Abstract: The invention relates to a heat exchanger element (10) comprising a bag formed from a compliant material like plastic sheet (11). The lower part of the bag ends to a condensate receiver (13), which is provided with a drain pipe (14) for the condensate. The upper part of the bag has means for introducing the vapour into the bag and distributing the liquid to be evaporated onto the outer surface of the bag. It is characteristic that inside the bag a perforated corrugated plate (12) is fitted in vertical direction with its width (L) chosen so that the bag tightens suitably around the corrugated plate. The length (P) of the corrugated plate (12) corresponds to a major portion of the length of the bag. A perforated corrugated plate (12') is fitted in horizontal direction against the outer surface of the bag with its length (P') substantially corresponding to the width of the bag.