Abstract: A plate-type heat exchanger for hot gas engines of the Stirling type includes stacked pairs of elongated rectangular plates joined at the longitudinal edges with spaces between the paired plates constituting the cold gas flow passages and spaces between plate pairs constituting the hot gas flow passages. Paired plates have mirror image protrusions protruding from the respective abutted longitudinal margins, which protrusion form the internal cold gas flow passages and also provide the spacing between adjacent abutting pairs that constitutes the hot gas flow passages. Abutting plates of adjacent stacked pairs are joined at the abutting transverse margins.

Abstract: In a cross flow tubular heat exchanger the tubes are arranged in a space between two concentrically, imaginary cylinders. Radially extending baffle plates ensure that the heat exchanging medium flowing outside the tubes and perpendicular to their direction will pass the central cylindrical space without tubes.

Abstract: An improved method of exchanging heat between combustion gases from combustion of fossil fuel with air and a fluid to be heated is obtained by initially introducing into the exhaust gases a volatile medium to be vaporized by said gases and subsequently condensing the vaporized medium by cooling the obtained mixture of combustion gases and vaporized medium to a temperature below the dew point. The cooling is performed by the fluid to be heated. The new method reduces the contents of polluting ingredients in the exhaust combustion gases and will keep the heat exchange structures clean.