Demonstration by laboratory experiments of thermosiphon effect in the closed loop carbon dioxide circulation system

The thermosiphon effect has been shown theoretically to exist in the closed loop CO2 circulation geothermal power generation systems. We verified this effect based on previous numerical studies that determined the conditions under which the thermosiphon effect can be established and we developed laboratory experimental apparatus with conditions analogous to those in the previous studies. The results of laboratory closed loop CO2 circulation experiments using this apparatus demonstrated the thermosiphon effect at initial injection pressures from 8.5 to 18 MPa and heater temperatures from 80 to 200 °C. With this experimental apparatus, higher heater temperatures produced higher heat output at the same injection pressures, and that the peak heat output was observed at injection pressures of 12–14 MPa. Furthermore, comparing CO2 with water as the thermal transfer medium indicated that the feasibility of the thermosiphon effect was increased by changing the medium from water to CO2.