Abstract: A heat exchanger of the type in which spaced apart plates define flow passages between them and alternating flow passages conduct different fluid media in heat exchanging relationship through the plates. One of the fluid media is a mixture of a gas phase into liquid phase and, according to the invention, the mixing device is provided in the passage for the mixture and is in the form of a bar which can brace the two plates flanking it against deformation under pressure. This bar has channels for one of the phases in a duct extending the length of the bar and communicating with the channels through spaced apart openings or orifices or with the passage downstream of the bar for the other phase through such openings or orifices.