Exergy Destruction Ratio Research Articles

Exergy based yearly performance analysis of a poly-generation system for a small-town application

The current study conducts a comprehensive year-round exergy analysis of an integrated system centered around a reversible solid oxide cell (RSOC), aimed at fulfilling the power and fresh water requirements of a small town, equivalent to 2.7 MW and 2000 m³/day, respectively. The integrated system encompasses four subsystems: the solar field, RSOC, organic Rankine cycle coupled with ejector cooling (ORC), and zero liquid discharge multi-effect desalination (MED-ZLD). The proposed system is analyzed using MATLAB. The annual exergy efficiency for each subsystem is examined, yielding average values of 11.9 %, 48.11 %, and 56.22 % for the solar field, ORC cycle, and MED-ZLD, respectively. Notably, the exergy efficiency of the Rankine cycle is higher in colder months compared to warmer ones. This phenomenon is attributed to the cycle's greater heat generation relative to the cooling it produces during the cold season. The RSOC exhibits noteworthy average exergy efficiencies of 93 % in electrolysis mode, 69.87 % in fuel cell mode, and an overall average exergy efficiency of 79.62 % throughout the year. The average exergy efficiency of the overall system is evaluated throughout the day, nighst, and the entire operational period. The results are values of 10.74 %, 34.31 %, and 23.34 %, respectively. This discrepancy is due to the primary energy supply source, which is solar energy during the day and input hydrogen during the night. The highest exergy efficiency is observed in December, while the lowest is in June. Furthermore, the study examines the distribution of exergy destruction and identifies cycles with significant impacts by analyzing the exergy destruction ratio across various months. The solar field is the primary contributor to daytime exergy destruction, peaking at 94.9 %. At night, the MED-SET cycle leads in exergy destruction, followed closely by the RSOC cycle operating as a fuel cell. The research also delves into exploring key contributors to exergy destruction in various cycles, shedding light on crucial insights into the intricate dynamics of the integrated system's performance.

Economic Analyses of a New Power and Cooling System at Low Temperature Applications

Recent research suggests that the implementation of more efficient combined cooling and power systems, which enable the cogeneration of electricity and cooling, can enhance the efficiency of hybrid plants. The present investigation is motivated by finding that, in the literature review on combined power and cooling systems, there is very limited information on the coupling of the organic Rankine cycle (ORC) and the ejector refrigeration cycle (ERC) with low sink temperatures. A suggested approach to do this involves using hot exhaust gas and waste heat engines to power an ORC hybrid system. To enhance the ORC–ERC system's performance, three heater configurations use waste heat from the ORC turbine exhaust, ejector, and engine waste heat to heat the working fluid. Renewable energy sources are the primary focus of most current research initiatives. The present research focuses on unique ORC and ERC systems, considered as combined power and cooling systems, with the goal of improving exergy performance at low temperatures. The suggested ORC–ERC can generate energy destruction of 69.85 kW at a source temperature of 155 °C, with an exergetic efficiency of 76.9% at the turbine. Setting the entrainment ratio at 0.5 results in a total sum unit cost of products (SUCP) of 465 $/kW‐h for the ORC–ERC. Furthermore, the 37.83% exergy destruction ratio introduces heat exchanger 2 (HE2) as the primary cause of the suggested ORC–ERC's irreversibility. A detailed parametric study reveals that altering the hot source temperature and entrainment ratio improves the system's SUCP. The current examination at high sink temperatures may be expanded to an advanced exergoenvironmental investigation.

Thermodynamic and parametric analyses of a zero-carbon emission SOFC-based CCHP system using LNG cold energy

A novel zero-carbon emission combined cooling, heating and power (CCHP) system is currently proposed. The thermal energy of the solid oxide fuel cell (SOFC) exhaust is recovered in a transcritical CO2 (T- CO2) power cycle. Relying on the efficient utilization of liquefied natural gas (LNG) cold energy, CO2 capture has been achieved at low energy consumption. The thermodynamic performance is evaluated by using energy and exergy analysis methods for this hybrid process. The electrical, exergy, and CCHP efficiencies are obtained as 60.37 %, 62.83 %, and 79.09 %, respectively. The CO2 condenser, with the largest exergy destruction ratio (18.60 %) and a low exergy efficiency (37.16 %), is regarded as the weakest point in terms of thermodynamic perfectibility. In addition, the influences of the current density, stack temperature and pressure, and fuel utilization rate have also been studied from different aspects of system performance. The current density, stack temperature, stack pressure, and fuel utilization rate are recommended as 0.3 A/cm2∼0.4 A/cm2, 900 °C, 5 bar, and 85 %, respectively. This research provides practical reference and pragmatic guidance for the integration, analysis, and optimization of SOFC-based CCHP systems.

Exergy performance analysis of hydrogen recirculation ejectors exhibiting phase change behaviour in PEMFC applications

A comprehensive analysis of flow behavior and exergy performance was conducted in hydrogen recirculation ejector, taking into account the phase change of humid hydrogen for proton exchange membrane fuel cell (PEMFC) systems. A two-phase nonequilibrium condensation CFD model integrating the entropy transport equations was established. The effect of phase change on ejectors’ performance under various primary pressure, secondary pressure and temperature, and back pressure were analyzed. When primary pressure was adjusted into 3.0 bar, a liquid fraction of 4.56 % was observed at the outlet, while the liquid fraction will increase to 15.35 % when the inlet pressure got to 5.0 bar. Then, the values of mass flow rate and liquid mass fraction on different sections under variable secondary temperature and back pressure were calculated. Finally, it is found that a larger primary pressure brought an increase in exergy destruction. So was exergy destruction ratio. However, increasing secondary pressure leads to the opposite result. With the increase of secondary temperature from 60 to 80 °C, exergy destruction increases from 330.28 to 390.23 kJ/kg but the destruction ratio decreases from 29.85 % to 26.19 %.

A COMMERCIAL TURBOFAN ENGINE MODELING AND EXERGY ANALYSIS

Turbofan engines are one of the most common types of engines used in modern commercial and military aircraft due to their efficiency and performance characteristics. In this study, a thermodynamic model is generated using GasTurb 14 software for a commercial two-spool, unmixed flow, and booster turbofan engine (CFM56-5A3) used in Boeing A320-212. Besides, an exergy analysis of the modeled turbofan engine is performed. Exergy performance criteria such as exergy efficiency, exergy development potential, exergy destruction ratio, productivity lack ratio, and fuel depletion ratio are evaluated for the engine components. In addition, how bypass ratio (BPR) affects net thrust and specific fuel consumption (SFC) for the modeled turbofan engine is investigated. As a result, the net thrust and SFC values of the modeled engine and the actual engine are overlapped with 14.0% and 7.2% deviation, respectively. The maximum exergy efficiency occurs at the high-pressure turbine as 0.992. When the bypass ratio is minimum, the maximum net thrust and SFC occur as 62.24 kN and 24.08 g kN-1 s-1, respectively. High pressure turbine has the minimum exergy development potential of 1528.5 kW.

Effects of using hydrogen on the exergetic and environmental damage performance of an UAV turbojet engine

In this study, the performance effects of using hydrogen instead of JP-8 fuel in an unmanned aerial vehicle (UAV) jet engine was investigated. Exergy analysis and environmental damage analysis were used to obtain performance parameters. These performance parameters were exergy destruction ratio, thrust-specific fuel consumption, air-to-fuel ratio, exergy efficiency, waste exergy ratio, environmental effect factor, sustainability index, and exergetic improvement potential values. Turbojet engine was operated at three different throttle settings (50%, 75%, and 100%) to examine the impact of different load types on the performance parameters. The results obtained by using JP-8 and hydrogen fuels at different throttle settings showed consistency. For all throttle settings, the highest exergy efficiencies took place in the nozzle as approximately 90%. On the other hand, the combustion chamber had the lowest exergy efficiencies for all conditions and took values between 30% and 40%. Calculated exergy destruction ratios indicated that the hydrogen use improved or saved the jet engine’s energy performance. Except the combustion chamber, compressor, turbine, and nozzle exergy destruction ratios decreased as 6.2%, 6.5%, and 10.8%, respectively. Moreover, the use of hydrogen fuel did not significantly change the performance parameters, in fact reduced the environmental impact approximately 113%. The findings indicated the potential benefits of hydrogen fuel use when compared to JP-8 fuel.

Maisotsenko Cycle for Heat Recovery in Gas Turbines: A Fundamental Thermodynamic Assessment.

This paper reports the Maisotsenko's cycle-based waste heat recovery system with enhanced humidification to exploit the maximum waste heat recovery potential of the gas turbine. This research uses an integrated methodology coupling thermodynamic balances with heat transfer model of air saturator. The performance of the system is deduced which are assisted with sensitivity analysis indicating the optimal mass flow rate ratio (0.7-0.8) and pressure ratio (4.5-5.0) between the topping and bottoming cycles, and the air saturator split (extraction) ratio (0.5). The net-work output, energy, and exergy efficiencies of the system are found to be ≈58.39MW, ≈55.85%, and ≈52.79%, respectively. The maximum exergy destruction ratios are found as 68.2% for the combustion chamber, 16.0% for the topping turbine, 5.7% for topping compressor, 4.9% air saturator. The integration of Maisotsenko's cycle-based waste heat recovery system with a comprehensive thermodynamic model, as demonstrated in this research, offers valuable insights into enhancing the efficiency, cost-effectiveness, and environmental impact of gas turbines. By presenting fundamental equations related to thermodynamic balances, this work serves as an invaluable educational resource, equipping future researchers and students with the knowledge and skills needed to advance the study of thermodynamics and sustainable energy solutions.

Analysis of entropy generation and exergy efficiency of the methane/dimethyl ether/air premixed combustion in a micro-channel

This work presents a numerical investigation on the entropy generation and exergy efficiency in a methane/dimethyl ether/air-fueled micro combustor. To this end, a three-dimensional numerical model established is first validated by comparing its predictions with experimental data in the literature. It is, then, applied to assess the effects of the inlet velocity and blending ratio on the entropy and exergy generation. As far as the entropy generation caused by chemical reactions is concerned, there exists a reaction step that contributes most to the overall entropy. The contributing rate of such a reaction is inhibited by increasing the blending ratio. Meanwhile, for a given fuel composition, the entropy generation due to chemical reactions and heat conduction is found to exhibit a monotonic trend with the inlet velocity, whereas the entropy induced by mass diffusion shows a non-monotonic dependence. Furthermore, the exergy destruction ratio induced by the chemical reaction plays a dominant role in the total exergy generation, irrespective of inlet velocity and blending ratio. Both the exergy loss and efficiency are shown to be increasing as the inlet velocity is elevated, along with the increase in the combustor wall temperature. In general, this work identifies how blended combustion affects the entropy and exergy generation in methane/dimethyl ether combustion systems and sheds light upon the underlying mechanism.

Energy and exergy analysis of a novel ejector powered CO2 liquefaction system (EPLS) and comparative evaluation with four other systems

CO2 emissions from industrial activities has been imposed several environmental problems to the human life. Mitigation actions like designing and implementing the CO2 capture systems is a beneficial way to reduce the amount of carbon dioxide in the atmosphere. In the last part of capturing process, the CO2 needs to be pressurized to be transported, stored, or used elsewhere. In the present study, five different systems for the carbon dioxide post-capture are designed and compared with each other which include a multi-stage compression, basic and modified Claude, the ejector boosted absorption systems, and the new introduced ejector powered liquefaction system (EPLS). The effect of several decision parameters on the performance of each system is evaluated and the detailed energetic and exergetic analysis of the components in each system is carried out. The results show that the new introduced EPLS system has better performance (in terms of COP and second law efficiency) than other four systems and the multi-stage compression system has the nearest values to the EPLS. The dependency of the EPLS performance to the main decision parameters including the pressure ratio and the intercooling temperature is considerably lower than other evaluated systems. In this regard, the multi-stage compression system indicates the largest dependence to the pressure ratio and intercooling temperature of compressors. The evaluations on the components of each system reveals that by the modifications in the Claude layout, the modified Claude system requires less cooling demand than other systems (585.5 kW at the basic conditions) and on the other hand, the DEBARS system has the lowest power consumption between the other systems (280.6 kW at the basic conditions). Evaluations on the exergetic efficiencies of components show that the intercoolers beside the compressors in the main subsystems and the liquid ejector in DEBARS, have the highest exergy destruction ratio in each system.

Multi-aspect evaluation of a novel geothermal-driven trigeneration system for cooling, heat, and power generation

This paper presents a novel trigeneration process that utilizes geothermal fluid and a gas turbine to generate electricity, heat, and cooling. The trigeneration system comprises a gas turbine cycle, dual flash geothermal-organic Rankine cycle, cooling production unit, and heat and power generation unit. A comprehensive parametric study is conducted from energy, exergy, economic, and environmental perspectives to evaluate the proposed process. Thermodynamic analysis shows that the energy and exergy efficiencies of the system are 46% and 47%, respectively. The total exergy destruction of the process is calculated to be 147,006 kW, with the gas turbine cycle and combustor contributing the highest and second-highest exergy destruction ratios at 66% and 45%, respectively. Environmental analysis reveals that the indirect emission of the proposed structure is zero, and the total carbon dioxide emission is related to the flue gas of the gas turbine unit, amounting to 44,010 kgCO2/h. Considering the production capacity of the three products, the carbon dioxide footprint is determined to be 17.44 kgCO2/MJ. Furthermore, the economic analysis indicates that the total annual cost of the proposed scheme is 56,817,774 $. The production costs for cooling, electricity, and heating are 0.3 $/kg(CW,5℃), 0.073 $/kWhe, and 0.174 $/kgST, respectively. This comprehensive evaluation demonstrates the efficiency and feasibility of the trigeneration process, making it a promising option for sustainable power generation with minimal environmental impact.

Exergy destruction analysis of a power generation system utilizing the cold energy of LNG

The purpose of this research is in-depth understanding of the internal causes of exergy destruction in various parts of the system and to identify potential improvements for the components. The focus is on a combined cycle power generation system that utilizes the organic Rankine cycle (ORC) and direct expansion cycle (DEC). To investigate the primary sources of exergy destruction in each component, advanced exergy analysis (AEA) is utilized. The result demonstrates that the net out power of the proposed system can reach 106.64 kW with energy efficiency of 11.22%, and exergy efficiency of 21.40%. The heat exchanger is identified as the primary contributor to exergy destruction, constituting 81.70% of the total ratio. Specifically, the condenser exhibits the highest exergy destruction ratio at 59.82%, indicating a need for prioritized optimization efforts. The findings of AEA reveal that the primary source of component irreversibility stems from the endogenous part. This shows that, while most exergy destruction is unavoidable, there remains room for system improvement. Regarding the turbine, its exergy destruction is primarily attributed to inefficiencies, leading to irreversibility. Nevertheless, there is exergy destruction that may be avoidable and can be reduced by 25.93 kW, which is 2.5 times greater than that of the heat exchanger. This finding underscores the high potential for improvement in ORC and DEC turbines, making them a priority for optimization efforts.

Dynamic modelling and performance prediction of a novel direct-expansion ice thermal storage system based multichannel flat tube evaporator plus micro heat pipe arrays storage module

Direct-expansion ice thermal storage (DX-ITS) system can improve the energy efficiency ratio (EER) by integrating the evaporator and the storage module. In this paper, a dynamic model for a DX-ITS system is developed to predict system behavior. This system consists of multichannel flat tube evaporator plus micro heat pipe arrays storage module, a 4-HP compressor using R134a, an air-cooled condenser with 40 m2 area and an electronic expansion valve. On this basis, the influences of the condenser's cooled-air temperature, cooled-air flow rate, and compressor speed on the system energy and thermodynamics performance are studied. Results show that the EER and the charging power could reach 2.24 and 5.41 kW, respectively, under cooled-air temperature, cooled-air flow rate, and compressor speed of 28.5 °C, 4660 m3/h, and 1450 rpm. The exergy efficiency is more sensitive to cooled-air temperature, which decreases by 22.48% from 11.52% to 8.93% as the cooled-air temperature increases from 18 °C to 35.5 °C. Moreover, the compressor has the highest exergy destruction ratio of 40%–55% in the exergy analysis of the system component, while the condenser has the lowest exergy destruction ratio of 7%–15%, indicating that optimizing the compressor is the key to improving the system's performance.

Herbal biochar preparation and its application as soil amendment: Is such disposal of traditional Chinese medicine residue cost-efficient towards carbon neutrality?

Herbal biochar from traditional Chinese medicine residue (TCMR) and related carbon-negative utilization could contribute to the realization of carbon-neutral disposal process of TCMR. For this purpose, herbal biochar preparation by low-temperature pyrolysis and its application as soil amendment is designed, and the integrated effects are assessed by a combined techno-economic, exergy, thermoeconomic and life cycle analyses based on the accounting of material flow, energy flow and environmental flow. Firstly, the economic benefits (i.e., net present value, internal rate of return and payback period) of the system is analyzed by combination of cost-benefit method and sensitivity analysis. Secondly, exergy analysis determines exergy destruction, exergy destruction ratio, exergy destruction coefficient, energy efficiency and exergy efficiency of pyrolysis system. Furthermore, by combining techno-economic and exergy analyses, exergy destruction cost and exergy economic coefficient are calculated to optimize pyrolysis system. Thirdly, the CO2 mitigation cost, carbon neutrality potential and environmental impact are evaluated via combining life cycle assessment with techno-economic and exergy analyses. The results indicate that the higher pyrolysis temperature shows preferable exergy efficiency, energy efficiency and thermodynamic performance. From 400 to 600 °C, herbal biochar preparation and its application can improve economic benefits by 12.9–15%. At 550 °C, such TCMR disposal process can reduce environmental impact to −8651.65 mPts, and the GHG emissions and CO2 mitigation cost of the life cycle process are 395.1 kg CO2-eq/t feedstock and 63.4 CNY/t CO2-eq, respectively. In general, herbal biochar preparation by low-temperature pyrolysis and related application as soil amendment can realize the carbon-negative disposal of TCMR by an economical and efficient way.

Energy efficiency assessment of hydrogen recirculation ejectors for proton exchange membrane fuel cell (PEMFC) system

The ejector is the core component for hydrogen recirculation in a proton exchange membrane fuel cell (PEMFC) system. However, in the past, the computational fluid dynamics (CFD) simulation of the ejector mainly focused on the influence of the change of the structural parameters on its performance, while the research on phase change condensation was lacking. Here, we proposed a two-phase flow model integrating the non-equilibrium phase change conservation equations and four categories of entropy transport equations, which analysed the phase change characteristics and the influence of different primary pressures on the property of ejector and internal entropy and exergy under the dry and wet gas models. We validated that the wet gas model has a good prediction ability with an MRE of only 2.53%. There was a significant difference between the dry and wet gas models, for example, the dry gas model predicted a larger Mach number and entrainment ratio, while the temperature and pressure were less than that of the wet gas model. Finally, the entropy and exergy were analysed, and the dry gas model overestimated the entropy generation, i.e, when the pressure of the primary inlet raised to 5.0 bar, the entropy generation overestimated by the dry gas model had reached 138.66 J kg-1K−1. The exergy destruction and exergy destruction ratio both increased with the rise of primary pressure. The dry gas model overestimated the exergy destruction and exergy destruction ratio, and the maximum overestimated values can reach 41.83 kJ/kg and 15.83%, respectively.

Thermodynamic analysis of the biomass gasification Allam cycle

The Allam cycle is a promising oxy-fuel combustion systems featuring high electricity efficiency and carbon capture level. In this paper, a novel biomass gasification Allam cycle is proposed. The thermodynamic performance of the system is studied, and the influence of the turbine inlet temperature, inlet and outlet pressure, and carbon capture pressure on the system efficiency is evaluated. The energy and exergy efficiency of the system is 38.80% and 40.74%. The exergy destruction of the overall system is 332.57 MW, where the gasifier has the highest exergy destruction ratio of 49.77%. As the turbine inlet temperature increases, the energy and exergy efficiency of the system improve by approximately 2.50% and 2.00%, respectively. The thermodynamic performance of the system enhances while increasing the turbine outlet pressure, whereas the system efficiency declines with higher turbine inlet pressure. As the carbon capture pressure increases, the energy and exergy efficiency decrease by 2.00% and 1.00%, respectively. The highest energy and exergy efficiency of the system could reach 40.88% and 42.20%. This work presents a practical method for efficiently utilizing biomass gasification for power generation.

Proposal of an environmental-friendly poly-generation model regarding the flue gas processing for the production of electricity, cooling, heating, freshwater, and methanol

In this paper, a novel poly-generation system with high thermodynamic performance and low carbon dioxide (CO2) emission is presented and analyzed from the 4E (energy, exergy, economic, and environmental) perspective. The newly designed structure consists a gas turbine cycle, transcritical CO2 cycles, a Kalina power cycle, a water desalination unit, a methanol production unit, and a chiller. Toward this goal, the flue gas leaving the gas turbine cycle is processed and utilized. Thermodynamic analysis demonstrates that the total energy and exergy efficiencies are attainable at 58.75% and 69.46%, respectively. In addition, the total exergy destruction rate equals 183105 kW in which the gas turbine cycle is the major source of irreversibility with a share of 51%. In addition, exergy analysis indicates that the combustor of the gas turbine cycle has the highest exergy destruction ratio (44.54%) among all equipment. Regarding the environmental aspect, the total CO2 emission and its emission intensity for the proposed process are 18678.42 kgCO2/h and 0.75 kgCO2/kgMeOH, respectively. Its indirect emission is responsible for 48.8% of the total emission as well. Attributable to the thermo-environmental results, the proposed process has a suitable performance compared to similar technologies. The economic analysis demonstrated that its total annual cost equals 60800563 $ and production costs of methanol, freshwater, heating, cooling, and power are 0.3 $/kgMeOH, 0.43 $/kgfreshwater, 0.16 $/kgLPS, 0.022 $/kgchilled water, and 0.069 $/kWh, respectively.

Comprehensive thermoeconomic study of a new solar thermosyphon-assisted multigeneration system

Nowadays, due to the global energy crisis, limited reservoirs of fossil fuels, and their negative environmental effects, the use of renewable energy sources and multigeneration systems have become good alternatives for conventional thermodynamic systems. One of these resources, whose technology has developed rapidly in recent years, is the use of solar energy for the simultaneous generation of various products. Therefore, in this research, a multigeneration system with several subsystems is introduced. The proposed system includes a solar energy collector to receive thermal energy, two thermal energy storage tanks, an organic Rankine cycle, and a Kalina cycle to generate electricity, a multi-effect distillation unit to produce fresh water, an electrolyzer to produce hydrogen, as well as heat recovery for hot water and hot air generation. In this multigeneration system, the cooling unit is designed with the help of a thermosyphon. The performance of the proposed system is studied from energy, exergy, environmental, and exergoeconomic viewpoints using Aspen HYSYS and EES software. The obtained results show that due to the addition of the thermosyphon unit to the refrigeration system, the exergy efficiency increases from 55.62% to 70.26%. As a result of this combination, the performance of the whole system is improved and the amount of costs are reduced. In addition, the parabolic collector system has the highest exergy destruction ratio, 39%, among the subsystems. Furthermore, the results of the exergoeconomic analysis indicate that the PEM water heater with 33.3% and the ejector with 22.7% own the highest cost destruction rates.

Exergoeconomic and exergoenvironmental analyses of a promising alumina extraction process from secondary aluminum dross in China

Secondary aluminum dross (SAD), listed as a hazardous waste in China, has become a big bottleneck for aluminum industry under massive accumulation and tight regulations. In the dilemma of few industrial treatment cases, an alumina extraction process from SAD proposed by us has been proved a promising technological-feasible process. A coupled exergoeconomic and exergoenvironmental analysis was used to identify key consumption reduction opportunities and potential for economic or environmental improvement of this process. Results showed that Calcination had the lowest exergy efficiency (32.16 %), which required waste heat recovery. Alumina Dissolution and Evaporation and Concentration had high exergy destruction ratio, which is necessary to improve steam utilization efficiency. Furthermore, the relative cost difference of Calcination was the highest (208.75 %) with the greatest potential for economic benefit optimization. Except for Filtration and Drying and Grinding and Sieving, exergoeconomic factors were all below 30 %, which need to adjust non-energy investment cost or equipment structure. The units with low exergy efficiency also had high relative environmental impact difference, among which Calcination was the most significant (183.61 %). Finally, a sensitivity analysis was performed on the identified units with low economic or environmental benefits. This study provides multi-dimensional guidance for the sustainable design, process optimization and industrialization of SAD recovery processes.

A combined cooling, heating and power system with energy storage of waste heat to hydrogen

To improve the recovery of waste heat, a natural-gas based combined cooling, heating and power (CCHP) system with waste-heat to hydrogen as energy storage is proposed. In the novel system, the steam reforming of methanol (SRM) is applied in between the internal combustion engine (ICE) and absorption chiller, and integrated with a hydrogen tank and proton exchange membrane fuel cell (PEMFC) for energy storage. The mathematical model is developed to identify the thermodynamic performances of the system in three operation modes (normal, storage, supplemental) under design and off-design conditions, and multi-objective optimization is conducted to explore the optimal system performances. The results show that the overall exergy efficiencies of the three modes and reference system are 41.71 %, 46.34 %, 43.63 % and 40.51 % with given conditions, respectively. Except for ICE, the reactor accounts for 10.2% and 11.1 % exergy destruction ratio in M1 and M2 modes, while PEMFC accounts for 15% in M3 mode due to the chemical reactions. The parametric analysis demonstrates that increasing reaction temperature of SRM, methanol flow rate or working pressure of PEMFC can enhance the system exergy efficiencies for all modes. The optimal points determined by two decision methods are coincident and the energy and exergy efficiencies are 80.50 % and 43.00 %, which have increased by 0.36 % and 3.09 % than that under design conditions. The study constructs a promising scheme for realizing hydrogen storage by recovering the waste heat, and the results have verified the feasibility of the system and provided thermodynamic basis for further system configurations.

Energy and Exergy Enhancement Study on PV Systems with Phase Change Material

A solar photovoltaic (PV) system produces electrical energy from solar energy. This green, sustainable system has low energy conversion efficiency due to the rise in PV temperature throughout the day. In order to keep the temperature of the panels close to ambient, this study examines the usage of hydrated salt (HS36) as a Phase Change Material (PCM) for PV cooling. The primary goal of this experimental study is to cool the PV panel by introducing PCM behind the PV system (PV-PCM), thus increasing its performance. An energy and exergy performance assessment was carried out on PV and PV-PCM systems. The result indicates that placing a PCM over the back of the solar panel’s back reduced the operational temperature by 25.4% and increased the panel’s electrical efficiency by 17.5%. PV-PCM systems’ maximum exergy efficiency increased by 12.57%, and their exergy destruction ratio decreased by 12.49%. The proposed PV-PCM system with HS36 PCM increased the PV panel performance and can be deployed in the PV system.