*3.2.2 Thermodynamic property*

The thermodynamic performance and economy of the ORC system are closely related to the physical properties of the working fluid, which will affect the efficiency, operating conditions, and equipment size of the ORC system. The thermophysical properties of working fluid mainly include the following:

## *3.2.2.1 Vaporization latent heat*

In terms of installation size and therefore the ORC cost, fluids with high latent heat and high density are proposed to be the preferable candidates [11] because the higher the latent heat, the greater heat is absorbed in the evaporation step; but at the same time, the higher the density, the lower are the specific volume and volume flow rate. Both could mean that the system can provide more power outputs with the same equipment size. However, some researchers [12] have an inverse opinion on the latent heat of vaporization, given that better operating condition is provided at the turbine inlet for fluids with low latent heat in the saturated vapor state for the application of low-grade waste heat recovery.

#### *3.2.2.2 Density*

High vapor density is important, especially for fluids showing a very low condensing pressure (e.g., silicon oils). A low density leads to a higher volume flow rate: the pressure drops in the heat exchangers are increased, and the size of the expander must be increased. This has a non-negligible impact on the cost of the system.

*Utilizing Computational Methods to Identify Low GWP Working Fluids for ORC Systems DOI: http://dx.doi.org/10.5772/intechopen.1003740*

#### *3.2.2.3 Specific heat*

Liquid's specific heat should be low so that it could decrease the work consumed by the pump and increase the work output indirectly. The working fluids with high liquid specific heats can absorb more heat from the hot source, which increases the output power of the ORC system.
