Abstract: A method for applying a heat exchanger in a drill hole and an apparatus for carrying out such method, comprising the steps of lowering at least one pair of heat-exchanging pipes helically wound and spaced apart by expandable spacers into a drilled hole and expanding the pipes into contact with the wall of the drilled hole by turning such pipes in the spiralled direction.

Abstract: The present invention relates to a method and a means for applying a heat exchanger in a drill hole (2) in rock, loose soils or the like for the purpose of heat recovery or storage, achieving a more efficient heat transfer between the defining surface (4) of the drill hole and a heating medium contained in the heat exchanger, wherein at least one heat-exchanging element (1) is lowered into the drill hole (2) and expanded in substantially radial direction so that the heat-exchanging element (1) is thus caused at least partially to be substantially in contact with the defining surface (4) of the drill hole.

Abstract: The invention relates to a means for electrically heating gases, comprising cylindrical electrodes (2,3) between which an electric arc (20) is generated. Between these two electrodes are arranged one or more spacers (6,7) whose length is from 100 to 500 mm.