| Project/Area Number |
21K03884
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 19010:Fluid engineering-related
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
HAWARD Simon 沖縄科学技術大学院大学, マイクロ・バイオ・ナノ流体ユニット, グループリーダー (20812986)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Project Status |
Granted (Fiscal Year 2022)
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| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000)
Fiscal Year 2023: ¥520,000 (Direct Cost: ¥400,000、Indirect Cost: ¥120,000)
Fiscal Year 2022: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2021: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
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| Keywords | extensional flow / microfluidics / rheology / polymer solution / viscosity / viscoelastic fluid / viscoelasticity / flow instability |
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| Outline of Research at the Start |
Extensional viscosity of viscoelastic fluids is of fundamental importance in fluid handling and processing operations. Extensional viscosity depends on the fluid strain and strain-rate, and likely on the mode of deformation: uniaxial, planar or biaxial. The 3D microfabrication of geometries designed to measure the extensional viscosity in different deformation regimes will advance the measurement of the extensional properties of viscoelastic fluids. The results will aid the understanding and optimization of processes such as fiber spinning, ink-jet printing, blow-moulding, etc.
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| Outline of Annual Research Achievements |
In FY2022, experiments were completed measuring the pressure drop and velocity field for viscoelastic polyacrylamide solutions (at dilute concentrations of 0.005 to 0.04 wt%) in a planar extensional flow device. Pressure drop and velocity field measurements have also been completed in the new uniaxial and biaxial extensional flow device developed during FY2021.
A new data analysis has been developed to estimate the extensional viscosity of Newtonian and viscoelastic fluids. This ensures that the expected (constant) extensional viscosity is obtained for Newtonian fluid, and also for the polymer solutions at small flow rates. At high flow rates the extensional viscosity of the polymer solutions increases up to a plateau value that depends on the mode of extension. For the dilute solutions tested, the plateau values in uniaxial and planar extension are equal to each other and double that found for biaxial extension. This is in agreement with the finitely-extensible non-linear elastic dumbbell model, which is often used to describe such fluids in theory. Two journal papers have been prepared based on the work conducted so far in FY2021 and FY2022, which are both currently under review in the Journal of Rheology.
Furthermore, experiments with viscoelastic polymer solutions revealed some interesting instability phenomena at high flow rates, which are worthy of a more detailed investigation. Our new data analysis method for estimation of the extensional viscosity also merits some additional experimental verification. These topics will be the focus of research in FY2023.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project has progressed very well through FY2022. As it was hoped, the core experiments are now complete and there is sufficient time in FY2023 to explore the onset of elastic instabilities in the uniaxial and biaxial extensional flow configurations. Characterization of the instabilities will be achieved using a LaVision volumetric (3-component) stereoscopic flow velocimetry set up. This is planned by the use of the more highly concentrated polyacrylamide solution (0.04%, which is the most prone to instability) in a solvent with the same refractive index as the glass microfluidic device.
Furthermore, we intend to reconfigure our uniaxial and biaxial extensional flow device to enable birefringence measurements to be made without requiring the polymer solution to have the same refractive index as the device. This will allow us to measure the width of the birefringent strand that forms along the device outlet, as a function of both the flow rate and the extensibility of the polymer, and will help to verify (or improve) our new data analysis method for computing the extensional viscosity. For these planned experiments we will employ dilute polystyrene of various molecular weights (i.e., various extensibility), and measurements will be made using a Photron high speed birefringence imaging set up. Numerical simulations of the flow using the finitely-extensible non-linear elastic dumbbell model are planned in order to compare with the experimental results.
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| Strategy for Future Research Activity |
We are in a strong position to achieve all the research objectives targeted in this project (and more). In FY2023, our first two papers (one describing the development of the uniaxial and biaxial extensional flow device, and the other detailing the extensional viscosity measurements in uniaxial, planar and biaxial extension) should be published in Journal of Rheology. We will also perform the first experimental characterization of the viscoelastic flow instabilities arising in uniaxial and biaxial extensional flow. In addition, we hope to perform the first comprehensive birefringence measurements characterizing the dimensions of the birefringent strands that develop in uniaxial, planar and biaxial extension of polymer solutions. These experiments, which can be compared with theoretical predictions, will allow us to verify or refine our determination of the extensional viscosity based on our new analysis approach.
We anticipate that the results of this project comparing the viscoelastic flow response in uniaxial, planar and biaxial extension will lead to significant new insights into polymer solution rheology. In the second half of FY2023, we hope to submit two or three additional research papers based on the results of the project.
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