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Publication Title | RADIAL-INFLOW TURBINES FOR ORGANIC RANKINE CYCLE POWER

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PRELIMINARY DESIGN OF RADIAL-INFLOW TURBINES FOR ORGANIC RANKINE CYCLE POWER SYSTEMS CONSIDERING PERFORMANCE AND MANUFACTURABILITY ASPECTS
Andrea Meroni1*, Matthias Geiselhart1, Wei Ba2 and Fredrik Haglind1
1 Department of Mechanical Engineering, Technical University of Denmark, Nils Koppels Allé, Building 403,
2800 Kongens Lyngby, Denmark
andmer@mek.dtu.dk (A.M.),
mgeis@mek.dtu.dk (M.G.),
frh@mek.dtu.dk (F.H.)
2 Department of Energy and Power Engineering, Tsinghua University, Xuetang Rd, Lee Shau Kee Science and Technology Building, 100084 Beijing, China bw15@mails.tsinghua.edu.cn (W.B.)
* Corresponding Author
ABSTRACT
In order to make organic Rankine cycle power systems economically feasible, it is essential to find a reasonable trade-off between the performance and the initial cost of system. In this context the expander plays an important role. High performance is often the main target in the preliminary design of the expander; however, ease of manufacturing and competitive cost might similarly contribute to a successful solution. The design of expanders for high efficiency and manufacturability is an unexplored field in organic Rankine cycle power systems.
In this paper, we propose a multidisciplinary approach to perform the preliminary design of radial-inflow turbines for organic Rankine cycle power systems, considering both performance and manufacturability aspects. The suitability of a turbine design is evaluated using two figures of merit: a manufacturability indicator and the turbine total-to-static efficiency. A mean-line model, estimating the turbine perfor- mance, is coupled to a model for the generation of a preliminary three-dimensional turbine geometry. In this way, the turbine performance and its manufacturability, predicted from the turbine geometry, can be simultaneously evaluated. A multi-objective optimization is then performed using the integrated design model to optimize both the turbine efficiency and manufacturability by varying the decision variables related to its geometrical and fluid-dynamic characteristics.
In order to show its relevance in a practical application, the method is applied to two radial-inflow turbines cases: a state-of-the-art turbine using air and a turbine using the working fluid Novec 649 for a heat recovery application. The results indicate that there exists a trade-off between turbine performance and manufacturability, and that it is possible to develop turbine solutions with similar values of efficiency with improved manufacturability indicator by up to 14-15 %.
1. INTRODUCTION
The current technological limits of organic Rankine cycle (ORC) power systems are extending towards small-to-micro scale applications (<100 kW). However, a major barrier for a full deployment of the ORC technology is the lack of cost-effective solutions, which would result in a more attractive specific cost and payback time. Thanks to their compact size, high specific work, high efficiency and low investment cost compared to the other expander technologies, radial-inflow turbines (RITs) are often selected for small-to-micro scale applications. The aerodynamic design of such machines is a challenging task and
5th International Seminar on ORC Power Systems, September 9-11, 2019, Athens, Greece
Paper ID: 57, Page 1

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MicroAD: This research and pdf compilation was sponsored Infinity Turbine Turn your waste heat into energy to save on grid based power or sell back to the grid Organic Rankine Cycle utilizes waste heat to make power. Infinity Turbine Waste Heat to Power Solutions

RADIAL-OUTFLOW-TURBINE: In a radial outflow turbine the organic fluid enters the disk axially in its center and expands radially through a series of stages mounted on the single disk. At the discharge of the last rotor row the flow passes through a radial diffuser and is then conveyed to the recuperator and or condensa- tion section of the system, through the discharge volute. In the early 20th century, Parsons Siemens and Ljungstrom developed the first steam based radial outflow turbines. These early model turbines required a large number of stages. For very high enthalpy drop fluids, such as steam, a single-disk/multi stage configuration was therefore deemed not suitable due to the very large diameter disk necessary to accommodate all the required stages. No further development of the radial outflow turbines oc- curred, as they were phased out for steam applications by axial turbines.

The Geothermal Radial Outflow Turbine: An innovative turbine configuration for geothermal applica- tions was developed by the Italian turbine manufacturer EXERGY. The technology, known as the organic radial outflow turbine was designed, engineered, manufactured and tested in Italy. A 1 MWe geothermal organic Rankine cycle (ORC) equipped with the EXERGY radial outflow turbine has been in operation since early 2013. The radial outflow turbine is a new type of turbine that have the potential to increase the geothermal binary power plants ef- ficiency by increasing the turbine efficiency. The operational results has been positive and demonstrates the viability of the technology and the possibility to develop it for bigger sizes.

Preliminary Design and Off-Design Analysis of a Radial Outflow Turbine for Organic Rankine Cycles: Recently, the advantages of radial outflow turbines have been outstanding in various operating conditions of the organic Rankine cycle. However, there are only a few studies of such turbines, and information on the design procedure is insufficient. The turbine target performance could be achieved by fine-tuning the blade angle of the nozzle exit. In addition, performance evaluation of the turbine against off-design conditions was performed. Ranges of velocity ratio, loading coefficient, and flow coefficient that can expect high efficiency were proposed through the off-design analysis of the turbine.

Study on applicability of radial-outflow turbine type for 3 MW WHR organic Rankine cycle: The article presents the results of study on the reasonability of using radial-outflow turbines in ORC. Peculiarities of radial-outflow turbine design utilizing modern design technologies and application to ORC was considered in the first part of the paper. For this particular cycle design, turbines of radial-outflow type were chosen. Their application enables the increase of mechanical output power by 11 percent compared to original radial-inflow turbines.

LOSS GENERATION IN RADIAL OUTFLOW STEAM TURBINE CASCADES: Small high-speed technology based radial outflow steam turbines are characterised by ultra-low aspect ratios, which can lead to rapidly growing secondary losses. The prelimi- nary evaluation of turbine performance is usually based on axial turbine loss predictions, which can be a source of error. The main objectives of this work are to find out how the losses are generated in radial outflow turbines when the aspect ratio is markedly below unity and how accurately axial turbine loss models can predict the trends. To achieve these objectives, a radial outflow turbine cascade having a blade shape and aspect ratios comparable with a prototype machine is examined. As a result of the study, it is suggested that for the examined radial outflow cascade the axial turbine loss correlations can predict the trends reasonably well. The rapidly increasing secondary losses are connected to the merging of secondary structures and also incidence at off-design.

PRELIMINARY DESIGN OF RADIAL-INFLOW TURBINES FOR ORGANIC RANKINE CYCLE POWER SYSTEMS CONSIDERING PERFORMANCE AND MANUFACTURABILITY ASPECTS: In order to make organic Rankine cycle power systems economically feasible, it is essential to find a reasonable trade-off between the performance and the initial cost of system. In order to show its relevance in a practical application, the method is applied to two radial-inflow turbines cases: a state-of-the-art turbine using air and a turbine using the working fluid Novec 649 for a heat recovery application. The results indicate that there exists a trade-off between turbine performance and manufacturability, and that it is possible to develop turbine solutions with similar values of efficiency with improved manufacturability indicator by up to 14 to 15 percent.

DESIGN AND FLOW ANALYSIS OF RADIAL AND MIXED FLOW TURBINE VOLUTES: Radial and mixed flow turbines which are an important component of a turbocharger consist essentially of a volute, a rotor and a diffuser. Vaneless volute turbines, which have reasonable performance and low cost, are the most used in turbochargers for automotive engines. Care has to be done in the design of the volute, whose function is to convert a part of the engine exhaust gas energy into kinetic energy and direct the flow towards the rotor inlet at an appropriate flow angle with reduced losses.

An Exploration of Radial Flow on a Rotating Blade in Retreating Blade Stall: The nature of radial flow during retreating blade stall on a two-bladed teetering rotor with cyclic pitch variation is investigated using laser sheet visualization and particle image velocimetry in a low-speed wind tunnel. The velocity field above the retreating blade at 270◦ azimuth shows the expected development of a radially directed jet layer close to the blade surface in the otherwise separated flow region. This jet is observed to break up into discrete structures, limiting the spanwise growth of the radial velocity in the jet layer. The discrete structures are shown to derive their vorticity from the “radial jet” layer near the surface, rather than from the freestream at the edge of the separated region. The separation line determined using velocity data shows the expected spanwise variation. The results of this study are also correlated in a limited range of extrapolation to the phenomena encountered on a full-scale horizontal axis wind turbine in yaw.

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