Model of the expansion process for R245fa in an Organic Rankine Cycle (ORC)
- 作者：J.M. Lujá ; n ; J.R. Serrano ; V. Dolz ; vidolrui@mot.upv.es ; J. Sá ; nchez
- 关键词：Organic Rankine Cycle ; Real gas ; R245fa ; Expansion process ; Equation of state
- 刊名：Applied Thermal Engineering
- 出版年：2012
- 期刊代码：8_13594311
- 类别：ce
- 出版时间：July, 2012
- 卷：40
- 期：Complete
- 页码：248-257
- 文件大小：1010 K
摘要
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聽MPa and 1.6MPa-0.1聽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%.