The Role of Dense Gas Dynamics on Organic Rankine Cycle Turbine Performance

Abstract

In this paper, we investigate the real gas flows which occur within organic Rankine cycle (ORC) turbines. A new method for the design of nozzles operating with dense gases is discussed, and applied to the case of a high pressure ratio turbine vane. A Navier–Stokes method, which uses equations of states for a variety of working fluids typical of ORC turbines, is then applied to the turbine vanes to determine the vane performance. The results suggest that the choice of working fluid has a significant influence on the turbine efficiency.

An influence of low-stability region on dense gas phenomena and their peculiarities in the ORC fluids

“…The h″ max maxima for all analysed ORC fluids corresponds to higher reduced temperatures than values relating to the s″ max , (see, Appendix Tables 2 and 3). These results confirm that in the high-density vapour of refrigerants and ORC fluids several peculiarities in fluid behavior should appear, both in the thermodynamic parameters and compressible flow conditions [5,7,10]. One of the most spectacular effects relates to the flow of so-called BZT fluids [5,10].…”

“…Some typical measures such heat capacity ratio and isentropic index are insufficient for presentation the change of real fluid and flow parameters. It is necessary to use more consistent approach, applicable both in a basic thermal-flow balances and the CFD numerical schemes [5,7]. Dense gas flow phenomena are still not well-recognised and its investigation, interpreting and mathematical backgrounds is an important part of many research institutions and industry [1][2][3][4][5]7].…”

“…It is visible, see Table 1, that according to the growth of molecular mass the value of acentric factor ω is also higher. This measure of fluid complexity directly relates to many important parameters characterising a particular fluid behaviour [5,7,8].…”

“…Other important consequence of application of the 'dry' or 'isentropic' fluids is an influence of real gas effects on the cycle performance parameters (produced power and efficiency) [2,7].…”

Non-ideal compressible-fluid effects in oblique shock waves

“…The characterisation of non-ideal compressible-fluid flows is not only of theoretical interest, but also is relevant to applications involving molecularly complex fluids in their dense-gas regime, such as machinery operating in Organic Rankine Cycle (ORC) and supercritical CO 2 power systems, turbogenerators, refrigerators and many others, see reference [14,15,16,17] The present work is organised as follows. In section 2, the Rankine-Hugoniot jump relations across surfaces of discontinuity are recalled along with the admissibility requirements.…”