| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 647336 | Applied Thermal Engineering | 2012 | 10 Pages |
An Organic Rankine Cycle (ORC) is considered as one of the most environmental-friendly ways to convert different kinds of low temperature energies, i.e. solar, geothermal, biomass and thermal energy of exhaust gases into electrical energy. Two important facts about the ORC must be considered: An organic fluid is selected as the working fluid and a high expansion ratio is usually presented in the machinery due to thermodynamic and efficiency factors. In the past, the pre-design of turbomachinery has been based on the usage of ideal fluid laws, but the real gas effects have a significant influence in the ORC working condition, due to its proximity to the saturation vapor line. In this article, the Equations of State (EoS) (Ideal gas, Redlich-Kwong-Soave and Peng–Robinson) have been evaluated in a typical ORC expansion in order to observe the inaccuracies of the ideal gas model with different thermodynamic variables. Finally an isothermal process followed by an isochoric process is proposed to reproduce the thermodynamic process of the organic fluid expansion by means of simpler equations. In the last point of this paper, several examples of this expansion process have been calculated, in order to analyze the proposed methodologies. It has been concluded that in typical expansion process of ORC (2.5 MPa-0.1 MPa and 1.6MPa-0.1 MPa), the PR and RKS equations show deviations between 6% and 8% in specific energy. These deviations are very low compared with the ideal gas equation whose deviations are above 100%.
► Evaluate the ideal gas behaviour of R245fa in typical working conditions of an Organic Rankine Cycle (ORC). ► Compare the ideal behaviour with other simple equations of state for real gas. ► Decide which equation of state has the highest precision in typical working conditions of an ORC. ► Derive the most important thermodynamic variables in each equation of state and decide the most accurate equation. ► Evaluate the speci_c output energy obtained in a typical ORC using dif-ferent equation of state compared.
