Originally Posted by Pinkman
Surely the idea must be to increase the transfer of heat between oil & fuel. How does remachining the physical face of the FOHE achieve that? Surely you either have to increase the recirculation rate of the oil or elongate the matrix to improve heat transfer. As I am clueless here I am happy to be abused on this!
No, the rate of heat exchange has been designed the way it is. Having more heat exchanged may make the oil too cold. The other name for the FOHE is "Fuel Cooled Oil Cooler", which clearly states is primary function: cooling the oil. Heating the fuel is only a secondary effect.
Originally Posted by airfoilmod
The schematic I have seems to show the From Engine Oil entering the FOHE at the Fuel exit. The FOHE Away Oil (cooled) seems to be exiting at the Face FOHE. I'd like to be wrong, since I think the Hottest Oil should be at the FOHE's Face.
Countercurrent flow heat exchangers are much more efficient than parallel flow desings. The design goal of the FOHE was not to melt ice on its fuel inlet face, but to cool the oil, and weight being a critical parameter in aviation, this was obviously the right engineering decision. I'd be surprised to see a lot of parallel flow HEs anywhere.
Bernd