Working fluid selection and operating maps for Organic Rankine Cycle expansion machines

Fluid selection for the Organic Rankine Cycle has been the object of an abundant literature. Most of the scientific publications focus on the cycle thermodynamic efficiency in or der to select the best candidate. However, other thermodynamics properties, such as molar mass, or vapor den sity condition the whole design of the cycle, and its cost. For example, the molar mass influences the number of s tages required in the case of an axial turbine; the volume ratio between expander supply and exhaust conditions the possibility to use a volumetric expander (whose internal volume ratio is limited); the vapor density at the expander exhaust determine the size of the expander, and of the condenser; etc. This paper considers a whole range of ORC applications, in terms of power (from the kW-scale to the multi-MW plants), heat source temperature (from 90°C to more than 300° C) or heat source nature (solar, biomass, waste heat recovery, geothermy, etc.). For each of these applications, a scr eening of the available fluids is performed, and their thermodynamics performance are compared with respect to the foreseen application. A detailed analysis of the most common expansion machines is then conducted, by comparing their respective operating maps for each fluid and for each application type. The considered expansion machines are the radialinflow turbine, the screw expander, and the scroll expand er, since they are the most widely used in commercial applications and/or in scientific literature.