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Owing to different temperature rages of power generation and refrigeration in the cogeneration system, for the sake of selecting the working fluids that are suitable for both power generation and refrigeration simultaneously, 17 commonly used working fluids are evaluated in this paper, based on an organic Rankine cycle coupled with a two-stage vapor compression cycle system in different geothermal fluid temperatures. The performances of working fluids under different working conditions, and the maximum power generation as well as cooling capacity are analyzed. Additionally, the main parameters are analyzed to optimize the system performance. The results indicate that net power output has a local maximum where it corresponds to the optimal evaporation temperature. Besides, the lower the critical temperature, the greater the thermal conductance, and the pressure ratio decreases with evaporation temperature. Hydrocarbons all have higher total heat source recovery efficiency. R1234yf, propane and R1234ze, R152a have excellent maximum net power output when the geothermal fluid temperature is low and high, respectively. R134a always has better maximum net power output and cooling capacity. The net power output is used for cooling, and the COP is closed, therefore, maximum net power output results in the maximum cooling capacity. In addition, that of propane and R1234yf are excellent until the geothermal fluid temperature are 140 °C and 120 °C separately. R1234ze and R152a are good when the geothermal fluid temperatures are 140 °C and 150 °C, respectively. [ABSTRACT FROM AUTHOR]

With ever increasing fossil fuel price and growing demands in cutting emissions, waste heat recovery (WHR) appears as a promising pathway to improve propulsion system performance, which can be potentially achieved by incorporating a recuperator. This paper explores the advantages and potentiality of further recovering exhaust heat from recuperated turboshaft engine through the concept of organic Rankine cycle (ORC) to improve fuel economy and thermal efficiency. For the intended application, working fluid selection is conducted after systematic consideration of thermophysical properties, environmental impact, health and safety issues. Furthermore, parametric analysis is carried out from the viewpoint of thermodynamics, and the genetic algorithm is also employed to obtain the maximum net power output. Targeting the implicit coupling between recuperator effectiveness and ORC performance, the potential advantages of the combined engine-ORC system are comprehensively evaluated at different operational regimes. The influence of flight condition is also discussed through sensitivity simulations for different altitudes. Results reveal that the combination of the recuperated engine with ORC cycle operated using acetone generally offers the greatest benefits, significantly reducing specific fuel consumption by 46%–59 % relative to the baseline simple-cycle engine, depending on the availability of heat source. This analytical work contributes to provide valuable insights into WHR technologies in the aviation industry. • ORC is proposed to recover exhaust heat from turboshaft engine with a recuperator. • Working fluid selection procedure suitable for aeroengine is conceived and applied. • Parametric investigation is conducted and GA is employed for optimization. • System performance is comprehensively evaluated at different operational regimes. [ABSTRACT FROM AUTHOR]

The Organic Rankine Cycle (ORC) is a widely-used waste heat recovery approach, that converts low-grade heat into shaft work. This paper introduces a graphical methodology using Exergy-Enthalpy (Ex-H) diagrams, for evaluating and designing ORCs. ORC thermodynamics can be represented by approximate triangular exergy profiles without compromising accuracy. The exergy profile of the heat-absorbing process is crucial to ORC performance. Approximate triangular exergy profiles can be constructed for any ORC configuration to predict ORC performances, such as work output, exergy loss, and thermal efficiency. Furthermore, a systematic graphical approach is developed for integrating waste heat streams and ORCs, with step-by-step procedures outlined. The evolution procedure of the ORC exergy profile can determine working fluid selection and operating conditions. This visually intuitive yet scientifically rigorous tool clarifies the complex relationships between fluids, parameters, and system performance. Two case studies demonstrate the method's effectiveness, confirming it as a valuable tool for ORC design. • A visually intuitive and theoretically robust tool is developed for design of ORCs. • Triangular exergy profiles are constructed to predict key performance metrics. • Two cases validate the accuracy and effectiveness of the Exergy-Enthalpy Diagram. • Simplified ORC designs achieve better performance than complex literature designs. [ABSTRACT FROM AUTHOR]

In China, the utilisation of low-temperature waste heat (especially at temperatures lower than 100 °C) plays a significant role in increasing the energy-consumption efficiency in the industry. The organic Rankine cycle (ORC) is considered as a promising method to recover the aforementioned part of the waste heat. In the study, six potential candidates, namely R141b, R142b, R245ca, R245fa, R600a, and R601a were screened from 12 dry or adiabatic organic working fluids based on their thermodynamic performances in the ORC. A multi-objective optimisation (MOO) was performed for the thermodynamic performance (exergy efficiency, EXE) and economic performance (levelised energy cost, LEC) by using non-dominated sorting genetic algorithm-II (NSGA-II). The Pareto frontiers were obtained for the six candidates with the algorithm, and each optimal compromise solution was accurately obtained with the fuzzy set theory. Based on the EXE and LEC of the optimal compromise solution, the total cost and power generation efficiency for the six candidates were determined. This was used to obtain an explicit evaluation index in economic performance, namely static investment payback period (SIPP), to identify that the R245ca corresponded to the most cost-effective working fluid with the shortest SIPP. This suggests R245ca was the fastest to cover the investment and cost of the ORC system. Furthermore, a fast decision-making method was introduced to select the optimal working fluid based on the grey relational analysis (GRA) by considering key physical property parameters of the working fluids. The results suggest that any potential working fluid to recover low-temperature waste heat in the ORC can be evaluated by the simplified grey relational degree (SGRD) proposed in the study. [ABSTRACT FROM AUTHOR]

The dual-loop Rankine cycle system is considered as the most effective way to recover the multi-grades waste heat of engine. However, the power consumption of mechanical pump is relative high, especially for that in the low-temperature loop of dual-loop Rankine cycle, which will influence the system efficiency and power output. Therefore, a thermofluidic pump driven by the engine coolant heat instead of electric energy is used to replace the mechanical pump of low-temperature loop in this paper. The effect of the design parameters on the performance of thermofluidic pump are analyzed firstly. There is always a reasonable height distribution among the components that makes the mass flow rate of thermofluidic pump achieve to maximum, which contributes to a smaller volume and less pressure fluctuation of pump. Then several working fluids are selected as the candidates for systems with thermofluidic pump and mechanical pump. Based on the comprehensive analysis (utilization rate of engine coolant, the energy and exergy efficiency, and output power), the R1234ze is regarded as the most suitable working fluid for both system with thermofluidic pump and system with mechanical pump. Afterwards, a comparison analysis between systems with thermofluidic pump and mechanical pump is implemented in the low-temperature loop. Results indicate that R1234ze based low-temperature loop with the thermofluidic pump has improvement of 7.6%, 9.1% and 7.7% on net power, thermal efficiency and exergy efficiency respectively compared with that of low-temperature loop with the mechanical pump. In addition, the mass flow rate will decrease by 8.6% in low-temperature loop, which conduces to reduce the size of component of cycle. All the results indicate that thermofluidic feed pump is an effective way to improve the performance of dual-loop system. [ABSTRACT FROM AUTHOR]

Large quantities of waste heat generated during industrial production offer an opportunity for waste heat recovery (WHR). Several case studies are selected using flue gas as heat source, which are representative of a fairly wide range of source temperature (200–700 °C). The objective function of WHR refers to maximization of net power output. With a view to seeking an optimal combination of cycle configuration, fluid and cycle parameters under different heat source condition, the following researches have been performed. Different types of power cycles (e.g., Rankine cycle, transcritical cycle and combined cycle) as well as different cycle configurations (e.g., saturated or superheating, with or without regenerator) are evaluated. In order to compensate the defects of conventional cycles in some case studies, a novel improved transcritical CO 2 cycle and two combined cycle designs are presented. Working fluid selection among the organics is performed. After the parametric optimization, comparison and analysis are carried out among different cycles. Results indicate that the regenerative organic transcritical cycle produces the maximum power output at source temperatures up to about 500 °C, and different optimum working fluids are obtained under different heat source temperature. The improved transcritical CO 2 cycle shows satisfying performance in source temperature range of 500–600 °C. One combined cycle produces the largest work at source temperature above 600 °C. The traditional steam Rankine cycle shows bad performance at source temperature below 500 °C due to its bad thermal matching with sensible source. At source temperature of 700 °C, steam Rankine cycle shows satisfying performance, and produces a power output close to that of the combined cycle. [ABSTRACT FROM AUTHOR]

General guidelines on how to choose the optimal working fluid based on the hot source temperature available are reported. Based on a systematic approach, 26 commonly used working fluids are investigated by optimisations at hot source temperatures in the range 50–280 °C at intervals of 5 K. The genetic optimisation algorithm is used to optimise net power output by an optimal combination of turbine inlet pressure and temperature, condenser pressure, hot fluid outlet temperature, and mixture composition for mixtures. The results suggest that the optimum working fluid in terms of maximum net power output has a critical temperature approximately 30–50 K above the hot source temperature. When two or more fluids with the same critical temperature are available, the ones with a positive slope of vapour saturation line are generally favoured. When mixtures are considered, the optimal mixture composition should be chosen so that the critical temperature of mixture is approximately 30–50 K below the hot source temperature and the temperature glide during condensing should approximate the temperature rise of the cold source. [ABSTRACT FROM AUTHOR]

The Organic Rankine Cycle (ORC) is receiving increasing attention as a waste heat recovery system. However, it is still a major challenge to quickly and practically choose the appropriate one among dozens of working fluids, considering many criteria. In this study, the comprehensive decision-making strategy for working fluid selection in ORC applications was proposed. The selection of working fluid was evaluated not only in terms of thermodynamics and economics but also considering safety and environmental concerns. A container ship was chosen for the case study. Optimization was carried out for the design condition using the Multi-Objective Gray Wolf Algorithm (MOGWA). The results obtained for 10 different working fluids were evaluated with a comprehensive decision-making strategy and R245fa was determined as the final working fluid. Moreover, off-design analyses and operational profile-based simulation were performed. The net work was calculated as 439.5772 kW and 420.1741 kW for the design condition and the overall operating condition, respectively. The electricity generation cost for the design operating condition was 0.0570 $/kWh, and this value for all conditions was calculated as 0.0596 $/kWh. Lastly, MOGWA and NSGA-II were compared to each other, and their performance was analyzed. The results showed that both algorithms had similar performance. • Comprehensive decision-making strategy for working fluid selection was proposed. • Thermodynamic, economic, safety and environmental criteria were considered. • A container ship with a capacity of 2200 TEU was selected for case study. • Multi-Objective Gray Wolf Algorithm was used. • Off-design analyses and operational profile-based simulation were performed. [ABSTRACT FROM AUTHOR]

Abstract: The selection of a suitable working fluid for a BC (Bottoming Cycle) system is one of the most important steps in maximising system performance and minimising the system size and cost. The presented work details a systematic approach in the selection of working fluids applied to a subcritical cycle with minimum superheat. Over 60 different synthetic, organic, and inorganic fluids were studied. The fluid selection study was decomposed into numerous fluid screening and fluid ranking criteria with common boundary conditions and assumptions. After the cycle was optimised for maximum overall conversion efficiency, the fluid ranking criteria allowed the objective assessment of the working fluids. Acetone, dichloromethane and trans-1,2-dichloroethylene were found as the best candidates for optimal performance and system related trade-offs, contrary to commonly used R245fa, ethanol and water. A BC integrated into an EGR (Exhaust Gas Recirculation) only engine platform to meet Euro 6 oxides of nitrogen emission is examined for improved fuel economy and reduced load on the engine cooling module. The BC simulation results for EGR and partial high temperature after-cooler heat recovery using the proposed new fluids show a specific fuel saving potential between 9.8 and 13.7% for a typical cruise and high load conditions. [Copyright &y& Elsevier]

• Improved layout the SPT integrated to the inverted Brayton cycle combined with ORC. • Use of air-fluid as the gas turbines working fluid and receiver with atmospheric pressure. • Providing the thermo-economic optimization of the optimal LCOE point, optimal efficiency conditions of the SPT. • Selecting the appropriate ORC working fluid to achieve maximum heat recovery. Today, the international community is obligated to utilize renewable energy due to accelerated energy consumption on the one hand and the necessity of environmental pollution reduction, on the other hand. Meanwhile, the Solar Power Tower (SPT) is at significantly optimum conditions for integration with conventional fossil power plants due to reaching temperatures of up to 1200 °C and a high-power generation capacity. The present paper demonstrates the optimal layout of the new hybrid-cycle power generation section with SPT. The Heliostat field was optimized as a transient optical model at all hours of the year by considering the city of Seville as a case study using the System Advisor Model (SAM). Subsequently, the cycle's thermo-economic model was developed using Engineering Equation Solver (EES) to minimize the Levelized Cost Of Electricity (LCOE). In the following, four fluids of n-Butane, R245fa, n-Pentane, and R123 were utilized for the final analysis as a downstream fluid. Through this process, the appropriate operating fluid was selected. The study results demonstrate an increase in the efficiency of the novel proposed cycle layout compared to a solar power tower power plant with standard pressurized air-fluid; moreover, it reduced fuel consumption, CO2 emission, and LCOE. The maximum efficiency and the minimum LCOE were53.25% and 61.8 $ / M W h , respectively. The n-Pentane fluid was recognized as the most appropriate fluid for the downstream cycle. Due to the optimization of solar parts, the number of heliostat field mirrors were 889, with a total area of 131,525 m 2 and a central tower height of 105.87 m. The novel presented cycle layout solves a portion of the pressurized air receiver limitations, enabling access to higher efficiency and lower LCOE with the real payback time (RPBT) of 3.876 years, the annual solar share of 23.1%, and reduction of CO2 production by 33,426 t o n / y e a r. Consequently, this study's proposed cycle layout signifies a promising future for using SPT with high efficiency and better environmental and economic conditions. [ABSTRACT FROM AUTHOR]

• A novel four-step approach for working fluid selection in geothermal sourced organic Rankine Cycle (ORC) systems. • R113 is proposed as new working fluid in ORCs instead of existing n-pentane. • Waste heat recovery (WHR) options from brine re-injection -where majority of the exergy destruction occurs- are examined. • Based on proposed approach at given re-injection temperature, R115 is selected as the working fluid of WHR cycle. A novel working fluid selection methodology is proposed for organic Rankine cycles (ORCs) coupled with low-grade geothermal sources by employing an existing dataset of an operating binary geothermal plant that works with n-pentane. Thermodynamic and thermoeconomic aspects of power production are combined to evaluate 29 different single-component working fluid candidates from different chemical branches in four-step elimination methodology. In terms of working fluid classification from physical point of view, results indicate that there is a direct relationship between vapor expansion ratio (VER) and net work output for dry working fluids. On the other hand, it is shown that isentropic fluids behave differently from dry fluids. Based on the proposed methodology, R113 is selected as a new working fluid for the existing plant instead of n-pentane. Results indicate that by applying the proposed methodology, it is possible to increase first and second law efficiencies of plant 0.59% and 3.18%, respectively, while reducing the levelized electrical cost (LEC) around 11% in comparison to base plant outputs with n-pentane. Furthermore, a case study is presented in addition the plant level analysis by implementing a hypothetical waste heat recovery cycle, configurated with proposed methodology, in order to reduce exergy losses originating from brine re-injection. It is shown that it may be possible to further reduce the LEC around 1% and increase the overall efficiencies 0.1% for the first law and 0.26% for the second law. However, it is necessary to be deliberate about these final results since they also demonstrate the sensitivity of LEC to the increases in second law efficiency rather than levelized capital investments. [ABSTRACT FROM AUTHOR]

Among various techniques of utilizing waste heat, ORC is receiving more and more attention for its high efficiency and flexibility. One of the toughest tasks in ORC waste heat recovery system is working fluid selection. The aim of the study is to investigate the effect of physical properties on overall ORC system costs and propose a general method of refrigerant's performance assessment of ORC system. The internal relationship between the enthalpy of vaporization, molecular weight, and molecular complexity, and the impact on investment cost were analyzed theoretically. The analysis and experiment using R12333zd(E), R1234ze(Z) and R1366mzz(E) as well as R245fa explain the internal mechanism of the effect of different working fluids on NPIT, which represents the ratio of the net power output to the total cost. The economic performances of several new environmental-friendly refrigerants are evaluated using the NPIT assessment. The results show that R12333zd(E) has the best performance and its maximal NPIT value is 0.0625, followed by R1234ze(Z), R1366mzz(E) and R245fa. In addition, when R1233zd(E) performs excellently, evaporation and condensation temperature are 127 °C and 30 °C, respectively. The physical properties of R1233zd(E) and R245fa are extremely close, which makes R1233zd(E) be an alternative refrigerant without redesigning components of ORC system. NPIT is the answer to the challenge of complex boundary conditions and system types with various operational parameters and it could guide the selection of operating condition and design of ORC system equipment. • A compatibility test of various low-GWP refrigerants was implemented. • a general method of refrigerant's performance assessment was proposed. • The impact of various low-GWP refrigerants behavior was analyzed. [ABSTRACT FROM AUTHOR]

• A new and simple ORC configuration for GTMHR waste heat recovery. • A method for optimizing GTMHR-ORC design parameters and working fluid. • An off-design simulation procedure for studying GTMHR-ORC performance. • Higher helium temperature leads to better design and off-design performance. Gas Turbine-Modular Helium Reactor (GTMHR) is a promising option to meet today's soaring energy demand. A GTMHR combined with organic Rankine cycles (ORCs) can deliver higher performance. This paper presents an exergoeconomic optimization for a combined system comprising a GTMHR and an ORC where the ORC recovers the GTMHR waste thermal energy. The system performance is optimized using a simulation-based optimization method with simultaneous determination of the design parameters as well as selection of the components and their respective compositions for the ORC working fluid. A parametric study is performed to study the effects of the key design parameters on the system performance. Moreover, an off-design simulation procedure is proposed, and the system off-design performance is analyzed. The results show that R134a (100%), R22 and R143a (11.27% and 88.73%), and R134a and R152a (54.54% and 45.46%) are the best ORC working fluid for low, medium, and high helium temperature cases, and their minimum levelized cost per unit exergy are 8.449 $/GJ, 8.116 $/GJ, and 7.862 $/GJ, respectively. Furthermore, helium temperature and pressure ratio are found to have the most significant influences on the system performance. Finally, it is observed that a combined system with higher design parameters exhibits better off-design performance, namely higher power output and efficiency. Therefore, the GRMHR-ROC system should be designed with a relatively high helium temperature if allowed. [ABSTRACT FROM AUTHOR]

• Thermo-economic analysis accounting for heat exchanger pressure drops in ORC systems. • Effects of pressure drops on system design, performance, working-fluid selection. • Comparison of predictions with conventional methods that ignore pressure drops. • Performance overestimations as high as >80% in some cases can be avoided. • Smaller heat exchanger cross-sections preferred within allowable exhaust backpressure. Organic Rankine cycle (ORC) systems are a promising solution for improving internal combustion engine efficiencies, however, conflicts between the pressure drops in the heat exchangers, overall thermodynamic performance and economic viability are acute in this space-constrained application. This paper focuses on the interaction of the heat exchanger pressure drop (HEPD) and the thermo-economic performance of ORC systems in engine waste-heat recovery applications. An iterative procedure is included in the thermo-economic analysis of such systems that quantifies the HEPD in each case, and uses this information to revise the cycle and to resize the components until convergence. The newly proposed approach is compared with conventional methods in which the heat exchangers are sized after thermodynamic cycle modelling and the pressure drops through them are ignored, in order to understand and quantify the effects of the HEPD on ORC system design and working fluid selection. Results demonstrate that neglecting the HEPD leads to significant overestimations of both the thermodynamic and the economic performance of ORC systems, which for some indicators can be as high as >80% in some cases, and that this can be effectively avoided with the improved approach that accounts for the HEPD. In such space-limited applications, the heat exchangers can be designed with a smaller cross-section in order to achieve a better compromise between packaging volume, heat transfer and ORC net power output. Furthermore, we identify differences in working fluid selection that arise from the fact that different working fluids give rise to different levels of HEPD. The optimized thermo-economic approach proposed here improves the accuracy and reliability of conventional early-stage engineering design and assessments, which can be extended to other similar thermal systems (i.e., CO 2 cycle, Brayton cycle, etc.) that involve heat exchangers integration in similar applications. [ABSTRACT FROM AUTHOR]

• A transcritical-subcritical parallel organic Rankine cycle system is proposed. • The proposed system shows better performance than others. • The optimization and design of proposed system is carried out. • R1233zd is the best candidate working fluid for proposed system. • The net power output of engine system is improved by 12.02%. In this study, a novel transcritical-subcritical parallel organic Rankine cycle system is proposed to recover the engine exhaust gas and coolant waste heat. Firstly, the proposed system is compared with the dual-loop organic Rankine cycle and parallel organic Rankine cycle systems. According to the results, the proposed system shows more net power output, higher thermal and exergy efficiency, and lower heat transfer requirement. Then the thermodynamic analysis including energy and exergy analysis are carried out, and the effects of design parameters including high-pressure turbine inlet temperature and pressure, low-pressure evaporation temperature on the performance of proposed system based on R601a are investigated. The results indicate that for a given high-pressure turbine inlet temperature, the net power output of system firstly increases and then decreases as high-pressure turbine inlet pressure increases and reaches to the maximum at turbine inlet temperature and pressure of 520 K and 8 MPa, and the net power output also shows a trend of firstly increasing and then decreasing with low-pressure evaporation temperature and reaches to the maximum at 330 K. Furthermore, five low global warming potential fluids are selected as working fluids of proposed system, and the results demonstrate that the R1233zd is the best candidate working fluid for proposed system. The maximum net power output of proposed system based on R1233zd reaches to 119.72 kW at the turbine inlet temperature and pressure of 530 K and 10 MPa, low-pressure evaporation temperature of 330 K, which achieves net power output increment of 12.02% for the engine system. Finally, an exergy destruction analysis demonstrates that the heat transfer processes have less exergy destruction for proposed system based on R1233zd compared with other working fluids. [ABSTRACT FROM AUTHOR]