In waste heat recovery, what is a common working fluid used in Organic Rankine Cycle (ORC) systems?

In waste heat recovery using Organic Rankine Cycle (ORC) systems, common working fluids include organic compounds such as refrigerants (e.g., R134a, R245fa), hydrocarbons (e.g., pentane, butane), and siloxanes (e.g., MM, MDM). An ORC system is a thermodynamic cycle that uses an organic fluid with a lower boiling point than water to convert waste heat into electricity. The working fluid is heated by the waste heat source, causing it to vaporize. The vapor then expands through a turbine, generating electricity. The expanded vapor is then cooled and condensed back into a liquid, which is pumped back to the heat source to repeat the cycle. The choice of working fluid depends on the temperature of the waste heat source and the desired operating conditions. Refrigerants are often used for low-temperature waste heat sources, while hydrocarbons and siloxanes are used for higher-temperature sources. The working fluid should have favorable thermodynamic properties, such as a high vapor pressure, a low boiling point, and a high thermal stability, to maximize the efficiency of the ORC system. Environmental considerations, such as global warming potential and ozone depletion potential, are also important factors in selecting a working fluid.