by the further heat passing wall 14 passes through the liquid layer in the reservoir 15 and through the further heat passing wall 11 to the space 9 and causes evaporation of liquid transporting medium contained inside said space on the further heat passing wall 11 the evaporation condensation process performed inside the space 9 is identical to that in the space 12 the evaporation heat released by the condensation of transporting medium on the heat passing wall 8 passes through said wall to the cyclic medium in the expansion space 4 in order to compensate for the caloric energy converted into mechanical energy during the expansion of the cyclic medium and also in order to compensate for the normal caloric losses if the heat transport from the heat source 16 to the heater 5 has to be interrupted for example for stopping the engine this can be carried out in a simple manner by removing the liquid from the reservoir 15 via the liquid outlet 18 and if necessary by further exhausting the reservoir 15 even if the heat source 16 continues supplying heat for example if it is a heat accumulator the supplied heat cannot attain the heater 5 the sole consequence is that an evaporation condensation process is performed only inside the space 12 until the vapour pressure in the portion of the space 12 adjacent the further heat passing wall 14 is equal to the vapour pressure at the heat passing wall 13 the latter being determined by the temperature of the heat source 16 as a matter of course the space.