SUPERCRITICAL CO2

The use of supercritical CO2 as a working fluid provides significant advantages in this application. A supercritical fluid is a substance at a temperature and pressure above its critical point. The critical point represents the highest temperature and pressure at which the substance can exist as a vapor and liquid in equilibrium. Above its critical point of 87.76°F at 1,070 psi (30.98°C at 73.78 bar), carbon dioxide is a supercritical fluid and adopts properties of both a gas and a liquid. Carbon dioxide as a working fluid for power cycles has many advantages. It is inexpensive, non-flammable, abundant in nature, and environmentally benign. Due to its relative high working pressure, a carbon dioxide system can be built that is more compact than systems using other working fluids. While water currently stands as the ultimate working medium for power, due to its thermal conductivity and heat capacity, carbon dioxide in a supercritical state offers advantages over water as a cooling medium. The viscosity, relatively high density, and volumetric heat capacity of supercritical CO2 make it easy to move and hold enough energy. CO2 is a clean, non-scaling, non-fouling working fluid, and provided it is maintained in a dry condition, it is non-corrosive. The single-phase heat transfer process of CO2 permits simpler, more efficient, and robust construction of the surface condenser.