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Design and Modeling of a Demonstration-scale ORC Cycle for the Liquid Air Combined CyclePryor, Owen M.; Conlon, William M.; Rimpel, Aaron M.; Venetos, Milton J.Energy storage is becoming an increasing focus for the future energy markets. One potential hybrid system for ling duration energy storage is the Liquid Air Combined Cycle (LACC). The LACC utilizes excess renewable energy to liquefy and store air during the charge cycle. During its discharge cycle, the system uses the exhaust heat from a conventional combustion turbine and an ORC bottoming cycle to vaporize and superheat the stored air that has been pressurized, which is subsequently expanded to atmosphere through a turbine. During the development of the cycle, it has been identified that the main technologies to advance the cycle are the ORC bottoming cycle machinery and the coupled operation between the liquified air subsystem and the ORC subsystem. This paper presents modeling and simulation of the LACC that involves ORC conditions that fall outside the operating regime of more common applications. Due to the low temperatures of liquified air, the ORC system operates on the order of -70°C for the pump, and the turbine has a pressure ratio around 40. The conceptual design of a demonstration system has been developed that focuses on these challenges in order to advance the overall system.- THERMODYNAMIC FEASIBILITY OF A PUMPED THERMAL ENERGY STORAGE DRIVEN BY OCEAN TEMPERATURE GRADIENTGhilardi, Alessandra; Baccioli, Andrea; Frate, Guido Francesco; Ferrari, LorenzoThe significant future penetration of variable renewable energy, necessary to decarbonize power production, will require energy storage to stabilize the electric grids. Electrochemical batteries may not be the best solution for all energy storage needs due to their limited lifetimes, performance degradation and use of critical raw materials. Pumped thermal energy storage (PTES) is an attractive solution since it does not suffer from the abovementioned limitations and might be preferable for long-duration applications. Particularly Thermally Integrated-PTES (TI-PTES), exploiting an external heat source during the charging or discharging phase, represents a significant improvement of this technology regarding the round-trip efficiency . Several TI-PTES systems have been proposed using solar and geothermal energy or industrial waste heat. This paper introduces a novel TI-PTES concept exploiting the temperature difference between the surface and deep oceanic Water in tropical areas. The system comprises a vapour compression chiller, a phase change material (PCM) cold storage, and an organic Rankine cycle. During the charging phase, the chiller operates between the cold seawater and the thermal storage, converting electric energy into a cooling effect. In these conditions, the chiller Energy efficiency ratio (EER) is in the range of 4.6 - 9.0 due to the deep seawater's low temperature. During the discharge phase, the organic Rankine cycle operates between the hot surface and the storage to produce electricity. Results show that the round-trip efficiency ranges from 0.30 to 0.52 depending on the fluids adopted in chiller and ORC and PCM storage temperature, making the investigated technology a promising alternative to other long-duration storage technologies.
- Evaluation of the performance of an axial one-stage 10kW turbogenerator through experimental testingKlimaszewski, Piotr; Klonowicz, Piotr; Witanowski, Łukasz; Suchocki, Tomasz; Lampart, Piotr; Ihnatowicz, Eugeniusz; Antczak, Łukasz; Zaniewski, Dawid; Jedrzejewski, ŁukaszThe paper describes the results of experimental research on a prototype one-stage turbo-generator with a nominal power of 10 kW and a rotational speed of 24 000 rpm. The expander at the Institute of Fluid- Flow Machinery, Polish Academy of Sciences was developed as part of the R&D project with Marani company. The unit construction consists of an overhanging rotor and shaft mounted on rolling bearings. The turbo-generator was tested on a specially constructed laboratory test stand in the first stage. Compressed air instead of refrigerant gas (R1233zd) was used. The test results converged with the parameters obtained using the RANS simulation. The convergence for the turbine mass flow was 97% of the value obtained in the CFD model, which is satisfactory. The power generated by the turbogenerator, which was compared at this stage, also achieved satisfactory convergence (95% to 97%) with the calculation model. These tests allowed determine the compliance of the adopted design assumptions and confirmed the correctness of the calculation tools used. The next stage of work was to examine the ORC unit in operating conditions. That stage was aimed at checking the correct work of the machine with the ORC system. The turbine achieved internal efficiency calculated from temperatures at a level slightly lower than that obtained from numerical calculations (total-to-static efficiency). The efficiency was equal to about 73%, and the difference between calculated and measured values do not exceed 0.25 pp. (percentage point). The electric efficiency was about 65% and a maximum electric power output of 6.8 kW was measured.
- REDUCED ORDER MODELLING OF OPTIMIZED HEAT EXCHANGERS FOR MAXIMUM MASS-SPECIFIC PERFORMANCE OF AIRBORNE ORC WASTE HEAT RECOVERY UNITSBeltrame, FabioWaste heat recovery (WHR) from aeroengines via compact organic Rankine cycle (ORC) units may increase the fuel efficiency of air transportation. Heat exchangers are arguably the key components of ORC systems for aeronautical applications and their design must be optimized to guarantee the best trade-off between fluid pressure drop, weight and induced aircraft drag. At present, no heat exchangers design guidelines are available for waste heat recovery systems aboard aircraft. This study, thus, contributes to defining a proper design methodology for ORC systems of such applications. The chosen test case is a supercritical ORC system with cyclopentane as the working fluid, which recovers waste heat from the auxiliary power unit of an aircraft. The exhaust gas temperature and mass flow rate of the power unit are known and kept constant in the analysis, and so are the ambient conditions, which define the cold sink of the ORC turbogenerator. Three design strategies targeting minimum mass and maximum net power output of the ORC unit have been assessed. In the first one, the multi-objective optimization is performed by prescribing a priori the geometry and frontal area of the heat exchangers. Thus, only the cycle parameters are optimized. The second method tackles, instead, the simultaneous optimization of the geometric parameters of the condenser and the cycle parameters. It was found that the integrated design allows for system mass reduction by 10 - 12% for a given ORC power output, highlighting the importance of performing the simultaneous optimization of the thermodynamic process and the heat exchanger geometry. Finally, the third method addresses the same optimal design problem by leveraging a reduced-order model of the condenser to predict the optimal design space of this component. The generated Pareto front obtained with this method is very similar to that found by optimizing simultaneously the complete condenser geometry and the cycle parameters. The mean deviation is about 2%. With just one heat exchanger surrogate model, the Pareto front was generated in one fourth of the computational time. This is due to the lower number of optimization variables and the faster objective function evaluation.
- ON AIR-COOLED CONDENSERS FOR ORC SYSTEMS OPERATING WITH ZEOTROPIC MIXTURESGalieti, Lorenzo; De Servi, Carlo; Alfani, Dario; Silva, Paolo; Bombarda, Paola; Colonna, PieroThe use of mixtures as working fluids of ORC systems is being intensively investigated because of the better temperature profile matching achievable in the heat exchangers, resulting in lower thermodynamic irreversibilities and increased efficiency. The gains are expected to be higher for lowtemperature air-cooled power plants, where the ratio between the auxiliary power consumption associated to the cooling of the working fluid and the net power output of the ORC plant is higher. For instance, a temperature glide in the condenser may enable a reduction in the fan consumption at the cost of an increased heat transfer area, and possibly a decrease in the minimum temperature of the thermodynamic cycle. This solution is expected to be attractive for geothermal applications: since the drilling of the geothermal well is by far the dominant cost, the additional investment for the condenser can be more easily compensated by the increased revenues related to the greater electrical power output. This study focuses on the modelling and sizing of an air-cooled condenser for geothermal ORC power plants operating with working fluid binary mixtures. A detailed fin and tube air cooled condenser model is developed and integrated with an in-house tool for the simulation of ORC systems. Working fluid thermodynamic properties are computed with the PCP-SAFT equation of state (EoS). The tool is used to investigate the effect of the condenser design assumptions on the geothermal plant maximum power output for an optimal working fluid mixture, whose composition is determined by optimizing the PCPSAFT parameters. The outcome is a pseudo-fluid mixture that represents the ideal working fluid for the given thermal source. The results indicate that the adoption of mixtures allows the air-cooler consumption and generally the minimum cycle temperature to be decreased, leading to an increased plant efficiency. In addition, design guidelines for the condenser are derived, based on the tradeoff between component size and plant efficiency. Finally, the optimization results show that if the onset of the mixture condensation occurs in the recuperator, it might be possible to reduce the fan consumption and size of the condenser simultaneously, albeit at the expense of an increased complexity of the regenerator design.
- EVALUATING THE WASTE HEAT SOURCES IN A VERY LARGE CRUDE CARRIER AND THE POTENTIAL INTEGRATION OF ORGANIC RANKINE CYCLE CONFIGURATIONSStainchaouer, Amalia; Schifflechner, Christopher; Wieland1, Christoph; Spliethoff, Hartmut
- Thermodynamic analysis of a novel pumped thermal energy storage system with waste heat integrationZhang, Meiyan; Shi, Lingfeng; Hu, Peng; Pei, Gang; Shu, GequnPumped thermal energy storage (PTES) system is a large-scale electricity storage technique, and the thermally integrated PTES system has been brought forward to raise the energy storage efficiency and extend feasible ways to utilize the low-grade waste heat (<100 °C). The solutions to raise the power-topower efficiency of the thermally integrated PTES system have aroused much attention worldwide. This paper presents an innovative thermally integrated PTES system, in which the two-stage heat pump with an economizer is incorporated into the PTES system. Despite utilizing the waste heat at charge time, the low-grade waste heat is also poured into the discharging process innovatively. The simulation model of the thermally integrated PTES system is established in the software MATLAB, and the physical properties of the substances are acquired from the software Refprop 10. The parameters of the PTES system are displayed and the power-to-power efficiency of the PTES system is investigated under various thermal storage temperatures. The results indicate that the power-to-power efficiency increases first and then declines as the low heat storage temperature rises when the high heat storage temperature is deemed. However, the energy storage density of the system dwindles with the increment of low heat storage temperature. The rise of the component efficiency contributes to the improvement of the powerto- power efficiency obviously, which can reach 87.3% as the isentropic efficiencies are 90%. The exergy destruction in the heat exchangers and mechanical components occupy a large proportion of the overall exergy destruction, which infers that the modification of the heat transferring and expansion/ compression processes are viable for performance enhancement.
- EXERGY-BASED METHODS FOR HEAT PUMPSHofmann, Mathias; Freißmann, Jonas; Fritz, Malte; H. Alexe, Jeremias; Witte, Francesco; Tsatsaronis, GeorgeHeat pumps are undoubtedly a relevant technology option for decarbonizing the residential sector’s heating supply and providing process steam in the industry. Nevertheless, thermodynamic analysis and evaluation of heat pumps needs to be more accurate. Exergy analysis provides a method that detects the real thermodynamic inefficiencies of the components and the overall process. Determining the exergetic efficiency also provides a statement about the process quality and the maximum possible potential for process optimization. In addition, heat pump concepts with different inputs (compression heat pumps, absorption heat pumps) can be consistently compared with each other. The exergoeconomic analysis enables the identification of the cost-generation process and the determination of the heat production costs. Thermal Engineering Systems in Python (TESPy) is a free and open-source software for the simulation and analysis of energy conversion systems like gas turbines, steam power plants, heat pumps, or refrigerators. Exergy balances are solved in postprocessing for all predefined components, and exergetic efficiencies are determined. Simulation results and comparative exergy analyses are presented for different heat pump concepts. The paper is intended to establish the exergy-based methods for heat pump analysis. The results show which concepts and components are suitable for providing indoor heat and process steam from renewable energy sources.
- Investigation of the turbulence level and the vortex shedding in a turbine cascade working with an organic vapor at subsonic Mach numbersHake, Leander; hanndermeier, SuStep; aus der Wiesche, Stefan; Matar, Camille; Cinnella, Paola; Gloerfelt, XavierDetailed turbulence and trailing edge vortex shedding measurements employing hot-wire anemometry and numerical simulations using a high-resolution unsteady Reynolds-averaged Navier-Stokes method were conducted for the high subsonic flow of the organic vapor Novec 649 through the VKI turbine cascade at elevated pressure and temperature level. Turbulent spectra downstream and upstream of the cascade were obtained and analyzed. The simulations indicated that acoustics waves (shed shockwaves) and locally supersonic flow occurred at the trailing edge even at a moderate isentropic exit Mach number of 0.7. Strong evidence for that loss-relevant mechanism was found in the hot-wire signals. The vortex shedding frequency depended primarily on the Reynolds number, not the Mach number.
- NUMERICAL INVESTIGATION OF A TRANSONIC DENSE GAS FLOW OVER AN IDEALIZED BLADE VANE CONFIGURATIONBienner, A.; Gloerfelt, X.; Cinnella, P.; Hake, L.; andaus der Wiesche, S.A joint numerical and experimental investigation of an idealized blade vane configuration, representative of an ORC turbine, is undertaken using Novec649 as the working fluid. First laminar-turbulent transition over the blade is studied by means of large-eddy simulation (LES). The geometry of the leading edge is modified to avoid an incipient separation. Afterwards, RANS simulations are carried out for both air and Novec649. The dense gas flow achieves a lower pressure ratio and exit Mach number compared to air, while shock waves generated at the blade leading edge are weaker. However, the dense gas induces a lower base pressure resulting in higher losses. Qualitative and quantitative comparisons with experiments and with a wall-modeled LES are also planned.
