Transcritical Cycle

A transcritical cycle is a closed thermodynamic cycle whose working fluid crosses between the subcritical and supercritical states, staying in the liquid region while it is compressed and in a vapor or supercritical state while it expands. In power generation the most widespread transcritical cycle is the ultrasupercritical steam Rankine cycle used to generate electricity from fossil fuels, and organic Rankine cycles extend the same idea to lower temperature heat sources such as geothermal energy and waste heat recovery. Transcritical cycles are also increasingly used in refrigeration with carbon dioxide as the working fluid, because carbon dioxide critical point of 31 degrees Celsius falls conveniently between typical cooling and heating temperatures, letting the cycle reject heat through a gas cooler instead of a conventional condenser and so simplify the equipment. Compared with a subcritical cycle, a transcritical cycle runs at a higher pressure ratio, which raises its efficiency for most working fluids, and it heats the fluid without the evaporation phase change that a subcritical cycle needs, improving the efficiency of that stage further. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/