10:30
Session 1A: Turbines-Design Aspects (1)
Chair: Piotr Klonowicz
10:30
20 mins
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Comparison of a scroll, a screw, a roots, a Piston Expander and a Tesla Turbine for Small-scale Organic Rankine Cycle
Olivier Dumont, Lorenzo Talluri, Giampaolo Manfrida, Daniele Fiaschi, Vincent Lemort
Abstract: based on an experimental comparison of piston, screw, scroll, roots expanders and Tesla turbine, the latter investigated by a specifically developed simulation model. First, based on a literature review, a comparison of these five expansion machines technologies is performed. Afterward, four expanders [2-4 kW] were tested in a small-scale ORC unit with R245fa as working fluid. The calibration of models based on the measurements allows the prediction of the isentropic efficiency under optimized conditions, in spite of the operating range of the test-rig. A 2D validated model simulates the performance of the machine Tesla Turbine. A comparison of costs and compactness of the 5 investigated expander technologies is also performed. Finally, based on the working charts achieved with the simulation models and on experimental and practical aspects, some guidelines are drawn to help the reader in the selection of the most suitable expander technology for a given application.
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10:50
20 mins
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Customized Small-scale ORC Turbogenerators– Combining a 1D-design Tool, a Micro-turbine-generator–construction Kit and Potentials of 3D-printing
Andreas Weiß, Václav Novotný, Tobias Popp, Gerd Zinn, Michal Kolovratnik
Abstract: Due to the various possible applications in the ORC waste heat recovery business i.e. different heat sources, heat flow rates, temperature levels, pressure levels and working fluids, it is not appropriate to design and build one standard turbogenerator to stock. Therefore, the authors developed a very flexible “micro-turbine-generator-construction-kit (MTG-c-kit)” by means of which a customized turbine generator can be designed and built for any required power output between 1 - 200 kW, for a wide range of working fluids and boundary conditions – quickly and cost efficiently. The architecture of this construction kit and its main features are introduced briefly in this paper. However, more focus is put on the developed 1D turbine design tool. It allows to design and optimize a single stage turbine for any fluid and any boundary conditions very quickly. The thermodynamic model and the applied loss models for the implementable axial impulse turbine or radial inflow cantilever turbine are discussed by means of a specific design example. Experimental results of two micro turbines, which were designed and built according to the above-mentioned approach, are presented and the agreement and discrepancies between measured and design data are discussed.
In order to further accelerate and cheapen those customized micro turbine generators for small and low temperature applications, we provide an outlook of possibilities of additive manufacturing methods like 3D-printing of plastic turbine wheels for example. These new possibilities provide potential to improve the competiveness of small-scale ORC in waste heat recovery. A prototype of a simple turbine design with plastic 3D printed wheels has been manufactured and first tests are presented.
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11:10
20 mins
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Preliminary Design of Radial-inflow Turbines for Organic Rankine Cycle Power Systems Considering Performance and Manufacturability Aspects
Andrea Meroni, Matthias Geiselhart, Wei Ba, Fredrik Haglind
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 performance, 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 %.
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11:30
20 mins
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Partial Admission Effect on the Flow Field of an ORC Tesla Turbine
Leonardo Pacini, Lorenzo Ciappi, Lorenzo Talluri, Daniele Fiaschi, Giampaolo Manfrida, Jacek Smolka
Abstract: Over recent years, Tesla turbine gained a renewed interest from the international scientific community, as it combines reliability, efficiency and low cost. These are key aspects for the success of an expander suitable for small-distributed energy systems, thus Tesla turbine could represent an attracting solution for the market.
The test case is a turbine with efficiency 29% for a 0.57 kW expander utilizing R1233zd(E) as working fluid. The three-dimensional fluid dynamics inside the stator, the stator-rotor gap and the rotor is determined by means of CFD analyses. The comprehensive evaluation of the set of the three regions is of paramount importance to determine the machine flow field, as it is significantly affected by the interactions amongst each component. In particular, the effects of discrete admission to the rotor are relevant in terms of flow field distortion, while the effects on the performance parameters (power and efficiency) are slighter. The performance results of the 3-D computational fluid dynamics are close to the ones of the 2-D in-house developed code, which assumes continuous admission to the rotor.
The results inside the rotor are shown in terms of velocity, pressure and temperature fields. Particular interest is focused on the distinctive shape of the temperature distribution inside the rotor, arising from the spiral trajectories of the fluid determined by the four admission nozzles.
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11:50
20 mins
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Techno-economic Comparison of Reciprocating-piston Expanders and Radial-inflow Turbines in Small- to Medium-scale ORC Systems
Dauda Ibrahim, Michael Simpson, Jian Song, Paul Sapin, Antonio Pantaleo, Pietro De Palma, Christos Markides
Abstract: Designing feasible and economically-viable organic Rankine cycle (ORC) systems for applications such as high-grade heat recovery from the exhaust gases (400 600 °C) of stationary internal combustion engines (ICEs) has two main challenges: (i) selecting and designing an appropriate expansion technology, amongst the other system components, and (ii) selecting the optimal working fluid, and operational system parameters. In this work, comprehensive component models are integrated into an ORC system model to evaluate the on- and off-design performance of a 2.5-MWe ORC engine using either a reciprocating-piston expander or a radial-inflow turbine. The performance of the reciprocating-piston expander is predicted using a dynamic lumped-mass model, and a one-dimensional model based on the mean-line method is used to predict the performance of the turbine. An initial working-fluid screening leads to R1233zd being selected for further consideration, given the minimal specific investment costs and low-pressure ratio of the resulting ORC systems, thus assisting the design of suitable expansion devices. The approximate design point obtained from the screening study is used to obtain optimised piston and turbine designs that are then used to produce full- and part-load performance maps that are integrated into the ORC system model. The ORC engine with a turbine is found to deliver 127 kW at full load, at a specific investment cost of 1660 £/kW, while the piston expander produces a lower net power of 68 kW, but at a lower cost of 1250 £/kW, while also showing greater robustness to variations in the heat-source conditions.
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12:10
20 mins
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Optimization of a High Expansion ORC Turbine Using a Genetic Algorithm
Stephan Smit, Quirijn Eppinga, Gustavo Otero Rodriguez, Rene Pecnik
Abstract: The expander of an organic Rankine cycle (ORC) turbogenerator is a critical component for the overall system performance. If a designer is able to increase the turbine efficiency by 10%, the overall cycle efficiency increases by 4%. However, methodologies and dimensionless diagrams used for steam and gas turbine design are unreliable for ORC turbines because (1) the expansion process takes place in the dense gas region, where the ideal gas law equation is not valid, and (2) the working fluid features a small enthalpy drop due to its molecular complexity, bringing about a large pressure ratio per turbine stage that, combined with the relative low speed of sound of the organic fluid, results in a highly supersonic flow in the stator outlet.
This work presents an aerodynamic optimization, by means of a genetic algorithm, of a cantilever rotor of a single stage high expansion (∼100) ORC turbine, operating with toluene (C 6 H 5 CH 3 ) as a working fluid. The rotor blade geometry is defined by 18 geometrical parameters and is generated using an in-house blade design tool. The physical integrity of the blade geometry is assured by constraints on the minimal thickness of the blade. The resulting rotor geometry is evaluated using a Reynolds-averaged Navier-Stokes solver in a quasi-three-dimensional (Q-3D) framework to account for the increase of area over the rotor stage. A mixing-plane model connects the stator and rotor domains, making the simulation steady state. To model the non-ideal gas properties the EOS by Robinson et al. (1985) is used. The objective of the optimization is to minimize the total enthalpy at the outlet of the turbine stage.
The optimized geometry successfully reduces a large flow separation in the rotor blade suction side which was present in the original design. As a result, the entropy production is reduced and the total-to-static efficiency has increased by 4.3%. In the future the design will be manufactured providing the possibility of assessing the performance of the blade and the corresponding flow solution.
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