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Evaporation-induced foam stabilization in lubricating oils.
V Chandran Suja1, A Kar2, W Cates2
1Department of Chemical Engineering, Stanford University, Stanford, CA 94305.
Summary
Foaming in nonaqueous liquids like lubricants is stabilized by solutocapillary flows, driven unexpectedly by differential evaporation. Mixing base oils can worsen this foaming effect.
Area of Science:
- Fluid dynamics
- Surface science
- Tribology
Background:
- Foaming is common in liquids, but mechanisms in nonaqueous systems, particularly lubricant base oils, are poorly understood.
- Existing research primarily focuses on aqueous foaming, leaving a knowledge gap in nonaqueous liquid behavior.
Purpose of the Study:
- To investigate the mechanism of foam stabilization in lubricant base oils.
- To evaluate lubricant foam stability using a novel single-bubble technique.
- To identify factors contributing to foam formation in nonaqueous lubricants.
Main Methods:
- Development and application of a new experimental technique for single-bubble analysis.
- Observation and measurement of bubble stability in lubricant base oils.
- Analysis of fluid flows within lubricant foams.
Main Results:
- Solutocapillary flows are identified as crucial for stabilizing lubricant foams.
- Differential evaporation of multicomponent lubricants, despite low volatility, drives these solutocapillary flows.
- Mixing certain lubricant base oils intensifies solutocapillary flows, leading to increased foaming.
Conclusions:
- Solutocapillary flows, originating from differential evaporation, are the primary mechanism for nonaqueous lubricant foam stabilization.
- The common industrial practice of mixing lubricant base oils can unexpectedly enhance foaming.
- Further research into lubricant composition and evaporation dynamics is needed to control foaming.
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