Abstract: A heat exchanger may include a core control assembly movable between compressed and uncompressed positions, and a core. The core may have a plurality of layers with a plurality of passages interleaved therebetween, a portion of the passages extending and open to the periphery of the layers. The core control assembly may be operably coupled to the core to compress the core when the core control assembly is in its compressed position and to permit the core to expand from its compressed state when the core control assembly is moved away from its compressed position. The expansion of the core increases a cross-sectional area of the passages at the periphery of the core.