Abstract: A heating system for improving the efficiency of a hot gas engine comprises a "heat pipe" type evaporator and condenser configuration forming a closed system for a condensing medium, such as sodium. The sodium is heated in the evaporator and vaporized. It flows through a conduit to the condenser where it condenses onto tubes which carry the hot working as for the engine, thereby heating the working gas. The condensed liquid sodium flows back through the conduit into the evaporator where it is again vaporized. This is a continuous cycle whereby a thermal power flow from the evaporator to the condenser is continuously induced by the heating of the sodium in the evaporator. The condenser comprises an outer cylindrical walled tube surrounding tubes which carry the hot working gas. These latter tubes are S-shaped and arranged in a bundle.

Abstract: An improved hybrid solar/combustion powered receiver, for use e.g. with a hot gas engine, the receiver being of the type having a housing and an aperture for admitting solar radiation to the cavity defined by the housing. The improved receiver includes a heat exchanger within the cavity and having the tubes tangentially spaced; multiple burners for providing a combustion gas flow path during combustion powered operation between and around the portions of the tubes upon which solar radiation impinges; and a fused silica, internally mounted window to seal the aperture against combustion gas leakage out of the receiver.

Abstract: The solar receiver for use e.g. with a solar-powered Stirling-type hot gas engine includes an internally mounted fused silica window for sealing the receiver aperture against thermal energy convection losses. The window has a folded cone configuration with an inverted radially outer truncated conical window member, and a radially inner conical window member joined at the base to the smaller base of the outer member. The larger base of the outer conical member is attached to the receiver housing to surround the aperture, and the angle of revolution of both members is about 20.degree.. At least 50% of the solar radiation escaping the receiver through the aperture undergoes at least three reflections prior to escaping.