Abstract: A heat exchanger is composed of vertical tubes of cuspate, symmetrical aerofoil section. The chords are parallel to the air flow. The tubes are in parallel rows that interpenetrate so that each tube forms parallel-sided passages with two tubes leading it. The ratio of width to length of these passages if between 0.3 and 1.0. The tubes are spaced apart at various levels by means of inclined spacers. At the top of the tubes water is fed around them from a launder via a system of spacers. The spacers lower down serve to redistribute the water running down the flanks of the tubes. At the base there is an inclined platform on which the water is collected and fed to a launder. This water may be recirculated with additions to replace water lost by evaporation.