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Microfluidic Mass Flow Controller

Manufacturers of analytical equipment are constantly looking for miniaturisation in instruments used to measure and regulate small gas flows in their systems. Together with Bronkhorst High-Tech TNO has developed the IQ+FLOW mass flow sensor whose footprint is just ¾ inch and which is a very precise and compact flow controller for gases. It is used on the injector side of, for instance, gas chromatographs.

The principle of the flow meter is thermal mass flow metering whereby the flow is locally heated and the temperature difference between the upstream and downstream side of the flow channel measured. TNO and Bronkhorst High-Tech have collaborated to develop a chip that contains thermopiles: temperature sensors able to very accurately measure a small temperature difference. The use of thermopiles in flow meters has a number of advantages:

  • It is a difference measurement: if there is no flow, there is no signal, so an intrinsically stable zero point.
  • Thermopiles register at just a small temperature difference (of milliKelvins!) a measurable signal; little power is needed therefore.
  • The dimensions of thermopiles can be limited, thus enabling the flow sensor to be compact.

TNO has used numerical simulations, combined with experimental facilities, to design the thermo-mechanical and microfluidic aspects of the flow sensor.

Chip design

To respond to the miniaturisation issue, TNO has been working with its customers Bronkhorst High-Tech and LioniX to develop a chip that forms the 'heart' of the flow controller. On this chip thermal sensors and actuators are integrated and the chip is built into a channel with a height of just 200 ¼m. The geometry of the channel has been so designed that the chip can be used in the required flow area: 20 to 2000 mln/min. The material chosen means that all materials are compatible with the application: analysis using Gas Chromatography. A key item in the design of the chip is the response time. The application requires that rapidly changing flows can be measured, within timescales of a few tens of milliseconds. This has been achieved by using a very thin membrane of glass where the heaters and sensors are affixed.

Collaboration BHT-TNO

The intensive collaboration between Bronkhorst High-Tech and TNO goes back to 1987 when TNO was able to model the flow sensor for a thermal flow measurement and thereby gain more information on the physical operation of the sensor. This led to the possibility to improve the instruments of Bronkhorst High-Tech and simplify the design process. At the beginning of the 1990s one of the first liquid flow meters emerged from the collaboration in which the thermopile tape developed by TNO was used. Bronkhorst High-Tech and TNO then drew up a framework agreement that helped set the foundation for energetic and effective collaboration. TNO has since been involved in long-term research assignments, process development and roadmapping for Bronkhorst. In addition, Bronkhorst High-Tech's customers are increasingly becoming involved in the research. Therefore, TNO also now has direct contacts with Bronkhorst High-Tech's customers in the semiconductor industry and the life sciences as well as with manufacturers of analytical equipment.

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Contact

Ing. Huib Blokland

  • Instrumentation
  • sensors
  • energy
  • gas networks
  • hydrogen

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