Continued from page 16
In the channel with double restrictions, Figure 6 (b), the averaged vector field is shown in Figure 8 for the NLGI 2 grease with low and high driving pressure, and for the NLGI 00 grease with a high driving pressure. The maximum flow velocity is found above the two restrictions. A higher pressure and lower NLGI grade result in a higher flow velocity. The flow depth between the restrictions increases with increasing pressure head and/or reducing NLGI grade (see Figure 8). In other words, increasing shear stress expands the borders of the yielded grease domain. Thus, the NLGI 2 grease remained stationary in the area between the restrictions at low pressure gradients (Figure 8a). On the other hand, for the NLGI 00 grease, the flow depth reached to the bottom of the cell at sufficiently high pressure gradients (Figure 8c). These results illustrate that the grease motion is strongly dependent on grease rheology, which is very important for understanding grease flow and lubricatiing efficiency in applications such as seals and bearings [7].
LINKS
www.appliednanosurfaces.com
boris.zhmud@appliednanosurfaces.com
References (1) Gow, G. M. “Think (Rheo-)Logically,”. Paper presented at 50th NLGI meeting. Kansas City.
(2) Yeong, S.K., Luckham, P.F., Tadros, Th.F. “Steady flow and viscoelastic properties of lubricating grease containing various thickener concentrations”, Journal of Colloid and Interface Science, 274 (2004) 285.
(3) Salomonsson, L., Stang, G., Zhmud, B. “Oil/Thickener Interactions and Rheology of Lubricating Greases”, Tribology Trans. 50 (2007) 302.
(4) Salomon, D., Zhai, H. “Rheological measurements of asphalt emulsions”, 3d World Congress on Emulsions, Lyon, France, Sept. 24-27, 2002.
(5) Hamnelid, L.”Consistency consists in σy 63rd NLGI Annual Meeting, Carlsbad, 1997.
”, Paper Presented at the
(6) Li, J., Höglund, E., Westerberg, L.G., Green, T.M, Lundström, T.S., Lugt, P.M., Baart, P. “µPIV measurement of grease velocity profiles in channels with two different types of flow restrictions,” Trib. Int. 54 (2012) 94.
(7) Li, J., “Lubricating Grease: Experiments and Modelling of Wall- Bounded and Free-Surface Flows”, Ph.D. thesis, Department of Engineering Science and Mathematics, Luleå University of Technology, Luleå, 2014; ISBN 978-91-7583-145-9.
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