Cross-flow heat exchanger systems and methods for fabrication thereof

A heat exchanger comprising:

• first and second manifold portions;
• an array of substantially-parallel first heat-transfer tubes between the first and second manifold portions, each first heat-transfer tube extends along a first direction, a first end of each first heat-transfer tube being in fluid communication with the first manifold portion, a second end of each first heat-transfer tube being in fluid communication with the second manifold portion, each first heat-transfer tube having an outer surface, a first inner surface defining a first conduit, and a second inner surface defining a second conduit;
• and
• one or more spacers disposed along the array of first heat-transfer tubes between the first and second manifold portions, each spacer having a plurality of openings therein, each first heat-transfer tube passing through a corresponding one of the openings in each spacer,
• wherein, for each first heat-transfer tube in a cross-sectional view perpendicular to the first direction:
• the outer surface forms a first shape that is non-circular, the first shape having a leading bulbous end and a tapered tail end, the first conduit being a closest conduit to the leading bulbous end,
• the first shape has reflectional symmetry with respect to a lateral axis extending along a second direction perpendicular to the first direction,
• the first inner surface forms a second shape different than the first shape, the second shape having reflectional symmetry with itself with respect to the lateral axis,
• the first shape is a droplet shape,
• the second inner surface forms a third shape in the cross-sectional view different than the first shape, and
• both the second shape and the third shape are circles or ellipses, and
• wherein each of the first heat-transfer tubes has only two conduits therein.