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Rise of Air Bubbles in Aircraft Lubricating OilsLubricating and antifoaming additives in aircraft lubricating oils may impede the escape of small bubbles from the oil by forming shells of liquid with a quasi-solid or gel structure around the bubbles. The rates of rise of small air bubbles, up to 2 millimeters in diameter, were measured at room temperature in an undoped oil, in the same oil containing foam inhibitors, and in an oil containing lubricating additives. The apparent diameter of the air bubbles was measured visually through an ocular micrometer on a traveling telescope. The bubbles in the undoped oil obeyed Stokes' Law, the rate of rise being proportional to the square of the apparent diameter and inversely proportional to the viscosity of the oil. The bubbles in the oils containing lubricating additives or foam inhibitors rose more slowly than the rate predicted by Stokes 1 Law from the apparent diameter, and the rate of rise decreased as the length of path the bubbles traveled increased. A method is derived to calculate the thickness of the liquid shell which would have to move with the bubbles in the doped oils to account for the abnoi'I!l8.lly slow velocity. The maximum thickness of this shell, calculated from the velocities observed, was equal to the bubble radius.
Document ID
19930082690
Acquisition Source
Legacy CDMS
Document Type
Other - NACA Technical Note
Authors
Robinson, J. V.
(Stanford Univ. Stanford, CA, United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1950
Subject Category
Nonmetallic Materials
Report/Patent Number
AD-A801536
NACA-TN-2033
Accession Number
93R11980
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Keywords
LUBRICATING OILS - FOAMING
LUBRICATING OILS - RPM AVIATION 120
LUBRICATING OIL COMPOUNDS - DOW-CORNING 200
GASES - BUBBLES
LUBRICATING OIL COMPOUNDS - AEROSOL OT
LUBRICATING OIL COMPOUNDS - GLYCEROL
LUBRICATING OILS - AEROSHELL 120
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