List,
One reason for a dry sump is removing the air from the oil. I don't know
( Dave ??) how much heat can be generated by air in engine oil but aeration
is a major cause of heat failure in hydraulic systems.
Bryan (The information junkie)
The following is from:
Controlling Oil Aeration and Foam
Marianne Duncanson, Exxon Company USA
Dissolved air is not readily drawn out of solution. It becomes a problem
when temperatures rise rapidly or pressures drop. Petroleum oils contain
as much as 12 percent dissolved air. When a system starts up or when it
overheats, this air changes from a dissolved phase into small bubbles.
If the bubbles are less than 1 mm in diameter, they remain suspended in
the liquid phase of the oil, particularly in high viscosity oils,
causing air entrainment, which is characterized as a small amount of air
in the form of extremely small bubbles dispersed throughout the bulk of
the oil. Air entrainment is treated differently than foam, and is most
often a completely separate problem. Some of the potential effects of
air entrainment include:
*
pump cavitation,
*
oil oxidation,
*
component wear due to reduced lubricant viscosity,
*
micro-dieseling due to the ignition of the bubble sheath at the
high temperatures generated by compressed air bubbles,
Base Oils Effects
In a system where foam is generated mechanically, switching to synthetic
oil may help.
*
Polyalphaolefin and hydrocracked oils, by virtue of their high
surface tension, show relatively low foaming tendency compared to
petroleum hydrocarbons.
*
Unadditized organic esters are essentially nonfoaming, but are
highly susceptible to contamination or to effects from additives.
*
Phosphate esters show foam build-up at low temperatures, but
above 122:F (50:C) they show very little foam tendency.
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