Dion Oudejans
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Semiconductor chip technology is enhancing our lives in many ways. Emerged from semiconductor technology, MEMS chip technology is also present in devices around you in the form of sensors. Think of your smartphone that captures your voice and senses the smartphone position, orientation and movement by means of Micro Electro Mechanical Systems (MEMS). Adding those features is barely impacting the physical dimensions of a smartphone: it still fits in your hand and pocket.

This blog is about instrument miniaturization by MEMS chip technology and the benefits of miniaturized gas flow instruments for application in the field of gas chromatography. As a MEMS Product Manager at Bronkhorst High-Tech, I can see the benefits of miniaturization by MEMS technology in such applications.

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IQ+ FLOW solution based on MEMS modules

Miniaturization by MEMS chip technology

Further miniaturization is achieved by combining MEMS modules in customer specific flow solutions.

Miniaturization

In a laboratory environment, it is advantageous to work with desktop-sized equipment. Advantages of increasing functionalities in table top equipment are: reduced space requirements, enhanced ease of operation and often reduced cost of ownership.

Gas chromatography equipment is a good example of a concentration of functionalities on a small footprint. Many types of gas composition and vapour composition can be analysed with high accuracy and for very low concentration levels. Additionally, there is a certain degree of automation involved. This is all within arm’s reach of a laboratory analyst.

Gas chromatography

The goal of gas chromatography analysis is to identify and measure the concentration of gas components in an analytical gas sample. Within the gas chromatograph (see picture 3), there is often a need for gas flow or pressure control. The picture shows a gas flow controller for the carrier gas stream (red) and a pressure controller for the split flow stream (yellow).

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The principle of gas chromatography involves a controlled carrier gas stream that passes an injector, column and detector. A sample gas is injected for a short period of time, creating a gas sample plug. The gas sample plug is separated into gas components across the column, which become visible as peaks during detection.

Picture 4 shows an example of a gas chromatography output.

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Headspace sampling

Let’s zoom in on dynamic headspace sampling that is used in combination with gas chromatographys. Headspace sampling refers to the gas space in a chromatography vial containing a liquid sample. The liquid sample is a solvent, containing material to be analysed. E.g. volatile organic compounds in environmental samples, alcohols in blood, residual solvents in pharmaceutical products, plastics, flavor compounds in beverages and food, coffee, fragrances in perfumes and cosmetics.

This is explained in picture 5. Dynamic headspace sampling is performed by purging the gas space and the adsorbent. The adsorbent collects the sample gas. After transport, the adsorbent is purged again to release the sample gas into a gas chromatograph.

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Where a gas flow controller comes into play is at purging the headspace with a constant Helium or Nitrogen flow for a pre-determined period of time at a specified temperature between 10 - 200 °C. The gas flow, containing the headspace sample gas, passes an adsorbent that collects the headspace sample gas.

The adsorbent is usually made of Tenax TA material. Now, the adsorbent is transported to the inlet of a gas chromatograph. While the adsorbent is heated between 20 - 350°C, a controlled Helium or Nitrogen gas flow passes the adsorbent to release the headspace sample gas into the inlet of the gas chromatograph. The gas chromatograph does its job to analyse the sample. Different signal peaks in time show the different components and their concentration.

IQ+FLOW gas flow meters and pressure controllers

For flow instruments, a number of specifications are important in headspace sampling and gas chromatography in general. The IQ+FLOW product line addresses these specifications with small instrument size, fast response, good repeatability, low power, low cost of ownership and the excellent support that you can expect from Bronkhorst.

Read more about the IQ+FLOW chip based product line

For more information about gas chromatography in combination with IQ+FLOW flow and pressure meters and controller have a look at our application note ‘Gas Chromatography'.

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The future of MEMS technology

Bronkhorst is committed to look ahead and find applications that can be enhanced with MEMS chip technology. Feel free to contact us for questions. We will keep you informed!

Read more about MEMS technology in our blog 'Miniaturization to the extreme: micro-coriolis mass flow sensor'

Kevin van Dijk
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For most people the classic summer treat is ice cream. Around 7 billion gallons of ice cream and other related frozen desserts are produced every year worldwide, with production peaking (as you might expect) in the summer months, according to the International Dairy Foods Association. Yet, the moment you consume an ice cream, you will probably not wonder how this delicacy is being made. To get that perfect ice cream, a mass flow controller is often used.

What does ice cream have to do with mass flow meters?

Ice cream contains many different ingredients, such as fat, sugar, milk solids, an emulsifying agent, flavouring and sometimes colouring agents. But there is one main ingredient that you may not have thought about, probably because you can’t see it—air. Ice cream is made by freezing and simultaneously blending air into the ingredients. So why is air so important?

If you have ever had a bowl of ice cream melt, and then refroze it and tried to eat it later, it probably did not taste very good. Moreover, if you leave a carton of ice cream out in the hot sun and let it melt, the volume of the ice cream would simply go down. Air makes up anywhere from 30% to 50% of the total volume of ice cream, therefore, aeration in the production process is crucial.

The amount of air in ice cream (often called overrun) affects the taste, texture and appearance of the finished product. Higher aeration will produce a tastier and smoother ice cream. A side effect of adding air to ice cream is that it tends to melt more quickly . Thus, for attaining an optimal structure of the ice cream, it is important to have a stable inlet air flow in the production process with a constant cream/air ratio. This can be achieved by using a mass flow controller.

The process of whipping ice cream into shape

To guarantee the right consistency and structure which ensures a full flavoured ice cream, the cream must contain the correct proportion and composition of air bubbles. Hence, aeration mixer manufacturers use a mass flow controller to dose an exact amount of air into the cooled mixer. Such a mass flow controller will ensure a continuous air delivery, proportional to the cream flow . The mass flow controller must be capable of maintaining its performance regardless of any possible back pressure variation. Occasionally, a check valve is mounted downstream of the mass flow controller. If inlet pressure drops, such valve will avoid ice back stream into the instrument. A pressure meter is also used with the purpose of monitoring the inlet pressure.

flowschemeofwhippingicecreamprocess

The SEM (Scanning Electron Microscope) picture below shows the ice cream microstructure. Air bubbles are a critical ingredient. Experts claim its optimal size, distribution and quantity are one of the secrets for having a creamy texture recipe. Hence, according to meet such demands, Bronkhorst has provided efficient solutions for enhancing continuous aeration processes.

Ice cream structure

So, the next time you head to the ice cream parlor with your friends, be sure to keep in mind the importance of Bronkhorst when it comes to that delicious refreshment.

EL-FLOW select

  • Watch the video about the EL-FLOW Select to learn more about the thermal mass flow instrument which can help you create ice cream.

Want to stay up to date on new flow solutions? Every month the latest tips in your e-mail box.

Hans-Georg Frenzel
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We all love cake, there’s no denying that, and especially with whipped cream. A celebration isn’t a celebration without a cake, whether you’re throwing a birthday party or attending a wedding. Or just when you’re having coffee with friends or family, simply because it’s delicious. Baking and decorating a cake takes a lot of time and patience. And that’s exactly why most choose the easy way of picking out an already finished piece , either from their local pastry chef or out of the freezer section at the supermarket. And today I would like to tell you something about how such a fancy cake is made.

Manufacturing the cake layers

It all starts with the base, which consists of one or more layers of cake that provide support to the whipped cream. These layers are factory produced, but they aren’t made in individual round spring forms. The dough is applied on a closed metal conveyor belt by using nozzles. This belt goes through an oven and at the end the individual shapes with the desired diameter are cut out of the dough.

Controlling air by using mass flow controllers

To make sure that these cake layers all have the same weight and consistency, foam technology is used in addition to the baking agent in the dough. In this case, a foam mixer generates a dispersion of dough and air which is then applied onto the baking steel belt. In this process, it is highly important that this dough always has the same consistency, density and quality. Thus it is not only necessary to control the delivery rate of the dough, but just as important is the amount of air. By using the Bronkhorst EL-FLOW Select mass flow controllers, precise control of the required air volume is ensured at all times throughout the whole process.

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Whipped cream

In cake decoration, the cake layers are covered with whipped cream and other sweet fillings. To produce whipped cream out of liquid cream, another foam mixer is used in combination with Bronkhorst mass flow controllers, proving their worth yet again by achieving continuous high accuracy and precise control. The whipped cream production is similar to dough production; however the requirements for this system are different.

Hygiene requirements: Cleaning in Place - CIP

In food production, high hygiene requirements apply. In the dough production process, the mixer is cleaned of residues by CIP (Cleaning In Place) using cleaning additives, guaranteeing a hygienic product. However, in whipped cream production, it’s highly important that all product-contacting surfaces in the foam mixer are clean and absolutely germ-free, since it’s a sweet dairy product and the cake needs to be preserved for a long period of time. This asks for even higher hygiene requirements, so these machines need a different cleaning approach. Using only CIP with cleaning additives can’t guarantee this, so they have to be sterilized in place (SIP) as well. Using a saturated steam at a temperature of 130° Celsius, the product area of the machine is thoroughly cleaned. This maintenance takes around 300 seconds to make sure all germs are killed. This gives the cake a longer shelf life when stored in the refrigerator or freezer.

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Hansa Mixer

Hansa Industrie-Mixer is a worldwide, medium-sized company that operates in the field of mixing machines and foam generators for the food and non-food industry. Technical equipment before and after the foam mixer is also included in the scope of delivery to the customers. These are not mass-produced products, but every system is customized and tailored to the needs of the customer. If you want to differentiate yourself from the competition, you need a custom-made machine and system. The heart of the foam mixer is a mixing head that uses the rotor/stator principle. Rotor and stator are fitted with rings of pins which are able to pass the pins on the opposite side when the rotor rotates in the stator. The generated turbulence and shear forces produce a fine dispersion from a pumpable medium and a foam gas, which in this case creates the used foam.

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Read more about aeration in Bronkhorst’s success story on how mass flow meters are important for adding the correct proportion and composition of air bubbles to ice cream.

James Walton
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Miniaturization is a trend you see in our daily life. The tiny house movement is something very popular at this moment, people choosing to downsize the space they live in by moving to a tiny house with an average space of 100-400 square feet. But also in industry miniaturization is a hot item. Mass flow meters and pressure controllers with minimal footprint fit this trend.

Footprint reduction

Having worked in both the Life Sciences and Analytical industries I am sympathetic to the ever increasing demands for small foot prints and faster instruments. It has been a continuing trend for many years that lab real-estate has become more and more expensive; this led to a drive for footprint reduction of instruments. You had to make sure that size didn’t make you expensive in bench space.

One of the drivers behind this process was the NeSSI system initiative (New Sampling/Sensor Initiative), sponsored by the Centre for Process Analysis and Control. The aim was to reduce the overall costs of engineering, installing and maintaining chemical process analytical systems. In the NeSSI system, mass flow meters and pressure controllers needed a standard footprint of 1.5’’.

Footprint of Mass Flow Meters and Pressure Controllers

This footprint is perfect for a large number of applications and end users, even for some of the Life Science OEM companies that have room to spare in their systems. However, when you are re-designing your system and you have the chance to incorporate new technologies, look at the placement of existing technology and maybe add more. It helps if you can reduce the footprint of the components that you use even further.

Reducing the footprint of a known, working technology has challenges of its own. The design and function of which will be driven by the physical characteristics of the measurement principle and therefore the sensor that it uses. To change this you need to look at alternative measurement technologies as a way to achieve the end goal of the industry, same functionality, same signal, smaller package.

Mass Flow Meters and Pressure Controllers for minimal footprint

Working in conjunction with the TNO, the Netherlands organisation for applied scientific research we designed a new range of mass flow meters and pressure controllers built around MEMS technology. This allowed us to offer solutions with a footprint of 0.75’’, halving the footprint and offering ultra-compact flow controllers.

Have a look at our blog MEMS technology to support compact gas chromatography equipment to read more about miniaturization by MEMS chip technology.

This has given our customers:

  • Compact assembly ensuring space efficiency
  • Analog or digital communication
  • Top mount and side ports modules, easily accessible
  • Pre-testing ’Plug and Play’ manifold assemblies, reducing customer test requirement

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To maintain the usefulness of the new instrument you have to have the same functionality. Along with a sensor on a chip, we need a new, smaller control valve, filter options and a smaller pneumatic shut-off valve. To save even more space and build time, customers requested a down-ported version.

The final addition that makes full use of the space saving created by the addition of new technology was to create a manifold system where a customer can design a number of flow channels into a manifold, all well within the internal space limitations they have for their instrument.

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This is one of the key themes of our blogs and it is referred to time and again. The Solutions based approach, ending up with a bespoke solution not a standard product with compromises. Innovation in technology must be driven by the customer. If you do not think that a standard flow or pressure solution will meet your needs then let us know and challenge our team, we will be your low flow fluid handling specialist.

Check out our chip-sensor based mass flow meter/controllers or the Pressure Controllers using MEMS technology.

This miniaturization trend is observed in many places as can be read in our blog Customized low flow measurement systems to support winning Solution factories

Dr. Jens Rother
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It is real common nowadays to use 3D printing techniques as process optimization in industrial production evironments. In our Bronkhorst premises in Ruurlo we also use 3D-printers for our own product and process development. 3D-Printers are indispensible within our production environment, it has brought us a new and very accessible and flexible way of manufacturing.

Within a few hours, we can evaluate the design of a component: will it really work in the way we expected it, does it really fit? You can read all about our experiences here in our blog ‘Product & process optimization by use of 3D printers’

But it also goes the other way around. Not only do we use 3D printers in the production proces of flow meters, but these flow meters and flow controllers are also used inside 3D-printers as well.

In this blog I would like to share an application with you explaining how mass flow meters are used in the 3D printing machines of one of our German customers in the machine building industry.

Selective laser melting (SLD)

3D-printing, also known as additive manufacturing, is a technique where products are made by building a product layer by layer. This is the opposite of machining operations such as drilling or milling, where pieces of materials are removed to yield the product.

Selective laser melting (SLM) is a 3D-printing technique where a layer of powder is deposited, after which a part of these powder particles is selectively melted together by means of laser heat.

The customer is a machine builder who makes 3D-printing machines that print metal parts out of steel, aluminium or titanium powder using this selective laser melting technique. Their customers are in the fields of aerospace, automotive and medicine & dental. High purity inert gases are necessary around the metal powder bed within the 3D-printer.

Example 3D Dental SLM

Application requirements

It is essential to have a gas atmosphere around the to-be-melted metal powder particles that is oxygen-free, to prevent the metal from oxidation during the laser melting. To that end, an inert shielding gas has to be applied: argon gas for steel and titanium, and nitrogen gas for alumium.

Flow solution with MASS-STREAM mass flow controller

For the end user of SLM's 3D-printing machine, there are two ways to establish a nitrogen atmosphere: either from the in-house nitrogen supply mains - if present - or from a nitrogen generator, which is an accessory to the 3D-printer. In the latter option, Bronkhorst becomes involved.

Flow scheme

Pressurised air from a compressed air supply or a compressor is supplied to the nitrogen generator, and its molecular sieve separates the air flow into two flows. Constituents such as oxygen, water vapour and argon are removed, and nitrogen with high purity (grade 5.0) remains.

Downstream of the generator, a mass flow controller (using direct through-flow measurement technique) is installed to control the nitrogen flow to the 3D-printer. This controller works in two operating modes.

Prior to the printing process, the 3D-printer has to be flushed, in order to establish the shielding gas atmosphere. To this end a high nitrogen flow of 60 to 90 liters per minute is necessary. Next, during the printing process itself, a small nitrogen flow of 3 to 10 liters per minute has to be supplied, for refreshing purposes and to compensate for leakage.

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

Check out the mass flow controller (MASS-STREAM™ D-6300 ) used in this application

Marcel Katerberg
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When it comes to accurately measuring and controlling flow rates in the range of 1 gram/hour and lower, not only a good mass flow controller is essential, but also a proper designed system and the presence of other important components come into play. As in any system, it will be as strong as its weakest link.

How to control low flow rates

For controlling low flow rates, the weakest link is usually not the mass flow sensor. A mass flow controller is capable of accurately measuring and controlling the flow rate, at its position in the system. However, there is no absolute confidence that this flow rate is accurate further up- or downstream of the flow controller. If no countermeasures are taken, the exact desired flow rate will not be delivered to the process. As the flow rate minimizes the relative internal volume of system components, such as piping, filters and valves, seem to increase. This affects the dynamics of the system as the response time will slow down resulting in a loss of direct control. So, when a set point is given and this is assumed to reach the process, expectations might not be met.

For instance, a popular setup to force a flow through the system is to make use of pressurized gas. However, gas will dissolve in the liquid to a saturation level proportional with the gas pressure. The dissolved gasses appear again as bubbles downstream in the system where the pressure has decreased. If a gas bubble passes the flowmeter or valve or enters the process it disturbs the stability of the flow.

Practically for low flow rate processes, it is sometimes hard to understand why and when the system works correct. And so many questions arise. Is the purity of the media correct? Are the process temperatures as they should be? Is the set rate or dosage correct? Is the pressure stable?

Challenges which can occur within low flow process

  • For the lowest flow rates it is hard to verify if, at any time, the flow entering the process is as expected. As mentioned, there may be various underlying causes:
  • Dissolved gasses in the liquid and uncontrolled gas bubble entrapment and release
  • Dynamic effects of multiple fluid transmission lines: e.g. in medical multi infusion systems
  • Compliance of the system: e.g. in plastic tubing or plastic syringes
  • Local heating and fluid expansion: due to the internal volume and power dissipation of solenoid valves
  • Ripple on the flow delivery when using pumps

‘Check out our blog about how to handle ultra low flow

Influence of dissolved gasses

This blog focusses on the influence of dissolved gasses in the liquid and the possible countermeasures. When dissolved gasses in the liquid undergo a pressure drop through the system, gas bubbles tend to appear. The bubbles not only cause discontinuity in the flow but also tend to change the flow rate in between the gas bubbles. Several experiments have been carried out to investigate the phenomena and match it with known theories.

Schematic setup ML120

Low flow experiment with Coriolis mass flow meters

In figure 1 a setup is shown of two Bronkhorst low flow Coriolis mass flow instruments (mini CORI-FLOW™ ML120) in series. The first instrument is a mass flow meter. The second instrument acts as a controller, controlling the flow with an accurate onboard proportional valve positioned in front of its sensor.

Test setup ML120 coriolis flow meter

In this specific case the fluid is pressurized using compressed air to force the liquid through the system. As the pressurized air comes into contact with the liquid, it will dissolve into the liquid proportional to the gas pressure. This experiment is to investigate the influence of dissolved gas in the liquid and the use of a degasser as a countermeasure for gas bubbles.

Experiment without degasser

Picture 3 shows the outcome of the experiment when the setup has run for a few hours without a degasser. Clearly visible is the effect of gas bubbles passing the sensor of the flow controller. This can also be seen in the density measurement of the second instrument. The density drops each time a gas bubbles passes the instrument. The density is directly measured by the Coriolis instrument. A Coriolis instrument is capable of measuring density by a change in natural frequency of its vibrating measuring tube when liquid is flowing through it.

Measurement results without degasser

As expected the gas bubbles are generated by the valve in the mass flow controller as there the pressure drop occurs. As this valve is in front of its meter (in instrument 2) the mass flow meter detects the gas bubbles and thus the mass flow controller responds to it by controlling the valve. The physical effect of gas bubble generation occurs at any place in the system with large pressure drop, in most cases directly behindthe control valve. This effect is independent of measuring principle or type of control valve. Another remarkable phenomenon is that there is a difference in between the measured flows of both devices. It seems that the first instrument (mass flow meter) shows a lower flow rate of about 3% less than the flow rate measured by the second instrument (mass flow controller).

An explanation for this is that a generated bubble downstream of the control valve causes the volume flow to expand and pushes the liquid forward. As the mass flow controller will maintain its set point value of 1 gram/hour the flowrate is “slowed down” to maintain the correct mass flow. Therefore the flowrate through the first flowmeter is 3% less in between the bubbles.

Average deviation from set point

Table 1: Average deviation from set point of 1g/h of measured mass flow rate

There is a difference in volumetric flow rate before and after the appearance of the gas bubbles. However, the average mass flow rate in the instruments in both experiments is within specification and thus the same, as shown in table 1. This table shows the average deviation from 1 gram/hour of each instrument in both experiments over the entire dataset as shown in the charts.

The 3% error matches ‘Henrys law,’ which tells us that the solubility of air in water is 22 milligram/liter per bar. If this number is divided by the density of air, the volumetric expansion explains the 3% increase in volume flow after the gas bubbles appear. So the total volume flow is 3% higher due to the gas bubbles and the mass flow drops to nearly zero at a gas bubble in 3% of the time. This explains why the average mass flow, including the gas bubbles, remains the same compared to when the gas was disolved.

Countermeasures for gas bubbles

In order to take out the dissolved gas before problems appear, a HPLC (high-performance liquid chromatography) degasser is used. This device uses a permeable tube to degas the liquid. The permeable tube is positioned inside a vacuum chamber where the vacuum is maintained by a small onboard vacuum pump. The device extracts most of the dissolved gasses in the used liquid.

‘Have a look at our blog ‘Chromatography, history and future trends’ to learn more about Chromatography.’

Furthermore, as the liquid is well degassed it is capable of easily dissolving any remaining small bubbles that are left behind in the system. In this way the system will end up fully filled with liquid without any pockets left with gas. As gasses are compressible, a properly degassed system makes the system stiff and very responsive. A system like this is capable of generating a continuous and stable flow towards the process with good control behavior.

Experiment with degasser

Picture 4 shows the measured outcome where the degasser is put up in front of the Coriolis mass flow instruments. It is clearly visible that the system can run for several hours without any drops or glitches in mass flow or density. Apparently, no air bubbles are present in the system or generated by the control valve. The small deviation between the instruments is within the specified accuracy of 0.2% of reading ± 20 milligram/hour zero stability.

Measurement result with degasser

Conclusion

In many low flow fluidic control systems the fluid is pressurized with a gas. When gas is entrained in the liquid flow it can appear as dissolved gas or as gas bubbles. In both cases it has no significant influence on the average mass flow. However, gas bubbles tend to disrubt the stability of the flow. The effect can be monitored by a fast and accurate flow meter. This physical effect occurs in any low liquid flow system with dissolved gases and pressure drop downstream and is independent of measuring principle or type of control valve.

It is recommended to use a degasser for generating a continuous, stable and responsive system towards the end process, especially in low flow measurements of liquids. An ideal solution for these low flow measurements would be a degasser in combination with a Bronkhorst mini CORI-FLOW ML120 mass flow meter/controller, as is used in this experiment.

As this mass flow controller has its control valve in front of the meter, the sensor is capable of monitoring the actual flow in the system. This results in an optimal and direct process control. The flow controller can be used for (ultra) low flow applications up to 200 gram/hour.

• These (ultra) low flow applications can be found in the Semiconductor market as described in our brochure ‘Low Flow Coriolis Competence’.

• Download the application story describing use of (ultra) low flow measurement in microfluidics.

• Read more about measuring very low flow leak rates in the automotive industry)