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Supercritical carbon dioxide (s CO 2) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when cooled and/or pressurised sufficiently.
Supercritical carbon dioxide sometimes intercalates into buttons, and, when the SCD is depressurized, the buttons pop, or break apart. Detergents that are soluble in carbon dioxide improve the solvating power of the solvent. [20] CO 2-based dry cleaning equipment uses liquid CO 2, not supercritical CO 2, to avoid damage to the buttons.
Efficient supercritical CO 2 power cycles requires that the compressor inlet temperature is close to, or even lower than, the critical temperature of the fluid (31 °C for pure carbon dioxide). When this target is reached, and the heat source is higher than 600–650 °C, then the sCO 2 cycle outperforms any Rankine cycle running on water ...
Critical carbon dioxide exuding fog while cooling from supercritical to critical temperature. The existence of a critical point was first discovered by Charles Cagniard de la Tour in 1822 [10] [11] and named by Dmitri Mendeleev in 1860 [12] [13] and Thomas Andrews in 1869. [14]
They are employed for example in Organic Rankine Cycles (ORC) [30] and supercritical carbon dioxide (sCO 2) systems [31] for power production. In the aerospace field, fluids in conditions close to saturation can be used as oxiders in hybrid rocket motors or for surface cooling of rocket nozzles. [32]
The prediction of a vapor–liquid equilibrium is successful even in mixtures containing supercritical components. The mixture has to be subcritical though. In the given example carbon dioxide is the supercritical component with T c =304.19 K [13] and P c =7475 kPa. [14] The critical point of the mixture lies at T=411 K und P≈15000 kPa.
Carbon dioxide (CO 2) is the most used supercritical fluid, sometimes modified by co-solvents such as ethanol or methanol. Extraction conditions for supercritical carbon dioxide are above the critical temperature of 31 °C and critical pressure of 74 bar. Addition of modifiers may slightly alter this.
Carbon dioxide is the lasing medium in a carbon-dioxide laser, which is one of the earliest type of lasers. Carbon dioxide can be used as a means of controlling the pH of swimming pools, [141] by continuously adding gas to the water, thus keeping the pH from rising. Among the advantages of this is the avoidance of handling (more hazardous) acids.