Rotary atomization of Newtonian and viscoelastic liquids
We study the dynamics of fragmentation for Newtonian and viscoelastic liquids in rotary atomization. In this common industrial process centripetal acceleration destabilizes the liquid torus that forms at the rim of a spinning cup or disk due to the Rayleigh-Taylor instability. The resulting ligament...
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| Other Authors: | |
| Format: | Article |
| Language: | English |
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American Physical Society
2020
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| Online Access: | https://hdl.handle.net/1721.1/126459 |
| _version_ | 1826211637254684672 |
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| author | Keshavarz, Bavand McKinley, Gareth H |
| author2 | Massachusetts Institute of Technology. Hatsopoulos Microfluids Laboratory |
| author_facet | Massachusetts Institute of Technology. Hatsopoulos Microfluids Laboratory Keshavarz, Bavand McKinley, Gareth H |
| author_sort | Keshavarz, Bavand |
| collection | MIT |
| description | We study the dynamics of fragmentation for Newtonian and viscoelastic liquids in rotary atomization. In this common industrial process centripetal acceleration destabilizes the liquid torus that forms at the rim of a spinning cup or disk due to the Rayleigh-Taylor instability. The resulting ligaments leave the liquid torus with a remarkably repeatable spacing that scales inversely with the rotation rate. The fluid filaments then follow a well-defined geometrical path-line that is described by the involute of a circle. Knowing the geometry of this phenomenon we derive the detailed kinematics of this process and compare it with the experimental observations. We show that the ligaments elongate tangentially along the involute of the circle and thin radially as they separate from the cup. We use these kinematic conditions to develop an expression for the spatial variation of the filament deformation rate and show that it decays away from the spinning cup. Once the ligaments are sufficiently far from the cup, they are not stretched sufficiently fast to overcome the critical rate of capillary thinning and consequently undergo capillary-driven breakup forming droplets. We couple these kinematic considerations with the known properties of several Newtonian and viscoelastic test liquids to develop a quantitative understanding of this commercially important fragmentation process that can be compared in detail with experimental observations. We also investigate the resulting droplet size distributions and observe that the appearance of satellite droplets during the pinch-off process lead to the emergence of bidisperse droplet size distributions. These binary distributions are well described by the superposition of two separate Γ distributions that capture the physics of the disintegration process for the main and satellite droplets, respectively. Furthermore, as we consider more viscous Newtonian liquids or weakly viscoelastic test fluids, we show that changes in the liquid viscosity or viscoelasticity have a negligible effect on the average droplet size. However, incorporation of viscous/viscoelastic effects delays the thinning dynamics in the ligaments and thus results in broader droplet size distributions. The ratio of the primary to satellite droplet size increases monotonically with both viscosity and viscoelasticity. We develop a simple physical model that rationalizes the observed experimental trends and provides us a better understanding of the principal dynamical features of rotary fragmentation for both Newtonian and weakly viscoelastic liquids. |
| first_indexed | 2024-09-23T15:09:08Z |
| format | Article |
| id | mit-1721.1/126459 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T15:09:08Z |
| publishDate | 2020 |
| publisher | American Physical Society |
| record_format | dspace |
| spelling | mit-1721.1/1264592022-10-02T00:57:12Z Rotary atomization of Newtonian and viscoelastic liquids Keshavarz, Bavand McKinley, Gareth H Massachusetts Institute of Technology. Hatsopoulos Microfluids Laboratory Massachusetts Institute of Technology. Department of Mechanical Engineering We study the dynamics of fragmentation for Newtonian and viscoelastic liquids in rotary atomization. In this common industrial process centripetal acceleration destabilizes the liquid torus that forms at the rim of a spinning cup or disk due to the Rayleigh-Taylor instability. The resulting ligaments leave the liquid torus with a remarkably repeatable spacing that scales inversely with the rotation rate. The fluid filaments then follow a well-defined geometrical path-line that is described by the involute of a circle. Knowing the geometry of this phenomenon we derive the detailed kinematics of this process and compare it with the experimental observations. We show that the ligaments elongate tangentially along the involute of the circle and thin radially as they separate from the cup. We use these kinematic conditions to develop an expression for the spatial variation of the filament deformation rate and show that it decays away from the spinning cup. Once the ligaments are sufficiently far from the cup, they are not stretched sufficiently fast to overcome the critical rate of capillary thinning and consequently undergo capillary-driven breakup forming droplets. We couple these kinematic considerations with the known properties of several Newtonian and viscoelastic test liquids to develop a quantitative understanding of this commercially important fragmentation process that can be compared in detail with experimental observations. We also investigate the resulting droplet size distributions and observe that the appearance of satellite droplets during the pinch-off process lead to the emergence of bidisperse droplet size distributions. These binary distributions are well described by the superposition of two separate Γ distributions that capture the physics of the disintegration process for the main and satellite droplets, respectively. Furthermore, as we consider more viscous Newtonian liquids or weakly viscoelastic test fluids, we show that changes in the liquid viscosity or viscoelasticity have a negligible effect on the average droplet size. However, incorporation of viscous/viscoelastic effects delays the thinning dynamics in the ligaments and thus results in broader droplet size distributions. The ratio of the primary to satellite droplet size increases monotonically with both viscosity and viscoelasticity. We develop a simple physical model that rationalizes the observed experimental trends and provides us a better understanding of the principal dynamical features of rotary fragmentation for both Newtonian and weakly viscoelastic liquids. 2020-07-31T12:37:46Z 2020-07-31T12:37:46Z 2020-03-05 2019-09 2020-03-05T21:07:11Z Article http://purl.org/eprint/type/JournalArticle 2469-990X https://hdl.handle.net/1721.1/126459 Keshavarz, Bavand et al. “Rotary atomization of Newtonian and viscoelastic liquids.” Physical review fluids, vol. 5, no. 3, 2020, article 033601 © 2020 The Author(s) PUBLISHER_POLICY PUBLISHER_POLICY en http://dx.doi.org/10.1103/PhysRevFluids.5.033601 Physical review fluids Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. American Physical Society application/pdf American Physical Society American Physical Society |
| spellingShingle | Keshavarz, Bavand McKinley, Gareth H Rotary atomization of Newtonian and viscoelastic liquids |
| title | Rotary atomization of Newtonian and viscoelastic liquids |
| title_full | Rotary atomization of Newtonian and viscoelastic liquids |
| title_fullStr | Rotary atomization of Newtonian and viscoelastic liquids |
| title_full_unstemmed | Rotary atomization of Newtonian and viscoelastic liquids |
| title_short | Rotary atomization of Newtonian and viscoelastic liquids |
| title_sort | rotary atomization of newtonian and viscoelastic liquids |
| url | https://hdl.handle.net/1721.1/126459 |
| work_keys_str_mv | AT keshavarzbavand rotaryatomizationofnewtonianandviscoelasticliquids AT mckinleygarethh rotaryatomizationofnewtonianandviscoelasticliquids |