Michaela Aufderheide
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Prof. Aufderheide has been working for more than 30 years in the field of cell-based alternative methods with a focus on inhalation toxicology, which studies the effect of airborne substances on the epithelial cells of the respiratory tract. For this research, she has developed special equipment together with colleagues: the patented CULTEX RFS module, which makes it possible to treat the cultivated cells with these active substances directly. Increasing pollution of the environment and workplaces demands new testing methods to predict the level of risk presented by such substances. The high sensitivity of biological testing systems requires a stable and precise technological set-up to test of such atmospheres where, in addition to the CULTEX technology, mass flow controllers are of vital importance in adjusting and controlling the aerosol flows over the cells.

The e-cigarette

The history of humankind is characterised by its receptiveness to stimulants. Since the beginning of time, these substances have included intoxicants such as alcohol, as well as smoking. Although we are all aware of the health risks, 'most people only give up their vices when they cause them discomfort' (William Somerset Maugham).

This adage is particularly true of smoking. It is widely known that excessive smoking increases the risk of cardiovascular diseases and lung cancer, yet we still yield to the temptation of the 'nicotine fix'. Epidemiological studies have repeatedly shown the harmful effects of this addictive pleasure, but attempts to quit smoking often fail, despite the certain knowledge that every cigarette can be one too many.

In response, the cigarette industry is propagating the e-cigarette as an alternative. Combustion of tobacco releases thousands of harmful substances that are of course inhaled by smokers as well. In contrast, the e-cigarette lets you inhale a vapour that does not contain any products which present a risk to your health; at least, it is claimed. This 'vapour' is created from an aromatic liquid (main ingredients include propylene glycol, glycerine, ethanol, various flavourings and nicotine, as required) using a vaporiser.

Accordingly, the electronic cigarette is marketed by the cigarette industry as a 'healthier' alternative to traditional cigarettes or a means to help people quit smoking. A lot of money is being invested to prove scientifically that e-cigarette products are less harmful than tobacco products. This statement is essentially true. However, it does not really answer the question about the effects of the 'vapour'. Epidemiological studies, such as those for cigarette smoking, are not available and no one can therefore rule out that excessive or long-term consumption could cause harm to users’ health.

Figure 1: A. CULTEX®RFS Compact with 6 transwell positions that are exposed separately to the test atmosphere. B. The test atmosphere is sucked centrally via the mass flow controllers into the module in a controlled manner, distributed radially to the cell culture vessels and drawn continually across the cells. Image description

In vitro studies

So how can I now approach this question? The only remaining option is to carry out in vitro studies. To do so, we use living cell cultures as an alternative to animal experiments.

Inhaled active substances first reach the epithelial tissues lining the lungs. These tissues are made up of a multitude of cells that serve to defend against or inactivate the inhaled substances based on their special functions. We find mucus-producing cells here whose secretions 'capture' harmful substances, as well as cilia-bearing cells that can transport the mucus away. Other cells have a detoxifying effect, while we have sufficient replacement cells in an intact body which can replace the function of damaged or dead cells. In the field of cell-based research, we can make these human cell populations available for research (see Figure 2A). These cells are cultivated in so-called transwells on microporous membranes, where they are fed nutrients from the underside of the membrane while the apical (outer) part of the culture can react with the surrounding atmosphere.

Figure 2: Cross-section of cell culture insert membranes with HE (Hematoxylin and Eosin) stained immortalized NHBE cells (CL-1548). After 21 days of cultivation at the air-liquid interface, the cells were exposed repeatedly (daily for five days and after a recovery phase of two days again on three subsequent days, maximum exposure cycle: 8 smoke exposure repetitions) to clean air (CA), mainstream cigarette smoke (CS; 4x K3R4F cigarettes per run according to ISO 3308, University of Kentucky, Lexington, KY, USA) and e-liquid vapor (EC) without nicotine (Tennessee Cured, Johnsons Creek, Hartland, WI, USA). K3R4F cigarettes were smoked by a smoking robot and operated as follows: 24 puffs with a volume of 35 mL in 2 s, a blowout time of 7 s and an inter-puff interval of 10s. The electronic cigarette type InSmoke Reevo Mini (InSmoke Shop, Switzerland) was handled in a comparable manner: 50 puffs (volume 35 mL, puff duration 2 seconds, low-out time of 7 seconds) with an inter-puff interval of 10 s.

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Mass Flow Controller – the guardians of cell exposure

Over a number of years, we have developed efficient cell exposure systems: the CULTEX®RFS module, which allows for a direct, stable and reproducible exposure of lung cells at the air-liquid interface ([ALI); see Figure 1A). Their stability in particular guarantees significant results, due to the aerophysically adjusted design of the CULTEX®RFS module on the one hand and the use of the computer-guided mass flow controller on the other (Bronkhorst IQ+FLOW series and EL-FLOW Select series), the control and design of which have been adapted to cell-based exposure. The flow control ensures a precise and reproducible atmosphere for the exposure of the cells to the test gases. It is primarily the robustness of the experimental design which delivers results that allow us to draw conclusions about the effect of the respective test atmospheres. In this case, the various cells were exposed in an unpressurised atmosphere to the e-cigarette vapour (50 puffs per run) and compared with normal cigarette smoke (24 puffs per run); the cells were exposed to the respective doses for 8 days. A control was provided in the form of cells exposed to clean air.

The remarkable results are summarised in Figure 2. Comparing histological preparations of cells treated with smoke and e-cigarette vapour to the clean air control confirms the expectation that cigarette smoke causes a clear reduction in mucus production as well as the number and occurrence of cilia. A comparable – albeit less pronounced – effect could also be observed for the e-liquid aerosol after this treatment period, however. Compared with the cells exposed to clean air, we observed a significant effect that certainly should give us pause for thought. The statement that the 'vapour is less harmful than smoke' must not be confused with the conclusion that the vapour is not harmful at all. In the future, this problem will have to be addressed in order to tackle long-term harm through preventive means.

Products used in this research are IQ+FLOW mass flow controller and EL-FLOW Select thermal mass flow controller.

Harry Bosvelt
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Maintenance represents a key issue for many organisations due to the ongoing digitisation of production processes. Maintenance can be broadly defined as all aspects relating to the effective performance of mass flow meters and controllers. Maintenance may consist of corrective maintenance – maintenance conducted when needed, e.g. after contamination – or preventive maintenance, where instruments are periodically returned for servicing or calibration. Today's instruments are increasingly future-proof and 'intelligent'. In addition to the rise of condition-based maintenance, we are also seeing a shift towards predictive maintenance, which helps reduce unscheduled downtime and wastage. Regulations are also having a growing impact on maintenance, with numerous markets introducing more and more instrument maintenance requirements.

The importance of effective maintenance

The maintenance of mass flow instruments is of crucial importance to Bronkhorst customers. Bronkhorst mass flow instruments have a highly robust design and are resistant to wear under normal circumstances. Instruments are increasingly being utilised under extreme process conditions. Effective maintenance can reduce the likelihood of sudden failures under such circumstances. Unexpected downtime triggers direct costs in terms of the extra hours that staff need to check and recommission the instrument. Moreover, this downtime also has a negative impact in terms of short-term yields or production quality and potential long-term reputational damage.

The aspect of maintenance plays a considerable role in Industry 4.0. Following the invention of the steam engine, mass production driven by electric engines and far-reaching automation, we are currently in the midst of the fourth industrial revolution. The current revolution is characterised by the application and exchange of data through high-speed network connections, yielding more efficient and intelligent production techniques. This development is also referred to as 'smart industry'. Among other motivating factors, Industry 4.0 is driven by the desire to reduce the cost of ownership. The associated digital technologies can be applied to cut maintenance costs by 30% or more and reduce unscheduled downtime by over 70%. *1) Given these high figures, there is certainly much room for improvement.

What did the maintenance of mass flow instruments look like in the past, what does it look like in the present and what – according to Bronkhorst – will it look like in the future? And what will be the role of Industry 4.0?

Maintenance through the years

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Corrective maintenance

In Bronkhorst's early days, corrective maintenance was still the industry standard. Most mass flow meters and controllers were still analogue and did not have any diagnostic parameters. Any instruments in need of maintenance were either shipped to Bronkhorst or serviced by a visiting technician. This method was extremely costly and time-consuming due to the lengthy downtimes involved. The company's worldwide service network was later restructured, and currently comprises 20 GSOs (Global Service Offices, authorised service departments around the world) and a 24/7 help desk. Spare parts were kept in stock in order to ensure rapid service.

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After-sales field support

Preventive maintenance

The digital age – which started after the turn of the century and is currently still more or less ongoing – marked the rise of preventive maintenance. Customers periodically returned their instruments to a Bronkhorst service department for maintenance and calibration. Although this still required a great deal of planning and time, the necessary downtime was more or less planned. Despite reducing the likelihood of unscheduled downtime, this form of maintenance offered no guarantees: things could still break down.

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Service department

Since 2004, instruments can be read remotely through a service we call 'Remote Support'. Working remotely, our support staff can observe the on-site situation and identify instabilities in the customer's process or other issues. The customer connects the instrument to a PC or laptop with online connectivity. The instrument's status can be read on the basis of internal diagnostic parameters. We then use the status indication or findings to identify appropriate measures in consultation with the customer. For example, we can adjust the control setting (PID values) if a process is not being regulated effectively.

A recent case in point: a Canadian customer recently called our Worldwide Support Line. He informed us that an analyser connected to his Bronkhorst vapour flow control (Controlled Evaporation Mixing, or CEM) system application was failing to detect water. Our Remote Support staff used Bronkhorst software to determine that the customer had incorrectly configured a specific control setting: the Bronkhorst liquid flow regulator was not receiving the correct setpoint value, causing the water supply control valve to stay closed. The solution? We worked with the customer to find the appropriate settings for the process, instantly resolving the issue. As a result, there was no need to ship the instrument to our service department or schedule a visit from our technician, saving valuable time and resources.

Ready for the future

As part of efforts to improve our Remote Support, we will soon be introducing an additional service in the form of Bronkhorst Expert Eye. Expert Eye is a smartphone app with video support. The app enables customers to connect with Bronkhorst service staff directly to receive live support. The video and audio connection allows us to provide immediate advice.

In the future, we aim to upgrade the intelligence of our instruments in order to service our customers more effectively. The data applied by our existing instruments contain valuable information on the instrument's condition or process quality of the mass flow controller's overarching system. We aim to apply these data towards more effective preventive maintenance, process monitoring and process optimisation.

We look forward to improving the app further in collaboration with our customers. Please feel free to contact us for further details on specific data solutions for mass flow controllers and condition-based and preventive maintenance.

Source: Driving Unconventional Growth through the Industrial Internet of Things (2015)

Jean-François Lamonier
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Jean-François Lamonier, a lecturer/researcher at the University of Lille, is an expert in the catalytic treatment of volatile organic compounds (VOCs). He leads the 'Remediation and Catalytic Materials' (REMCAT) research team in the Laboratory of Catalysis and Solid State Chemistry (UCCS), which specialises in the catalytic removal of atmospheric pollutants emitted by both fixed and mobile sources (such as factories and vehicles, respectively). In this blog post, he tells us about his research and explains how his team uses measuring instruments and flow controllers.

Focus areas for the REMCAT research team

REMCAT (Remediation and Catalytic Materials) research team of the Laboratory of Catalysis and Solid State Chemistry (UCCS)

The REMCAT team comprises six lecturer/researchers. Our work is focused on catalytic after-treatment of atmospheric pollutants, primarily nitrogen oxides (NOx and N2O) and volatile organic compounds (VOCs). Our team possesses broad knowledge in the field of heterogeneous catalysis: from catalyst synthesis to characterisation of new catalytic formulations, evaluation of their performance through comprehensive testing, advanced characterisation of catalysts using operando infrared spectroscopy, reaction kinetics and reactor modelling.

Air pollution treated efficiently by combining non-thermal plasma with catalysis

This set of skills in environmental catalysis allows us to develop original processes that involve combining different technologies to devise a cheaper, more effective and more environmentally-friendly method of treating air pollution. In this context, we collaborate with various national and international research groups, such as the 'Research Unit Plasma Technology' (RUPT) at the University of Ghent. This research unit specialises in developing plasma reactors; we lend them our expertise in heterogeneous catalysis to help develop processes to couple non-thermal plasma with catalysis. This research is being conducted in an International Associated Laboratory on 'Plasma-Catalysis', which we recently created under the auspices of the European INTERREG V 'DepollutAir' project, which is currently funding our research.

Using adsorption functionality in plasma-catalytic transformation processes

Traditional plasma-catalytic processes to remove volatile organic compounds (VOCs), which are present in industrial waste gases, require a continuous energy supply. Our approach is to insert an earlier step in the plasma-catalytic transformation process involving adsorption of the pollutant. This enables the plasma to work sequentially to remove the volatile organic compounds and means the adsorbent is regenerated, resulting in substantial energy savings. Our team is lending its expertise to the development of new adsorbent/catalyst materials and to the advanced characterisation of these materials.

Using flow meters and flow controllers in the catalytic treatment of volatile organic compounds (VOCs)

In our research, we need to generate mixtures of VOCs to simulate industrial waste gases. As these waste gases are different for each type of industry and we need to be as representative as possible of industrial realities, we have to be able to generate gas flows with highly variable VOC levels, containing VOCs of many different types, such as formaldehyde, toluene, chlorobenzene, trichloroethylene and butanol.

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Dilution system with Coriolis flow meter

To this end, we use a dilution system supplied by Bronkhorst, which comprises a Coriolis flow meter, a pressure regulator (overflow valve) and a number of mass flow controllers. We needed a device that would enable us to achieve low concentrations of VOCs, because increasingly restrictive standards have resulted in a decrease in atmospheric VOC levels. We also needed the system to be as flexible as possible, so it could adapt both to the nature of the various liquids injected into the system to be transformed into gases and to the VOC levels in the waste gases, which can range from 10 to 1000 ppmv.

Catalytic formulations

The relative humidity of the waste gases is an important parameter to take into consideration when developing catalytic formulations. As you might imagine, the presence of steam can have a positive or negative effect on the performance of the catalytic process. Consequently, the system for generating the gases must also be able to generate a variable relative humidity in the gas mixture.

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Furthermore, to develop a catalytic formulation suitable for industrial applications, we not only need to verify that the catalyst is both active and selective (in other words, that the catalyst can produce the desired products), but also that it is stable over time. It’s hard to imagine a catalyst that only works for a single day and has to be replaced the next day.

That’s why we need to reproduce an industrial waste gas stream that remains constant for several days. If we’re performing a catalytic test over the course of a single day, we might consider using a bubbler system. However, when we need to check the stability of the catalysts over time, we conduct long-term tests to see if the catalyst is capable of maintaining its activity over several days. It would be more complicated to conduct tests over time using a traditional system, but the Bronkhorst system generates a constant, continuous, smooth flow of VOCs into the air. This is a distinct advantage that enables us to validate our process.

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To find out more about Bronkhorst’s dilution solutions Click here for more information about the research of Jean-François Lamonier and the REMCAT team from the Laboratory of Catalysis and Solid State Chemistry.

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Jornt Spit
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This time’s guest blogger is Dr Jornt Spit. He’s a researcher at the Radius research group at Thomas More University of Applied Sciences in Belgium, and has a background in biochemistry and biotechnology. The Radius researchers are working on renewable biomass, involving the cultivation of algae and insects that are then processed into valuable raw materials for a bio-based economy. As part of their research activities, they use Bronkhorst mass flow controllers to enable precision flow of carbon dioxide.

CO2: a valuable alternative carbon source

In recent years, carbon dioxide (CO2) has been steadily attracting attention as a valuable source of carbon. Of course, the rising concentration of CO2 in the atmosphere is a major and growing concern, and this is driving an increasing focus on sustainability in society. In line with this, we at Thomas More are working to achieve a more circular economy and a more bio-based economy. This means obtaining materials, chemicals and energy from renewable (energy) sources, and not from fossil fuels. Alternative biomass could become a major source in this approach.

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Currently, the main activity of our research group is cultivating renewable biomass, partly in the form of algae. We’re doing this under controlled conditions in the horizontal tubes of a photo-bioreactor. We use pure gaseous CO2 as the source of carbon. We’re cultivating algae with a view towards various applications. Algae can be very useful in the cattle feed sector, for instance, or in the food sector, the health products or ‘neutraceuticals’ sector or the cosmetics sector. Our research group is not heavily involved in further developing these applications – we’re focusing on optimising the cultivation of the algae, or in other words the process technology aspect.

Algae for conversion into valuable raw materials

Micro-algae form a really large and diverse group. More than 50,000 different species of algae have been identified and there are probably many more, running into hundreds of thousands. They are single-celled organisms, but can sometimes also form colonies. Algae are photoautotrophic organisms, which means that they use CO2 as a source of carbon and then convert this into sugars by means of photosynthesis. The micro-algae that we cultivate contain a particularly large amount of interesting substances: proteins, sugars and fats being the main groups. In addition, the micro-algae also make high-value chemicals such as pigments and antioxidants. To give one example, we at Radius cultivate a special alga that produces the valuable red colourant phycoerythrin. You can pretty much regard algae as tiny factories that can produce all kinds of substances that we need – so in order to synthesize these substances, we don’t need to completely reinvent the wheel. The various algae cells have evolved under evolutionary pressure to make these interesting substances, simply using a little sunlight, CO2 and a few nutrients. That means there’s a huge potential for utilising these substances.

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An algae culture increases in density through cell division. If conditions are right, then the algae will continue their cell division until a culture reaches its maximum density. At this point, the algae are harvested, so the algae biomass itself is the product. In our closed photobioreactors, we achieve a density of 1 to 2 grams of dry material per litre. When this point is reached, we take the algae out. This biomass can be directly used for food purposes or as cattle feed, but we can also further process the biomass, ‘break it open’ and extract the most interesting substances. If we take this latter approach, it’s called bio-refining or extraction. The whole process of cultivating, harvesting and further processing the algae presents a major challenge. That’s because each step is important and has to be carried out as efficiently as possible to ensure that the entire operation is profitable.

Mass flow controllers for precision flow of CO2

To optimise growth, it’s important to select an alga that grows well under the conditions we can provide in our unit. Not all algae species can absorb CO2 with the same efficiency, and not all algae grow equally fast. In our research, we find out which temperatures are best for growing the various species of algae, and how much light a particular alga needs. Here on the campus, we use natural sunlight: the photobioreactors are in a greenhouse. As a result, the algae grow during the day, when the sun shines, and not at night. One of the research questions we are investigating as part of the ‘EnOp’ Interreg project is: if we add extra CO2 to the reactor, how much faster will the algae grow, and which algae types absorb the CO2 most efficiently? In order to answer this question, we need mass flow controllers, because we want to know exactly how much CO2 we have added.

The CO2 is mixed with inflowing air that is channelled to the reactor, after which the CO2 dissolves in the liquid culture fluid, which also contains other nutrients. Since CO2 (carbon dioxide) is a weak acid, the pH level of the fluid steadily falls. This has a negative effect, because most algae grow best at a pH level between roughly 7 and 8. However, as the algae grow, they absorb CO2 from the fluid, making the pH rise again. The acidity level is a highly critical factor – if the pH moves outside the desired zone, then the algae tend to flocculate. The dosing system is therefore linked to the pH level, to optimise the supply of CO2 as precisely as possible. In this way, we can establish the maximum growing speed of the alga and how much CO2 we need to add to achieve this.

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If we add too much CO2, then the pH of the fluid will fall too strongly, and the algae won’t grow enough. If we don’t add enough CO2, that in itself isn’t a problem, but the algae will grow more slowly, because their growth is limited by lack of carbon dioxide. For each alga, an optimum amount of CO2 can be added. Moreover, the CO2 needs to be given time to dissolve in the fluid. If the CO2 doesn’t dissolve, then it will ultimately escape from the reactor again, which means you’re simply wasting CO2. Whether the CO2 is effectively dissolved and absorbed therefore needs to be taken into account as well. The design of the reactor plays an important role in managing this aspect.

As you might have noticed, precision is very important in this process. The mass flow controller ensures that we can keep the whole process stable around the right pH level and that we know exactly how much CO2 has been added.

…and the future?

If this process is scaled up to actual production scale, then logistics will become a major factor in determining where the CO2 comes from. In principle, it’s possible to use exhaust gases straight from factories, but then you need to remove substances like sulphur oxide and nitrogen oxide, which are also present in these flue gases. If the levels of these substances are too high, they will inhibit the growth of the algae. There are technical solutions to this problem, however. The next question is: how far away can the algae factory be from the CO2 source? If this distance is too great, then the CO2 will have to be transported in another, controlled form, such as bicarbonate. Another option is to develop CO2 air-capture units that enable local extra CO2 to be extracted from the air. The University of Twente is working on this technology in another Interreg algae growth project, known as IDEA and currently running in North West Europe. The Radius research group at Thomas More UAS is also involved in this project. In technological terms, we know it’s possible, but the crucial point is how much the technology will cost.

Links to:

• Read the complete application story ‘Controlled CO2 supply for algae growth’; • More information about Thomas More UAS; • More information about the ‘Enop’ project for energy storage using CO2 conversion technologies; • More information about the ‘IDEA’ project for implementation and development of economically viable algae-based value chains.

Jornt Spit was interviewed by Eddy Brinkman to produce this blog (Betase/Bronkhorst)

Dirk Jan Boudeling
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Today I would like to share an application story with you using mass flow meters in an application at Umicore in Suzhou (China). Umicore is one of the world’s leading producers of catalysts used in automotive emission systems. The company develops and manufactures high performing catalysts for, among other things, gasoline and diesel engines to transform pollutants into harmless gases, resulting in cleaner air.

Umicore’s production location in Suzhou ‘Umicore Technical Materials’ is using Bronkhorst Mass Flow Controllers and Vapour Systems for research and testing of automotive emission catalyst materials. Newly developed catalytically active materials of Umicore consist of oxides and precious metals, such as platinum and palladium, incorporated into a porous structure which allows intimate contact with the exhaust gas.

What catalyst materials does Umicore test?

Umicore in Suzhou uses various test benches in which newly developed catalytic materials are tested on performance (read: low output of toxic emissions). “Umicore develops new catalysts directly with top-tier automobile manufacturers in China. We are testing new formulations of materials and shapes of the catalysts on performance” explains Mr. Yang Jinliang.

Umicore project with Bronkhorst flow meters

How are the mass flow meters and controllers applied for identical testing and simulation?

The Bronkhorst mass flow meters and controllers are used to accurately deliver the right amount of several gases in a mixture that simulates the exhaust of an engine in different circumstances. “To really compare the performance of newly developed formulations, we have to be sure that the operational conditions of our tests are identical.” Mr. Yang explains that this requires the use of high performance mass flow controllers to accurately mix the simulated exhaust gas.

“We need flow control equipment which is reliable and has excellent repeatability during our simulation runs. Therefore Umicore developed the test equipment together with the Bronkhorst flow specialists.” Umicore runs various simulations. “We simulate exhaust gases of engines under various life cycle simulations and operating conditions. For example, the exhaust gas of the car is different if the engine is still cold or if the engine has a high number of revolutions.”

Test bench for ageing simulation

One special test bench of Umicore simulates the ageing of the catalyst materials. This has been achieved by heating the ambient temperature of the Catalyst up to 800° Celsius for a couple of hours up to 24 hours in a test run while adding the simulated exhaust gas. “Here the Bronkhorst instruments prove high stability under the harsh testing conditions,” says Mr. Yang.

Test bench for ageing simulation with flow meters

Exhaust gas simulation recipe

In order to simulate engine exhaust gas, Umicore mixes multiple gases. In general the following reactions take place in the catalytic converter:

1.Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2

2.Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

3.Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O.

To mix these gases, EL-FLOW Select digital mass flow controllers are being used. In order to maintain the gas mix under the same pressure, an EL-PRESS pressure controller instrument is used to control the pressure simultaneously with the flow.

Exhaust gases of engines also contain evaporated H2O. For this purpose the Bronkhorst ‘Controlled Evaporation Mixer’ (CEM) is used. All digital mass flow controllers, pressure controller and the CEM are connected with a computer that runs a software program to control the instruments.

In the ageing simulation test-bench of Umicore, high-temperature mass flow controllers of Bronkhorst are applied. The Bronkhorst EL-FLOW Select controllers have remote electronics to resist gas temperatures as high as 110° Celsius and still control the gases with high accuracy and excellentrepeatability.

Mr Yang Umicore

How do you like the support of Bronkhorst products in China?

When asked about Bronkhorst support and service in China, Mr. Yang is very enthusiastic: “All Bronkhorst experts in China are very professional and have quick response. Especially during the start-up phase of our project, when we needed it most, my contacts were determined to support us. The system runs smoothly, but it’s comfortable to know that Bronkhorst is having one of its Global Service Offices in Shanghai if we need calibration or service.”

Bronkhorst Global Sales Office

• Learn more about another application in this market: Simulation of exhaust gas to test lambda probes. • Do you want to stay up-to-date with our new applications? Subscribe for our newsletter

James Walton
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One of my favourite phrases is, ‘buy cheap, buy twice’. This is never more apparent than when purchasing new flow meters or looking at ways to protect existing ones if necessary. There are various accessories that you can add-on flow meters. With mass flow meters and controllers, the accessory of choice often is a communication cable, these are essential in allowing you to communicate with an instrument and see/access the very information that you purchased the instrument to make available. However, one accessory is often over-looked and can be far more essential to the long-term performance and life-time cost of running an instrument, especially in industrial applications; filters. In this blog I would like to share my ideas about filters, in particular the ones used for gas flow meters.

Why using filters for your mass flow meters?

This simple add-on to a new flow meter can protect against a multitude of issues like: • Debris from contaminated gas lines • Particles that exist in industrial gases • Small amounts of oil from compressors

Filters are especially useful in applications where you have to deal with ‘dirty’ gases, gases with particles. This can be the case in an industrial environment, but also in research applications.
You may think that in research applications you work with clean gases, but tiny particles can also occur here. Not only the particles in gases can be a problem, the dirt stored in the piping can be harmful as well.

By using filters you can filter the gas before entering the flow meter to make sure that the gas at the inlet of the instrument is clean. This way you avoid contamination which can lead to a number of avoidable costs. With avoidable costs I mean costs due to down-time, service costs, calibration costs and engineering time to remove and re-install the damaged instrument.

Inherent to its construction, a thermal mass flow meter or controller for gases is more or less sensitive to contamination. The thermal flow meters for gas can be divided into two sensor principles: • Gas flow meters using the bypass principle • Gas flow meters using the CTA principle (Constant Temperature Anemometry)

Thermal mass flow meters for gases – Bypass principle

If we look at flow meters using the ‘bypass’ principle, these instruments are more sensitive to contamination. In these instruments only part of the gas stream flows through the sensor (bypass), the rest will flow through the laminar flow element. This flow element - flow splitter - contains small discs with high-precisions flow channels. You can imagine that these channels may be clogged by contamination.

More information about the ‘bypass’ principle

Image description Bypass principle

Thermal mass flow meter for gases – CTA principle

Instead of the bypass principle, instruments can also be designed by the CTA principle, also called Constant Temperature Anemometry, inline principle or direct-through principle. This principle has no bypass sensor but has a ‘straight’ flow channel. This construction is less sensitive to humidity and contamination.

More information about the ‘CTA’ principle

Image description CTA (Constant Temperature Anemometry)

Contamination of mass flow meters

To increase the MTBF (Mean Time Between Failure) it is important to make sure that the gas or liquid entering the instrument is dry and clean, in particular when using flow instruments with a bypass sensor. Depending on your fluid you can select different types of filters.

Our mass flow meters and controllers are designed for low flows and therefore have delicate and finely machined parts. This is needed to enable us to quantify the flow rates of gases that we can achieve with a good level of accuracy and repeatability.

When you consider the potential damage that is possible from the different sources of contamination, and the delicate nature of the internal working of a mass flow controller, it would appear to be a very straightforward decision to include a filter in your next purchase of a Mass flow controller.

Filters for gas flow meters and controllers

For gas flow meters and controllers we have filters available which are placed in line with the instrument (our so called IN-LINE models). Filters are easy to use, you just screw them into the inlet of the flow instrument, and it guarantees a clean gas inlet. It contains a 316L sintered metal filter cartridge that is suitable for general purpose filtration and can be cleaned with either a suitable solvent or by replacing the cartridge if heavily soiled.

Image description Various filters

If the gas contains large particles, we advise the use of a pre-filter. This pre-filter is recommended because it will remove a high percentage of the heavy particles, as it has a cartridge with a larger porosity than the actual filter, before they reach the main filter and reduce pressure drop from clogging and excessive maintenance/cleaning requirements.

Discover our filter models on our website and select your filter accordingly!

In a previous article we have already mentioned the importance of filters when installing a mass flow meter.

“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 inline filter upstream of the mass flow meter or controller, and if back flow can occur, a downstream filter or check valve is recommended too”. Read more tips before installation in this blog: Top 10 tips for installation