Delft University of Technology Magnetic fluid bearings & seals Methods, design & application Lampaert, S.G.E. DOI 10.4233/uuid:361ba18e-298a-483c-bfb9-0528a4ee6119 Publication date 2020 Document Version Final published version Citation (APA) Lampaert, S. G. E. (2020). Magnetic fluid bearings & seals: Methods, design & application. https://doi.org/10.4233/uuid:361ba18e-298a-483c-bfb9-0528a4ee6119 Important note To cite this publication, please use the final published version (if applicable). Please check the document version above. Copyright Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10. Magnetic Fluid Bearings & Seals: Methods, Design & Application Stefan G.E. Lampaert Part 1: Main matter ii Magnetic Fluid Bearings & Seals: Methods, Design & Application Dissertation for the purpose of obtaining the degree of doctor at Delft University of Technology by the authority of the Rector Magnificus Prof.dr.ir. T.H.J.J. van der Hagen, Chair of the Board for Doctorates to be defended publicly on Wednesday 30 September 2020 at 15:00 o’clock by Stefan Georges Emile LAMPAERT Master of Science in Mechanical Engineering, Delft University of Technology, The Netherlands born in Terneuzen, The Netherlands iii This dissertation has been approved by the promotor[s]. Composition of the doctoral committee: Rector Magnificus, chairperson Dr.ir. R.A.J. van Ostayen Delft University of Technology, promotor Ir. J.W. Spronck Delft University of Technology, copromotor Independent members: Prof.dr. P.C. Rem Delft University of Technology Prof.dr. I. Sherrington University of Central Lancashire Prof.dr.-ing. I.F. Santos Technical University of Denmark Prof.dr.ir. M.B. de Rooij University of Twente Prof.dr.ir. J.L. Herder Delft University of Technology Keywords: ferrofluid, magnetorheological fluids, rheology, lubrication theory, self-healing, load capacity, stiffness, friction, hydrodynamic bearing, hydrostatic bearing. Published by: TU Delft Library Printed by: Gildeprint Enschede Copyright © 2020 by Stefan G.E. Lampaert Email: [email protected] ISBN: 9789464190427 An electronic copy of this dissertation is available at the TU Delft Repository iv “He achieved success who has lived well, laughed often, and loved much; Who has enjoyed the trust of pure women, the respect of intelligent men and the love of little children; Who has filled his niche and accomplished his task; Who has never lacked appreciation of Earth's beauty or failed to express it; Who has left the world better than he found it, Whether an improved poppy, a perfect poem, or a rescued soul; Who has always looked for the best in others and given them the best he had; Whose life was an inspiration; Whose memory a benediction. “ Bessie Anderson Stanley, 1904, What is success? v vi Table of contents Table of contents ...................................................................................................................... vii Summary ................................................................................................................................... ix Samenvatting ............................................................................................................................ xi Prologue ................................................................................................................................... xiii 1 Introduction ...................................................................................................................... 1 2 Ferrofluid bearings ........................................................................................................... 7 3 Ferrofluid gas/liquid seals .............................................................................................. 13 4 Basics of rheological textures ......................................................................................... 17 5 Rheological textures in thrust bearings ........................................................................ 21 6 Rheological textures in journal bearings ...................................................................... 25 7 A lubrication theory for Bingham plastics .................................................................... 29 8 Self-healing bearings ...................................................................................................... 33 9 Rheological characterization of magnetic fluids ........................................................... 37 10 Conclusions ..................................................................................................................... 41 11 Recommendations ........................................................................................................... 45 References ................................................................................................................................. 47 Personal reflection ................................................................................................................... 57 Acknowledgements .................................................................................................................. 59 Curriculum vitae ...................................................................................................................... 61 Thesis project output ............................................................................................................... 63 Appendices ................................................................................................................................ 69 vii viii Summary The bearing and the seal are two commonly used tribological components since nearly all moving machinery relies on them for proper operation. Even a small improvement in these components can have a big impact on both the market and the environment. The two main problems of these components are wear and friction. In addition, seals suffer from the problem of leakage which is fundamental to both their functioning as well as their performance. The application of magnetic fluids has the potential to be beneficial for these systems. Magnetic fluids consist of a suspension of magnetic particles in a carrier fluid. This gives them the unique properties of being attracted to a magnetic field and changing their rheological behaviour in the presence of a magnetic field. These special properties can give these bearing and sealing systems unique behaviour, potentially improving their performance. Therefore, this thesis has two main objectives. The first objective is to further investigate the potential of magnetic fluids in bearing and sealing system. This part consists of exploratory, fundamental and early stage research. The unique properties of magnetic fluids are eventually used in ferrofluid bearings, ferrofluid seals, bearings with rheological textures and self-healing bearings. The second objective is to develop the necessary knowledge to bring these concepts to society in the form of applications. The research on ferrofluid bearings as described in this thesis consists of different experimentally validated models for the load capacity, torque capacity, out of plane stiffness, rotational stiffness, friction and operational range for both ferrofluid pocket bearings and ferrofluid pressure bearings. These models are suitable to determine the most important bearing parameters which makes it possible to design a bearing system according to desired specifications. The most recent demonstrator shows specifications that are competitive with conventional bearing systems. The research on ferrofluid seals as described in this thesis has resulted in the first seal concept that does not show any leakage over time. The concept relies on a replenishment system that makes sure that that degraded ferrofluid is removed and replaced by fresh ferrofluid. This gives the system a theoretical infinite lifetime, as long as the replenishment system continues to work. The research on bearings with magnetorheological fluids as described in this thesis has resulted in the new design concept of rheological textures. A rheological texture is defined to be a local change in the rheological behaviour of the lubricant in the lubricating film such that a local change in lubricant transport and flow resistance occurs. The idea is to replace geometrical surface textures of more traditional bearings with these rheological textures to enhance the performance of the bearing. This work has in addition provided a new lubrication theory for Bingham plastics that properly models the behaviour. Furthermore, a new ix experimental method is developed to characterize the rheology of magnetic fluids at high shear rates. The last significant result of this research is the new concept of a self-healing bearing using a lubricant with a suspension of magnetic particles: the application of a local magnetic field with high gradients in the lubricating film causes the particles to settle at locations where the magnetic field gradient is high. This creates geometrical