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Giostri, Andrea
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Andrea
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Giostri
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ASSESSMENT OF TRILATERAL ORGANIC RANKINE CYCLE FOR SOLAR APPLICATIONS WITH INNOVATIVE TURBOEXPANDER CONCEPTRomei, Alessandro; Giostri, Andrea; Spinelli, AndreaLow-temperature solar collectors coupled with thermal energy storage can enable stable and carbonfree energy production. The key issue is to efficiently convert solar energy into electricity without resorting to complex architecture that may hinder the technical and economic feasibility of the entire system. In this work, we propose a fully integrated organic Rankine cycle (ORC) with the solar field and energy storage, targeting 200 kW. The system consists of a single circuit of the selected organic fluid that passes through the solar collectors, the thermocline thermal energy storage, and the ORC unit. The organic fluid remains liquid inside the solar field and the thermal energy storage, leading to a trilateral thermodynamic cycle. Leveraging the thermodynamic behavior of molecularly complex fluids, the radial-inflow turbine expands from saturated liquid to superheated vapor. Following the idea of White (App. Therm. Eng., 192 (2021), 116852), the nozzle cascade expands the two-phase flow mixtures and delivers superheated vapor to the rotating cascade. In this way, the rotor processes dry organic vapors without incurring mechanical damage or suffering from additional losses due to twophase interactions. Three maximum temperatures are investigated, and each of them entails a different fluid selection to have the liquid-to-vapor expansion through the stator. Preliminary designs of the radial-inflow turbines are carried out by employing a meanline code, validated for single-phase organicfluid flows, revealing that feasible designs can be obtained. Based on these results, the proposed technology appears feasible and promising on the technical ground.- Pareto front analysis for the design and the working fluid selection in ORC-based pumped thermal energy storage technology in both pure electric and cogenerative applicationsAstolfi, Marco; Alfani, Dario; Giostri, AndreaCarnot Batteries are a sub-technology of Pumped Thermal Energy Storage concept where closed cycles are used in both charging and discharging phase. In charging mode, cheap off-peak electricity from the grid is used to store heat at a temperature different than the ambient one (generally higher) while in discharging mode the stored heat is exploited for power production. Carnot Batteries can be designed with different thermodynamic cycles (Brayton cycle, Steam Rankine cycle, Organic Rankine cycle) and can adopt different types of thermal energy storage technologies. For low duration storage (daily or weekly cycling) sensible or latent energy storage with phase change materials can be adopted, while for long duration storage (months, seasonal) the use of thermochemical reactions could be a valid option, as proposed by H2020 RESTORE project. Performance of Carnot Batteries is highly affected by the thermal storage temperature, the condensation temperature in discharging mode and the availability of residual heat at a temperature higher than the ambient one for boosting the heat pump coefficient of performance in charging cycle. This paper focuses on the optimal design of a reversible thermodynamic system working as a heat pump (HP) cycle in charging mode and as an organic Rankine cycle (ORC) in discharging mode. A dedicated numerical model developed in Python is employed to compare the techno-economic performances of different working fluids and select the most promising candidates. Main difficulty is related to the use of reversible heat exchangers which design impacts both on the charging and discharging operation, strongly affecting the system round trip efficiency, and requiring a discretized off-design modelling. A Pareto front of optimal round trip efficiency against total area of heat exchangers is obtained by varying the main design parameters, such as heat transfer temperature differences and heat exchangers pressure drops. Results show that for a given overall heat transfer area low critical temperature fluid are mainly penalized by poor HP performance due to high compressor specific work, while high critical temperature fluids are mostly penalized by high pressure drops caused by the low fluid density. The most eaching a RTE close to 35% for the pure electric configuration at its maximum RTE over total heat transfer area parameter
