Two-phase loop thermosyphon using carbon dioxide applied to the cold end of a Stirling cooler

• Two-phase loop thermosyphon using CO2 was experimentally studied for Stirling cycle.
• A maximum in heat conductance was achieved when superheat was close to zero.
• Maximum heat conductance obtained was 46.72 W K−1.
• 85% of the results from a first principle model developed fell within ±20% band.

This work focuses on an experimental investigation of a carbon dioxide thermosyphon loop designed to fulfill the geometric and temperature requirements of a specific FPSC (Free Piston Stirling Cooler). Experiments were carried out varying the temperature difference between the heat source, i.e. air at the entrance of the evaporator and heat sink, i.e. internal surface of the condenser, refrigerant charge and evaporator airflow rate. The experimental results were explored using the thermal conductance concept applied to each heat exchanger and also to the whole loop. It was found that the loop was able to carry a maximum heat transfer rate of 514 W with a heat source-sink temperature difference of 11 °C. A first principles model was also developed and 85% of the calculations fell within ±20% of measurements. Further exploration of the model showed a good capability to capture trends and be an aid in the thermosyphon design phase.