A binary-fluid heat and mass exchanger has a support structure with a plurality of horizontal vertically spaced groups of tubes mounted thereon. Each group of tubes comprises a pair of horizontal spaced hollow headers. A plurality of small diameter hollow tubes extend between the headers in fluid communication therewith. Fluid conduits connect a header of one group of tubes with a header of an adjacent group of tubes so that all of the groups of tubes will be fluidly connected. An inlet port for fluid is located on a lower group of tubes, and an exit port for fluid is connected to a higher tube group to permit fluid to flow through the tubes in all of the groups. A second inlet port for introducing a solution of fluid downwardly over the tubes is located above the support structure. An outlet port is located at the top of the support structure to convey generated vapor upwardly through the groups and out of the heat exchanger. A fluid exit port is located below the support structure for the removal of fluid collected from the various groups of tubes.