A heat exchanger comprises a seamless body, and the seamless body may include a substantially cylindrical configuration defining a radial direction, a circumferential direction, a longitudinal axis, a first cylindrical wall and a plurality of fins. Each fin may extend at least partially in the radial direction and helically along the longitudinal axis. Also, each fin may be at least partially hollow defining an internal flow passage, and each fin of the plurality of fins may be at least partially spaced away from an adjacent fin, defining an external flow passage.