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• Zeotropic mixture of Hexane and R245fa is used as the working fluid. • Condenser and ORC evaporator contribute 75.3% to total exergy destruction. • Energy and exergetic performance of the system is maximum at mass fraction of 0.5. • The system can achieve the exergetic efficiency of 58% at optimal condition. In this study, a multi evaporator vapor-compression refrigeration (mVCR) system driven by Organic Rankine Cycle (ORC) is proposed as a refrigeration system for supermarkets, restaurants, etc. The system is analyzed for its thermodynamic performance in terms of coefficient of performance (COP s) and exergetic efficiency (η ex). A zeotropic mixture of hexane and R245fa is used as working fluid over pure fluid to assess its impact on the thermodynamic performance of the system. Moreover, the system is optimized using an evolutionary algorithm called genetic algorithm (GA) to determine the optimal values of the operating parameters for the maximum exergetic efficiency of the system. The results indicate that COP s and η ex are maximum at the mass fraction of 0.5 of the zeotropic mixture. The maximum values of COP s and η ex are 0.425 and 31.1% respectively. The system can achieve an exergetic efficiency of 58% at the optimal set of operating parameters. The corresponding optimal values of the temperature of the ORC evaporator, VCR evaporator 1, VCR evaporator 2, and the condenser are 388 K, 268 K, 268 K, and 303 K respectively. [ABSTRACT FROM AUTHOR]

This paper presents an energy and exergy analysis of a domestic refrigeration system using R1234yf as a drop-in replacement for R134a. We base our analysis on a series of independent tests using two refrigerants, namely R1234yf and R134a. The test equipment consists of a fully instrumented domestic refrigeration system. A computational model is developed to work out the thermodynamic parameters such as coefficient of performance, exergy destruction ratio, exergy-based rational efficiency, component efficiency defect as well as the dimensionless exergy balance for both refrigerants. The parameters varied in the analysis were the evaporator and condenser temperatures as well as the amount of refrigerant used in the system. The results indicate that irreversibilities are mainly concentrated in the compressor, this is the case both for R1234yf and R134a. This exergy analysis proposed for evaluation of refrigerants in domestic refrigerators permitted to determine that R1234yf may not be a likely alternative to R134a. [ABSTRACT FROM AUTHOR]

A new organic Rankine cycle (ORC) architecture: partial evaporating organic Rankine cycle (PEORC) with the zeotropic mixture R245fa/R227ea as working fluid is presented in this paper. The thermodynamic first law analysis as well as the second law analysis were applied to evaluate the system performance. A techno-thermodynamic evaluation on heat exchangers and the expander was also performed in this research. The mass fraction of R227ea (corresponding to zeotropic mixture) and the expander inlet vapor quality (corresponding to PEORC) are chosen as the independent variables. The results showed that both the new cycle architecture: PEORC and zeotropic mixture working fluid can improve the thermodynamic performance and more importantly they can be combined together to further enhance the system. The optimized PEORC with R245fa/R227ea is able to generate about 24.7% more power than the traditional subcritical organic Rankine cycle (SCORC) with R227ea as working fluid. However, the heat exchanger economy may become worse, which should be considered. The results also revealed that the mixture working fluid mainly reduces the exergy loss in the condenser because of the temperature glide characteristic while the PEORC mainly reduces the exergy loss in the evaporator by improving the temperature matching between heat source and working fluid. [ABSTRACT FROM AUTHOR]

This study explores the implementation of two large micro-channel heat exchangers as evaporators in a refrigeration cycle intended for thermal management onboard future space vehicles. Examined are thermal performances of the two heat exchangers, thermodynamic performance of the refrigeration cycle, and system instabilities. Because of quality differences, different two-phase flow patterns and dryout effects are encountered in the two heat exchangers. A trade-off exists between optimum performances of the evaporators and compressor, with former favoring outlet quality values below unity to guard against dryout, and the compressor favoring a quality equal to or exceeding unity to preclude internal damage to the compressor from entrained droplets. Thermodynamic analysis of the refrigeration cycle shows exergy destruction is minimum when the avionics HX’s outlet quality is close to unity. The system is shown to be susceptible to instability resulting from interactions between compressible volumes both upstream and downstream of the condenser, and inertia of liquid in the condenser. This instability is manifest by pressure oscillations that are sensitive to both flow rate and evaporator heat input. [ABSTRACT FROM AUTHOR]

Energy and exergy analyses are carried out for hydrogen production via Gas Turbine Modular Helium Reactor/Organic Rankine Cycle (GTMHR/ORC) system coupled with a proton exchange membrane electrolyzer. A comprehensive parametric study is performed and the effects of some significant variables as compressor pressure ratio, turbine inlet temperature, evaporators’ temperature, pinch point temperature difference in the evaporators and degree of superheat at the ORC turbines inlet on the exergy efficiency, rate of produced hydrogen and sustainability index of the integrated system are investigated. Using direct search method by the Engineering Equation Solver (EES) software, the combined system is optimized to achieve the maximum exergy efficiency. Results show that the exergy efficiency difference between the combined system and GTMHR cycle increases with an increase in pressure ratio. Also, it is observed that the rate of produced hydrogen increases with increasing turbine inlet temperature and takes the maximum value with change in evaporators’ temperature. Under the optimized condition, exergy efficiency, rate of the produced hydrogen and sustainability index of the proposed combined system are calculated to be 49.21%, 56.2 kg/h and 1.972, respectively. [ABSTRACT FROM AUTHOR]

In this study, a detailed exergy evaluation of a commercial tomato paste plant with a double-effect evaporator was conducted in order to provide information on the system thermodynamic inefficiencies. Using energy and exergy balance equations, all components of the plant were analyzed individually and their exergetic parameters were calculated on the basis of actual operational data. The required data were obtained from Nazchin tomato paste factory located in Tehran, Iran. In addition, it was attempted to quantify the exergy utilized for processing a given amount of the tomato paste. The results showed that over 82% of the total destroyed exergy in the plant occurred in the boiler combination as the main component wasting exergy. Furthermore, exergy analysis introduced this combination as the main equipment rejecting exergy to the ambient where 4.79% of its total exergy input was lost. The rational exergy efficiency of the first- and second-effect evaporative units was found to be 65.33% and 56.60%, respectively. The specific exergy consumption of the tomato paste production was also determined as 16.83 MJ/kg. Generally, exergy concept and its extensions could be served as a powerful assessment technique to optimize the design and performance of multiple-effect evaporation systems employed in food industry. [ABSTRACT FROM AUTHOR]

In this study, the performance of a novel photovoltaic/thermal (PV/T) air dual-heat-source composite heat pump hot water system was investigated experimentally and analyzed theoretically. First, a system that simulates a solar PV/T collector by electric heating was built and tested to validate the superiority of the hot water system. The system was divided into dual-heat-source operating mode and single-heat-source operating mode. Results showed that the average COP and COP sys for dual-heat-source operating mode were 2.49 and 2.24, respectively, and for single-heat-source operating mode were 1.40 and 1.31, respectively, which indicate that the former had better system performance. Then, the actual PV/T collector was used in the system. The results showed that the average electrical gain and heat gain were 278 W and 664 W, respectively. The average electrical efficiency and heat efficiency were 14.5% and 36.02%, respectively. Meanwhile, the comprehensive efficiency was more than 50%. The average COP and COP sys of the heat pump were 4.08 and 3.07, respectively, along with the system exergy efficiency of 0.33. Therefore, the PV/T air dual-heat-source composite heat pump hot water system has excellent performance and is worth promoting and applying. [ABSTRACT FROM AUTHOR]

Highlights: [•] A full factorial analysis is conducted upon a triple absorption heat transformer. [•] The most influential variable settings are determined. [•] Condensation temperature and pinch heat transfer gradient have the greatest influence. [•] Points of optimum exist for the temperatures of the two absorber evaporators. [•] The generator causes the most irreversibility. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we designed a multifunctional heat pump system using just one scroll compressor and which can be run in four different modes, namely air to air, air to water, water to water and water to air, in order to make an experimental energetic and exergetic performance comparison. Experimental system consists of two condensers and two evaporators and uses R22 as working fluid. One of the evaporators and condensers uses water and the others use air as heat source/sink. Heating capacities of four heat pump types are equal to each other. It is realized by adjusting the mass flow rate and temperature level of external fluid of condenser. Results show that the heat pump unit which has the maximum COP (coefficient of performance) value is water to air type with 3.94 and followed by water to water type with 3.73, air to air type with 3.54 and air to water type with 3.40. Ranking of four heat pump types with respect to their mean exergy efficiency is as follows; water to air type with 30.23%, air to air type with 30.22%, air to water type with 24.77% and water to water type with 24.01%. Exergy destruction rates of the systems were investigated in this study and the results revealed that the heat pump type which has the maximum exergy destruction is air to air type with 2.93 kW. The second highest one is air to water type with 2.84 kW. The third highest one is water to air type with 2.64 kW and last one is water to water type with 2.55 kW. It is understood that the temperature of the evaporator external fluid affects the exergetic efficiency of the system more than the mass flow rate. In contrast to the previous, the dominant parameter which has more important effect on the exergy destruction of the heat pump unit is the mass flow rate of evaporator external fluid. [Copyright &y& Elsevier]

Abstract: Higher efficiencies and optimal utilization of geothermal energy require a careful selection of the working fluid in organic Rankine cycles (ORC). The objectives of this study are to analyze and explain the effect of using alternative dry fluids on the efficiencies of the ORC and compare them with other refrigerants. In addition, the effect of the critical temperature on the thermal and exergetic efficiencies will also be determined. Results showed that iso-pentane is a good replacement for R-113, while neo-pentane outperformed C5F12. In addition, n-butane showed better efficiency than RC-318, R-236fa, and R-245fa. The best working fluid in the studied system was n-hexane, while R-227ea was the worst. It was also found that efficiencies correlate with the critical temperature of the working fluid where a strong functionality was noticed in the studied range. The contribution of the evaporator to the total exergy destruction was the most relevant, while the pump contribution was marginal. It is concluded that thermodynamically, hydrocarbons are superior to some refrigerants and could be the next generation working fluids for geothermal or waste heat recovery systems. [ABSTRACT FROM AUTHOR]

• AEA was used to separate azeotropic mixture of ACN/EtOH/H2O via TCED process. • A superstructure TCED with four-parallel evaporator ORC system is built. • Four advantageous working fluids are selected to enhance the performance of ORC. • The intensification process shows better energy-saving and economic performance. The energy analysis and optimization of process system aiming to solve the problems of high consumption, low efficiency and unreasonable use of energy in the process of energy utilization has been widely researched and developed in recent decades. In this work, advanced exergy analysis was carried out for the triple-column extractive distillation (TCED) process separating ternary azeotropic mixture of ACN/EtOH/H2O. The total exergy destruction is 1097.69 KW. The avoidable exergy destruction, is 29.20%, mainly caused by the cooler and three condensers. Based on the thermodynamic analysis results, a superstructure TCED with four-parallel evaporator organic Rankine cycles (FPE-ORC) system is proposed, four working fluids were selected. An improved genetic algorithm is used to obtain the optimal operating parameters of the ORC system by using the exergy efficiency and annual net profit (ANP) of the ORC as two conflict objective functions. Compare with existing process, the FPE-ORC system with working fluid R600 provides the highest exergy efficiency of 12.27%, with working fluid R600a leads to the best economic benefit of 6.43 E + 4 dollar/year. [ABSTRACT FROM AUTHOR]

Abstract: Although the idea of using a solar collector as the evaporator in the traditional heat pump cycle was first proposed in the year 1955, studies on the subject began in the late 70s. One of the keystones for obtaining sustainable development is also the use of exergy analysis. In this regard, the main objectives in doing the present study are twofold, namely (i) to review studies on direct-expansion solar-assisted heat pump systems (DX-SAHPs) and (ii) to present a mathematical model along with an illustrative example, which is used for heating an office space in Solar Energy Institute of Ege University, Izmir, Turkey, by floor heating with a DX-SAHP system. The system uses a 4m2 bare flat-plate collector as the evaporator, while the working fluid is chosen to be R-22. Water is heated by the heat pump and heat is delivered to the office space by floor heating. Exergy equations for the system are derived, while exergy calculations are made. The exergy efficiency values for the individual components of the DX-SAHP system are found to range from 10.74% to 88.87%. It is expected that this study will be very beneficial to everyone involved or interested in the exergetic design, analysis and performance assessment of DX-SAHPs. [Copyright &y& Elsevier]

This paper proposes a modified refrigeration cycle (MRC) with zeotropic mixture R290/R600a for refrigerator-freezer applications. In the MRC, the use of two parallel compressors enables the two evaporators to be operated at two proper evaporation temperatures, which reduces the irreversibility of evaporator heat transfer processes. Noted that a subcooler is installed between the two loops for improving the system performance. Moreover, the MRC applies a phase separator to ensure more low-boiling point refrigerant to go to the freezer evaporator for increasing the freezer evaporation pressure. Energy and exergy performances of MRC are investigated based on a thermodynamic model. The simulation results indicate that compared with the conventional refrigeration cycle (CRC), the COP and exergy efficiency of MRC obtain the same improvement of 30.4% at a fixed condensation temperature of 35 °C. In addition, from the viewpoint of exergy analysis, the high priority in need of improvement for the MRC is ordered as the compressors, condensers, expansion valves, two evaporators, subcooler and internal heat exchanger. Generally, applying the MRC could be an effective and practical method to enhance refrigerator-freezer energy efficiency. • A modified parallel compression refrigeration cycle with R290/R600a is proposed. • Influence of various operating parameters on performance of the cycle is investigated. • Irreversibility of each component and exergy efficiency of the cycle are examined. • The cycle outperforms the conventional cycle in both energetic and exergetic aspects. [ABSTRACT FROM AUTHOR]

• Medium-low grade waste heat recovery via ORC for stationary and on-board systems. • Irreversibility reduction through dual pressure heat recovery vapor generator. • Cycle optimum design for maximum energy and exergy cycle efficiency. • Heat transfer coefficients calculation and heat exchange surface assessment. • Benefit-to-cost analysis and heat exchanger cost assessment. The full exploitation of the upper thermal source is the key for enhanced energy performances of ORC-based units for medium and low-grade waste heat recovery. The adoption of a dual evaporation pressure cycle layout has the potential to reduce the heat exchange irreversibility at the evaporation section and to assure a higher net power available at the expander shaft, particularly in small scale units and in presence of upper thermal sources with a highly variable heat release characteristic. The adoption of the dual evaporation pressure technology to small scale recovery units represents a major technological breakthrough and an element of novelty, observing that, at present, the possibility to split the evaporation process in multiple pressure levels is considered mostly with reference to steam generators and boilers. The study investigates the potential energy and exergy advantage of a dual pressure heat recovery vapor generator, with respect to a base-single evaporation pressure layout, for a recovery unit with a mechanical power in the 1–15 kW range, for stationary (100 °C–150 °C hot source temperature) and on-board (350 °C–300 °C hot source temperature) applications. A dedicated optimization procedure allows the maximization of either the net power recovered or the cycle energy efficiency, dependently on the final application of the unit. The exergy efficiency of the heat recovery vapor generator is assessed and its dependence on the fluid characteristics and the main cycle variables discussed, along with the relationship between the energy and exergy gain for the enhanced heat exchange. A preliminary economic analysis provides a first indication of the financial merit of the dual evaporation pressure layout with respect to a base single evaporation pressure configuration. [ABSTRACT FROM AUTHOR]