Abstract: A heat exchanger, such as a condenser, for use in a automobile air conditioning system includes a plurality of flat tubes for conducting the refrigerant and a plurality of corrugated outer fins fixedly sandwiched between the flat tubes. First and second header pipes are fixedly and hermetically connected to the flat tubes and, thereby, communicate with the interior of the tubes. A plurality of diagonally arranged projected stripes are formed on inner surfaces of the flat tubes. First portions of the projected stripes project from a lower inner surface of the flat tubes, and second portions of the projected stripes project from an upper inner surface of the flat tubes. The first and second portions of the projected stripes are in contact with one another at the points of intersection therebetween.

Abstract: In a Stirling engine comprising: a cylinder having an expansion space; a housing accommodating a heat accumulating unit; and a heating unit through which said expansion space is communicated with the heat accumulating unit, the heating unit is formed by using a flattened pipe, and preferably heat transferring fins, and reinforcing members for preventing the increase in volume of the flow path in the heating unit are provided in the latter, so that in connecting the heating unit to the cylinder and the housing, the number of assembling steps is decreased, and the heating unit is sufficiently large in dead volume ("flow path sectional area" x "flow path length") and in heat transfer area.