Heat exchanger with heat transfer augmentation features

A heat exchanger comprising;

• a plurality of first channels extending longitudinally, each first channel comprising;
• a plurality of first internal fins extending from and integrally formed with an internal wall of each first channel, wherein first internal fins of the plurality of internal fins are arranged in a spiraling orientation along the internal wall;
• and
• a plurality of external fins extending from and integrally formed with an external wall of each first channel;
• and
• a plurality of second channels, each second channel defined by the external walls of the plurality of first channels, the plurality of external fins, and an outer wall connecting the plurality of external fins;
• wherein the plurality of second channels is fluidly isolated from the plurality of first channels.