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Influence of surface modifications and channel structure for microflows of supercritical carbon dioxide and water
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.ORCID iD: 0000-0003-2445-4624
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
2016 (English)In: Journal of Supercritical Fluids, ISSN 0896-8446, E-ISSN 1872-8162, Vol. 107, 649-656 p.Article in journal (Refereed) Published
Abstract [en]

Miniaturization offers a possibility to increase the performance and decrease the time scales of systems. Existing microsystems using supercritical CO2 mainly utilizes multiphase segmented flows. To allow for a broader toolbox for future systems, also parallel flows are useful which eases the separation of the different phases. Here, the effect of different surface coatings are studied for multiphase flows of scCO2 and H2O in flat microchannels, with and without a 4 μm high ridge guide, which allows for pinning of the fluid interface inside the 190 μm wide and 35 μm high channel. Three different surfaces with different wettings towards scCO2 and H2O are studied, where a surface terminated with a hydrocarbon-based silane was observed to be neutral in the H2O/scCO2 system, a surface terminated with a fluorocarbon-based silane was hydrophobic, and an uncoated glass surface was hydrophilic.

Using two flow rates of 5:5 μl/min (CO2:H2O) and 6.5:3.5 μl/min (CO2:H2O), a parallel flow between scCO2 and H2O was observed for uncoated and flat channels where the H2O flow pushed the CO2 to the side, before the flows eventually breaks up into segments. With a ridge guide in the middle of the channel, the interface was pinned at half the channel width, although still breaking up into segments. The neutral hydrocarbon-based surface coating with approximately 90° contact angles resulted in evenly created segments without a ridge guide. Including a guide in the middle of the channel, a parallel flow was observed throughout the channel, although occasionally small CO2 segments entered the H2O outlet. Using the fluorocarbon-based silane resulted in an unstable segmented system with pressure fluctuations.

Using surface modifications, an increased control can be achieved for either segmentation or parallel flow where a neutral surface is favored for a stable flow behavior. Together with a ridge guide, the fluid interface was pinned at the center. 

Place, publisher, year, edition, pages
2016. Vol. 107, 649-656 p.
Keyword [en]
Microfluidics, Supercritical CO2, Silane coating, Parallel flow, Segmented flow, Surface modification
National Category
Engineering and Technology Chemical Engineering
URN: urn:nbn:se:uu:diva-253554DOI: 10.1016/j.supflu.2015.07.027ISI: 000366077100077OAI: oai:DiVA.org:uu-253554DiVA: diva2:815183
Swedish Research Council, 2011-5037Knut and Alice Wallenberg Foundation
Available from: 2015-05-29 Created: 2015-05-29 Last updated: 2016-01-13Bibliographically approved
In thesis
1. Microsystems for Harsh Environments
Open this publication in new window or tab >>Microsystems for Harsh Environments
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When operating microsystems in harsh environments, many conventionally used techniques are limiting. Further, depending on if the demands arise from the environment or the conditions inside the system, different approaches have to be used. This thesis deals with the challenges encountered when microsystems are used at high pressures and high temperatures.

For microsystems operating at harsh conditions, many parameters will vary extensively with both temperature and pressure, and to maintain control, these variations needs to be well understood. Covered within this thesis is the to-date strongest membrane micropump, demonstrated to pump against back-pressures up to 13 MPa, and a gas-tight high pressure valve that manages pressures beyond 20 MPa.

With the ability to manipulate fluids at high pressures in microsystems at elevated temperatures, opportunities are created to use green solvents like supercritical fluids like CO2. To allow for a reliable and predictable operation in systems using more than one fluid, the behavior of the multiphase flow needs to be controlled. Therefore, the effect of varying temperature and pressure, as well as flow conditions were investigated for multiphase flows of CO2 and H2O around and above the critical point of CO2. Also, the influence of channel surface and geometry was investigated.

Although supercritical CO2 only requires moderate temperatures, other supercritical fluids or reactions require much higher temperatures. The study how increasing temperature affects a system, a high-temperature testbed inside an electron microscope was created.

One of the challenges for high-temperature systems is the interface towards room temperature components. To circumvent the need of wires, high temperature wireless systems were studied together with a wireless pressure sensing system operating at temperatures up to 1,000 °C for pressures up to 0.3 MPa.

To further extend the capabilities of microsystems and combine high temperatures and high pressures, it is necessary to consider that the requirements differs fundamentally. Therefore, combining high pressures and high temperatures in microsystems results in great challenges, which requires trade-offs and compromises. Here, steel and HTCC based microsystems may prove interesting alternatives for future high performance microsystems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 50 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1263
Microsystems, harsh environments, high pressures, high temperatures, supercritical microfluidics
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
urn:nbn:se:uu:diva-253558 (URN)978-91-554-9272-4 (ISBN)
Public defence
2015-09-11, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Available from: 2015-08-19 Created: 2015-05-29 Last updated: 2015-09-07

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