Zeotropic Working Fluid Research Articles

Performance analysis and optimisation of waste heat recovery system based on zeotropic working fluid

As a new type of energy storage technology utilizing thermal energy, the Carnot battery is one of the most promising large-scale energy storage technologies due to its unlimited geographical conditions, simple structure, and high energy storage density. In this work, a thermodynamic model is established for a Carnot battery energy storage system that makes full use of waste heat resources, and the effects of the heat storage temperature, the components and mass fractions of the zeotropic working fluids on the various performances of the system are investigated. The temperature matching of the working fluids with different temperature glides in the heat exchangers are analyzed by using different mass fractions of R1234ze(E)/ R601a in heat pump and organic Rankin cycle systems, and the exergy flow charts and exergy loss of each component in the system are further investigated. The results show that the selection of the zeotropic working fluid with an appropriate temperature glide can effectively improve the system performance by improving the temperature matching degree and reducing the exergy loss in the heat transfer process. Compared with the evaporator, the temperature match of the condenser plays a more important role in the system performance. The use of R1234ze(E)/R601a in the heat pump improves the cofficient of performance by 4.46%-8.98% compared with that of pure R601a when the heat storage temperature increases from 110.0℃ to 140.0℃, and the use of zeotropic working fluid in the organic Rankin cycle also improves the performance by 8.12%-11.58%. For the power recovery of the whole pumped thermal energy storage system, the power-to-power efficiency improvement of the system using R1234ze(E)/R601a is 12.69%-20.11% and that using R1234yf/R601a is 12.46%-17.73% compared with the use of pure R601a. The power-to-power efficiency of R1234ze(E)/R601a (60/40) and R1234ze(E)/R601a (20/80) in the heat pump and organic Rankin cycle, respectively, are as high as 73.93% at a heat storage temperature of 130.0℃, which is 19.75% higher than the 61.74% for pure R601a.

Performance analysis of zeotropic organic Rankine cycle with a vapor-liquid injector

To improve the performance of small-scale organic Rankine cycle (ORC), an ORC with a vapor-liquid injector (IORC) using zeotropic mixture R601a/R245fa as working fluid is proposed. Parametrical investigations of the injector and system are carried out. The research results of injector show pure R601a has the highest injector pressure lift and exergy efficiency. The working fluids with higher temperature glide tend to have lower exergy efficiency. The increase of injector entrainment ratio and injector area ratio decreases pressure lift and exergy efficiency. The research results of system shows that the introduction of the zeotropic working fluid and injector can complement advantages and disadvantages of each other. Taking R601a/R245fa (60 %:40 %) as working fluid, IORC has higher net power than basic ORC (BORC) when pump efficiency is lower than 88 % and hot water temperature drop is less than 51 °C. There exists an injector entrainment ratio which makes net power maximum. Increasing injector area ratio decreases net power. Increasing injector entrainment ratio and decreasing injector area ratio reduce cooling water. Increasing injector entrainment ratio and injector area ratio makes heat exchanger economy worse.

Assessment of Ecofriendly Zeotropic Working Fluids in Organic Rankine Cycle for Renewable Energy Harvesting

The shift toward renewable energy has drawn significant attention to zeotropic mixtures in the organic Rankine cycle (ORC). However, synthetic zeotropic mixtures are detrimental to the environment due to high global warming potential. In this context, this study explores the potential of natural zeotropic binary mixtures as an alternative to synthetic zeotropic mixtures in a transcritical ORC system. The performance of two natural zeotropic mixtures and three synthetic zeotropic mixtures (hydrofluorocarbons, hydrofluoroolefins) are analyzed and compared using turbine inlet pressure and carbon dioxide (CO2) concentration as objective functions. The comprehensive thermodynamic analysis focuses on energy (first‐law) and exergy (second‐law) efficiencies, heat transfer, environmental performance, and economic aspects. The thermal and exergy efficiencies of the natural zeotropic mixture consistently outperform other mixtures by a maximum of 8% and 18%, respectively, for the conditions studied. The net power‐to‐environmental impact ratio of natural zeotropic mixture outweighs other zeotropic mixtures by more than 50%. The heat transfer analysis also favors natural zeotropic mixture at CO2 concentrations below 60% while maintaining cost parity with synthetic zeotropic mixtures. The results emphasize a holistic approach involving performance, heat transfer, environmental impact, and cost as parameters while choosing zeotropic mixtures for sustainable energy harvesting.

Experimental and simulation study on a zeotropic ORC system using R1234ze(E)/R245fa as working fluid

Organic Rankine Cycle (ORC) is a highly promising technology for converting heat to power, which has a widespread application in renewable energy utilization and waste heat recovery. Zeotropic working fluids are widely investigated to enhance the performance of ORC. In the present study, an experimental study on zeotropic mixture R1234ze(E)/R245fa is conducted under specified operating conditions and the operating behaviors of the ORC system are evaluated. An ORC simulation model (BP-ORC) based on a back propagation neural network and heat exchanger simulation modules is developed. The contribution factors that trigger the differences in heat transfer and system performance among the various working fluids are investigated. The operating behaviors of the heat exchangers and system are simulated for the working conditions beyond the experimental study. R1234ze(E)/R245fa (0.25:0.75 and 0.50:0.50) features a wider operating range of mass flowrate than R245fa due to their relatively lower density. The net power output of R1234ze(E)/R245fa (0.50:0.50) is 4.63 % higher than that of R245fa at a mass flow rate of 0.164 kg/s due to its relatively higher heat transfer performance. The variation of density and operating pressure plays a significant role in influencing the heat transfer behaviors and system performances.

Dual pressure condensation heating high temperature heat pump using eco-friendly working fluid mixtures for industrial heating processes: 4E analysis

To make better use of waste energy for the industrial heating processes, dual pressure condensation heating high temperature heat pump system (DPS) is proposed, to achieve the purpose of step heating. Meantime, environmental-friendly working fluid hydrocarbons are selected as the components of the mixtures. The energy, exergy, environmental and economic (4E) analysis models are established, and the system performance is optimized, compared with single-stage (SS) system and fossil fuel-fired boilers. There is an optimal intermediate water temperature corresponding to the highest system energy efficiency. The maximum COP of 5.29 is achieved when R600a/R601a (50/50) is adopted, improved by 18.23% and 24.18% compared with DPS and SS systems using pure working fluid. By using zeotropic working fluid, the irreversible heat transfer loss can be significantly reduced. The overall exergy loss with R600a/R601a (50/50) is 21.68–41.27% and 12.26–16.69% lower than pure SS and pure DPS systems, respectively. In terms of environmental and economic aspects, DPS with zeotropic working fluid shows excellent performance. In comparison with boiler, pure DPS and pure SS system, the reduction of carbon emissions through the whole lifetime is 81.22%, 15.35% and 20.04%, and the life cycle cost is decreased by 93.91%, 9.70–15.05%, and 27.89–38.07%.

Unlocking the multi-mode energy-saving potential of a novel integrated thermal management system for range-extended electric vehicle

The thermal management system of range-extended electric vehicles (REEV) is essential for energy saving. There is a lack of modification methods for enhancing its performance under multiple operating modes. Herein, we present a combined cooling and power cycle-based basic integrated thermal management system (ITMS) for the REEV and propose a generalised performance improvement approach adapted to multiple operating modes. Composed of a waste heat recovery and a cooling subsystem, the basic ITMS can achieve heat recovery and thermal management of the range extender's coolant and recirculated exhaust gas and cools the passenger compartment and battery packs. The factors limiting the basic ITMS are identified through parametric analysis: the low evaporative pressures constrained by the low-temperature waste heat (engine coolant) and cooling target (passenger compartment). In order to unlock the multi-mode potential of the ITMS, we introduce the liquid-vapour separation condenser to separate the working fluid (zeotropic mixture) into two mixtures with different volatility. The high-volatility mixture is utilised to absorb the low-temperature engine coolant's waste heat and generate the low-temperature cooling energy for the passenger compartment, lifting evaporative pressures while keeping the condensation pressure unchanged. Then, a multi-mode comparison verifies the modified system. When the vehicle operates with the range extender on and with/without cooling demand, the vehicle fuel consumption rate can be reduced by 6.6% and up to 12.5%, respectively. When the vehicle runs in pure electric mode and with cooling demand, the ITMS's electrical consumption can be lowered by 7.4%. Accordingly, matching the volatility of the zeotropic working fluid and the thermal management objects enables REEV's ITMS to fulfil substantial energy savings in multiple operating modes.

Exergoeconomic and environmental analyses of a geothermal-powered tri-generation system: A study of CO2 emission reduction

A geothermal-powered tri-generation system is presented and discussed from thermodynamic, exergoeconomic, payback period, extended-environmental, and exergoenvironmental perspectives. The designed system consists of an organic flash cycle assisted by a two-phase ejector and a vapor compression cycle that utilizes a zeotropic working fluid of Isobutane/Pentane. To further recover waste heat, an electrolyzer unit is utilized as a subsystem for producing H2. All the system outputs except for the exergoenvironmental index and exergoeconomic factor reach the highest point when the mass fraction of Pentane increases. According to a parametric study, the greatest variations in system products are related to changes in the flash tank temperature. Furthermore, the system outputs indicate a non-linear relationship with the mass fraction of Pentane. The temperature of evaporators has a substantial influence on the system's cooling capacity. Meanwhile, the remaining output parameters remain steady or show minor changes. By increasing the flash tank temperature, the costs related to electricity, cooling, and H2 all decreased before gradually increasing. The two-phase ejector has the highest exergy destruction rate because of the energy lost in the mixing process.

Thermal design and zeotropic working fluids mixture selection optimization for a solar waste heat driven combined cooling and power system

Considering the limitation of fossil fuel resources and their environmental effects, the use of renewable energies is increasing. In the current research, a combined cooling and power production (CCPP) system is investigated, the energy source of which is solar energy. Solar energy absorbs by solar flat plate collectors (SFPC). The system produces power with the help of an organic Rankine cycle (ORC). An ejector refrigeration cycle (ERC) system is considered to provide cooling capacity. The motive flow is supplied from the expander extraction in the ERC system. Various working fluids have been applied so far for the ORC-ERC cogeneration system. This research investigates the effect of using two working fluids R-11 and R-2545fa, and the zeotropic mixtures obtained by mixing these two fluids. A multiobjective optimization process is considered to select the appropriate working fluid. In the optimization design process, the goal is to minimize the total cost rate (TCR) and maximize the exergy efficiency of the system. The design variables are the quantity of SFPC, heat recovery vapor generator (HRVG) pressure, ejector motive flow pressure, evaporator pressure, condenser pressure, and entertainment ratio. Finally, it is observed that using zeotropic mixtures obtained from these two refrigerants has a better result than using pure refrigerants. Finally, it is observed that the best performance is achieved when R-11 and R245fa are mixed with a ratio of 80 to 20%, respectively and led to 8.5% improvement in exergy efficiency, while the increase in TCR is only 1.5%.

Comprehensive analysis and multi-objective optimization of power and cooling production system based on a flash-binary geothermal system

The sustainable and environmentally-benign nature of geothermal energy motivates the current investigation to design a cogeneration of power and cooling system. The designed system consists of a double-flash binary system with an organic Rankine cycle and ejector refrigeration cycle integration as the waste heat recovery system. The subsystem's performance is enhanced through the zeotropic working fluid implementation. The energy, exergy, and exergo-economic assessments were utilized to compare two zeotropic mixtures' performances and select an appropriate working fluid. This comparison is carried out by comprehensive sensitivity analysis to study their performance under variable operational conditions. The results reveal that the Pentane-Isohexane has higher performance leading to 1.9 MW of net power and 290.15 kW of cooling load generation. Hence, the total exergetic efficiency and payback period are obtained to be 58.33% and 6.70 years. Considering the energy/economic optimization scenario enhances the cooling load generation to 574 kW and reduces the net power to 1.85 kW, while the exergy/economic scenario increases the net power production to 1.99 MW and declines the cooling load. By considering the overall performance indexes, the exergy/economic scenario with 6.56 years payback period provides a higher performance and the best optimization scenario.

Performance Improvement of OTEC-ORC and Turbine Based on Binary Zeotropic Working Fluid

In this paper, the composition of binary nonazeotropic working fluids is explored from the perspective of improving OTEC-ORC efficiency, and the turbine is designed to accommodate with the working fluid. It is found that the OTEC-ORC using a R152a/R32 mixture as the working fluid is significantly higher than the OTEC-ORC thermal efficiency and system efficiency of the pure NH3, and the optimal composition of the mixed working fluid R152a/R32 is determined to be 85 : 15 with the thermal efficiency and the system efficiency of 2.8% and 1.7%, respectively, improving by 35.7% and 151.2% compared to the NH3 ORC. According to the determined working fluid, a one-dimensional (1-D) design and CFD simulation analysis simulation are carried out on the turbine. The 1-D calculation results are in good agreement with the three-dimensional (3-D) results. At the design point, the turbine output is 83.84 kW, and the isentropic efficiency is 87.53%. At the off-design point, turbines have better off-design performance, indicating that the designed turbine also has good adaptability.

Experimental investigation of condensation heat transfer of zeotropic refrigerant/oil mixtures in plate heat exchanger

Plate heat exchanger (PHE) has been wildly used as the condenser of the organic Rankine cycle (ORC). As a potential zeotropic working fluid of ORC system, it is of great significance to study the condensation heat transfer of the mixture of R245fa/R141b and lubricating oil in PHE for the development of ORC system. In this paper, an experimental study on the condensation heat transfer coefficient (HTC) of a mixture of R245fa/R141b (0.5/0.5 by mass) and polyester oil (POE) in a plate heat exchanger (PHE) has been carried out. In addition, the results were compared with those of R245fa and R141b. The parameters in the experiment range from 0 to 0.9 for vapor quality, 0%–4% for oil concentration and 20 to 60 (kg·m−2·s−1) for mass flux. The results showed a 20% reduction in HTC for R245fa/R141b with 4% oil concentration compared to oil-free refrigerant. In addition, the HTC of R245fa/R141b-POE mixture was between that of R245fa/POE and R141b/POE. The oil enhancement factor of different refrigerant/POE mixtures was less than 1.0, which could be well predicted by the Eckels correlation with a maximum mean absolute deviation (MAD) of 13.4%. The product of the predicted enhance factor and HTC predicted by the Jung et al. correlation agreed well with the tested HTC of different refrigerant/POE mixtures in the PHE. The maximum MAD of different refrigerant/POE mixtures was 20.6%, and 96.3% of predicted results were within ±30% deviation. A new correlation with a maximum MAD of 15% was proposed, which predicted the condensed HTC of refrigerant/POE mixture by using its physical properties.

Power, cooling, freshwater, and hydrogen production system from a new integrated system working with the zeotropic mixture, using a flash-binary geothermal system

The current paper proposes a new hybrid system based on a binary-geothermal system to generate power, cooling capacity, freshwater, and hydrogen. This system includes an internal integration of the organic Rankine cycle and ejector refrigeration cycle with zeotropic working fluids, proton exchange membrane electrolyzer, and reverse osmosis desalination unit. The system is analyzed by developing a precise model in the Matlab software, and then a multi-objective grey wolf optimization is employed to optimize the proposed system performance. The net present value, payback period, and sum unit cost of products are considered the system's economic performance criteria to study the system's feasibility for investment. Results indicate that the Isobutene-R114 provides the best net output power, and the R12-R114 combination has the best cooling performance. Also, the R12-R114 reports the best overall performance as the organic Rankine cycle working fluid. Based on optimization results, the exergy and thermal efficiency reached 17.84% and 34.24%, respectively. The system could provide 856.06 kW net output power, 2410.54 kW cooling capacity, 0.743 kg/h hydrogen, and 40.22 kg/s freshwater with a sum unit cost of 25.5 $.GJ−1, and the total profit and payback period of 6.82 $M and 3.76 years.

Thermodynamic analysis and evaluation of a novel composition adjustable Carnot battery under variable operating scenarios

Discontinuity of production resulting in supply imbalance is the main problem hindering renewable energy development. Carnot battery (CB) is a recently emerged large-scale power storage technology to solve the supply imbalance of renewable energy power generation. Improving the component performance of CB under variable operating conditions is crucial to guarantee the life-span performance of the CB. In the present study, a composition-adjustable CB is proposed. The application and optimization of the zeotropic mixture improved the heat match in the heat transfer component. The composition adjustment is conducted to relieve the excess operating parameter deviation of mechanical components. Thermodynamic analysis and optimization models are formulated, and a genetic algorithm is applied to solve the models. Case studies under several operating scenarios are conducted to verify the superiority of the proposed composition-adjustable CB over a conventional CB and a zeotropic CB. Results show that under a benchmark operating scenario, compared with conventional CB, the round-trip efficiency and exergy efficiency of CB using zeotropic working fluid are improved by 22.40% and 16.78%. Considering the limitation of the mechanical components under variable operating scenarios, composition-adjustable CB has the largest operating range. Three CBs demonstrate different operating strategies to maintain the flexible and efficient operation of the mechanical components, among which the operating performance of composition-adjustable CB is the best. During the discharging process, the exergy efficiency of the expander in composition-adjustable CB is up to 18.19% and 0.94% higher than that of zeotropic CB and conventional CB, respectively. Overall, compared with conventional CB and zeotropic CB under variable operating scenarios, the average round-trip efficiency of composition-adjustable CB is improved by 56.34 % and 26.98 %, respectively; the average exergy efficiency of composition-adjustable CB is improved by 51.26 % and 25.21 %, respectively.

Proposal and multi-aspect assessment of a novel solar-based trigeneration system; investigation of zeotropic mixture’s utilization

• Proposal of a novel cogeneration of power, cooling, and heating using solar energy. • Utilization of zeotropic mixtures for efficiency improvement. • Evaluation of the system performance from the energy and exergy viewpoints. • Highest exergy and energy efficiencies of 20.26 % and 15.81 % . In this study, a novel power, cooling, and heating cogeneration system was devised. In the proposed system, parabolic trough solar collectors were used as the primary energy source. Also, the zeotropic mixtures were employed as the working fluid of the dual-pressure organic Rankine and ejector refrigeration cycles for efficiency improvement. The system was analyzed from the energy and exergy viewpoints in MATLAB software using library data of Refprop and Coolprop toolboxes for obtaining the thermodynamic properties of working fluids. The best performance of the system was obtained under some circumstances, including a constant rate of solar radiation (DNI) as 1000 W · m - 2 and using 410 solar collectors with an area of 28976 m 2 , and employing Pentane ( 0.5 )/Trans-2-Butene ( 0.5 ) and Isobutane ( 0.2 )/Isopentane ( 0.8 ) as the zeotropic working fluids in the dual-pressure organic Rankine cycle and the ejector refrigeration cycle. In these conditions, the electrical power, cooling load, and heating capacity were calculated by 4082.6 k W , 51.52 k W , and 1 616.4 k W . Also, total exergy loss of the system was obtained by 22.19 M W , and the highest exergy and energy efficiencies were computed by 20.26 % and 15.81 % , respectively.

Economic, exergoeconomic analyses of a novel compressed air energy storage-based cogeneration

In this paper, the performance of a compressed air energy storage system is improved by an ejector refrigeration subsystem with zeotropic working fluid. According to the results, Pentane/Trans-2-Butane is found as the best zeotropic mixture. To obtain the proposed system's optimum performance, an optimization analysis is conducted based on multi-objective particle swarm optimization algorithm. Based on optimization results, the optimum round trip efficiency and exergetic round trip efficiency are 52.04% and 58.70%, respectively, and the exergy destruction rate reduces by about 8.3% at charging time and 2% at grid peak time. Also, the coefficient of performance for the ejector refrigeration subsystem is improved from 0.22 at the base case to 0.25 at the optimum conditions. Moreover, economic analysis is considered to analyze the profitability and availability of the system for possible establishment. Therefore, when the selling prices determined for the power in the charging and discharging periods and cooling load are respectively taken into account 0.022 $/kWh, 0.20 $/kWh, and 0.15 $/kWh, the system has good economic feasibility and reaches the payback period of 5.24 years. In this conditions, a profitability of 2.5 $M can be obtained at the end of system lifetime.

Thermal decomposition and interaction mechanism of HFC-227ea/n-hexane as a zeotropic working fluid for organic Rankine cycle

Organic Rankine Cycle (ORC) is an effectively technology for the utilization of industrial waste heat and renewable energy. Zeotropic working fluids are more attractive than pure working fluids due to their lower exergy losses, higher cycle efficiencies and higher work outputs. The thermal stability is the major limitation factor for the selection of working fluid in the high temperature ORCs. This paper investigates the thermal decomposition and interaction mechanism of HFC-227ea/n-hexane as a zeotropic working fluid by using ReaxFF reactive molecular dynamic simulations and density functional theory calculations. The thermal decomposition process, the effects of temperature and HFC-227ea to n-hexane ratio on the thermal decomposition of HFC-227ea/n-hexane zeotropic working fluid, and the interaction between HFC-227ea to n-hexane for the thermal stability of zeotropic working fluid were investigated. The results showed that the hydrogen bond formed between HFC-227ea and n-hexane in HFC-227ea/n-hexane zeotropic working fluid improved the thermal stability of n-hexane and weakened the thermal stability of HFC-227ea. Therefore, the thermal stability of the HFC-227ea/n-hexane zeotropic working fluid is better than that of pure n-hexane and weaker than that of pure HFC-227ea.

Parallel and in-series arrangements of zeotropic dual-pressure Organic Rankine Cycle (ORC) for low-grade waste heat recovery

Due to the recent interest in renewable energy and waste heat for power generation, organic Rankine cycle (ORC) has drawn considerable attention. By applying a dual-pressure evaporation strategy, the exergy loss in the evaporators can be reduced significantly, resulting in an enhanced system performance. In this study, detailed modelling analyses have been conducted to evaluate the effect of zeotropic working fluids on the performance of two dual-pressure ORC (DPORC) arrangements, namely, DPORC-P (parallel) and DPORC-S (in-series), where the working fluid pair R245fa and R152a has been selected to form a representative zeotropic mixture. It has been found that as a zeotropic mixture is used, both systems show improved cycle net power outputs. Interestingly, the highest power outputs occur at mass fractions that result in matching temperature profiles between the hot and cold fluids in the condenser. At a heat source temperature of 120 °C, a DPORC-S always has a greater net power output regardless of the mass fraction of the zeotropic mixture; as heat source temperature reduces, the difference of power output between the two systems tends to drop: for a heat source temperature of 90 °C, a DPORC-P has a better performance as the mixture mass fraction is between 0.4 and 0.9. The influence of zeotropic fluids to the heat transfer of the condenser has also been investigated and it indicates that a significantly larger heat transfer area is required for a zeotropic fluid; based on a fixed heat transfer area, the performance enhancement of a zeotropic system is only seen as the condenser heat transfer area is considerably large.

Thermodynamic and economic sensitivity analyses of a geothermal-based trigeneration system; performance enhancement through determining the best zeotropic working fluid

In this paper, a novel geothermal-based trigeneration system producing electricity, cooling, and freshwater is devised. The whole setup comprises a flash-binary geothermal cycle, an ejector refrigeration cycle, a dual-pressure organic Rankine cycle, and a reverse osmosis unit. In the dual-pressure organic Rankine cycle, the utilization of the zeotropic mixture is examined for performance improvement. The overall system is analyzed from energy, exergy, and economic viewpoints. Likewise, the system is inspected by the thermodynamic and economic sensitivity analyses based on the best working fluid. By specifying the Butene/Isopentane zeotropic mixture as the best working fluid, it is revealed that from 10932kW of the input exergy to the system, 5561.74kW is destructed within different components. In this way, the recovered exergy rate by net output electricity is equal to 3633.33kW, by cooling load is 1663.44kW, and by freshwater is 104kW. Also, the optimum net output power and total energy and exergy efficiencies were obtained to be 3.65 MW, 25.06%, and 35.06%, correspondingly. In this situation, the sum unit cost of products and payback period of the system were 14.50 $.GJ−1 and 3.66 years, respectively.

Zeotropic working fluid selection for an organic Rankine cycle bottoming with a marine engine

Organic Rankine cycle (ORC) is an effective approach for low-grade energy utilization. It is important to improve the efficiency of an ORC when the heat source temperature varies. In this study, a method of selecting zeotropic mixture for a bottoming ORC with changeable heat source temperature is presented. The effects of the operation conditions of the marine engine and the ambient temperature are investigated. First, the optimal performances of the ORC using 40 pure working fluids are determined and compared. Then, two zeotropic mixtures benzene/m-xylene and cyclopentane/toluene are selected and the mechanism of temperature match with the heat source and sink is explored. Finally, the performance improvement with benzene/m-xylene using the composition adjustment method is evaluated. The results indicate that the suitable pure working fluids are isopentane and R245ca for a low exhaust temperature while toluene and m-xylene are the best when the exhaust temperature is high. Using the zeotropic mixtures benzene/m-xylene and cyclopentane/toluene can obtain a high performance over the operation range of the marine engine. When the exhaust temperature is 225 °C, the net power and exergy efficiency of benzene/m-xylene are improved by 6.9%–21.9% and 6.5%–22.0%, respectively, compared with the pure fluids benzene and m-xylene. When the exhaust temperature increases to 380 °C, these improvements decrease to 1.9%–6.8%. If a zeotropic mixture is used, the critical temperature of the component with a high-boiling point should be close to the maximum operation temperature of the heat source, and the temperature glide should first match with the temperature increase of the heat sink. If the heat sink temperature is fixed, it is impossible to enhance the ORC performance using the composition adjustment method. However, the composition adjustment method is effective when the temperature of the heat sink varies with the ambient temperature. The net power and exergy efficiency of the ORC are improved by up to 21.9% and 22% in winter using benzene/m-xylene. However, these improvements are less than 6.8% in summer.

Energy, exergy, and exergoeconomic analyses and optimization of a novel thermal and compressed air energy storage integrated with a dual-pressure organic Rankine cycle and ejector refrigeration cycle

The current work analyzes an innovative thermal and compressed air energy storage cycle integrated with a dual-pressure organic Rankine cycle combined with an ejector refrigeration cycle for power and cooling cogeneration. The bottoming cycle employs zeotropic mixtures, including Pentane (0.5)/Butane (0.5) and Pentane (0.5)/Trans-2-butene (0.5), as working fluids for performance improvement. The system assessment includes three crucial viewpoints: energy, exergy, and exergoeconomic. A parametric study is performed to examine the effects of some key parameters on the performance of the devised system. Also, a multi-objective optimization program based on the MOPSO algorithm is conducted to find an optimal trade-off between thermodynamic performance and economic attractiveness of the system considering two decision-making techniques of TOPSIS and LINMAP. The results showed that the sum unit cost of the product has less value for Pentane (0.5)/Trans-2-butene (0.5). Also, it is found that the performance of Pentane (0.5)/Trans-2-butene (0.5) as the zeotropic working fluid is better. Therefore, this fluid is considered as the working fluid for the optimization procedure. Besides, based on the achieved results, the optimum round trip efficiency and sum unit cost of the product are 54.25% and 13.51 $.GJ−1, respectively.