The working principle of the organic Rankine cycle is the same as that of the Rankine cycle: the working fluid is pumped to a boiler where it is evaporated, passed through an expansion device (turbine, screw, scroll, or other expander), and then through a condenser heat exchanger where it is finally re-condensed.

The ORC has been used to exploit low-quality heat from a number of different sources. They have been used with low-temperature geothermal reservoirs and can be added as bottoming cycles for a range of different heat engine generating systems.

ORC: How it works Where heat pumps use electrical power to create thermal energy for various purposes, an ORC system uses heat energy to generate electricity. In a typical ORC design, a thermal energy source feeds an evaporator to drive an expander or “reverse compressor”, which in turn generates the electricity.

For the heat carrier inlet temperatures of 280 °C and 350 °C are considered. Rankings based on the thermal efficiency of the ORC and on the heat capacity flow rates of the heat carrier as well as on the volume and the heat flow rates show cyclopentane to be the best working fluid for all cases studied.