1,012,179. Refrigerating; air conditioning. R. C. SCHLICHTIG. Dec. 17, 1962, No. 47585/62. Headings F4H and F4V. [Also in Division F1] A reversible heat engine 10, Fig. 1, comprises a pressure exchanger having a pressure transfer duct 72 formed as a Venturi to effect pressure inversion impulse flow of gas from only one compartment of the pressure exchanger to only one other such compartment at a given time. The pressure exchanger comprises a rotor 22 disposed within a housing 12 and having a plurality of spaced vanes 26, the casing being in communication with the atmosphere, for example, through a manifold 38 which includes a deflecting scroll case 40 for gas leaving the pressure exchanger and intake ducts 42 preferably preceded by a precooler 46 and leading to ports 88 for air entering the pressure exchanger. A sealed heat exchanger enclosure 50 is connected to the housing 12, the enclosure having therein a heat exchanger 54 on to which is sprayed a liquid 11, e.g. heated water, liquid fuel or liquid chemical absorbent such as calcium chloride solution. The heat exchanger 54 may be made of stone. A deflecting scroll case 56 is secured to the housing 12 for directing air from the pressure exchanger on to the heat exchanger 54, the scroll case 56 having therein openings 90 for gas from the enclosure 50 to enter the pressure exchanger. A sump and trap 57 receives surplus liquid from the enclosure 50. A reversible air motor 58 communicates with the atmosphere, and with the enclosure 50 through a duct 60, the motor 58 being connected to an electric dynamo/motor 64. The pressure transfer duct 72 interconnects ports 68 and 70 in the housing 12, the port 68 being in communication with outgoing intervane compartments of the pressure exchanger and the port 70 being in communication with incoming intervane compartments. An intake section 74 of the duct 72 converges eccentrically with respect to the port 68 and an outgoing section 80 is streamlined. More than one pressure transfer duct may be provided if they interconnect in parallel identical intervane compartments and function in the manner of a single pressure transfer duct. In operation, precooled ambient air is carried by the rotor 22 to be discharged therefrom into the enclosure 50 for heating by the liquid 11; the air is thus increased in pressure and a portion thereof is returned to the atmosphere by the rotor 22 while the remainder operates the air motor 58. As the outgoing intervane compartments of the rotor 22 carrying the returning pressurized air come into communication with the port 68 part of the air passes through the duct 72 to raise the pressure of the air in the incoming intervane compartments. Any tendency for a substantial gas flow in the reverse direction through the duct 72 is prevented by the eccentric intake section 74 thereof. When the heat engine 10 is operated as a heat pump the liquid 11 absorbs heat from the air in the enclosure 50 by contact and/or evaporation and the air motor 58 is driven by the electric dynamo/motor 64 to maintain the pressure in the enclosure. The cooled gas passing through the pressure exchange is further cooled by expansion as it comes into communication with the port 68 and may be used for refrigeration and air conditioning. The heat exchanger 54 and the spray 52 for the liquid 11 may be replaced by a dry type of heat exchanger 112, Fig. 5 (not shown), through which flows cold water. In a second embodiment, Fig. 4 (not shown), the air in the enclosure 50 is heated by the combustion of a solid reactant within the enclosure, surplus heat being removed by a heat exchanger, e.g. a water-boiler tube for steam generation. The enclosure 50 may be the combustion chamber of a conventional heat engine and the solid reactant may be solid fuel or a chemical absorbent, e.g. silica-gel. In a third embodiment, Fig. 5 (not shown), a vacuum is maintained in the enclosure 50 by cooling the air therein and the transfer duct 72 is reversed so that incoming air pressurizes outgoing air in the pressure exchanger. Flow of ambient air into the enclosure 50 drives the air motor 58. The heat engine of this embodiment may be operated as a heat pump, the air motor 58 being driven by the electric dynamo/motor 64 to maintain the vacuum in the enclosure 50 and the air being heated by the heat exchanger 112. In a fourth embodiment, Fig. 6 (not shown), the heat engine 10 described with reference to Fig. 1 is operated with a vacuum being maintained within the enclosure 50. In operation, preferably hot or vapour-laden air is supplied to the enclosure 50 by the pressure exchanger.