Design Parameter Influence on Losses and Downstream Flow Field Uniformity in Supersonic ORC Radial-Inflow Turbine Stators

The design of organic Rankine cycle (ORC) turbines often requires dealing with transonic flows due to the cycle efficiency requirements and the matching of the temperature profiles with heat sources and sinks, as well as the nature of organic fluids, often featuring high molecular weight. Consequently, the use of convergent–divergent turbine stators has been widely established as a solution in the published literature for use in both axial- and radial-inflow machines. With respect to the latter layout in particular, the available design guidelines are still limited. The present work shows the results of an investigation into a series of ORC radial-inflow convergent–divergent nozzles that differ with respect to the vane count and the designed metal angle of the outlet. These stators were designed by fitting the divergent portion of a sharp-edged minimum-length nozzle, designed by means of the method of characteristics (MoC) adapted to dense gases, into a radial-inflow turbine stator. The geometries were analysed by means of steady-state RANS CFD calculations, and the results were used to assess the influence of the design parameters on the nozzle losses and downstream flow field uniformity, showing that conflicting trends exist between optimum stator efficiency and optimum downstream flow field uniformity.

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Influence of Supersonic Nozzle Design Parameters on the Unsteady Stator-Rotor Interaction in Radial-Inflow Turbines for Organic Rankine Cycles

10.1115/gt2021-59123 ◽

2021 ◽

Author(s):

Alessandro Cappiello ◽

Raffaele Tuccillo

Keyword(s):

Power Plants ◽

Supersonic Nozzle ◽

Organic Rankine Cycle ◽

Rankine Cycle ◽

Expansion Ratio ◽

Design Parameters ◽

Large Expansion ◽

Downstream Flow ◽

Organic Fluids ◽

Stator Design

Abstract Organic Rankine Cycle (ORC) technology represents an interesting option for improving the efficiency of existing power plants and industrial processes as well as exploiting renewable and renewable-equivalent energy sources. The use of Radial-Inflow Turbine (RIT) for ORC plant sizes below 100 kW is promising, although the application remains challenging. In fact, the single stage arrangement imposed by economic constraints and hence the large expansion ratio, together with the large molecular weight, which characterizes organic fluids, usually result in highly supersonic flows, so making the use of transonic stators often mandatory. Particularly, the influence of RIT stator design parameters on losses and the level of unsteadiness seen by the subsequent rotor is still scarcely addressed in published literature. Previous work by the authors investigated the effect of some stator design parameters on stator loss and downstream circumferential uniformity. The present work investigates the effect of the convergent-divergent stators design parameters and the resulting downstream flow field non-uniformity on the unsteady stator-rotor interaction and loss generation in ORC Radial-Inflow Turbines. To this end, two stator and rotor configurations which differ by the stator design parameters (i.e., discharge metal angle and number of vanes) have been tested by means of 3D unsteady CFD calculations accounting for real-gas properties. The results show that larger stator-rotor interaction is present for the case featuring higher vane count and lower outlet metal, which also features the largest fluctuations of power output and pressure force on blade, together with a substantially lower average total-to-static efficiency.

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Design of Small-Scale Radial Inflow Turbine Integrated into Organic Rankine Cycle

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.524-527.3907 ◽

2012 ◽

Vol 524-527 ◽

pp. 3907-3913

Author(s):

Hui Wang ◽

Xin Ling Ma ◽

Xin Li Wei

Keyword(s):

Low Temperature ◽

Flow Field ◽

Simple Structure ◽

High Efficiency ◽

Waste Heat ◽

Organic Rankine Cycle ◽

Rankine Cycle ◽

3D Models ◽

Small Scale ◽

Radial Inflow Turbine

Organic Rankine Cycle (ORC) is dramatically suitable for low temperature waste-heat generation. The small-scale radial inflow turbine is introduced to integrate into the ORC characterized by simple structure, low parts count, high efficiency, especially getting high efficiency under the condition of smaller flow. This turbine is comprised of four main parts named by the volute, the nozzle (stator), the impeller (rotor), and the diffuser respectively. This paper introduces how to design and model the parts in detail, discusses modeling skills and shares experience. The structure of the volute and impeller is so complicated that parts are not easy to model. These 3D models can directly import to both ANSYS and FLUENT to analysis the flow field in order to achieve the optimize parameters.

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Experimental analysis of organic Rankine cycle power generation system with radial inflow turbine and R245fa

Advances in Mechanical Engineering ◽

10.1177/1687814020921663 ◽

2020 ◽

Vol 12 (5) ◽

pp. 168781402092166

Author(s):

Lei Li ◽

Le-ren Tao ◽

Qing-qing Liu

Keyword(s):

Output Power ◽

Organic Rankine Cycle ◽

Rankine Cycle ◽

Maximum Efficiency ◽

Design Parameters ◽

Working Fluid ◽

Inlet Temperature ◽

Cycle System ◽

Turbine Efficiency ◽

Radial Inflow Turbine

Small turbines must operate at high rotational speeds to generate adequate output power. In this study, a radial inflow turbine using R245fa as the working fluid is miniaturised and is designed to have a rotational speed of 30,000 r/min. The organic Rankine cycle system is not simplified, and a preheater and a superheater are installed. The turbine is experimentally analysed in the organic Rankine cycle system. The experimental results show that with an increase in the inlet pressure, the turbine output power and system efficiency increase; moreover, the turbine efficiency first decreases and then increases slightly after the pressure exceeds 1.5 MPa. The turbine efficiency decreases first and then increases and attains the minimum value at an inlet temperature of 100°C–105°C. When the flow rate is 0.82 m3/s, the speed reaches its maximum value of 28,000 r/min, and a maximum output power of 17.37 kW is generated. The maximum efficiency of the turbine is 0.885 and that of the system is 0.1625. The experimental data and design parameters of the turbine provide a reference for further design optimization.

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