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An adjustable ejector with a needle is deemed as an effective device to improve the performance of the transcritical CO2 refrigeration cycle with a wide operating conditions. In this paper, a homogeneous CFD model is built up to compare the performance of the adjustable and fixed ejectors with the same key structural sizes. By validating the numerical results with the experimental data, the k-e RNG and k-e Realizable are considered to predict the performance of the CO2 ejector well. Furthermore, an exergy analysis model is proposed to obtain the exergy fluxes of the primary and secondary flows are obtained, respectively. The results discover that the main exergy transfer (interaction between the primary and secondary flows) locates in the suction chamber. Meanwhile, the higher exergy loss is observed in the suction chamber of the adjustable ejector due to flow separation along the needle and higher viscous dissipation of oblique shock wave, which results in 5%–11% lower entrainment ratio than that of the fixed ejector. However, the higher velocity in the fixed ejector results in higher friction of the wall and more intense flow separation in the diffuser which causes higher exergy loss in the mixer and diffuser. Accordingly, the exergy efficiency of the adjustable ejector is only 0.5% lower than that of the fixed ejector. In spite of the special case in this paper, the adjustable ejector is considered to be able to achieve a similar exergy efficiency with the fixed ejector.

The main objective of this investigation is to introduce an economic and feasible hybrid energy system to provide the required load for a household in Rayen, Iran. The case study is a building with 20 families. The power consumption of a family at a peak is considered by 4 kW. So, this combined system must provide a power of 80 kW. First a hybrid organic Rankine cycle is proposed and assessed by exergy and exergoeconomic methods. The results of exergy analysis indicate the overall exergy efficiency of the system is 7.29%. As well as, the greatest exergy destruction is related to the photovoltaic panels with a value of 337.16 kJ. The outcomes of the exergoeconomic assessment showed that, the highest and lowest capital investment cost rate belong to the photovoltaic panels (54233 $/year) and condenser (7092 $/year), respectively. Also, the product cost rate is calculated by 5.2 million $/year. In continue, to identify the key parameters which influence on the total performance of the ORC system, a parametric analysis is done. Because of the hybrid organic Rankine cycle has a high amount of the cost of energy, seven renewable hybrid energy systems are proposed and modeled by HOMER software. The results show the optimum energy system for this residential area is the hybrid PV – wind-diesel – battery. This configuration has a net positive cost of 268,592 $ and a cost of energy of 0.197 $/kWh. At the end of this study, to find the impact of the variations of the fuel cost and peak load on system performance, a parametric analysis was carried out.

A heat recovery system is employed for power generation from a PEM fuel cell’s waste heat. The proposed system involves the parallel organic Rankine cycle for utilizing the provided heat and hydrogen boil-off gas (BOG) stream as a heat sink for the cycle. Also, this stream generates power by using an expander and prepares some chilled water that enhances system performance. The PEM fuel cell as the major component of the system is modeled and then the parallel two-stage ORC (PTORC) and BOG streams are analyzed in points of the energy and exergy view. Exergoeconomic concept is applied to evaluate the economic view of the system besides energy and exergy analyses. Also, a sensitivity analysis is performed by system key parameters which provided some valuable information to comprehend the performance of the overall system. The results show that the proposed system can generate 1353 kW power. Exergoeconomic factor, energy efficiency and exergy efficiency of the overall system are computed to be 26.21%, 58.15%, and 36.64%, respectively. Also, it is concluded that the higher current density and lower operating temperature, will raise the total cost rate.

The organic Rankine cycle has been widely explored for energy recovery from several heat sources. In this paper, the maximization of the energy recovery of the exhaust gases from the General Electric LM 2500 gas turbines in a floating production offloading unit is studied in order to meet the demands of heat (pressurized hot water) and electricity over oil production lifetime. An off-design model of the system is developed to check the viability of an organic Rankine cycle under dynamic operating conditions. Energy and exergy analysis of the proposed system are conducted to determine main irreversibilities and performance characteristics of the system and, finally, the economic benefits of the energy recovery system application are discussed. The organic Rankine cycle is very flexible in the heat recovery in dynamic demand conditions, contributing up to 20.3% in electricity generation, which causes an increase in overall system efficiency of up to 11.3% and up to 18.3% in the utilization factor, as well as an average reduction of 22.0% in carbon dioxide emissions in the floating production offloading unit electricity generation process. The exergy efficiency of the system reaches 55.8% and the heat recovery devices are the most irreversible equipment in organic Rankine cycle, contributing up to 68% of the total exergy destroyed. The economic analysis demonstrated the attractiveness of the organic Rankine cycle implementation, allowing a net present value to Brazil's current economic scenario of up to USD 16.8 million.

This work introduces and develops the concepts of solar exergoeconomic and exergoenvironmental maps for photovoltaic systems. These maps are developed to complement the information provided by solar exergy maps for recognizing the most appropriate sites for hosting photovoltaic power plants. A detailed case study is carried out to demonstrate how the proposed approaches can be practically applied to promote solar photovoltaic systems. More specifically, the exergoeconomic and exergoenvironmental performances of a 100 kW grid-connected photovoltaic plant are assessed for several Iranian cities over the year based on actual climatic, economic, and environmental impact data. The spatio-temporal solar maps for unit exergoeconomic cost and unit exergoenvironmental impact of electricity generation are then developed for the investigated climatic conditions for the first time. In order to demonstrate the suitability and reliability of the developed maps, their interoperations are assessed and compared to those for exergy efficiency. The results show that solar exergoeconomic and exergoenvironmental maps provide more valuable information on the performance of solar photovoltaic systems than exergy efficiency maps, demonstrating their robustness for optimum site selection and plant sizing. In addition, the exergy efficiency maps may result in inappropriate site selection of photovoltaic solar farms. The central, south, southeast, and some west parts of Iran are the most suitable locations for implementing photovoltaic power fields from exergoeconomic and exergoenvironmental viewpoints. The developed approaches can also be used for locating and sizing other renewable energy systems under different climatic conditions.

In this study, a geothermal power plant endowed with actual operational conditions and its equipment are evaluated using exergoenvironmental analysis from the perspective of environmental impact. Environmental impacts related to equipment (including construction, operation/maintenance and disposal), exergy destruction and pollution formation are taken into consideration. Moreover, effects of ambient temperature and brine input temperature with respect to environmental impact factors of the system are also discussed. Though this analysis, relative difference of specific environmental impacts, exergoenvironmental factor and total environmental impact are determined as 122% and 2.5% and 2285 Pts/h, respectively. The results of the study show that 98% of total environmental impact for the geothermal power plant is the cause of exergy destruction of the equipment involved. For this reason, improvement of exergetic efficiency for equipment should be considered rather than construction, operation/maintenance and disposal changes of system equipment. Hence, it is probably possible to have a higher capacity plant by getting a better condenser performance, as well as strengthening the vaporizers and the pumps. Besides, approximately 44 Pts/h of non-condensable gas-NCG (CO2 mostly) released from vaporizer to atmosphere caused environmental impact of the system to be measured as high environmental impact value of electricity equal to 0.108 Pts/kWh. In conclusion, conditions during which the ambient temperature decreases and brine input temperature increases, the system’s environmental impacts concurrently decrease. This study is expected to serve as a guidework for researchers involved in environmental impacts of geothermal power plants and improvement of the plants in terms of environmental impact.

In this research, energy level based exergoeconomic evaluations are performed for a novel biomass and natural gas fired polygeneration system of electricity, hot water, chilled water and hydrogen production. The proposed system mainly consists of a biomass gasifier, a proton exchange membrane (PEM) electrolyzer, a gas turbine cycle (GT), an absorption chiller, and a ground source heat pump cycle. Conventional and energy level based exergoeconomic performances of the proposed system are compared; related exergy and economic analysis are also performed. In addition, the variations in unit exergy cost of products (electricity, hot water, chilled water and hydrogen) are studied under economic factors. The results show that energy and exergy efficiency of the electrolyzer and the proposed system decrease with the increasing current density of the PEM electrolyzer. The unit exergy cost of electricity and hydrogen are 5.24 $/GJ and 20.41 $/GJ under the energy level based exergoeconomic method, respectively, which are higher than that under the conventional exergoeconomic method (electricity: 4.38 $/GJ, hydrogen: 19.00 $/GJ), while the unit exergy cost of hot water and chilled water under the energy level based exergoeconomic method are lower than that under the conventional exergoeconomic method. Moreover, the exergoeconomic factor and relative cost difference of the system equipment also show distinctions under the conventional and energy level based exergoeconomic methods. The presented polygeneration system is a promising technology to utilize renewable energy and improve the flexibility of the integrated system; and the energy level based exergoeconomic method shows certain rationality and feasibility in the system analysis.

Due to the high level of pollutant emissions from traditional marine diesel engines, Liquefied Natural Gas (LNG) as clean energy is becoming a better choice for main engines to replace the traditional fuels. Meanwhile, in order to improve the energy efficiency of the marine power system, the Organic Rankine Cycle (ORC) has been regarded as the most suitable solution to recover the waste heat for the power generation of vessels. In this paper, both the waste heat of the main engine and the cold energy of LNG have been fully considered, and a novel triple ORC process has been proposed for the waste heat and cold energy recovery of LNG-fueled vessels. It adopts the exhaust gas of the main engine and the cooling water from the engine jacket as heat sources, and uses the cold energy of LNG and the sea water as cold sources. Based on the 15 optional working fluid conditions, the heat source utilization rate, system exergy efficiency, net output power, and system cost are, respectively, combined as two objectives, and the multi-objective adaptive firefly algorithm is used to optimize the thermodynamic performance of the system. The optimization results of different heat and cold sources as well as the design parameters have been discussed. Finally, the system's exergy loss has been analyzed to make suggestions for further improvement. The results show that this novel ORC system can better meet the energy recovery requirements of LNG-fueled vessels, with higher net output power, lower cost, and greater energy recovery efficiency. The largest exergy loss of the system exists in the condensers of the stages 2 and 3, and the expanders in the various stages. Therefore, subsequent cooling energy recovery and the use of Stirling engines can be considered to further improve the system efficiency. National Research Foundation (NRF) The authors acknowledge the financial support provided by the Fundamental Research Funds for the Central Universities (No. 3132018248), the National Natural Science Foundation of China (Nos. 51906026, 51876019, 51779026), the Innovation Talent Support Program of Liaoning Province (LR2017048), the Transportation Industry High-Level Talent Training Program, the National Research Foundation of Singapore, the Swedish Research Council and the Swedish National Energy Agency.

An integrated system for the simultaneous production of electricity and fresh water is proposed based on a solid oxide fuel cell (SOFC). In this system, a Kalina cycle is utilized to recover waste heat from the SOFC stack. Furthermore, a thermoelectric generator is employed to recover the heat dissipated in the Kalina condenser. In the proposed configuration, the energy required for reverse osmosis desalination can be supplied by a Kalina cycle and a thermoelectric generator. The system uses methane as its primary fuel. Electrochemical equations for the fuel cell are considered, as are thermodynamic and exergy-economic relations for the components of the system. The effects on the performance of the proposed hybrid system of variations in design parameters such as current density, SOFC inlet temperature, fuel utilization factor, inlet pressure of the Kalina cycle turbine and concentration of water-ammonia solution in the Kalina cycle are examined. The SOFC stack is seen to make the highest contribution to the total exergy destruction of the system. To strive simultaneously for maximum efficiency and minimum total cost, optimization is carried out using a genetic algorithm. The total optimum point of the system is the trade-off between the optimization objectives. At this point, the net electrical power production is about 1.3 MW and the production rate of fresh water reaches 226 m3/day, while the exergy efficiency and total cost rate are 54% and 36.8 $/hr, respectively.

Thermal energy storage is essential whenever there is a mismatch between the supply and consumption of energy. When the air conditioning system is applied in transport, a great challenge occurred due to frequent fluctuations of cooling load which causes comfort degradation and even healthy concern. In this study, we evaluate charging performance including charging time, transient charging rate, overall energetic and exegetic efficiency of the designed device under different operating conditions. Evolutions of PCM temperature with processing time both in the axial and radial directions are also investigated. What’s more, the dynamic exergy efficiency is studied for the first time to assess the optimal charging depth and charging time. The experimental results show that the charging time can be reduced by 49% and 28% by dropping the charging temperature from 15 to 11 °C and increasing the inlet air velocity from 0.70 to 1.20 m/s. The designed energy storage device has flexible charging rates with the maximum value of 1.3 kJ/s, high thermal efficiencies at 87% and overall exergy efficiencies up to 70%. Both the drop of the inlet air temperature and the rise of the inlet air velocity contribute to the energy efficiency. The analysis of dynamic exergy efficiency shows that the maximum exergy efficiency can reach around 90% with the optimal charging time varying from 10 to 52 min. The corresponding optimal charging depth varies between 46% and 58% under the studied conditions. These findings could provide guidelines for the design and optimization of PCM energy storage device specifically when it is used in the transport field.

An innovative bi-evaporator electricity/cooling cogeneration system fueled by biogas is introduced. The plausibility of the introduced integrated power plant is examined from thermodynamic and economic vantage points. Later, single- and multi-objective optimization of the reckoned system are achieved by selecting appropriate parameters as decision variables and thermal and exergy efficiencies and total unit product cost (TUPC) of the system as objective functions. Four optimum modes of thermal efficiency optimum design (TEOD), exergy efficiency optimum design (EEOD), cost optimum design (COD), and multi-objective optimum design (MOOD) are selected for optimization and the attained results are compared with each other. In MOOD mode, it was found that the recommended system could generate optimum overall cooling load and net electricity of 641.7 kW and 1137 kW, respectively, achieving thermal efficiency of 62.69%, exergy efficiency of 38.75%, and TUPC of 7.75 $/GJ. It was substantiated that integrating the introduced cogeneration system with biogas-fueled gas turbine (GT) cycle could improve the thermal and exergy efficiencies up to 67.33% and 19.15% in the base mode and 77.84% and 15.94% in the optimum mode (MOOD mode), respectively. In MOOD mode, the TUPC of the integrated system is around 32.69% lower than that value in the GT cycle. The outcomes of the 2nd law evaluation portrayed that among all components, the combustion chamber attributes as the utmost destructive part of the system, followed by the vapor generator. Also, to examine how the introduced set-up reacts to any external fluctuations, a thoroughgoing sensitivity examination based upon given parameters was fulfilled.

This paper proposes a solar-assisted hybrid combined cooling, heating and power (CCHP) system that consists of an internal combustion engine, solar heat collectors, an absorption heat pump, a heat exchanger, and a thermal storage tank. On the basis of thermodynamic modelling and validation, the hybrid system was investigated from its energy, exergy, exergo-economic and exergo-environmental performances. The heat storage ratio and supplemental heat ratio were defined to consider the dynamic off-design operations and evaluate the contributions of thermal storage and supplement under the static design conditions, whose impacts on system efficiency and unit cost of products were discussed. For a specific case study, the energy and exergy analyses with the Sankey diagrams indicated that the hybrid system achieves annual energy efficiency of 76.3% and exergy efficiency of 22.4%. The unit costs of products were determined using exergo-economic analysis based on energy level, and the costs of products including and excluding carbon dioxide emission cost were compared. Compared to the conventional CCHP system without solar energy, the hybrid system saves 11.3% of natural gas to reduce carbon dioxide emission and shortens the capital payback period by 1 year.

In this study, a novel power generation cycle is presented which is a combination of the modified Kalina Cycle and the Gas Turbine-Module Helium Reactor system. The rejected heat from the GT-MHR cycle is supplied to drive the modified KC. Energy and exergy analysis is conducted applying Engineering Equation Solver (EES) software. Furthermore, concerning the mathematical modeling, the parametric study is implemented to assess the effect of the key parameters on the performance criteria of the GT-MHR with Kalina cycle. Additionally, the thermal efficiency of the system is optimized using Genetic algorithm. The result of the optimization demonstrates 53.2% for the thermal efficiency under the optimal values of 37.39% for ammonia concentration, 402 K for vapor generator temperature, 20.82 bar for vapor generator pressure, 9.582 bar for separator 2 pressure, and 2.603 for compressor pressure ratio. From the exergy analysis of the system, it is shown that the reactor core has the highest contribution to the exergy destruction rate. Although, the obtained exergy efficiency of the system is 53.2%. It is striking to regard that the combined KC and GT-MHR has higher energy and exergy efficiencies comparing to stand-alone KC and GT-MHR.

The proposed system uses the thermal energy storage characteristic of the solar pond to power a multi-effect desalination (MED) process with a total fresh water production of approximately 14,000 m3 annually. Pressure retarded osmosis (PRO) alongside photo-assisted chloralkali reactor are employed to utilize the brine rejected from the desalination process. The inclusion of PRO is proposed to take advantage of the salinity difference that occurs as a result of the preparation of the solar pond and desalination process. The quest for zero salt discharge in the proposed energy system configuration is undertaken through the introduction of a photo-assisted chloralkali reactor, which is conducted utilizing the power generated from PRO, and solar pond storage arrangement. This solar pond and desalination coupling system will achieve independence from conventional energy sources, which will lead to a significant contribution to the reduction of greenhouse gas emissions caused by fossil-fuel driven desalination. At solar irradiation of 600 W/m2, the overall energy and exergy efficiencies can reach 16.4% and 1.4%, respectively. The annual average overall energy efficiency of 11.4% is achieved utilizing the integrated system, whereas the average overall exergy efficiency is about 0.9%. Parametric studies are performed to examine the impacts of ambient conditions, irradiance, solar pond geometry, brine salinity, and the total number of MED effects on the performance of the overall integrated system. In addition to the sensitivity analysis, the potential to improve overall energy and exergy efficiencies and fresh water production of the proposed system is demonstrated.

In this research, a three-layer feed-forward artificial neural network (ANN) model has been developed for glass-tedlar photovoltaic thermal (PVT) air collector incorporating thermoelectric cooler (TEC). The ANN model is used for estimating the fluctuating outputs of the glass-tedlar PVT-TEC air collector, i.e. thermal energy gain, electrical energy gain, overall thermal energy gain and overall exergy gain, as a result of intermittent and varying weather conditions. The traditional modelling techniques, used for predicting the output performances of a PVT system, rely on analysis of complex relationships between different components of PVT collector, solution of differential equations and several design parameters. ANN model, however, aids in approximating the outputs by learning through training examples and hence, does not involve complex analysis and calculations. The developed ANN model is based on global solar radiation, diffuse solar radiation and ambient temperature, as inputs. Further, the outputs of glass-tedlar PVT-TEC air collector [Case I] are compared against glass-glass PVT-TEC air collector [Case II], using ANN model. The monthly and annual outputs of glass-tedlar PVT-TEC air collector [Case I] have been estimated for New Delhi, India. Also, a comparison between the annual results of Case I and Case II, obtained using ANN model, has been presented.

Dual-loop organic Rankine cycle is a great potential technology to recover engine waste heat for energy saving. Transcritical cycle can improve exergy efficiency of heat transfer process in the evaporator, and zeotropic mixtures furtherly can improve thermal match with heat source and sink. Thus, a transcritical-subcritical dual-loop organic Rankine cycle system using zeotropic mixtures is adopted for engine waste heat recovery, and system without and with regenerator is considered. The whole system is assumed in the steady state, R600a/R601a and R134a/R245fa mixtures are used as working fluid of transcritical and subcritical cycle, respectively. Parametric analysis and optimization about turbine inlet temperature and pressure of high-temperature loop, evaporation temperature of low-temperature loop are carried out. According to the results, the designed parameters have great effect on performance of system, and for the system without and with regenerator, the optimal turbine inlet temperature, pressure and evaporation temperature are 260 °C, 11 MPa, 85 °C and 250 °C, 10 MPa, 85 °C respectively. Moreover, the effects of components of mixtures on the performance of system are analyzed. The results demonstrate that system with zeotropic mixtures can significantly improve the performance of system. The system without regenerator using R600a/R601a (0.2/0.8) and R134a/R245fa (0.4/0.6) shows the maximum power output of 97.49 kW which is higher 5.48–20.00% than pure fluids, and system with regenerator using R600a/R601a (0.3/0.7) and R134a/R245fa (0.4/0.6) achieves the maximum power output of 97.95 kW, increment of 6.52–19.78% compared with using pure fluids. And the power output of engine can be improved by 9.79% and 9.83% for the system without and with regenerator, respectively. Furthermore, the exergy destruction analysis demonstrates that zeotropic mixtures can reduce heat transfer exergy destruction and total exergy destruction of system.

A novel trigeneration system consisting of organic Rankine cycle (ORC) and absorption-compression cooling and power system (ACCPS) is proposed to recover diesel engine waste heat. A compressor is used between evaporator and absorber in ACCPS. Moreover, a screw expander is applied in ACCPS to increase power generation and domestic hot water (DHW) is prepared by DHW heat exchanger (HX) in ORC. Exergoeconomic analysis using the specific exergy costing (SPECO) method is implemented for system assessment. Base case and parametric analysis as well as the effects of using expander and compressor in ACCPS on total performance of the system are examined. The results show that the best thermo-economic performance of the system is achieved when ORC condensation temperature and generator outlet temperature have respectively the lowest (85 °C) and the highest (80 °C) values. It is difficult to select the proper ORC evaporation temperature, because the lower this temperature is, the higher net power output is obtained while higher ORC evaporation temperature leads to less total cost rate and more total energy efficiency of system. Moreover, system exergy efficiency has an optimum point versus variation of ORC evaporation temperature. By increasing expander inlet steam quality, ACCPS coefficient of performance (COP) and total energy efficiency of system decrease; however, due to increase in net power output and system exergy efficiency respectively equal to 18.23% and 3%, total system performance improves from exergy viewpoint. By utilizing a compressor in ACCPS and increasing its pressure ratio, the performance of ACCPS improves from energy viewpoint; however, system thermo-economic performance decreases.

Combined cooling heating and power (CCHP) is a promising energy supply technology which is widely installed in buildings due to its feasibility from techno-economic, performance and environmental points of view. In present paper, a novel cogeneration system based on compressed air energy storage (CAES), organic rankine cycle (ORC) and hybrid compression-absorption refrigeration cycle is proposed. The main objective of the proposed system is to improve the efficiency of the CAES system by providing cooling capacity from the rest of hot gases in turbine exhaust through employing an ORC driven refrigeration system. Also, the effect of the maximum to minimum pressure ratio of CAES vessel as a critical parameter on CAES volume and round trip efficiency (RTE) has been scrutinized. Using the environmentally-friendly compression-absorption refrigeration system, high temperature thermal energy storage (HTES) and R407C as the organic working fluid decrease fossil fuel consumption and make the proposed system fully environmentally-friendly. The results indicate that 2280 kW electrical energy and 416.7 kW cooling capacity are simultaneously generated during peak period. As a result, with 13.15% RTE enhancement in comparison to the individual CAES system, it reaches to 65.15% based on the proposed modification. Also, the results show that the overall exergy efficiency and total exergy destruction of the components are 49.17% and 1419 kW, in which the pressure regulating valve and the air turbine have the highest irreversibility and exergy destruction.

The paper presents a Computational Fluid Dynamics (CFD) model of the cold alpha-type Stirling engine. The developed mathematical model comprises of Unsteady Reynolds Averaged Navier-Stokes (URANS) set of equations, i.e. continuity, momentum and energy equations. Moreover, the developed mathematical model comprises a non-equilibrium description of the regenerator, by the introduction of the energy conservation equation for the regenerator matrix. It was implemented in the framework of commercial CFD software ANSYS Fluent. The work presents an in-depth analysis of the influence of the numerical mesh and applied turbulence model on the obtained results. The model was used to analyse the influence of the regenerator on the performance of the cold Stirling engine at different operating conditions. It appeared that on an average application of the regenerator increased the engine specific work by 10 J/kg and this increase is significantly higher at a high rotational speed of the engine. At the same time, the engine efficiency averagely was increased by 10 percent points and again this increase was significantly higher at higher rotational speeds of the engine. Especially, the influence of the heat source and sink temperatures on the engine operation were analysed. It appears that the lower are temperatures of a heat source and sink the more pronounced is the presence of the regenerator in the engine. Finally, the influence of the elementary parameters: particle diameter and porosity of the solid matrix which constitute the regenerator filling was investigated. It was shown that for the analysed engine the optimal value of the regenerator packing porosity equals about 0.72 it results in the specific area of the regenerator equal around 1675 m2/m3. Obtained results can be used to analyse the possibility of application of Stirling engines to recover low-temperature exergy of regasified Liquified Natural Gas (LNG), which for small regasification units can be alternative for commonly utilised Ambient Air Vaporizers (AAV) and it aside for regasification of LNG it could produce electric energy.

The objective of this paper is to investigate comprehensively energy, exergy and financial parametric analyses of a solar flat plate collector (FPC) using heat pipes. A validated 1-D mathematical model was established and implemented in MATLAB to assess the collector performance. Hourly meteorological variables for one complete year in Fez (Morocco) were fitted and incorporated into the computation tool to describe accurately the thermal behavior of the whole collector. The combined effects of various climatic data, operating and design parameters were analyzed energetically and exergetically based on hourly and monthly performance indexes. Multi-objective optimization using a dimensionless-geometrical index was practiced to find out the best operating scenario achieving the highest energy and exergy outputs at a reduced cost. The best compromise between thermal/exergy performances was obtained at 986.93 W/m2 for the incident solar radiation, 12.18 °C for the ambient temperature and 1.50 m/s for the wind velocity. Also, it was found that the best combination of operating conditions is 45 °C inlet temperature and 0.036 kg/s mass flow rate. Fixing the number of heat pipes to 13 leads to an optimized collector design in terms of energetic, exergetic and financial performances. The obtained results confirm that an appropriate design of the collector should be undertaken carefully depending on the prevailing meteorological conditions to achieve optimum energetic/exergetic and economic performances.

The integration of supercritical CO2 (SCO2) cycle instead of steam Rankine cycle may be a revolutionary technique to increase the efficiency of coal-fired power plants. To effectively extract exergy from the fluegas and convert exergy to power, the characteristics of hot end (heat reservoir) and cold end (heat sink) should be fully considered, and the system multi-parameters should be optimized. In this study, based on a benchmark coal-fired power plant integrated with a recompression SCO2 power cycle, quantitative efficiency enhancements of system improvements of the hot end and cold end for SCO2 power cycle are calculated and compared. The optimized efficiency of benchmark coal-fired plant integrated with recompression SCO2 power cycle is 45.43%. When the fluegas at the economizer outlet is effectively used, the power plant efficiency can be increased by 1.32%. With single and double reheats to decrease the heat transfer irreversibility of the hot end, the power plant efficiency can be increased by 1.77% and 2.24%, respectively. Cold end optimization with single intercooling and cold air preheating can increase the power plant efficiency by 0.32% and 0.33%, respectively. Finally, a simple structure system and a complex structure system are proposed. With optimal system parameters, the power plant efficiencies of the complex and simple systems are 49.32% and 48.52%, respectively.

Resource efficiency is a key component of sustainable policies and practices, particularly in industries with high energy demands. Using empirical data, this paper evaluates the long-term performance (1960–2009) of the United Kingdom steel sector through the exergy-based metrics of “resource efficiency” and “useful exergy efficiency”. The analysis is broken down into two production pathways: the basic oxygen furnace and the electric arc furnace. The scope includes electricity generation and steel refining. It incorporates energy and material inputs, as well as by-products as useful outputs. The exergy-based indicators demonstrate the benefit of measuring both the quality and quantity of resources. The results are contextualised to gain insights into the long-term impact of political and socioeconomic transitions on resource consumption trends. Over the period, the sector’s overall resource efficiency went from 19% to 32%. Between 2% and 4% of this improvement results from the reincorporation of by-products into production processes. The basic oxygen furnace route’s resource efficiency increased by 9% whilst the electric arc furnace route rose by 20%. These improvements occurred via the promotion of successful energy saving policies rather than the diversion of large amounts of scrap inputs into the furnaces. This paper shows that both the resource efficiency and useful exergy efficiency indicators are a valuable complement to the benchmark metrics (energy intensity and material efficiency). This is because they can quantify the interactions and trade-offs between energy and material flows.

Multi-objective optimization of a hybrid building integrated photovoltaic/thermal (BIPVT) system and earth-air heat exchanger (EAHE) is studied. According to the position of the BIPVT and EAHE systems, two different configurations (i.e. configuration A and configuration B) are examined. In the heating mode of the configuration A, the cold outdoor air is twice preheated by passing through the EAHE and BIPVT systems. In the cooling mode of the configuration A, the hot outdoor air is precooled by flowing inside the EAHE system and the photovoltaic (PV) modules are cooled using the building exhaust air. The cooling mode of the configuration B is similar to the configuration A, while in the heating mode of the configuration B, the outdoor air first enters the BIPVT collector and then passes through the EAHE system. The annual total amount of produced energy and exergy are considered as the objective functions. The effective parameters in the optimization process include the air mass flow rate, the length, width and depth of BIPVT channel and the length and depth of EAHE system. The outcomes revealed that the annual total energy and exergy outputs of the optimum configuration A are 96448.6 kWh and 10015.5 kWh, respectively, while these values for the optimum configuration B are respectively 98537.5 and 9888.4 kWh.

Organic Rankine cycle is a power system for the widely use of medium- to low-grade (

Vaporizers are the key heat transfer device in the regasification process of liquefied natural gas (LNG), especially for the conventional onshore LNG receiving stations. This paper has proposed a novel intermediate fluid vaporizer by employing multi-stream plate-fin heat exchanger (MPFHE-IFV). Compared to traditional shell-and-tube IFVs, it can not only achieve a higher heat transfer efficiency with more compact structure using MPFHE but also realize the recovery and reuse of LNG cold energy with intermediate fluid. In this ingenious design, the self-evaporating gas of cryogenic liquid is adopted as the intermediate medium of IFV so that the equipment freezing can be effectively avoided under large flow conditions. A thermal-hydraulic design model has been established for MPFHE-IFV to determine the detailed structural dimensions as well as the heat transfer performance, and a corresponding multi-objective optimization algorithm has been adopted to obtain the minimum equipment volume, the optimal channel arrangement and fin structure, the maximum cold energy recovery efficiency and the optimal number of internal cycles. Meanwhile, the transmission process of the cryogenic exergy in MPFHE-IFV has been revealed according to the analysis of the system temperature-entropy diagram. Finally, two experimental cases based on the liquid nitrogen regasification process are conducted to evaluate the practical performance of the novel MPFHE-IFVs using the design and optimization method proposed in this paper. The results indicate that this new type of IFV can reach the highest cold energy recovery efficiency up to 95% within the 8% error range when the heat transfer capacity is 11.5 kW and the heat medium flow rate is near 330 L/h. National Research Foundation (NRF) The funds supported this work include the National Research Foundation of Singapore under the grant NRF2014EWT-EIRP003-014, NRF2013EWT-EIRP004-019, NRF2011NRF-CRP001-090, the Fundamental Research Funds for the Central Universities No. 3132018248 and the National Natural Science Foundation of China No. 51906026, No. 51876019, No. 51779026. Their support is gratefully acknowledged.

The thermal performances of proposed compression-absorption refrigeration assisted by a heat-driven turbine (CRHT) at low evaporating temperature were numerically investigated. According to the ideal isentropic process and the isentropic efficiency, the mathematical models of the micro tube and the compressors are built up. The CRHT system was modeled and simulated by considering the mass conservation, energy conservation, mechanical power conservation, and exergy generation equation of each component. For the case of basic design, the operating parameters, energy balance and the total thermal conductance of each component are calculated and analyzed. The effects of generation temperature, evaporating temperature of R134a, ammonia mass fraction of NH3/H2O, and compression ratios on thirteen key operating parameters were simulated and discussed. The COP of the CRHT system is compared with those of the two-stage absorption refrigeration system and the heat-driven compression-absorption refrigeration system in literatures, which proves that the proposed CRHT system possesses the best thermal performance. The exergy losses of each component were calculated and compared. It is indicated that the heat transfer areas of components should be optimized appropriately.

A detailed exergy cost and thermoeconomic analysis applied to a Rankine Cycle (RC) coupled to a Multi-Effect Distillation (MED) plant was performed. The aim of this work is to identify the impact of design and operating conditions on the exergy and thermoeconomic costs of the final products, electricity, and freshwater, and to assess the distribution of the destroyed exergy, the fuel, and the plant costs. The plant model considers a high disaggregation model, which includes MED plant and condenser parasitic losses, a seawater pumping system and a brine energy recovery system. It also considers solar molten salts as the RC fuel, which is the typical fluid used in solar tower plants. The impact of RC + MED plant part-load operation, ambient temperature, MED plant size, and location plant’s altitude was evaluated and an analysis of operational day of the RC + MED plant was carried out. Results indicate that the plant part-load operation has a significant influence on the unit exergy and thermoeconomic product costs, while the ambient temperature evidences only a minor effect on the water costs. As well, the largest MED plant sizes (above 50,000 m3/day) offer the lowest electric and water costs, while the altitude strongly increases the water costs.

The paper presents a study of retrofitting of a combined heat and power (CHP) plant aimed to increase the electric to heating power ratio. The modification would involve diverting part of the steam to the gas turbine, instead of letting it go to the steam turbine, using injection technique into a combustion chamber. Therefore, two potential retrofitting approaches are analyzed: steam injection gas turbine (STIGT) and combined steam injection gas turbine (CSTIGT). STIGT is a classic solution where live steam is diverted before the valves of a steam turbine. In CSTIGT steam is received from the turbine extraction. Both solutions increase electric power output of the cycle (STIGT by 1.33 MWe, CSTIGT by 2.68 MWe), decrease heating power (STIGT by 52.90 MWth, CSTIGT by 31.75 MWth) and decrease CHP energy efficiency (STIGT by 32 pp., CSTIGT by 22 pp.). The exergy analyses indicate that the highest exergy losses occur in the combustion chamber (61.30 MW for the reference cycle). Steam injection increase this value by 7.34 MW in STIGT and 5.65 MW in CSTIGT. However, decreasing of combustion temperature prevent the NOx emission by more than 8 g/MWh for both solutions.

Exergetic analysis consists in the evaluation of the exergetic balance on experimental data. When applied to an internal combustion engine, exergetic analysis can identify sources of inefficiency and potentialities for utilizing exergy that would be rejected. To perform this analysis, experimental data were acquired for different operating conditions of a spark-ignition engine by using gasohol and hydrous ethanol as fuels. With these data, an exergetic analysis was carried out by evaluating the effects of engine operating parameters on associated irreversibilities. Afterwards, a comparison between the exergetic analyses of hydrous ethanol and gasohol was presented. Finally, first and second law efficiencies were evaluated as functions of engine speed, engine load and air–fuel ratio. Exergy distributions of hydrous ethanol at different conditions and the accounts of exergy losses during engine operations were also evaluated.

Cyclohexanone ammoximation is widely used as an efficient method to synthesize cyclohexanone oxime in industrial production. In this study, the cyclohexanone ammoximation production process was explored based on reaction kinetics in order to reduce its energy consumption and total annual cost. The effects of the reaction temperature, space time, and raw material ratios on the cyclohexanone oxime yield were analyzed. Under the optimized operating conditions, the maximum C6H11NO yield was 99.86%, and the minimum total annual cost was 5.988 × 107 $ per year. Dynamic control of the cyclohexanone ammoximation production process was further explored under the optimized conditions. The proposed control structure could achieve effective control and maintain the desired product yield when flow rate and composition disturbances were introduced. The energy and exergy analyses of the cyclohexanone ammoximation process show that its energy efficiency can be improved from a thermodynamic perspective. The combination of a steady state simulation and dynamic control, thermodynamic analysis, and economic performance evaluation provide insight into the improvement and operation of the cyclohexanone oxime production process.

A transcritical CO 2 heat pump (HP) system for residential space heating integrated with direct dedicated mechanical subcooling (DMS) is proposed, and mathematical models are developed to study the ...

A novel SOFC-HCCI engine hybrid power generation system fueled with alternative fuels is proposed and modeled in this paper. The steady-state modeling shows that it is feasible to use SOFC anode off-gas as the downstream HCCI engine fuel for additional power generation under certain fuel utilization and operating temperature. Through parametric and exergy analyses, it is found that the hybrid system without additional H2 can achieve a net electrical efficiency of approximately 59% and an exergy efficiency of 57%, slightly higher than the SOFC-GT hybrid system. In this hybrid system, the components of HCCI engine and its exhaust gas dominate the exergy destruction, which contributes nearly 75% but has a relatively low contribution to the total power. Based on this, the methods of recycling exhaust gas waste heat to drive hydrogen desorption of metal hydride as H2 addition for HCCI engine and H2 recirculation for SOFC anode off-gas are suggested to significantly improve the system overall efficiency due to the consideration of thermal efficiency. The high overall efficiency up to 79.54% and fuel flexibility demonstrate that the novel hybrid system is a promising energy conversion system.

LNG re-gasification process usually occurs through heat exchange with seawater, causing a large amount of exergy destruction. However, in this study, this process is employed as the heat sink of a geothermal driven multi-generation system. Because of the high temperature difference between the heat source (geothermal fluid) and the heat sink (LNG re-gasification process), a cascade of two organic Rankine cycles is placed between them. The system also includes an absorption refrigeration cycle and a PEM electrolyzer to form an efficient multi-generation system. A comprehensive analysis is carried out to assess the performance of the system both thermodynamically and economically. Furthermore, the paper presents a parametric study to illustrate the influences of major parameters on the system performance. To simultaneously optimize total cost rate, hydrogen production capacity, and exergy efficiency of the system, a multi-objective optimization procedure is developed (through coupling Genetic Algorithm with Artificial Neural Network) and applied to the system. Consequently, a system design with a total cost rate of 423.5 ($/hr), hydrogen production capacity of 276.1 (kg/hr), and exergy efficiency of 24.92% is obtained as the optimal solution. The proposed system shows great improvements in cooling, power generation, and hydrogen production capacities compared to literature.

In this study, thermo-ecology based performance investigations for a combined system consists of Brayton gas cycle, Rankine mercury cycle and Rankine steam cycle, which is called Gas/Mercury/Steam power generation system (GMSPGS), are carried out depending on the most used performance characteristics such as power generation, density of power generation, destructed exergy, second law efficiency (exergetic performance efficiency) with respect to destructed exergy and power generation, ECOP and EFECPOD. The impacts of system design and operating parameters for gas cycle part, mercury cycle part and steam cycle part on the performance characteristics are parametrically examined in detailed. The used parameters are inlet temperature and pressure of the air, mass flow rate of the air, pressure ratio, equivalence ratio, turbine speed, residual gas fraction (RGF), mercury temperature of the gas-mercury heat exchanger (GM-HEX), low-pressure mercury turbine (LPMT), medium-pressure mercury turbine (MPMT), high-pressure mercury turbine (HPMT), steam temperature at the mercury-steam heat exchanger (MS-HEX), the pressures of low-pressure steam turbine (LPST), medium-pressure steam turbine (MPST), high-pressure steam turbine (HPST), open feed water heater (OFWH) and condenser (COND). The results demonstrated that the performance specifications are substantially affected by the component properties. Beside the theoretical model examined in the paper, a data obtained from artificial neural networks (ANNs) is also presented to model the system. It is shown that a limited number of parameters is enough for good approximations.

Designing energy conversion systems with high efficiencies and low pollutant emission is essential for sustainable development. A new cogeneration system including a high-temperature proton exchange membrane fuel cell, integrated with a solar methanol steam reformer, and a Kalina cycle is proposed to produce electricity and heat. Using energy, exergy and cost balance, the proposed system is analyzed from the viewpoints of exergy, economy, and environmental impact. A Parametric study is performed and shows that a higher fuel cell temperature is in favor of the total product unit cost and carbon dioxide mass specific emission. Also, the exergy efficiency is maximized, and the total product unit cost as well as the carbon dioxide mass specific emission are minimized at some specific values of anode recirculation ratio. Optimization results show that the average daily exergy efficiency can increase by up to 29.3% and the total product unit cost as well as the carbon dioxide mass specific emission can decrease by up to 17.72% and 16.3%, respectively compared to the corresponding values under the base conditions. It is concluded that combining a Kalina cycle with a high-temperature proton exchange membrane fuel cell along with utilizing solar energy for reforming process yields an efficient energy conversion system with low emission.

The present study focuses on energy and exergy analyses of the trigeneration system consisting of heliostat field, organic Rankine cycle with the heat exchanger, and ejector-absorption chiller which has the merits of refrigerating a thermal load of below than 0 °C with solar energy more efficiently along with the generation of process heat and electric power in an eco-friendly manner. A parametric study is carried out to investigate the effect of varying the influencing operating variables on trigeneration system output, and its energy and exergy efficiencies. It is found that the exergetic output of isobutane operated system increases from 2562 kW to 4314 kW while for propane operated system it is raised from 1203 kW to 2028 kW when the direct normal irradiations are increased from 600 to 1000 W/m2. Results of energy and exergy utilization show that for isobutane ORC fluid, out of 100% solar energy supplied to the system 65.42% can be produced as energetic output and rest 34.58% is lost via thermal exhaust to ambient. On the other hand, out of 100% solar exergy supplied only 13.98% is the produced exergy, 84. 89% is the exergy destroyed due to irreversibilities, and rest 1.13% is the exergy loss.

Low temperature combustion (LTC) is a new mode for efficient and clean combustion in engines, and the process is mainly controlled by chemical reaction kinetics of fuel. In this paper, the numerical model of exergy analysis for LTC engine was established. The temperature, pressure and species concentration were obtained by using the homogeneous charge compression ignition (HCCI) engine model of Chemkin-Pro software with the simplified mechanism of toluene reference fuel (TRF). The exergy items were further calculated to explore the effect of different intake conditions on exergy destruction in LTC process. It was found that the irreversibility related to the combustion proceeding mainly happened in low temperature and high temperature reaction zones. With the increase of exhaust gas recirculation (EGR) rate, the proportion of working exergy increases but the irreversibility destruction of combustion decreases. Besides, N2 component concentration in EGR gas has the greatest influence on the distribution of exergy.

In the present study, a novel and flexible experimental facility of an organic Rankine cycle system is constructed. Four extra heat exchangers than traditional test bench are equipped for the system performance testing with different evaporator and condenser or heat transfer examinations of the evaporator and condenser. The combination of an expansion valve and a cooler is designed to simulate the expander with desired type and expansion characteristic. Meanwhile, a scroll expander is installed in parallel. Preliminary investigations are motivated to explore the operating characteristics of the novel experimental facility under different conditions and to quantitatively discover the system improvement potentials for further optimizations. After the steady-state operation evaluation, the system is investigated by varying the heat source temperature and heat sink temperature as well as the working fluid pump stroke. The constant expander isentropic efficiency scenario is simulated through the combination of the expansion valve and cooler, and it is also validated by the installed expander. Results show that the power output of the system and electricity consumption of the working fluid pump are in the ranges of 2.42–3.55 kW and 0.44–0.49 kW, respectively, and the system thermal efficiency varies from 5.2% to 7.3%. Moreover, the system is then deeply explored by using exergy analyses to reveal the potential for performance improvement. The conventional exergy analysis tells that the evaporator has the largest exergy destruction. However, the advanced exergy analysis gives a more realistic improvement potential and suggests that the expansion process should be firstly improved.

This study analyzes a new renewable energy-based multigeneration system, in which the energy sources are efficiently utilized to generate several useful commodities such as hydrogen, oxygen, desalted water, and refrigeration along with electricity. Osmotic power from desalination brine solution is harvested to contribute to the electricity generation and to reduce the environmental impact of brine. The system units are concentrated photovoltaics/thermal (CPVT), wind turbines, thermal energy storage (TES), hydrogen electrolyzer, hydrogen fuel cell, multistage flash (MSF) distillation, vapor compression refrigeration (VCR) cycle, and pressure retarded osmosis (PRO). The energetic and exergetic performance of the overall system, as well as the system units, are calculated based on the first and second law of thermodynamics. Further, a comprehensive parametric study is conducted to investigate the effect of varying environmental and operational conditions, and the input parameters on the production rate, exergy destruction rate and efficiencies. For maintaining the high efficiency of CPV operation, the heat generated on photovoltaic (PV) cells is dissipated by an effective cooling system. This heat is then stored in the TES to be further utilized in desalination. The TES is used for eliminating energy fluctuations in the system and for a continuous operation by storing the energy for the time, when energy from the sun is not available. The electricity from CPV and wind power is used in the VCR cycle and hydrogen electrolysis. The fuel cell can be operated during the time of peak electricity demand. After performing thermodynamic analysis over the system, the overall energy and exergy efficiencies are determined as 73.3% and 30.6%, respectively. The exergy destruction rates of the components are specified. In brief, generation of multiple commodities is assured based on a clean operation by a novel integration of multiple clean energy sources in one system.

A smart hybrid power plant comprising a waste-fired CHP (combined heat and power) plant accompanied by a small-scale organic Rankine cycle was recently designed and analyzed thermodynamically. The objective of this hybridization is to maximize the share of electricity production of waste-CHP plants rather than a higher heat production rate in a cost-effective manner. In this work, utilization of the exergy of the hot flue gas of the waste-fired CHP unit in order to increase the potential of the organic Rankine cycle for maximizing the net power output of the hybrid cycle is proposed and techno-economically analyzed. In addition, the effect of using alternative environmentally-friendly organic working fluids on the performance of the system was investigated. The results of the study show that by the flue gas potential utilization of the same CHP unit, the size of the organic Rankine cycle may increase significantly, leading to a larger power output of the plant. As such, the net exergy and energy efficiency values of the combined plant in various operational conditions are improved compared to its primary configuration by, respectively, about 10% and 20%, when both of the main CHP cycle and the organic Rankine cycle are working at nominal load. In addition, this exergy utilization is beneficial economically as well, decreasing the payback period of the parallelization project by about 10% (from 7.4 years to 6.7 years). The alternative organic working fluid does not make a significant change in the technical and economic performance indices of the system.

In this paper, several cost metrics for application to a combined heat-and-power plant fueled by a zero-marginal cost energy source are studied. The mature levelized cost concepts are extended with some novel metrics such as the levelized cost of exergy. The results are given for a geothermal combined heat-and-power plant, connected to two different types of district heating systems and for two scenarios for the heat and electricity prices (high and low). For a low price scenario, the conventional costing method based on two separate prices for electrical and thermal energy is the most appropriate. Also for a high price scenario, the conventional costing method is the most appropriate for heat demands at low temperature. However, for higher-temperature heat demands, the exergy costing method results in the highest revenues for the combined heat-and-power plant. The authors recommend the use of the novel levelized cost of exergy metric as different types of energy are priced with a single value. Depending on the amount of energy and the usefulness of the energy type, an appropriate cost can be allocated to each product of a multi-energy system.

In this paper, the new configuration of transcritical CO2 refrigeration cycle combined with a thermoelectric subcooler and an ejector (TES + EJE) is proposed. The thermoelectric subcooler is installed after the gas cooler in the transcritical CO2 refrigeration cycle with an ejector. Comparisons are carried out with the conventional transcritical CO2 refrigeration cycle (BASE), CO2 cycle with a thermoelectric subcooler (TES) and CO2 cycle with an ejector (EJE). Maximum cooling coefficient of performance (COPc) is obtained for the new TES + EJE cycle with a simultaneous optimization of subcooling temperature and discharge pressure. The improved new cycle exhibits higher COPc and lower discharge pressure compared with the other three cycles. Compared with the BASE cycle, the maximum COPc of the TES + EJE cycle is increased by 39.34% and the corresponding optimum discharge pressure is reduced by 8.01% under given operation conditions of 5 °C evaporation temperature and 40 °C gas cooler outlet temperature. The effects of the subcooling temperature, discharge pressure, gas cooler outlet temperature and evaporation temperature on the TES + EJE system performance are also discussed by energy and exergy analysis and results present here.

In this article, water and TiO2-H2O nanofluids are used as heat exchange mediums. The heat transfer and resistance coefficient of corrugated tubes with different corrugation pitches are studied by experimental method. The economy of experimental system is evaluated from the aspects of quantity and quality of energy by thermal and exergy efficiencies respectively. The heat transfer performance of nanofluids in the smooth tube can be enhanced by 2.64–16.9% compared with water under the same working conditions, while the corrugated tubes can improve the heat transfer performance by 4.8–66.3%. When the mass fraction of the nanofluid is 0.5%, the corrugated tubes with different corrugation pitches can increase the heat transfer by 36.3% (P = 6 mm), 40.3% (P = 4 mm) and 44.5% (P = 2 mm) respectively. For thermal efficiency, the results prove that when the Reynolds number is larger than 6000, the comprehensive evaluation indexes of corrugated tubes are much larger than that of smooth tube, and the maximum can reach 1.5637. For exergy efficiency, the research results show that the exergy efficiency of the smooth tube is better than that of the corrugated tubes.

Systems based on Organic Flash Cycle (OFC) are promising technologies for waste heat recovery application due to a better match of the hot and cold heat transfer curves. However, the large amount of exergy lost during the throttling process, results in a low thermal efficiency for OFC. In this work, ejectors are introduced in basic OFC to replace the low pressure throttle valve, high pressure throttle valve and both two throttle valves, which namely Single Ejector and Single Flash evaporator based OFC (SESF-OFC), Single Ejector and Double Flash evaporators based OFC (SEDF-OFC) and Double Ejectors and Double Flash evaporators based OFC (DEDF-OFC), respectively. The thermodynamic analysis including energy analysis, exergy analysis, the parametric analysis and comparison analysis are evaluated by using steady-state mathematical model and thermodynamic laws. The ejector allows a high pressure fluid to entrain and compress a low pressure fluid to a medium pressure. Hence, the mass flow rate or expansion ratio of turbine can be enhanced, results in all of three ejector based OFCs are more efficient than the basic OFC. When the high temperature fluid with temperature of 453.15 K is set as heat source, the maximum global second law efficiency (ηII,G) of 38.95% belongs to DEDF-OFC followed SEDF-OFC (37.92%), SESF-OFC (33.68%) and basic OFC (31.43%). The SEDF-OFC is more efficient than SESF-OFC, which indicates that the high pressure throttle valve replaced by ejector is a more effective method than the low pressure throttle valve done. Moreover, the four OFCs have been compared with conventional Organic Rankine Cycle (ORC), and the comparison results show that the ηII,G of basic OFC and SESF-OFC are lower than that of ORC, while SEDF-OFC and DEDF-OFC are more efficient than ORC, and the average increment of SEDF-OFC and DEDF-OFC are 10.37% and 15.01%, respectively. Hence, the ejector based OFCs are alternative methods for waste heat recovery application with a high efficiency.

In this study, a new combined gasification process using various waste materials for multigenerational operation, containing the hydrogen, power, heating-cooling and hot water generation. In the present multigenerational plant, a waste material gasifier component is combined with the Brayton cycle, Stirling engine cycle, single effect absorption cooling cycle and proton exchange membrane electrolyzer for multiple outputs generation. To analyze and evaluate this integrated system, a comprehensive thermodynamic analysis and assessment for the multigeneration plant components is introduced, the second-law efficiency, associated with the overall system and its sub-systems are described, and the impacts of some arrangements and working statuses on the plant efficiency are investigated. The study results show that, this integrated plant has an overall energetic efficiency of 61.57% and an overall exergetic efficiency of 58.15%, when the produced net power is 94 MW, and also hydrogen generation rate is 0.077 kg/s, respectively.

The extensive use of organic Rankine cycle (ORC) in waste heat recovery motivates the employment of ORC technique to recover the waste heat in coal-fired plants. A novel combined cooling-heating and power (CCHP) system integrated Organic Rankine Cycle (CCHP-ORC) for recovering the waste heat of bottom slag in coal-fired plant is first proposed in this paper. A MATLAB procedure with REFPROP database is developed for the proposed system based on the mass, energy and exergy balances of each component. With the application of Analytic Hierarchy Process (AHP) method, R1234ze(E) and heptane/R601a are adopted as the optimal working fluids for the Sing Fluid CCHP-ORC and Dual Fluid CCHP-ORC systems, respectively. Parametric studies are conducted to investigate the effect of superheat degree of turbine inlet temperature, chilled water mass flow rate and condenser temperature on the coefficient of performance, thermal efficiency, heat exergy, cooling exergy, total exergy production and exergy production rate. The results show that the superheat degree of turbine inlet temperature benefits the enhancement of the exergy production rate. The enhancement of chilled water mass flow rate leads to an increase in coefficient of performance and refrigerating capacity while the cooling exergy, total exergy production and exergy production rate decrease. Except for exergy production rate in Dual Fluid CCHP-ORC system, the rise of condenser temperature leads to a decrease of performance parameters. As the condenser temperature rises from 25 °C to 40 °C, the thermal efficiency of Cycle2 declines 19.4% and 18.3% respectively in the Sing Fluid CCHP-ORC system and Dual Fluid CCHP-ORC system.

Biogas for supply of power plants can play a paramount role in reducing greenhouse gas emission and extra cost of a fossil fuel based plants. Regarding this aspect of biogas heat source, a novel biogas-based multigeneration system is proposed and modeled under privilege of first and second laws of thermodynamics, economic, and environmental perspectives. Furthermore, multi-criteria optimization of this integrated system is carried out from 4E (energy, exergy, exergoeconomic, and environmental) analysis standpoints. The introduced multigeneration system is able to produce optimum cooling capacity, heating capacity, net power, distilled water, and hydrogen of 123.59 MW, 0.73 MW, 280.35 MW, 18.14 kg/s, and 0.2432 kg/s, respectively. Under this circumstance, the thermal efficiency, exergy efficiency, unit product cost (UPC) of the system, and environmental penalty cost rate are calculated 72.75%, 50.21%, 6.79 $/GJ, and 168 $/h, respectively. Additionally, among all components, reactor core and among different sub-systems, the gas turbine-modular helium reaction (GT-MHR) cycle has the highest contribution to the overall exergy destruction. Finally, a complete sensitivity study based on key thermodynamic, thermoeconomic, and environmental parameters is performed and results are extended and discussed.

Fuel cells offer one of the most eco-friendly and efficient ways of energy production. In this study a thermodynamic and exergoeconomic assessment of a proton exchange membrane fuel cell (PEMFC) system at steady-state operation condition are carried out. Thereafter, the feasibility of integrating a proton exchange membrane Electrolyzer (PEME) to supply required fuel for a PEMFC, operating in the same outlet power range is investigated. The results demonstrate that increasing the current density rises the following parameters in the system: the power and power density rates of the PEMFC and PEME, the exergy destruction rate of each component, the hydrogen production and consumption rates in the cycles, the PEME output voltage, cost rate of power generation and the power cost of the PEMFC. By increasing the PEMFC output voltage, the energy and exergy efficiencies reduce. Moreover, rising the outlet temperature of the PEMFC increases the power and power density rates of the PEMFC and also the energy and exergy efficiencies of the system. While increasing the outlet and operating temperature of the PEME increases the power consumption rate and reduces the energy and exergy efficiencies. The highest energy efficiency of the PEMFC is 36.7% and corresponding maximum exergy efficiency is found 54%, while the lowest values are found 31% and 45.3%, respectively. The cost rate of the power generation by PEMFC is varied between 7.96 × 10−4 and 1.33 × 10−3 $/s and the corresponding rate of the exergy unit cost range is 115.6–132.2 $/GJ.

A novel trigeneration integrated system is proposed and analyzed in this paper. The present system utilizes gas turbine exhaust gas for heat recovery and capturing carbon dioxide after expanding in the turbine and generating electricity. Moreover, a Cu-Cl thermochemical cycle is incorporated in the system to produce hydrogen, and a multi-effect desalination is integrated to provide fresh water to the Cu-Cl cycle and for domestic use as well. The present integrated system is modeled and simulated using the Aspen Plus software package for chemical processes and Engineering Equation Solver for the remaining subsystems. Both energy and exergy analyses are performed to study and assess the proposed system through energy and exergy efficiencies. Therefore, the overall energy and exergy efficiencies of the proposed trigeneration system are found to be 39.72% and 55.2% respectively.

Nowadays, gas turbines (GTs) are increasingly used in China, with a relatively low performance. Organic Rankine cycle (ORC) is promising to recover the flue gas heat recovery from GT. To efficiently enhance the heat recovery, two-stage series evaporation is combined with non-isothermal phase change of non-azeotropic mixtures. Thus, two-stage series organic Rankine cycle (TSORC) with six non-azeotropic mixtures, composed of R245fa and hydrocarbons, as the working fluids are investigated. The cycle performances of TSORC with non-azeotropic mixtures are compared with those of the ORC with pure working fluid. Moreover, a case study was conducted to illustrate the performance enhancement by TSORC with the non-azeotropic mixture for fuel gas waste heat from C200HP. The results show that the net power output, thermal and exergy efficiencies of the TSORC are superior to those of the ORC at the same mass fraction, especially for the net power output. Comparing with the stand-alone gas turbine of C200HP, the TSORC with cyclohexane/R245fa[0.8/0.2] increases the efficiency of C200HP system by 35.48%, and the power generation efficiency of the C200HP-TSORC system achieves 44.71%. The TSORC with non-azeotropic mixtures as the working fluids is advisable and can be popularized in engineering applications.