Freezing and sublimation of carbon dioxide is achieved by the use of liquid nitrogen and geothermal heat by way of capillary tubes (3 and 4, fig 2), which may be located in preferably spherical chambers 7 that may have fluted entrances and exit pipes 8,9 , into which the capillaries may protrude. The heated and expanded CO2 is delivered to the turbine blades 2 at high pressure by way of helically corrugated pipes with fluted inlets and outlets that increase the flow rate. Additional solar energy may be applied to the gas as it passes through the turbine. The CO2 gas exiting the turbine is preferably directed back to a spherical chamber wherein capillaries filled with liquid helium or liquid nitrogen may be used to freeze the CO2 before the capillaries containing geothermal heat again warm the solid CO2 causing sublimation. Valves may be used to prevent the gas leaving this chamber until a certain pressure is achieved. After heating the CO2, the geothermal heat may be exchanged in a heat recovery system.
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