Originally posted by MI5edtoDeath
> that oil is used as a coolant
Didn't want to get into an argument about this, but that statement is correct as I have shown. Oil IS used to cool components. It is not used to
cool the 'engine' itself, only auxiliary components.
> that oil is pressurised to prevent from boiling
This AFAIK is not true because oil boils at something like 300C, and would never get that hot to start with. But it could
be true, the theory
The oil IS pressurized, but only to make it move through the system.
Both assertions are wrong because you cannot use added pressure to keep something from boiling.
Actually you can. All fluids boil at a higher temp at higher pressures. Water will boil at less than 100C on a mountain top for example. It's got
to do with the release of vapor.
Also oil has a poor heat transfer rate because it retains heat hence the use of the term "calories" which is a value to a fixed volume. This
volume is the oil in the circuit.
No it has good heat transfer, it retains the heat thus carrying it away from the competent being cooled. Calories is a unit of HEAT. The oil is
constantly getting hot and being cooled, circulating heat away from the components.
Auxiliary parts of a jet engine that require coolants use kerosene or air. Oil is an incidental contributor.
Not all component can use air, and nothing is cooled by the kerosene.
A jet of coolant that is a significantly different temperature than the temperature of the gas flowing through the engine itself will have a different
density. The density of the gas that flows through the engine divided by the density of the coolant gas is known as the density ratio. This is a very
important controlling parameter in the operation of the engine cooling.
So you see, the primary cooling element is air and internally to a jet engine coolant gas may also be used. So please refer to the above quote
Yes for the engine, the compressor and combustion sections. There are all the auxiliary components that are not discussed in that quote.
The difference between coolant gas temperature and the temperature of gas in a jet engine is significant. The ratio of hot oil to a cooled oil
is not significant because ratio is very low. It has a marginal effect. Oil is not used as a jet engine coolant.
No it is not used as a jet engine coolant, I already said that. It is used to cool bearings, reduction gearbox, seals. etc.
The calories in the Exxon document is about the relative values of the oil itself and not the jet engine!
That is not quite true. Relative values of the oil itself? No, it is the percentage of the oils use, 90% is removing calories, heat, away from
components. That is what oil is used for in ALL engines.
SELECTING A HIGH TEMPERATURE HEAT TRANSFER FLUID SYNTHETIC OR HOT OIL?
calorie or calory (ˈkælərɪ)
— n , pl -ries
Compare Calorie cal , gram calorie , Also called: small calorie a unit of heat, equal to 4.1868 joules ( International Table calorie ):
formerly defined as the quantity of heat required to raise the temperature of 1 gram of water by 1°C under standard conditions. It has now largely
been replaced by the joule for scientific purposes.
edit on 6/11/2012 by ANOK because: (no reason given)