Waste heat utilization

A self-actuated exhaust fan is useful for removing waste heat from fluids, especially gases. The process is provided for extracting a first gas from a hot gas source. The first gas has a temperature above ambient temperature. Condensed working fluid is vaporized in an evaporator by extracting the first gas from the hot gas source and passing the first gas in contact with heat transfer surfaces of the evaporator by a first fan. The first fan is driven by an engine. The working fluid so-vaporized is allowed to enter the engine through an inlet port and exhaust through an exhaust port and thus operate the engine. The exhausted working fluid vapour is condensed in a condenser by passing cooler outside air in contact with heat transfer surfaces of the condenser by means of a second fan. The second fan is also driven by the engine. The condensed working fluid is transferred from the condenser to the evaporator by means of a feed pump which is driven by the engine. An advantage of the arrangement is that the working fluid is sealed within the system and normally requires no make-up and releases no fluid to the atmosphere.