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RESEARCH PAPERS

# Direct Observations of Emulsion Flow in Elastohydrodynamically Lubricated Contacts

[+] Author and Article Information
Haixia Yang, Steven R. Schmid

Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556

Ronald A. Reich, Thomas J. Kasun

Surface Science and Tribology Division, Alcoa Technical Center, Alcoa Center, PA 15069

J. Tribol 128(3), 619-623 (Mar 27, 2006) (5 pages) doi:10.1115/1.2198211 History: Received November 03, 2005; Revised March 27, 2006

## Abstract

The lubrication mechanisms with oil-in-water emulsions have been extensively investigated based on the measurements of film thickness and/or tractions in the past few decades. However, direct observation of the emulsion flow, as a more direct method of evaluating suggested explanations, has been greatly restricted by the available instruments, especially the cameras used in collaboration with high-speed bearing simulators. In this paper, a newly devised digital video camera and a microscope were used to directly observe the emulsion flow in an elastohydrodynamic lubrication (EHL) inlet region at a wide range of speeds ($0.012m∕s$ up to $1.5m∕s$). Both EHL line and point contacts were considered. Previous observations of low speed oil droplet “stay,” “reverse,” and “penetration” behavior for low-speed line contact were confirmed and extended into high-speed line and point cases, and the results were compared with point contact where significant side flow was observed. Three tight emulsions with different mean droplet sizes were examined on an EHL rig to clarify the droplet behavior and investigate the effect of droplet size on entrainment.

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## Figures

Figure 1

Experimental results of Zhu (3), with regimes of emulsion behavior identified

Figure 2

Direct observations by Nakahara (12). U=rolling speed, W=load, Q=volume flow rate of emulsion supply, and X is distance from the center of contact.

Figure 3

Experimental setup optical system, consisting of a digital video camera and a stereo microscope mounted above the elastohydrodynamic lubrication (EHL) rig

Figure 4

Droplet size distributions of three emulsions with mean droplet sizes of 10, 5, and 2μm, respectively

Figure 5

Emulsion flow in the vicinity of line contact. Each image is roughly 1000×700μm.

Figure 6

Extent of oil pool varies with rolling speed (2μm emulsions)

Figure 7

Effect of droplet size on oil pool formation (5vol% emulsions)

Figure 8

Effect of initial oil concentration on oil pool formation

Figure 9

Emulsion flow in the vicinity of point contact. Each image is roughly 1000×700μm.

Figure 10

Sketch of the top view of unsegregated oil droplets in point contact

Figure 11

Trajectories of oil droplets in point contact (1vol%, 5μm emulsions)

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