A330 Fuel Temp

[rooaaiast]

I have noticed at the end of cruise that the Trim Tank fuel temp is always 5-10 degs higher than the Outer Tank temp. Yet both are roughly of similar surface areas exposed (prior to TFR) to the same cold soak.
No FCOC or IDG's involved. Anyone know why this is so?

[mathy]

You have demonstrated two key points. Firstly it is not temperature alone that is the determining factor but enthalpy usually written as H = U + pV where U is the total internal energy, p is the boundary pressure and V is the volume.

Clearly the tanks you refer to are not identical so the enthalpy in each is different.

The tanks being constructed differently and housed differently will not have the same heat transfer coefficient “k”. If you measure a time interval from t1 to t2 and calculate enthalpies H1 and H2 and the ambient enthalpy Ha then according to Newton's Law of Cooling

k(t1 - t2) = - natural logarithm[(H1 - Ha)/(H2 - Ha)]

Of course in a simple situation where the total internal energy of each tank is constant it is sufficiently accurate to substitute temperatures T1 and T2 for enthalpies H1 and H2. For example the aircraft is now on the ground and you simply want to know how long it will be before the fuel temperature rises to a certain temperature.

You can use the same formula for brakes.

[fantom]

OK, disregarding the trim tank (in the tail of the aircraft) why are the wing tank temperatures different - left and right -after a long cruise?

[JABBARA]

Rooaaiast

That is simply because the trim tank is just behind the engine exhaust. Stabilizer hit by hot gases.

Thanks,

[rooaaiast]

Mathy,
Thanks for that. Obviously a complex question. Just another mystery of the "Magic Bus" I guess.

[hetfield]

Hhhm, I'm not current on A330 but have flown 340 many moons ago.

Isn't the fuel used for cooling of eng oil and IDG?

Which in turn means fuel is heated up a bit?