Evaporative heat exchange apparatus with finned elliptical tube coil assembly

An evaporative indirect heat exchanger comprising:

• a plenum having a generally vertical axis,
• a coil assembly,
• a distributor for distributing an external heat exchange liquid onto a coil assembly, an air mover for causing air to flow in a direction through the plenum, and
• said coil assembly mounted within the plenum such that the external heat exchange liquid flows externally through the coil assembly in a generally downward vertical flow direction, and the air flows externally through the coil assembly interacting with the external heat exchange liquid to evaporate and cool the external heat exchange liquid and internal process fluid within the coil assembly,
• wherein the coil assembly comprises inlet and outlet manifolds and a plurality of tubes connecting the manifolds, each tube comprising a plurality of horizontally oriented segments arranged vertically relative to one-another in a single vertical plane, wherein each segment has a longitudinal axis and a generally elliptical cross-sectional shape having a major axis and a minor axis where the average of the major axis length and the minor axis length is a nominal tube outside diameter, and where the major axis of each segment of a tube is aligned with the single vertical plane,
• wherein the tubes are arranged in the coil assembly in a staggered arrangement of a first and second set of alternating tubes in which each tube in said first set of tubes is fixed in the coil assembly at a first vertical position, and each of said second set of alternating tubes is fixed in the coil assembly at a second vertical position which is displaced from said first vertical position, wherein the tubes have external elliptical spiral fins on an outer surface of the tubes, wherein the fins have:
• a spacing of 1.5 to 3.5 fins per inch (2.54 cm) along the longitudinal axis of the tubes,
• a height extending from the outer surface of the tubes a distance of substantially 23.8% to substantially 36% of the nominal tube outside diameter, and
• a thickness of substantially 0.007 inch (0.018 cm) to substantially 0.020 inch (0.051 cm), wherein each of the tubes of said first or second set of alternating tubes is horizontally spaced, center-to-center, from an adjacent tube in a same set of alternating tubes by a distance (DH) that is substantially 100% to substantially 131% of the nominal tube outside diameter, and wherein each of the tubes in said first set of tubes is vertically displaced, center-to-center, relative to adjacent tubes in said second set of tubes by a distance (DV) that is substantially 110% to substantially 300% of the nominal tube outside diameter.