Three embodiments of a heat exchanger assembly for cooling an electronic device are shown respectively in FIGS. 1-2, 3 and 4 and each comprises a flange, a dome, a plurality of condensing tubes, a shroud, and a boiler plate. In the first embodiment shown in FIG. 1, the dome is semi-spherical in shape and the distance measured axially along the center axis equals the distance measured laterally from or perpendicular to the center axis. In the second and third embodiments shown in FIGS. 3 and, 4, respectively, the distance measured axially along the center axis is greater than the distance measured laterally from or perpendicular to the center axis. The domes in the second and third embodiments are an ellipsoid and a semi-logarithmic body, respectively. In all embodiments, a plurality of condensing tubes aligned in fan rows and arced rows extend from the dome to distal ends to facilitate more-efficient heat transfer.