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[en] Highlights: • Performance of novel oil-free co-rotating scroll expander presented. • Water injection allows reaching quasi-isothermal expansion process. • Comparison between experimental data, semi-empirical and deterministic models. • Flank leakage, water injection and rotor speed effects have been analyzed experimentally. • Design guidelines for co-rotating scroll improvement proposed. - Abstract: Efficient compressed air energy storage requires reversible isothermal compression and expansion devices. The isothermal compression and expansion processes can either be approached by several stages with intercooling or by the more convenient injection of a liquid, often water. While volumetric machines are readily available for dry processes the compression and expansion of a gas with the presence of liquid is still problematic. The concept of a co-rotating scroll has been identified as a promising technology to cope with the presence of liquid. The current paper discusses the first experimental results of an oil-free co-rotating scroll prototype tested in expansion mode on a wide range of rotational speeds, varying water injection flow rates and with different nominal flank clearances. A maximal overall isothermal efficiency of 34% and a maximum output power of 1.74 kW_e_l were measured with this first prototype, providing the proof of the technical feasibility of the oil-free co-rotating scroll expander concept. The experimental data indicate a positive effect of water injection suggesting good heat transfer behaviour between the water and the air in the individual chambers, which is a result of the relatively long residence time compared to other volumetric concepts. The experimental sensitivity analysis yields a strong dependency of the machine performance on both the nominal flank clearance and on the injected water rate. The analysis through a semi-empirical model suggests the inversion of a classical trend, i.e. the increase in total leakage area with rotor speed. This is resulting from the centrifugal loads acting on the flanks and deforming them to produce increased radial and flank clearances. The injection of water is suggested to significantly decrease the leakage. A deterministic reduced order model of the co-rotating scroll expander was developed in order to better understand the governing phenomena within the machine and to provide design guidelines for further prototypes. A novel leakage model takes into account for the structural deformation of the flanks and the scroll involutes as a result from the rotor speed. By means of this comprehensive thermodynamic model, mechanical power, mass flow rate and exhaust temperature were predicted within a range of ±12% and ±4 K respectively compared to experimental data. The calibrated model suggests an achievable isothermal efficiency of 87% for an improved co-rotating scroll concept, thus offering promising perspectives not only for compressed air storage, but also for wet expansion in Absorption Power Cycles, trilateral flash cycle and Organic Rankine Cycles.
[en] Up to now, the use of ammonia/water absorption cycles has been mainly limited to the production of refrigeration or air conditioning but due to the relatively high generator pressure some authors have proposed the integration in parallel of an expander to produce cooling and power simultaneously. This feature could provide many benefits in the future such as the use of solar thermal energy to partially cover the heating, cooling and electricity demand of a building. In the other hand the life cycle cost of the absorption system is improved because of the increase in the number of running hours in periods in which there is no demand for cooling but the demand for electrical power is still important. This paper shows a new combined absorption system using a scroll expander and three different working fluids using ammonia as refrigerant: ammonia/water, ammonia/lithium nitrate and ammonia/sodium thiocyanate. The scroll expander performance maps were obtained experimentally and modeled to predict the power production, rotational speed and exhaust temperature of the expander and included in the complete absorption cycle model build using Engineering Equation Solver (EES) Software. This system produces different amounts of cooling and power at the desired power/cooling ratio to cover varying demand profiles. - Highlights: • New combined absorption system using a scroll expander and three different working fluids. • Characterization the scroll expander with ammonia as working fluid. • Sensitivity to the heat source, sink and chilled water temperatures on the new combined absorption system