Fluid heat exchanger

An annular heat exchanger suitable for a Stirling engine is provided. The heat exchanger has helical fins, and an outer reinforcing sleeve about the fins. The sleeve improves the pressure resisting ability of a thin separating wall between a pressurized fluid and an outside working environment, resulting in a high-pressure heat exchanger with high heat transfer efficiency. In addition, the sleeve and helical fins together define fluid passages for the flow of heating fluid. The heat exchanger according to the invention has the ability to resist high pressures at high temperatures without distortion, has improved heat transfer capability, better reliability, and lower production cost than prior art heat exchangers.