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This work is focused on the thermodynamic optimization of Organic Rankine Cycles (ORCs), coupled with absorption or adsorption cooling units, for combined cooling heating and power (CCHP) generation from biomass combustion. Results were obtained by modelling with the main aim of providing optimization guidelines for the operating conditions of these types of systems, specifically the subcritical or transcritical ORC, when integrated in a CCHP system to supply typical heating and cooling demands in the tertiary sector. The thermodynamic approach was complemented, to avoid its possible limitations, by the technological constraints of the expander, the heat exchangers and the pump of the ORC. The working fluids considered are: n-pentane, n-heptane, octamethyltrisiloxane, toluene and dodecamethylcyclohexasiloxane. In addition, the energy and environmental performance of the different optimal CCHP plants was investigated. The optimal plant from the energy and environmental point of view is the one integrated by a toluene recuperative ORC, although it is limited to a development with a turbine type expander. Also, the trigeneration plant could be developed in an energy and environmental efficient way with an n-pentane recuperative ORC and a volumetric type expander. [ABSTRACT FROM AUTHOR]

This paper addresses the issues linked to simulation failures during integration in finite-volume flow models, especially those involving a two-phase state. This kind of model is particularly useful when modeling 1D heat exchangers or piping, e.g., in thermodynamic cycles involving a phase change. Issues, such as chattering or stiff systems, can lead to low simulation speed, instabilities and simulation failures. In the particular case of two-phase flow models, they are usually linked to a discontinuity in the density derivative between the liquid and two-phase zones. In this work, several methods to tackle numerical problems are developed, described, implemented and compared. In addition, methods available in the literature are also implemented and compared to the proposed approaches. Results suggest that the robustness of the models can be significantly increased with these different methods, at the price of a small increase of the error in the mass and energy balances. [ABSTRACT FROM AUTHOR]

• R1234ze(Z)/acetone and R1234ze(Z)/isohexane are possible refrigerants for HTHP. • A good assessment of the BIPs is needed to estimate the cycle performance. • Mixture composition and cycle parameters depend on the BIPs for both mixtures. • For the two mixtures the COP variation is small when tuning the BIPs. High temperature heat pumps (HTHPs) represent an interesting option to upgrade waste heat up to 200 °C for industrial application. In order to achieve such high temperatures, suitable refrigerants are needed. In this paper, two zeotropic mixtures composed of a hydrofluoro-olefin (HFO) and a hydrocarbon, namely R1234ze(Z)/acetone and R1234ze(Z)/isohexane, were examined as the refrigerant for HTHP applications. The main objective of the present study is to determine the binary interaction parameters (BIPs) of the two zeotropic mixtures from experimentally-determined thermodynamic properties and analyze how HTHP performance assessment would change after tuning the BIPs. For R1234ze(Z)/acetone, after tuning the BIPs, the phase change temperature glide did not change that much. However, the composition corresponding to the highest temperature glide changed significantly. On the other hand, for R1234ze(Z)/isohexane, the phase change temperature glide changed significantly with tuned BIPs, while the composition for the maximum temperature glide was quite similar in the two cases. A thermodynamic optimization framework was used for simulation of the HTHP cycle. Simulation results using estimated BIPs showed that for R1234ze(Z)/acetone the optimum coefficient of performance (COP) was 3.95, while it slightly changed to 3.94 (around 0.25% change) after tuning the BIPs. However, the optimum composition of the mixture was quite different for the estimated and fitted BIPs. For R1234ze(Z)/isohexane the COP was 3.90 using estimated BIPs, while it changed to 3.83 (around 1.7% change) once the fitted BIPs were used. These results indicate the importance of tuning the BIPs for zeotropic mixtures and different impacts depending on the performance parameters analysed. [ABSTRACT FROM AUTHOR]

Overthe last few decades, researchers have developed a number of empiricaland theoretical models for the correlation and prediction of the thermophysicalproperties of pure fluids and mixtures treated as pseudo-pure fluids.In this paper, a survey of all the state-of-the-art formulations ofthermophysical properties is presented. The most-accurate thermodynamic properties areobtained from multiparameter Helmholtz-energy-explicit-type formulations.For the transport properties, a wider range of methods has been employed,including the extended corresponding states method. All of the thermophysicalproperty correlations described here have been implemented into CoolProp,an open-source thermophysical property library. This library is writtenin C++, with wrappers available for the majority of programming languagesand platforms of technical interest. As of publication, 110 pure andpseudo-pure fluids are included in the library, as well as propertiesof 40 incompressible fluids and humid air. The source code for theCoolProp library is included as an electronic annex. [ABSTRACT FROM AUTHOR]

• An optimizer was developed to evaluate binary mixtures as refrigerant in heat pump. • Three relevant cases with different sources/sink temperature profile were identified. • For sensible sink/source cases binary mixtures improve the performance significantly. • Binary mixtures can also reduce compression ratio and compressor outlet temperature. • Water/ammonia is a suitable refrigerant once flammability is an issue in the process. High-temperature heat pumps represent an emerging technology with a great potential in supplying clean heat to energy intensive industries. Suitable refrigerants for high-temperature heat pumps (up to 200 °C) have not been identified yet. This work aims to analyze the performance of binary mixtures as working fluid in high-temperature heat pumps delivering heat up to 200 °C with a special focus on zeotropic mixtures. Three relevant processes with different heat sources and sinks were selected to integrate the heat pump: latent/latent (e.g. distillation processes), latent/sensible (e.g. superheated steam drying), sensible/sensible (e.g. pressurized water production). To determine the best working fluid and cycle configuration for each process, an optimization framework was developed with the maximization of the coefficient of performance as objective function. For the first case with a latent heat sink and heat source, the best performing binary mixtures were near-azeotropic with slightly higher coefficient of performance compared to pure fluids. Moreover, binary mixtures provided several advantages such as the reduction of the compression ratio and compressor outlet temperature compared to pure fluids. A similar behavior was observed for the second case with a latent heat source and a sensible heat sink. For the third case with a sensible heat sink and heat source, binary mixtures resulted in a higher coefficient of performance (10 %) compared to pure fluids. Most of the best performing mixtures were hydrocarbons with high risk of flammability. Water/ammonia was the only mildly-flammable mixture among the top mixtures. [ABSTRACT FROM AUTHOR]

Highlights: [•] ORC optimization for different target applications. [•] Model developed to allow computation in subcritical and transcritical operation. [•] Regenerative and non-regenerative cycles evaluated through second law efficiency. [•] Common working fluids: R134a, R245fa, Solkatherm, n-Pentane, MDM, Toluene. [•] Thermodynamic and technological approaches lead to optimal design guidelines. [ABSTRACT FROM AUTHOR]