Use Of Organic Fluids Research Articles

Impact of shape-optimization on the unsteady aerodynamics and performance of a centrifugal turbine for ORC applications

This paper presents the results of the application of a shape-optimization technique to the design of the stator and the rotor of a centrifugal turbine conceived for Organic Rankine Cycle (ORC) applications. Centrifugal turbines have the potential to compete with axial or radial-inflow turbines in a relevant range of applications, and are now receiving scientific as well as industrial recognition. However, the non-conventional character of the centrifugal turbine layout, combined with the typical effects induced by the use of organic fluids, leads to challenging design difficulties. For this reason, the design of optimal blades for centrifugal ORC turbines demands the application of high-fidelity computational tools. In this work, the optimal aerodynamic design is achieved by applying a non-intrusive, gradient-free, CFD-based method implemented in the in-house software FORMA (Fluid-dynamic OptimizeR for turboMachinery Aerofoils), specifically developed for the shape optimization of turbomachinery profiles. FORMA was applied to optimize the shape of the stator and the rotor of a transonic centrifugal turbine stage, which exhibits a significant radial effect, high aerodynamic loading, and severe non-ideal gas effects. The optimization of the single blade rows allows improving considerably the stage performance, with respect to a baseline geometric configuration constructed with classical aerodynamic methods. Furthermore, time-resolved simulations of the coupled stator-rotor configuration shows that the optimization allows to reduce considerably the unsteady stator-rotor interaction and, thus, the aerodynamic forcing acting on the blades.

Comparison between ORC and CO2 power systems for the exploitation of low-medium temperature heat sources

Low-medium temperature heat sources in the range 5–50 MWth are made available by many industrial fields but they may also be of interest for biomass, geothermal and solar energy applications. ORC has been proposed in the last 20 years as a reliable solution for the exploitation of these energy sources since the alternative represented by steam cycles leads to an inefficient conversion of such small available thermal powers. However, the use of organic fluids involves a number of safety and environmental issues, either related to fluid flammability (for hydrocarbons) or to their high Global Warming Potential (for halogenated fluids), and of limitations to the achievable cycle maximum temperature, due to fluids thermal decomposition. To overcome these limitations, in recent years CO2-based transcritical and supercritical cycles have been proposed as a viable option for this kind of applications. The present work aims to present a comparison between four CO2 cycle configurations and four ORC layouts using a working fluid selected from 47 candidates. The final result is a set of performance maps that allow for an easy selection of the best solution for applications exploiting low-medium temperature heat sources.

Optimal Aerodynamic Design of a Transonic Centrifugal Turbine Stage for Organic Rankine Cycle Applications

This paper presents the results of the application of a shape-optimization technique to the design of the stator and the rotor of a centrifugal turbine conceived for Organic Rankine Cycle (ORC) applications. Centrifugal turbines have the potential to compete with axial or radial-inflow turbines in a relevant range of applications, and are now receiving scientific as well as industrial recognition. However, the non-conventional character of the centrifugal turbine layout, combined with the typical effects induced by the use of organic fluids, leads to challenging design difficulties. For this reason, the design of optimal blades for centrifugal ORC turbines demands the application of high-fidelity computational tools. In this work, the optimal aerodynamic design is achieved by applying a non-intrusive, gradient-free, CFD-based method implemented in the in-house software FORMA (Fluid-dynamic Opti-mizeR for turboMachinery Aerofoils), specifically developed for the shape optimization of turbomachinery profiles. FORMA was applied to optimize the shape of the stator and the rotor of a transonic centrifugal turbine stage, which exhibits a significant radial effect, high aerodynamic loading, and severe non-ideal gas effects. The optimization of the single blade rows allows improving considerably the stage performance, with respect to a baseline geometric configuration constructed with classical aerodynamic methods. Furthermore, time-resolved simulations of the coupled stator-rotor configuration shows that the optimization allows to reduce considerably the unsteady stator-rotor interaction and, thus, the aerodynamic forcing acting on the blades.

Selection Maps For ORC And CO2 Systems For Low-Medium Temperature Heat Sources

Low-medium temperature heat sources in the range 5 - 50 MWth are made available by many industrial fields but they may also be of interest for biomass and solar energy applications. ORC has been proposed in the last 20 years as a reliable solution for the exploitation of these energy sources since the alternative represented by steam cycles leads to an inefficient conversion of such small available thermal powers. However, the use of organic fluids involves a number of safety and environmental issues, either related to fluid flammability (for hydrocarbons) or to their high-Global Warming Potential (for halogenated fluids), and of limitations to the achievable cycle maximum temperature, due to fluids thermal decomposition. To overcome these limitations, CO2-based transcritical and supercritical cycles have been proposed, in recent years, as a viable option for waste heat recovery applications. The present work aims to present a fair comparison between CO2 and ORC power plants for waste heat recovery applications.

Safety and CO2 emissions: Implications of using organic fluids in a ship’s waste heat recovery system

This paper considers the practical application of exhaust gas waste heat recovery from the main engines of merchant ships. A water-based Rankine Cycle is used as a baseline and this is compared with five organic Rankine cycle systems using benzene, heptane, hexamethyldisiloxane, toluene and R245fa. The thermodynamic model of the waste heat recovery system is described. This is then applied in a case study utilising an Aframax tanker. The case study allows the comparison of the different waste heat recovery systems in more realistic scenarios. The efficiency of the different systems is compared as well as their potential to reduce CO2 emissions, ship impact, and economic viability are also discussed. The paper closes with consideration of the safety and regulatory issues associated with the use of organic fluids in the marine environment.

Thermodynamics and Fluid Mechanics of a Closed Blade Cascade Wind Tunnel for Organic Vapors

The organic Rankine cycle (ORC) offers great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low-temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to dense gas behavior and the low speed of sound. The design and performance predictions for steam and gas turbines have been initially based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of a specially designed closed cascade wind tunnel. In this contribution the design and process engineering of a continuous running wind tunnel for organic vapors is presented. The wind tunnel can be operated with heavy weight organic working fluids within a broad range of pressure and temperature levels. For this reason, the use of classical design rules for atmospheric wind tunnels is limited. The thermodynamic cycle process in the closed wind tunnel is modeled, and simulated by means of a professional power plant analysis tool, including a database for the ORC fluid properties under consideration. The wind tunnel is designed as a pressure vessel system and this leads to significant challenges particular for the employed wide angle diffuser, settling chamber, and nozzle. Detailed computational fluid dynamics (CFD) was performed in order to optimize the important wind tunnel sections.

Systematic comparison of ORC configurations by means of comprehensive performance indexes

The Organic Rankine Cycle (ORC) is considered as an emerging technology for power generation through heat recovering from different thermal sources, based on the use of organic fluids as working medium. This paper presents a numerical study to assess the relevance: i) of the thermodynamic cycle, ii) of the main design parameters and iii) of the working fluid, on the achievable performance.The ORC performance is here calculated in terms of six different thermodynamic indexes, offering comprehensive information, namely: cycle efficiency, specific work, recovery efficiency, turbine volumetric expansion ratio, ORC fluid-to-hot source mass flow ratio and heat exchangers size parameter.In the framework of a systematic investigation approach, various possible modifications to the simple ORC plant layout are here analyzed and compared, in order to improve the ORC recovery performance; arrangements such as recuperation, superheated cycle, supercritical conditions, regenerative cycle and their combinations are taken into account.The investigation is carried out by means of an in-house developed calculation tool, based on a thermodynamic property database of the considered fluids, including aromatics, siloxanes, refrigerants and hydrocarbons.A comprehensive parametric analysis of these cycles at different hot source temperature and different evaporation pressure values is carried out. The objectives of this investigation are to provide useful guidelines to select the ORC configuration, the most appropriate fluid and to define the operating parameters, depending on the specific application. Thermodynamic results are also related with sizing of ORC components and thus can be used for economic assessment of the different ORC design alternatives.