CASE
STUDY

Optimized liquid pumping by
pump-parameter matching(sensor-enabled mediarecognition)

September 2021
Authors:
Florian Siemenroth
Patrick Reith

Case study: Optimized liquid pumping by pump-parameter matching
September 2021

Smart adaption of pumpparameters for different
liquids

Digital and Smart Media
Recognition

Membrane-based micropumps like the mp6 micropump can be controlled by the frequency (howoften per second the membrane is actuated) and the driving voltage of the actuating elements(controlling the stroke of the membrane). Both parameters need to be adjusted to match the viscosityof the liquid and the desired flow rate. Especially applications in which different liquids are handled
by the same pump profit from automating this manual step.
For that purpose, this Case Study is demonstrating that our mp6 micropump in conjunction with
Sensirion’s SLF3C-1300F sensor can recognize the liquid and with this creating the possibility toautomatize the pump-parameter-adjustment.

What is microfluidics?
Microfluidics is the fine art of creation and manipulation of small portions of fluids, often realized by flow
within small, sub-millimeter-scale channels. These small dimensions allow the fluid flow to be controlledwith exquisite precision (Seifert, Thiele; 2020).

About the mp6 micropump
The available, industrialized and commercialized example is the mp6 micropump by Bartels MikrotechnikGmbH. This micro pump is a positive displacement membrane pump utilizing piezo buzzers. The alternating
displacement of the piezo acutators l lead to the following typical fluidic values of the pump:▪
▪

Liquids (eta = 1 mPas): q = 5 - 8000 µl/min in free flow and p > 600 mbarGas: q > 25 ml/min in free flow and p > 150 mbar

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Optimized liquid pumping by pump-parameter matching
September 2021

About the Sensirion SLF3x series – Liquid Flow Sensors
Sensirion sensors as flow controlling elements were used in this case study, namely, Type SLF3C-1300F,
which is calibrated for water and Isopropanol. This sensor can measure flows of up to 40ml/min (SLF3C1300F) with a turndown-ratio of 1:200 (ratio lowest to highest flow rate) and a response time of less than
20ms. In addition to the flow rate, the SLF3C offers a feature for a media recognition by measuring thethermal conductivity of the liquid inside the sensor: At zero-flow its heater-sensor-element is used to
study thermal behaviour of the liquid, calculating the thermal conductivity, and passing the result to theuser in arbitrary units (a.u.) ranging from 100 a.u. (air) to 10’000 a.u. (water).

Figure 1:
Typical Sensor of the SENSIRION AG (left) and the working principal of these sensors (right).
References / Photos: both SENSIRION AG.

Dependency of flow rate on pump parameters and the properties of the liquid
The pump principle of the mp6 micropump is based on the piezo effect, so a piezo actuator exerts aconstant force on the fluid. If there are different fluids with different rheological characteristics, such asdensity or viscosity, the pump performs differently at the same parameters.

Source: https://glossar.item24.com/en/glossary-index/article/item//dalemberts-principle-2.html

When the density changes, the mass of a defined portion of liquid changes too. The piezo actuator only
provides a constant force, so if the pump frequency is increased, the acceleration increases and therefore
the force of inertia is increase as well. The constant force from the piezo actuator is overwhelmed andthe performance is lower although the pump parameters are increased.
In very simple terms, the viscosity is a degree of “how easy or hard it is to move layers of liquid”. Thismeans that the more viscous a liquid is, the harder it is to move the layers of a liquid or the harder it is
to move the liquid in general.

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Optimized liquid pumping by pump-parameter matching
September 2021

Source: https://www.azom.com/article.aspx?ArticleID=16985

So, again, the shear stress counteracts the force of the piezo actuator, increasing the frequency would
mean to increase a counteracting force of the piezo force which leads to a lower pump performancealthough the driving parameters (frequency) of the pump are increased.
Therefore, it is often necessary to know which fluid is meant to be pumped to adjust the mp6 micropump
to its optimal working point. In an ideal case, one would use a viscosity sensor. As this would require anadditional sensor, we use the SLF3C-1300F sensor which, beside the already used flow rate, also provides
the thermal conductivity as output value. This we can use to distinguish between different media anduse a look-up table for the viscosity in order to adjust the pump parameters.

Sensor based media recognition and its application to adjust pump-parameters
Prior to the experiment, the thermal conductivity of the different media we want to distinguish wasdetermined. Water was found to give an output of around 10’000 a.u. while our water/gylcerin-mixture
gives approximately 7500 a.u.

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Optimized liquid pumping by pump-parameter matching
September 2021

In our experiment, we now use the mp6 micropump to pump water. As you can see, that with a low
frequency, we achieve a low pump rate.

We then stop the flow and take a reading with the SLF3C-1300F. It gives us a value of 10’500 a.u. given
the fact that we did not implement a temperature compensation for this experiment, this value is closeenough to the calibrated value for water (10’000 a.u.) to identify the liquid in the pump as being water.

Next, we use a much higher frequency. It shows that the pump rate remains low. This indicates that ourfrequency is now too high. The water is not able to follow the rapid pump strokes. We therefore lower theactuation frequency of the pump a little bit and with this, hit the maximum pump rate. This frequency
could also be saved in a look-up table as the optimum actuation frequency for pumping liquids that mainlycontain water.

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Optimized liquid pumping by pump-parameter matchingSeptember 2021

Afterwards we switch to a different liquid. A mixture between glycerin and water with a viscosity of 18mPas. We use the same actuation frequency for the pump we found to be optimal with water. It showsthat we achieve a very low pump rate.

Which makes sense, as the viscosity is way different from water. In order to optimize the pump rate, weincrease the frequency. This leads to a further decrease of the pump rate. This means that the optimized
frequency has to be lower. We use the SLF3C-1300F sensor to take a reading of the thermal conductivity
and find it to be 7’500 a.u. this indicates that we have the glycerin/water mixture in our sensor and pump.
We can clearly differentiate between the two liquids (water and water/glycerin).

We lower the actuating frequency and find the maximum pump rate at 50 Hz. We have now determined
the optimal pump actuation frequency of water and our water-/glycerin mixture.
All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Optimized liquid pumping by pump-parameter matching
September 2021

For future experiments we can identify with the SL3C-1300F-sensor with liquid is present in our systemand choose the optimal pump frequency accordingly with a look-up table.
A video of the whole experiment can
https://www.youtube.com/watch?v=gnkpqsM-buY

befoundon

yourYouTubechannel:

Conclusion:
The performance of the mp6 micropump by Bartels Mikrotechnik depends on the viscosity of fluids.
Utilizing the SLF3C-1300F sensor by Sensirion, which is capable on measuring the thermal conductivity ofa liquid gives us the chance to distinguish between different liquids and thus assign the thermal
conductivity to a specific liquid. Now, one can adjust the micropump to reach the optimal working point
for a specific liquid. So, all in all, the SLF3C-1300F offers a reasonable solution to react smart and in-situ
to rheological changes within a fluidic system.
As an outlook, the SLF3C-1300F can measure a specific property of a liquid, the thermal conductivity. This
will also let us measure mixtures and its concentrations.

Components and systems used:•••

mp6 micropump by Bartels Mikrotechnik
SLF3C-1300F sensor by Sensirion
mp-Multiboard inlc. mp-Highdriver4 by Bartels Mikrotechnik

Acknowledgement:
Our partner, Sensirion from Stäfa, Switzerland, was instrumental in defining our research path, whereby
we were able to develop a great solution for microfluidic system that can distinguish between different
liquids. For that, we are extremely grateful and we are looking forward to our close collaboration. In case
you are interested in the above-described microfluidic componenents or if you are interested in getting intouch with either one of us, Sensirion or Bartels Mikrotechnik, please feel free to contact us. You can findthe contact details below.

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Optimized liquid pumping by pump-parameter matching
September 2021

Bartels Mikrotechnik is a globally active manufacturer and development service provider
in the field of microfluidics. In the microEngineering division, the company supports
industrial customers in the modification, adaptation and new development of highperformance and market-oriented product solutions through the innovative means ofmicrosystems technology. The second division, microComponents, produces and distributes
microfluidic products and systems, especially for miniaturized and portable applications.
Our key products are micropumps that convey smallest quantities of gases or liquids andare used in a variety of ways in biotechnology, pharmaceuticals, medical technology andnumerous other applications.
Bartels Mikrotechnik with passion for microfluidics!

Follow Bartels:

Contact us:
Bartels Mikrotechnik GmbH
Konrad-Adenauer-Allee 1144263 Dortmund Germany

www.bartels-mikrotechnik.de
info@bartels-mikrotechnik.de
Tel: +49-231-47730-500

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.