Evaporator with coated and corrugated tubes

An evaporator comprising a plurality of horizontal, vertically elongated tubes arranged to support a vertical film of saline water, and to evaporate water from the film by heat transfer from a condensate film of condensing vapor within the tubes, characterized in that:

• the horizontal tubes are vertically and circumferentially corrugated in at least a specified outer profile comprising alternating outer ridges and grooves on an outer face of the tubes, the specified outer profile selected to thin the film on the outer ridges to enhance heat transfer therethrough and evaporation therefrom.

A method of enhancing heat transfer across horizontal evaporator tubes which are vertically elongated, the method comprising corrugating an outer face of the tubes in at least a specified outer profile comprising alternating outer ridges and grooves on an outer face of the tubes, to thin a falling water film on at least part of the outer face, to increase heat transfer across the thinned film.

An evaporator comprising a plurality of tubes arranged to support a vertical film of saline water, and to evaporate water from the film by heat transfer from a condensate film of condensing vapor within the tubes, the tubes having a heat transfer coefficient hO that deteriorates to a heat transfer coefficient hm as a result of scaling, wherein reaching hm requires cleaning the tubes from the scaling after a period TO, the evaporator characterized in that the tubes comprise an outer coating having a heat transfer coefficient hC larger than hm and smaller than hO, the outer coating selected to increase a cleaning period to TC larger than TO.