Abstract: Geothermal energy is recovered from an underground zone of relatively hot strata via a borehole into which is inserted a heat pipe system containing a working fluid, the heat pipe system comprising an assembly of two tubes in concentric relation, the inner tube being constituted by a relatively small diameter capillary for the return of working fluid to the vicinity of the zone of the relatively hot strata. The working fluid is preferably assisted in its return under gravity by means of a pump. The system includes heat exchange means operable to recover thermal energy from the working fluid. A third and outermost tube may be used to reduce heat losses, this third tube enclosing the two tubes over all but that part of their length which is in the zone of relatively hot strata.

Abstract: A vapor generator and heat exchanger, particularly suited for use in a substantially cylindrical cavity in a pressure vessel includes high and low temperature sections of the vapor generator positioned coaxially with the annular outer section terminating a distance from the end of the central or axial section to form at the one end an annulus arranged between the central or axial section and the pressure vessel wall. A plurality of reheater or heat exchanger sections and various inlet and outlet conduits are positioned in the annulus. A heating fluid is directed first transversely over the tubes of the reheater sections, then along the tubes of the central or axial high temperature section after passing over the outer annular low temperature section.

Abstract: A vapor generator is described wherein a lever system is utilized to move helical connecting tubes communicating between two tube bundles subject to thermal expansion of different amounts. The lever system is actuated by thermal expansion of different amounts of two different structural elements within the vapor generator.