Abstract: A heat exchanger is provided. The heat exchanger includes a stack assembly with a plurality of plates and a plurality of frames arranged in an alternating stacked relationship with the plates along a predetermined direction. Each of the plates has a plurality of first openings and each of the frames has a plurality of second openings. A plurality of first and second fluid channels extends through the stack assembly along the predetermined direction and through the plurality of first and second openings. A first fluid flow path includes a first inlet channel in fluid communication with the plurality of first fluid channels, and a first outlet channel in fluid communication with the plurality of second fluid channels. A second fluid flow path is in thermal contact with the first fluid flow path and fluidically isolated from the first fluid flow path.