The invention relates to a method for executing an alternating evaporation and condensation process of a working medium on a heat transfer surface provided simultaneously as an evaporation and condensation surface. The method is characterized in that, during a respective operating cycle from in each case an condensation process and in each case an evaporation process, a condensate film of the working medium which forms during the condensation process is stored permanently in situ on the heat transfer surface and is then evaporated from the heat transfer surface during the evaporation process. In terms of the apparatus, the heat transfer surface (2) is in the form of an in-situ store for a condensate film (6) of the working medium which covers the heat transfer surface and does not drip off and remains on the heat transfer surface during the condensation process and evaporates during the evaporation process.