Direct observation of the impact of water droplets on oil replenishment in EHD lubricated contacts


Water is one of the most significant causes of lubrication failure. There is little research on the direct observation of the impact of water on lubrication properties. In this study, the influence of water on oil replenishment under different elastohydrodynamic (EHD) lubricating conditions is evaluated using optical interferometry and infrared microscopy, and a dimensionless criterion when water influences the film thickness is proposed. Evidence shows that the scour displacing effect and emulsification of water/oil are the main reasons for the reduction in film thickness. Once a water droplet enters an oil reservoir around the critical contact zone, it hardly moves away. This aggravates starvation, reduces the center film thickness of the contact, and leads to lubrication failure of the mechanical components.


  1. [1]

    Needelman W M, Barris M A, LaVallee G L. Contamination control for wind turbine gearboxes. Power Eng 113: 112–112 (2009)

    Google Scholar 

  2. [2]

    Kotzalas M N, Doll G L. Tribological advancements for reliable wind turbine performance. Philos Trans R Soc London, Ser A 368: 4829–1850 (2010)

    Google Scholar 

  3. [3]

    Terrell E J, Needelman W M, Kyle J P. Current and future tribological challenges in wind turbine power systems. In ASME/STLE 2009 International Joint Tribology Conference, Tennessee, USA, 2009: 495–497.

  4. [4]

    Patchett B M, Yarmuch M A R. Hydrocarbon Contamination and Diffusible Hydrogen Levels in Shielded Metal Arc Weld Deposits. Welding Journal 89: 262–265 (2010)

    Google Scholar 

  5. [5]

    Fitch J C, Jaggernauth S. Moisture—The second most destructive lubricant contaminate, and its effects on bearing life. P/PM Technology 12: 1–4 (1994)

    Google Scholar 

  6. [6]

    Wan G T Y. Elastohydrodynamic film thickness of water based hydraulic fluids. Ph.D Thesis. London (UK): Imperial College University, 1983.

    Google Scholar 

  7. [7]

    Wan G T Y, Kenny P, Spikes H A. The elastohydrodynamic properties of water-based fire-resistant hydraulic fluids. Tribol Int 17: 309–315 (1984)

    Article  Google Scholar 

  8. [8]

    Matter P. Seal oil contamination. Ind Lubr Tribol 35(3): 84–86 (1983)

    Article  Google Scholar 

  9. [9]

    Johnson M, Spurlock M. Strategic oil analysis: Instrument-based on-site lubricant analysis. Tribol Lubr Technol 66: 26–27 (2010)

    Google Scholar 

  10. [10]

    Johnson M, Spurlock M. Strategic oil analysis: Setting the test slate. Tribol Lubr Technol 5: 20–27 (2009)

    Google Scholar 

  11. [11]

    Zhu J. Online industrial lubrication oil health condition monitoring, diagnosis and prognostics. Ph.D Thesis. Chicago (USA): University of Illinois, 2013.

    Google Scholar 

  12. [12]

    Roddis A. Reducing moisture contamination in bearing lubrication. Sealing Technology 2: 6–9 (2006)

    Article  Google Scholar 

  13. [13]

    Troyer D. Establishing moisture contamination targets for hydraulic systems. Machinery Lubrication 28–32 (2004)

  14. [14]

    Moon M. How clean are your lubricants? Trends Food Sci Tech 18: 74–79 (2007)

    Article  Google Scholar 

  15. [15]

    Johnson M. Lubricant management: Dynamic circulating systems. Tribol Lubri Tech 65: 32 (2009)

    Google Scholar 

  16. [16]

    Tiwari R, Khatana M. Lubrication oil replacement technology. IJRTET 7(3): 8–11 (2012)

    Google Scholar 

  17. [17]

    King R A, Mckehzie P. Microbial degradation of marine lubricating oils. Ind Lubr Tribol 29: 4–25 (1977)

    Article  Google Scholar 

  18. [18]

    Cyriac F, Lugt P M, Bosman R, Venner C H. Impact of water on EHL film thickness of lubricating greases in rolling point contacts. Tribol Lett 61(3): 1–8 (2016)

    Article  Google Scholar 

  19. [19]

    Chen J, Yan F Y, Wang J Z. Corrosion wear properties of TC4 titanium alloy in artificial seawater. Tribology 32(1): 1–6 (2012)

    Google Scholar 

  20. [20]

    Chen H, Wu F, Zhao W J, et al. Influence of epoxy value on the tribological performances of epoxy resin coatings in seawater environment. Tribology 34(6): 601–607 (2014)

    Google Scholar 

  21. [21]

    Chen R L, Wang Y, Lei H. Flow characteristics of nano-confined water under dynamic load by molecular dynamics simulation. Tribology 36(6): 673–678 (2016)

    Google Scholar 

  22. [22]

    Damiens B, Venner C H, Cann P M E, Lubrecht A A. Starved lubrication of elliptical EHD contacts. J Tribol-T ASME 126: 105–111 (2004)

    Article  Google Scholar 

  23. [23]

    Liu X, Huang L, Guo D, Xie G X. Infrared thermography investigation of an evaporating water/oil meniscus in confined geometry. Langmuir 33: 197–205 (2017)

    Article  Google Scholar 

  24. [24]

    Ball bearing lubrication: The elastohydrodynamics of elliptical contacts. New York (USA): Wiley Interscience, 1981.

  25. [25]

    Jacod B, Pubilier F, Cann P M E, Lubrecht A A. An analysis of track replenishment mechanisms in the starved regime. Tribology Series 36: 483–492 (1999)

    Article  Google Scholar 

  26. [26]

    Hurley S, Cann P M, Spikes H A. Lubrication and reflow properties of thermally aged greases. Tribol Trans 43: 221–228 (2000)

    Article  Google Scholar 

  27. [27]

    Cann P M, Lubrecht A A. The effect of transient loading on contact replenishment with lubricating greases. Tribology Series 43: 745–750 (2003)

    Article  Google Scholar 

  28. [28]

    Cann P M E, Damiens B, Lubrecht A A. The transition between fully flooded and starved regimes in EHL. Tribol Int 37: 859–864 (2004)

    Article  Google Scholar 

  29. [29]

    Gershuni L, Larson M G, Lugt P M. Lubricant replenishment in rolling bearing contacts. Tribol Trans 51: 643–651 (2008)

    Article  Google Scholar 

  30. [30]

    Nagata Y, Kalogiannis K, Glovnea R. Track replenishment by lateral vibrations in grease-lubricated EHD contacts. Tribol Trans 55: 91–98 (2012)

    Article  Google Scholar 

Download references


This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 51805505, 52075514, and 51605460).

Author information



Corresponding authors

Correspondence to Lu Huang or Dan Guo.

Additional information

Xiang LIU. He received his Ph.D. degree in 2015 from State Key Lab of Tribology, Tsinghua University, Beijing, China. He studied the mechanism of oil lubrication during Ph.D. period. Now he is an associate research fellow in National Institute of Metrology, Beijing, China. His research area mainly focuses on the volume and density metrology method.

Jintao WANG. He received his bachelor, master, and doctor degrees from Xi’an Jiaotong University in 1998, 2001, and 2006, respectively. He is working for Volume and Density Laboratory of National Institute of Metrology as a research fellow, and the main research field is volume and density metrology method.

Lu HUANG. She received her Ph.D. degree in 2016 from State Key Lab of Tribology, Tsinghua University, Beijing, China. She studied the mechanism of grease and oil lubrication during Ph.D. period. Now she is an associate research fellow in National Institute of Metrology, Beijing, China. Her research area mainly focuses on the evaluation of lubricants and matierials, and nano-particle characterization.

Dan GUO. She received the M.S. degree in engineering mechanics in 1995 from Xi’an Jiaotong University, Xi’an, China and Ph.D. degree in engineering mechanics in 1999 from Tsinghua University, Beijing, China. She joined the State Key Laboratory of Tribology at Tsinghua University from 1999. Her current position is a professor and the deputy director of the laboratory. Her research areas cover the properties of friction at the micro/nano-scale, mechanism of interaction among nanoparticles and surface in ultra-smooth surface planarization, and the formation and lubricayion failure in harsh conditions.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

To view a copy of this licence, visit

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Liu, X., Wang, J., Huang, L. et al. Direct observation of the impact of water droplets on oil replenishment in EHD lubricated contacts. Friction (2021).

Download citation


  • free water droplet
  • point contact
  • starved condition
  • film thickness