Performance Analysis of a Revolving Vane Expander in an Organic Rankine Cycle with Hydrofluoroolefins (HFOs) in Place of R134a

orc2019 Tracking Number 2

The Organic Rankine Cycle (ORC) is a promising method to exploit low to medium temperature heat sources. Though it is a mature technology, the selection, sizing and optimisation of the expander used to extract energy is still an active topic of research since it can strongly affect the performance of the ORC. Among the types of volumetric expanders, the use of rotary vane expanders is advantageous, particularly in small-scale applications, due to their simplicity, low manufacturing and maintenance cost, low noise, and high volumetric expansion ratios. However, they generally perform poorly in comparison to other rotary machines because of their inevitable leakage and friction losses, leading to low isentropic efficiencies. A Revolving Vane (RV) expander, in which both the rotor and cylinder rotate, unlike conventional vane-type mechanisms, has been shown to exhibit a significant reduction in friction losses [1]. Such a machine has been previously studied in compressed air and refrigeration systems, but not in an ORC system. In this study, the first law of thermodynamics is used to evaluate the performance of a Revolving Vane expander within an ORC system using R1234yf and R1234ze(E). These fluids are popular replacements for R134a, since they have low global warming and zero ozone depletion potentials. Previously developed mathematical models of the RV expander [1, 2] have been adopted for the study. Various operating conditions are simulated to find the optimal performance parameters of the expander using the chosen working fluids. The results demonstrate the potential of the RV expander for small-scale ORC applications. Moreover, the characteristics of the expander at various operating conditions are observed, showing that the expander design is suitable for small-scale ORC applications. Reference 1. Subiantoro, A. and K.T. Ooi, Comparison and performance analysis of the novel revolving vane expander design variants in low and medium pressure applications. Energy, 2014. 78: p. 747-757. 2. Subiantoro, A. and K.T. Ooi, Analysis of the Revolving Vane (RV-0) expander, part 2: Verifications of theoretical models. International Journal of Refrigeration, 2012. 35(6): p. 1744-1756.