Preliminary Design of a Centrifugal Turbine for Organic Rankine Cycle Applications

Pini, Matteo; Persico, Giacomo; Casati, Emiliano; Dossena, Vincenzo

doi:10.1115/1.4023122

Cited by 74 publications

(44 citation statements)

References 9 publications

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“…The high-order turbine model consists of a meanline program for the preliminary design of turbomachinery [26], coupled with a library for fluid property estimation, which has been extended with a fluid model especially developed for the application of this method [21]. The results presented here have been obtained on a Windows 64-bit computer, equipped with a 3.60 GHz processor with eight processors and 16 GB of RAM.…”

Section: Methodsmentioning

confidence: 99%

“…A meanline code for the preliminary design of turbomachinery [6,26] is coupled with the in-house computational fluid library [21] in which fluid model (5) has been implemented. Among various inputs, the design model requires the turbine rotational speed X, the rotor inlet diameter D 2 , and the mass flow _ m. The successful application of the active subspaces method requires that the mathematical model is continuous and differentiable, therefore X; D 2 and _ m must be normalized, such that the input parameters are fluid independent.…”

Section: Normalized Input Of the Turbine Model For Preliminary Designmentioning

confidence: 99%

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Active subspaces for the optimal meanline design of unconventional turbomachinery

Bahamonde

Pini

Servi

et al. 2017

Applied Thermal Engineering

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h i g h l i g h t sA reduced-order model is proposed for the design of unconventional turbomachinery. The surrogate combines fluid selection, cycle configuration, and turbine geometry. The surrogate outperforms the standard model with negligible computational cost. The new response surface reveals the dominant inputs for turbine performance. The preliminary fluid dynamic design of turbomachinery operating with non-standard working fluids and unusual operating conditions and specifications can be very challenging because of the lack of know-how and guidelines. Examples are the design of turbomachinery for small-capacity organic Rankine cycle and supercritical CO 2 cycle power plants, whereby the efficiency of turbomachinery components has also a strong influence on the net conversion efficiency of the system. These machines operate with the fluid in thermodynamic states which, for part of the process, largely deviate from those obeying to the ideal gas law. This in turn implies the presence of so-called non-ideal compressible fluid dynamics effects. a r t i c l e i n f oActive subspaces, a model reduction technique, is at the basis of the methodology presented here, which is aimed at the optimal meanline design of unconventional turbomachinery. The resulting surrogate model depends on a very small set of non-physical variables, called active variables. The procedure integrates into a single constrained optimization framework the selection of the working fluid, the thermodynamic cycle calculation and the preliminary sizing of the turbomachinery component.As a demonstration of the advantages of the proposed approach, the design of a 10 kW mini organic Rankine cycle turbine with a turbine inlet temperature of 240 C is illustrated. In this case, approximately the same maximum efficiency is estimated for three dissimilar turbines operating with different working fluids and rather different thermodynamic cycles. The use of active subspaces allows the seamless evaluation of the sensitivity of results to input parameters, both those related to the machine and the working fluid. The novel design procedure is compared in terms of computational efficiency to a conventional approach based on the coupling of a genetic algorithm directly with a meanline code. Results show that the calculation based on the use of surrogate models is more than two orders of magnitude faster. The surrogate can be used to solve any design problem within the specified boundaries of the design envelope. Results are affected by uncertainty on the estimation of losses and of non-ideal compressible fluid dynamics effects, which, in turn, do not affect the applicability of the method, which will become quantitatively accurate once this information will be available. Work to this end is underway in various laboratories.

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Section: Methodsmentioning

confidence: 99%

Section: Normalized Input Of the Turbine Model For Preliminary Designmentioning

confidence: 99%

Active subspaces for the optimal meanline design of unconventional turbomachinery

Bahamonde

Pini

Servi

et al. 2017

Applied Thermal Engineering

Self Cite

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“…Similar to other preliminary design codes available in the literature, such as zTurbo [18], TURAX is based on one-dimensional approximation supported by proper correlations for the estimation of the losses and flow angles [19,20]. The code is integrated with the optimization toolbox available in the Matlab framework [21] to obtain the turbine layout which maximizes the total-to-total isentropic efficiency.…”

Section: Optimization Toolsmentioning

confidence: 99%

Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B: Application on a Case Study

et al. 2016

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Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low-and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first application of a design method where the thermodynamic cycle optimization is combined with calculations of the maximum expander performance using the mean-line design tool described in part A. The high computational cost of the turbine optimization is tackled by building a model which gives the optimal preliminary design of an axial-flow turbine as a function of the cycle conditions. This allows for estimating the optimal expander performance for each operating condition of interest. The test case is the preliminary design of an organic Rankine cycle turbogenerator to increase the overall energy efficiency of an offshore platform. For an increase in expander pressure ratio from 10 to 35, the results indicate up to 10% point reduction in expander performance. This corresponds to a relative reduction in net power output of 8.3% compared to the case when the turbine efficiency is assumed to be 80%. This work also demonstrates that this approach can support the plant designer in the selection of the optimal size of the organic Rankine cycle unit when multiple exhaust gas streams are available.

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“…Radial inflow, radial outflow and axial turbines are the most common turbo-machines in the literature [95][96][97]. As opposed to volumetric machines, turbo-machines are convenient in the high power output range, while they become inefficient for low power production.…”

Section: Expander Selectionmentioning

confidence: 99%

Small Scale Organic Rankine Cycle (ORC): A Techno-Economic Review

et al. 2017

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Abstract:The Organic Rankine Cycle (ORC) is widely considered as a promising technology to produce electrical power output from low-grade thermal sources. In the last decade, several power plants have been installed worldwide in the MW range. However, despite its market potential, the commercialization of ORC power plants in the kW range did not reach a high level of maturity, for several reasons. Firstly, the specific price is still too high to offer an attractive payback period, and secondly, potential costumers for small-scale ORCs are typically SMEs (Small-Medium Enterprises), generally less aware of the potential savings this technology could lead to. When it comes to small-scale plants, additional design issues arise that still limit the widespread availability of the technology. This review paper presents the state of the art of the technology, from a technical and economic perspective. Working fluid selection and expander design are illustrated in detail, as they represent the bottleneck of the ORC technology for small-scale power production. In addition, a European market analysis is presented, which constitutes a useful instrument to understand the future evolution of the technology.

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Preliminary Design of a Centrifugal Turbine for Organic Rankine Cycle Applications

Cited by 74 publications

References 9 publications

Active subspaces for the optimal meanline design of unconventional turbomachinery

Active subspaces for the optimal meanline design of unconventional turbomachinery

Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B: Application on a Case Study

Small Scale Organic Rankine Cycle (ORC): A Techno-Economic Review

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