to good electrical and thermal conductivity, graphene offers possibilities to increase the speed and capacity of chips (for computers and smartphones).

We continue to closely monitor the developments of graphene and we will keep you informed.

Dr. Christian Monse (IPA)
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The emission of nitrous oxides (e.g. NO2) into our atmosphere is a global issue these days. Everywhere researchers and developers are working on better and more accurate simulation and measurement methods, as well as on the development of more efficient catalysts. This applies both to stationary combustion processes (e.g. power plants, steel production and chemical base materials) and to mobile applications in the automotive sector to reduce the NO2 with selective catalytic reduction (SCR). Ammonia or ammonia forming compounds (urea) are added to form pure nitrogen and water.

NOx, a generic term for nitrogen oxides that are most relevant for air pollutions, is a mixture of different nitrogen oxides; nitric oxide (NO) and nitrogen dioxide (NO2). The focus here is on NO2 radicals and its dimer dinitrogen tetroxide N2O4. NO2 is toxic and emissions to the environment should be kept as low as possible. However, NO2 occurs as a by-product in a large number of combustion processes, so that both technical developers in the industry and developers of occupational and preventive medicine have to deal with this substance.

However, this equilibrium also poses the problem of measuring and controlling gas flows containing NO2 in higher concentrations. Especially when using pure NO2, which is in balance with its dimeric form N2O4, which is temperature and pressure dependent and additionally influenced by light and surface conditions (at 27°C only 20% is present as NO2, the remaining 80% as dimer N2O4). The mixture is very sensitive to moisture and can react with humidity to nitric acid (HNO3) and nitrous acid (HNO2), which in turn are highly corrosive.

Gas mixtures with NO2

For investigations of combustion processes with NO2 emission or the testing/ new development of catalysts, a precisely known flow rate of gas mixtures with NO2 must be realised. This applies not only to catalysis but also to the effect of NO2 on the organism and the environment, because NO2 is highly toxic due to its reactivity.


In one of our projects a system consisting of a gas cylinder, needle valve, backwash unit, transfer lines and mass flow controller should be constructed, which can dose nitrogen dioxide (NO2) in the range between 0- 6 g/h against room pressure.

Challenges with thermal mass flow

Common mass flow meters and mass flow controllers work with thermal measuring principles (with bypass sensor or according the CTA principle (Constant Temperature Anemometry)). Thermal sensors operate on the principle of heat transport in the sensor element. This method depends on the type of gas, since the heat transport depends directly on the heat capacity and the thermal conductivity of the gas to be metered.

Since NO2 has a temperature and pressure-dependent equilibrium with N2O4, the parameters in the sensor element can change constantly. Consideration of the equilibrium using a single conversion factor to a reference gas is not sufficient, especially for pure NO2 or N2O4. Through gravimetric tests, we have determined that massive under-dosing can occur at a dosage of pure NO2 (approx. 10 % of the target value).

A further challenge with a thermal mass flow controller in the closed state, corresponding to a flow rate of 0 ml/min, is that it can produce pseudo signals of up to 10% of the maximum dosing range. The reason for this is that the sensor element contains a mixture of NO2 and N2O4, which is constantly influenced by the active heating of the sensor element. Thus, a heat transport in the device is faked and a flow rate is indicated.

The solution: Use of a Coriolis mass flow controller

The remedy here is a Coriolis mass flow controller instead of a thermal mass flow controller due to its different working principle. It does not matter to what extent the balance of NO2 and N2O4 is on one side or the other, since it is all about the transported mass. When using a Coriolis mass flow controller, however, it must be ensured that the medium to be metered is in a defined physical state, i.e. either in a completely liquid or gaseous state.

Coriolis Mass Flow Meter Mini CORI-FLOW ML120

The boiling point of NO2 at atmospheric pressure is 21 °C, so the complete dosing system, consisting of gas cylinder, needle valve, backwash unit, transfer lines and mass flow controller, can be heated here. Since evaporative cooling occurs inside the mass flow controller when dosing NO2 at the pressure relief point, the temperature there must be set significantly higher than 21 °C. Only at a temperature of at least 45 °C is it ensured that the dosing functions in the range between 0-6 g/h without fluctuations due to condensing and re-evaporating NO2. In this setup a Bronkhorst mini CORI-FLOW ML120 was used, which is the Coriolis instrument with the lowest flow control range in the world. So it is possible to dose even these small gas amounts of NO2.

Check the nitrous oxides (NO2) dosage

The dosed NO2 quantity is checked with the aid of gravimetric measurements. NO2 is transferred via a heated transfer line to a glass U-tube with stopcocks where it is frozen out at -50 °C. The shut-off valves are then closed, the condensate thawed to room temperature and weighed. A total of five different mass flows were tested. The figure shows the result of the check and confirms the very small deviations between the desired and actual dosing quantities. In addition, it can be seen that the mass flow controller operates linearly in the tested range between 0.1 and 4.0 g/h (single points: 0.1; 1.0; 2.5 and 4.0 g/h with error bars drawn in).


This proves that precise control for small quantities of NO2 can be achieved even at low inlet pressures. As mentioned, nitrogen dioxide (NO2) is a substance of the mixture nitrogen oxides (NOx). Reducing the level of NOx can also be done with Selective Catalytic Reduction (SCR). In case of Selective Catalytic Reduction (SCR) Ammonia or ammonia forming compounds are added to form pure nitrogen and water.