Coolant penetrating cold-end pressure vessel

A method for fabricating a heat exchanger for transferring thermal energy across a cooler from a working fluid to a coolant, the method comprising:

• a. forming a spiral shaped section of tubing;
• and
• b. casting a material over the annular shaped section of tubing to form a heat exchanger body.

In a closed-cycle thermal engine, of the type contained within a pressure vessel and having a piston undergoing reciprocating linear motion within a cylinder and a working fluid heated by conduction through a heater head, the improvement comprising:

• a heat exchanger for cooling the working fluid, the heat exchanger comprising a first material in thermally conductive contact with the working fluid, and a second and distinct material in thermal conductive contact with a coolant fluid;
• and
• a coolant tube providing for circulation of the coolant fluid to outside the pressure vessel.

A method for transferring heat from a working fluid of a closed-cycle thermal engine, the closed-cycle thermal engine characterized by a pressure vessel including a crankcase volume filled with a charge gas, the method comprising:

• transferring heat from the working fluid to a coolant that is separated from the working fluid at all points by at least two distinct solid materials;
• and
• circulating the coolant through coolant tubing to a region outside the pressure vessel.