Abstract: A heat exchanger has a cylindrical shell closed at its ends. A large conduit of circular cross-section, which extends longitudinally through the shell, is concentric with the shell to define a central passage for a first heat exchange medium such as a cool gas, and an outer annular passage for a second heat exchange medium, such as a hot liquid. Four radially oriented fins divide the two passages into quadrantal chambers or zones, and two tubes, one extending into each end of the shell, carry the second medium into and remove it from the annular passage.