Abstract
In recent years, Organic Rankine Cycle (ORC) technology has received growing interests, thanks to its high flexibility and to the capability to exploit energy sources at temperature levels difficult to be approached with conventional power cycles. These features allow exploiting renewable and renewable-equivalent energy sources, by either improving the energy conversion efficiency of existing plants or using waste heat from industrial process. As far as the expander is concerned, a high potential solution is represented by turbo-expanders, which allow reduction of plant clutter and complexity, so enhancing the potential impact on the diffusion of small power ORC-based plants. The present work concerns the design of a RadialInflow Turbine for a bottoming Organic Rankine Cycle in the tens of kW scale. Design boundary conditions are retrieved by a zero-dimensional model of a solar-assisted micro gas turbine in cogenerating mode. The design process is started by means of an in-house mean-line design code accounting for real gas properties. The code is used to carry out parametric analyses to investigate the design space for several working fluids encompassing different classes, namely refrigerants and siloxanes. The program is used to assess the effect of design variables and working fluid on the turbine performance and turbine design characteristics. Subsequently, the most promising design candidates are selected and three-dimensional first guess stator and rotor geometries are built on these preliminary designs. Stationary and rotating passages are then meshed and analyzed by means of RANS CFD based solution of the stator – rotor interaction.
Highlights
More and more stringent emission regulations along with increasing attention to environmental issues have led the Organic Rankine Cycle (ORC) technology to a growing interest both from scientific community and market, as witnessed by the continuous growth of the installed ORC-based units, [1]
Da Lio et al [6] by means of the preliminary design method by Aungier [7,8] showed that, for a RadialInflow Turbines (RIT) expanding R245fa, the optimal specific speed was lower than that achieved with air ideal gas and that optimal velocity ratio was departing from the air ideal gas one at high volumetric expansion ratio only
Once suitable preliminary designs are selected for each fluid, three-dimensional vane and blade shapes are built based on the preliminary design specifications and the vane and blade passages are further analyzed by means of steady-state RANS CFD calculations
Summary
More and more stringent emission regulations along with increasing attention to environmental issues have led the Organic Rankine Cycle (ORC) technology to a growing interest both from scientific community and market, as witnessed by the continuous growth of the installed ORC-based units, [1]. Conventional design guidelines developed for ideal gases, might not generally hold for ORC turbines In this regard, Mounier et al [5] provided an update of Baljè’s diagram to small radial machines operating with organic fluids at high expansion ratios and they found that the shape of the iso-efficiency curves was altered. Da Lio et al [6] by means of the preliminary design method by Aungier [7,8] showed that, for a RIT expanding R245fa, the optimal specific speed was lower than that achieved with air ideal gas and that optimal velocity ratio was departing from the air ideal gas one at high volumetric expansion ratio only They found that optimal volumetric expansion ratio was larger for radial-inflow turbine than for axial-flow type, together with slightly larger efficiency values. Once suitable preliminary designs are selected for each fluid, three-dimensional vane and blade shapes are built based on the preliminary design specifications and the vane and blade passages are further analyzed by means of steady-state RANS CFD calculations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
