Abstract: A method of operating a heat pump having at least one circuit for circulation of a refrigerant comprising a compressor, a once-through path, complete counterflow type condenser as a high-temperature heat output means, an expansion valve and a low-temperature heat output means (evaporator or a segregated low-stage circuit for circulation of a lower-boiling-point refrigerant), which comprises choosing a supercool degree, which is equal to the difference between a saturation temperature and an outlet temperature of the refrigerant, to satisfy the conditions that a temperature effectiveness of refrigerant liquid as defined by the formula: ##EQU1## is at least 40% and the temperature difference of the denominator is at least 35.degree. C. As a result, boiling water of ca. 100.degree. C. or other high-temperature fluids can be discharged with a large temperature difference.

Abstract: The air-fuel ratio of an air-fuel mixture to be supplied to a combustion chamber is controlled in accordance with a feedback control mode or a lean control mode. In the feedback control mode, the air-fuel ratio is feedback-controlled to be maintained around the stoichiometric air-fuel ratio. In the lean control mode, the air-fuel ratio is controlled to be maintained at a leaner side of the stoichiometric air-fuel ratio. Ignition plugs are ignited at a first ignition timing which is comparatively advanced in the lean control mode and at a second ignition timing which is behind the first ignition timing in the feedback control mode.The ignition plugs are ignited at the second ignition timing for a predetermined period of time after switching from the lean control mode to the feedback control mode and at the first ignition timing for a predetermined period of time after switching from the feedback control mode to the lean control mode.

Abstract: An apparatus for producing a wire fin tube for heat transfer which comprises a wire fin forming station, a fin guiding station, a wire fin delivery station, a tube feeding device and a welding device, whereby a plurality of wires are simultaneously shaped into wavy wires which in turn are wound around a tube in the form of plural helices. The fin guiding station is characterized by having at least two different paths of different lengths whereby the wavy wires are wound around the tube in at least two different phases.

Abstract: Apparatus for efficiently producing a wire fin tube for heat transfer which comprises fin-forming means for shaping a plurality of wires to a wavy shape, said fin-forming means including a pair of gears; means for guiding the wavy wires in an upstanding state including guide plates spaced apart a selected distance; means for feeding a revolving tube in a crossing direction, to the wavy wires so that the wires can be wound on the tube; means for controlling the operative speed relation of the fin forming means and the tube feeding means so that the wavy wires may be helically wound on the tube under a moderate tension so as to maintain the upstanding state and the same pitch as the distance of the guiding means; and means for welding the wire fins to the tube.