Method and apparatus for preferential cooling

A heat exchanger for exchanging heat between a first fluid and a different temperature second fluid in a gas turbine engine comprising:

• a shell including a flow divider separating said shell into two compartments;
• a first circuit disposed in said shell for channeling said first fluid, and having a plurality of parallel flow tubes aligned together at one end thereof to collectively define a primary inlet and aligned together at an opposite end thereof to collectively define a primary outlet;
• said flow tubes being generally U-shaped in configuration with parallel legs thereof straddling said shell divider for positioning said primary inlet and said primary outlet on opposite sides of said divider;
• a second circuit disposed in said shell adjacent to said first circuit for channeling said second fluid in counterflow with said first circuit for exchanging heat therebetween, and having a secondary inlet at one end disposed through said shell adjacent to said primary outlet, a first secondary outlet at an intermediate location in series flow with said secondary inlet, and a second secondary outlet at an opposite end in succession with said first secondary outlet and being disposed through said shell adjacent to said primary inlet, said first secondary outlet being disposed through said shell between said primary outlet and both said primary inlet and said second secondary outlet for discharging said second fluid therefrom at different temperatures;
• and
• said second circuit further including a plurality of baffles spaced apart from each other inside said shell to define a serpentine crossflow channel over said flow tubes for exchanging heat between said first and second fluids flowable therethrough, said baffles extending outwardly from said divider into both said compartments for channeling said second fluid from said secondary inlet across said tubes and through said two compartments in turn for discharging a first portion of said second fluid from said first secondary outlet, and for discharging a remaining, second portion thereof from said second secondary outlet.