Exergy Performance Research Articles

Energy and exergy evaluation in a densified biomass burner using cocoa shells, intended for air heating for the artificial drying of food

Residual biomass as a renewable resource provides alternatives for energy generation, turning a problem into an opportunity for the industry. This study aims to analyze the energy and exergy performance of a biomass burner that uses cocoa shells as fuel for air heating and subsequent artificial drying of food. The study involves a conventional exergy analysis evaluating the energy performance of the equipment and proposing improvements to enhance the thermal efficiency of the system. The research consists of six phases: it begins with defining the input data of the system, followed by determining the thermodynamic properties of the working fluid (air), the exergies of the biofuel and the working fluid are calculated, energy and exergy balances are performed in the heat exchanger of the burner, and efficiencies are obtained. Finally, a sensitivity analysis is conducted to understand the burner’s behavior under different scenarios. The results showed an average exergy efficiency of 9.8%. By increasing energy efficiency in the sensitivity analysis, the outlet temperature rises to 164°C; however, exergy destruction decreases by 48.7%. One of the significant conclusions of this study proposes modifying the coil design to improve the exergy efficiency of the system due to its heat transfer capacity to the air.

Enhancing Energy, Exergy, and Environment Performances of Ultra-Low-Temperature Three-Stage Cascade Refrigeration Cycle: Optimization and Comparative Analysis

Enhancing Energy, Exergy, and Environment Performances of Ultra-Low-Temperature Three-Stage Cascade Refrigeration Cycle: Optimization and Comparative Analysis

Theoretical Analysis of Energy, Exergy, and Environmental-Related Aspects of Hydrofluoroolefin Refrigerants as Drop-In Alternatives for R134a in a Household Refrigerator

Abstract There are increasing trends to eliminate refrigerants with a high global warming potential (GWP) and use alternative environmentally friendly refrigerants in refrigeration systems. In this regard, this study presents a triple analysis of the energy, exergy, and environmental-related aspects of low-GWP hydrofluoroolefin refrigerants—R1234yf, R1234ze(E), and R1336mzz(Z)—as substitutes for the high-GWP R134a, which is used in a 200-liter household refrigerator having a 157 W cooling power. Pressure ratio, volumetric refrigeration capacity, power consumption, and coefficient of performance were studied as energy performance parameters. Exergy destruction rate and total exergy efficiency were studied as exergy performance parameters. Total equivalent warming impact was studied as an environmental performance parameter. All parameters were calculated under a condenser and ambient temperature of 30 and 40 °C, respectively, and a variable evaporator temperature of −5 to −30 °C. The outcomes revealed that R1234yf and R1234ze(E) give thermal performance close to R134a and higher environmental performance, while R1336mzz(Z) did not show thermal performance close to R134, nor did it show a clear improvement in environmental performance. R1234yf can be used as a direct replacement for R134a, but R1234ze(E) is considered a better alternative provided that the R134a compressor is replaced with a compressor with a higher displacement. The pure R1336mzz(Z) cannot be used in a refrigerator.

Enhancing exergy and economical performance of a waste heat power generation system: Multi-objective optimization and comparative analysis

Enhancing exergy and economical performance of a waste heat power generation system: Multi-objective optimization and comparative analysis

Energy and exergy analysis and performance optimization of buildings integrated with transpired solar collectors and phase change materials

Transpired solar collectors (TSCs) are one of the cost-effective air heating technologies that can be easily installed on building facades to provide heated fresh air to condition indoor space. The economics of TSCs can be further enhanced by integrating with phase change materials (PCMs). This study presents the performance investigation and optimization of a building-integrated TSC and PCM system (TSC-PCM). The interactions between PCM thermal properties, their locations in the building envelope, and TSC design parameters were investigated. Based on the modeling of the TSC-PCM by using energy balance and enhanced enthalpy method, a series of orthogonal tests, which varied PCM type, thickness, and location within building envelopes, and TSC suction flow rate were conducted. Multivariate testing, through the Taguchi method, was then applied to identify the optimal design combination. The results showed that the suction flow rate of the TSC-PCM on the external wall showed the highest influence on enhancing indoor thermal performance (up to 77.6%), followed by PCM location on the external wall (up to 9.2%). The optimized TSC-PCM system improved the thermal comfort increase index (TCI) to 3.7 and achieved a maximum thermal efficiency of 401.8%, with an exergy improvement of 26.9% in comparison with the use of the TSC-only. The optimized TSC-PCM system increased the average indoor room temperature to 18.8 oC, which was 6.8% and 18.2% higher than the use of the TSC-only and a baseline without using PCM and TSC, respectively.

Multi-objective optimization of a biogas-fired gas turbine incorporated with closed Brayton and ejector power/cooling co-generation cycles

Fossil fuels have long been the primary source of energy for human consumption. However, with increasing population growth and industrialization, electricity demand continues to rise, necessitating a sustainable and clean energy supply to mitigate environmental damage and support global development. This research proposes a gas turbine-based power plant that utilizes renewable biogas as its fuel source. To enhance the plant’s efficiency, the gas turbine is integrated with a closed Brayton cycle, complemented by compressor intake cooling. This cooling process is achieved through a combined power and ejector refrigeration unit, which recovers waste heat from the gas turbine. The energy, exergy, and economic performance of the proposed plant are thoroughly analyzed, with exergy efficiency and unit product cost serving as the objective functions for multi-criteria optimization. The results demonstrate that compressor intake cooling improves both thermodynamic and economic performance under all operating conditions. At the optimal design point, the system with intake cooling achieves an exergy efficiency of 39.38%, compared to 33.64% for the system without it. Additionally, while the system with intake cooling requires higher initial investment, it offers lower unit product costs, making it a more economically viable option.

Energy, Exergy, and Economic Performance Comparison and Parametric Optimization of Organic Rankine Cycles Using Isobutane, Isopentane, and Their Mixtures for Waste Heat Recovery

The possibility of applying the organic Rankine cycle (ORC) to further recycle the low-grade waste heat efficiently is studied in the present work. The energy, exergy, and economic models of the ORC system are established, and the isobutane, isopentane, and their mixtures are selected as the organic working mediums (OWMs). Due to the slip characteristics of mixed OWM, four operational conditions of the ORC system are proposed, and then the contrastive analysis of energy, exergy, and economic performances under the four operational conditions are conducted. Finally, the optimal mixture mass fraction and crucial parameters of the ORC system are separately determined through the bi-objective optimization. The results show that the ORC system using the mixed OWM can achieve a larger net power output and exergy efficiency by comparing the pure OWM when the condensing temperature is set as the saturated vapor temperature during the condensation process. The electricity production cost first rises and then decreases with the rising mass fraction of isobutane in mixed OWM, and the ORC system using the isopentane can achieve the smallest electricity production cost. By taking the low-grade flue gas of 433.15 K as the ORC heat source, four operational conditions have the same optimal ORC crucial parameters, namely the evaporating temperature of 393.15 K, condensing temperature of 308.15 K, and superheat degree of 0 K. The pure OWM of isobutane can achieve better overall performance by setting the condensing temperature as the saturated liquid temperature.

Comparative optimization of the thermal performance for H2 – Metal hydride heat storage and heat pump systems

Metal hydride is very promising in hydrogen storage and simultaneously the thermal effect in the reversible hydrogenation process makes it possible in heat storage and heat pump area. The interaction of H2 – Metal – hydride pair and its further applications need comprehensive thermodynamic design and performance optimization. Therefore, this work makes thermodynamic comparative research of heat storage and heat pump systems by adopting H2 – Metal-hydride pair. According to the investigation, the thermodynamically optimal charging-discharging temperatures (Tm1,Tm2), the heat source temperature (Th1) and the ambient temperature (Tc1) meet the relationship of Tm1Tm2=Th1Tc1 for the heat storage system. Given the operating pressure (p), there exists a well-matched temperature (T) range to maximize the exergy performance of metal hydride heat storage system. Meanwhile, the running p-T is positively correlated, e.g., when the charging pressure is set at 0.2 MPa to 0.3 MPa, the well-matched T varies from 307 K to 317 K. When the discharging pressure is set at 0.4 MPa to 0.7 MPa, the well-matched T varies from 304 K to 320 K. For the metal hydride heat pump system, the optimal performance lies in maximizing the transported heat. Given the operating T, there exists a well-matched pressure range for the heat sink device, e.g., for the heat releasing process, when operating T is set at 353 K, 363 K, 373 K, 383 K and 393 K, the well-matched p are 2.3 MPa, 3.3 MPa, 3.8 MPa, 4.6 MPa and 6.1 MPa. Both the heat storage and heat pump performances are also affected by the operating pressure – temperature −transported heat, presenting improved region and degraded region. The optimal thermodynamic criterion and the matchability of the operating parameters provide a theoretical guidance for the MH-based thermodynamic system design and operation.

Liquid air energy storage system with oxy-fuel combustion for clean energy supply: Comprehensive energy solutions for power, heating, cooling, and carbon capture

Liquid air energy storage systems have garnered significant attention in the energy storage sector because of their high energy density and geographical independence. However, despite their substantial potential for improving renewable energy-based systems, their commercialization is hindered by their low round-trip efficiency. Furthermore, dependency on other thermal systems and environmental challenges remain unresolved, despite efforts to address these limitations. This study proposes an independent liquid air energy storage system that offers effective energy solutions, including the ability to provide power, heating, and cooling with improved efficiency and sustainability. Moreover, in-depth assessments of the energy, exergy, economic, and environmental performance were conducted. Under rated conditions, the system delivers 118.19 MW of power, 38.64 MW of heating, and 81.07 MW of cooling, achieving a round-trip efficiency of 80.56 %. Additionally, the system generates nitrogen as a by-product, providing further economic benefits. An economic analysis revealed that it yields a net present value of $636.51 million and an internal rate of return of 25.67 %. Environmentally, the system uses an oxy-fuel combustion method to capture 99.997 % of carbon dioxide emissions from natural gas combustion without consuming additional energy. These findings will contribute to the future development of sustainable and eco-friendly energy supply systems.

Advanced exergy analysis and performance enhancement of air‐cooled solar recompression supercritical carbon dioxide systems

Advanced exergy analysis and performance enhancement of air‐cooled solar recompression supercritical carbon dioxide systems

Analysis and comparison performance of four organic Rankine cycle configurations for a hot, non-temperate climate solar project: Thermodynamic, economic, exergoenvironmental, and environmental

This paper aims to compare the energy, exergy, economic, exergoenvironmental, and environmental (5E) performance of four different organic Rankine cycle (ORC) configurations using benzene as the working fluid, in a solar project in a hot, non-temperate climate. The configurations analyzed include a two-stage series ORC (DSORC) and a three-stage series ORC (TSORC), as well as their respective regenerative variants (R-DSORC) and (R-TSORC). To ensure a fair assessment, a computer program was developed with Engineering Equation Solver (EES) software in order to study the influence of operating parameters on the performance of these systems, providing them with the same total thermal potential. Under basic operating conditions, simulation results show that R-TSORC is the most competitive, with a net power output of 1642 kW, an energy utilization factor of 18.11%, and an exergy efficiency of 25.06%. In addition, it achieves an annual emission reduction in CO2 equivalent of 34210 tonnes, with an exergetic sustainability index of 0.2404. Consequently, the payback period is 4.155 years, and the levelized cost of electricity is 0.06479 $/kWh, which is lower than the cost of self-generated electricity for industries in Cameroon. The results reveal that R-TSORC could be deployed in solar micropower plants located in hot, non-temperate climates. Its ability to efficiently harness solar energy makes it a relevant solution for regions facing problems of access to electricity.

Techno-economic evaluation and multi-objective optimization of a cogeneration system integrating solid oxide fuel cell with steam Rankine and supercritical carbon dioxide Brayton cycles

Developing highly efficient thermodynamic cycles is of great importance in the area of distributed energy system, there are still many non-negligible problems on feasibility assessment and performance evaluation in the application of some emerging technologies, especially involving the fuel cells and carbon dioxide power cycles. This study proposes a distributed heat and power cogeneration system composed of a solid oxide fuel cell, a gas turbine, a steam Rankine cycle, a supercritical carbon dioxide Brayton cycle, and a heat exchanger. The system mathematical model is constructed, and the investigation on system energy, exergy, economic, environmental, and techno-economic performance is performed to demonstrate the technology’s feasibility and applicability. The simulation results indicate that the system can provide 367.03 kW of power and 58.02 kW of heating at the design point, and the overall electrical, exergetic, and energy efficiencies are 68.38 %, 72.41 %, and 79.19 %. The total cost rate of system is achieved to be 11.62 $/h with the system carbon dioxide emission and payback period being 0.2829 kg/kWh and 10.87 year. It can be concluded from the sensitivity analysis that the increases of the compressor pressure ratio, fuel flow rate, and SOFC inlet temperature contribute to improving the system electrical efficiency, while the carbon dioxide emission and the payback period can be reduced. Finally, multi-objective optimization of the cogeneration system is further performed to provide a strategy of performance improvement for system designers and decision makers. The optimization result indicates that though the system carbon emission is increased by 0.25 %, the system payback period and levelized cost of energy are obtained to be 9.88 year and 0.2836 kg/kWh, which are decreased by 9.11 % and 1.47 % compared to the design point.

Thermodynamic, economic and regulation strategies analysis of a phosphoric acid fuel cell combined heating and cooling

Phosphoric acid fuel cells (PAFCs) not only generate electricity but also produce a substantial amount of waste heat. This study introduces a novel conceptual framework that integrates a PAFC, a gas turbine, and a waste heat recovery unit to provide combined cooling, heating, and power (CCHP) services for various applications. The system's operational versatility is achieved by manipulating valve openings, allowing for the regulation of waste heat utilization across six distinct operational modes. A thermodynamic model has been developed and validated to evaluate system performance under diverse design conditions and configurations.A comprehensive analysis examines the impact of key variables on system metrics, including efficiency, exergy, and economic performance. Additionally, the analysis assesses system exergy losses and economic viability, revealing that the PAFC module experiences the highest energy loss, followed by the ARS and ORC, while the DHW exhibits the lowest relative losses. Furthermore, the economic evaluation underscores the system's adaptability, suggesting that it is a potentially viable option for CCHP production.

Study on energy and exergy performance of a new hybrid perforated photovoltaic/solar air heater integrated with encapsulated phase change materials: An experimental study

The current study conducts energy and exergy analyses on an innovative hybrid perforated photovoltaic/solar air heater (PV/SAH) using passive and active methods to improve thermal and electrical efficiencies. Since increasing PVs’ temperature reduces their electrical efficiency, various techniques have been employed to handle this problem, employing effective cooling strategies. This study uses an experimental approach to analyze two cooling strategies: encapsulated phase change material (PCM) units as a passive method and forced-convection mechanism as an active method. Two scenarios were considered: hybrid PV/SAH with and without encapsulated PCM units at two mass flow rates of 0.05 kg/s and 0.07 kg/s. The results illustrate that the encapsulated PCM reduced the PV and outlet temperatures by 2 °C and 4 °C, and 3 °C and 1.5 °C at the mass flow rates of 0.05 kg/s and 0.07 kg/s, respectively. The lower the outlet temperature, the lower the thermal efficiency. Hence, using the PCM units decreased the thermal efficiency but improved the electrical efficiency. The PCM units caused a reduction in daily overall energy efficiency by 12.41 % and 8.36 % at the mass flow rates of 0.05 kg/s and 0.07 kg/s due to reducing thermal efficiency. Unlike the energy efficiency, the PCM units improved the daily overall exergy efficiency by 6.28 % and 8.71 % at the mass flow rates considered. Hence, using passive and active methods is a robust technique to improve the hybrid systems’ performance.

Exergy Analysis of Gas Turbine Open Cycle with Pressure Gain Combustion Based on Humphrey Cycle

Abstract This paper describes an exergy comparison of the pressure gain combustion (PGC) gas turbine (GT) with conventional GT. PGC has recently emerged as a promising approach to achieve major performance improvements in the current gas turbines operating on the Joule cycle, where the potential for major performance upgrades has nearly plateaued. However, the inherently unsteady and periodic nature of this combustion technology presents challenges in modelling the PGC process and understanding its impact on the cycle. In this work, PGC is represented by a steady-state model of constant volume combustion based on the Humphrey cycle, along with a constant pressure combustion loss model for capturing practical losses. Exergy performance was analysed in terms of exergy destruction for three air-cooled GT cycles with different combustors: a conventional isobaric combustor, an optimistic PGC combustor with no losses and a realistic PGC combustor with losses. Gas turbine cycles were modelled in WTEMP (Web-based Thermo-Economic Modular Program) software, a modular and flexible cycle analysis tool developed by TPG at the University of Genova. Simulations were performed at compressor pressure ratios from 5 to 40 at turbine inlet temperatures of TIT=1300°C and TIT=1700°C, and results were analysed in terms of exergy destruction and exergy efficiency. It was found that a PGC combustor with optimistic losses recovers more exergy than a conventional combustor due to pressure gain. At a cycle pressure ratio of 20 and 1700°C TIT, the PGC combustor with a pressure ratio of 1.35 resulted in an exergy efficiency of 79.6% compared to 77.9% of the Joule combustor. However, with realistic loss from inlet pressure drop and constant pressure combustion in the PGC combustor, the PGC combustor showed higher irreversibility than conventional combustor but the overall benefit on the cycle was retained at low compressor pressure ratios. Moreover, the percentage increase in turbine irreversibility from blade cooling was found to be slightly lower for the PGC cycle as compared to Joule.

Exergy Efficiency and Energy Efficiency of Double Air Pass Solar Tunnel Air Dryer: A CFD Analysis

This work presents, the computational fluid dynamics simulation of a forced convection double air pass solar tunnel drying system to study the temperature distribution, the flow behaviour of the air stream, and the exergy performance. Realizable k-epsilon non-equilibrium wall function turbulence model, discrete ordinate radiation model, and species transport were used. The average temperature, thermal efficiency, and exergy efficiency were found to 59.2 oC, 30%, and 9.41%, respectively. The result revealed that the uniform temperature and velocity distribution throughout the heating and drying chamber. Therefore, the newly developed double air pass solar tunnel dryer enhances the air temperature and the exergy performance leads to the increment of drying rate and reduction of drying period.

Performance assessment of solar tower collector based integrated system for the cogeneration of power and cooling

Integrating solar energy systems is an essential measure in advancing worldwide sustainability objectives and offers a sustainable, environmentally friendly approach to reducing greenhouse gas emissions and pollutants. To this direction, the proposed system integrating solar tower collector, supercritical CO2, organic Rankine cycle, and single effect absorption refrigeration cycles shows potential as an efficient and sustainable solution for meeting energy and cooling demands. A detailed thermodynamic evaluation has been performed to gain valuable understanding of the energy and exergy performance, enabling the assessment of thermal and exergy efficiencies, exergy destructions, and heat losses. Results show that this study found the thermal efficiency of the proposed system to be 47.35 % for R245fa, 48.59 % for R123, and 52.32 % for toluene. In addition, the exergy efficiency was obtained at 40.99 % for R245fa, 42.41 % for R123, and 46.67 % when toluene is used as a working fluid. With all investigated working fluids of organic Rankine cycle, toluene achieved the highest thermal and exergy efficiency of the proposed power-cooling cogeneration system, while R245fa achieved the lowest energetic and exergetic performance. Among the various ORC working fluids investigated under operating conditions, toluene demonstrated the highest turbine power output (3202 kW), whereas R245fa exhibited the lowest turbine power output (2804 kW). The refrigeration output for all ORC working fluids studied was found to be 988.8 kW. Additionally, the primary contributor of exergy destruction rate in the proposed system was determined to be the solar tower receiver, contributing 73.24 %, 67.80 %, and 66.19 % to the total for the toluene, R123, and R245fa working fluids, respectively.

Thermo-economic analysis on trans-critical compressed CO2 energy storage system integrated with the waste heat of liquid-cooled data center

Compressed CO2 energy storage (CCES) technology has the advantages of high energy storage density, low economic cost, low carbon emission, which is suitable for the construction of large-scale and long-time energy storage system. Besides, as a scene with massive heat, the electricity consumption of servers in data center is mostly converted into heat. Thus, the purpose of this work is to integrate a trans-critical compressed CO2 energy storage system with the waste heat of data centers, so as to improve the system performance and reduce the operating cost of data center. Based on different operating principles of compressors, a single-stage compression system (System-CP) and a double-stage compression system (System-VP) are constructed. To analyze and compare the energy and exergy performance of these two systems under design conditions, a quasi-dynamic model is developed by considering the variations of pressure and temperature in the storage tank. On this basis, an economic model is developed to obtain the economy performance for the systems. The obtained results show that the round-trip efficiency (RTE) of System-CP and System-VP are 64.67 % and 67.41 %, respectively. For the energy storage capacity 15 MW × 5 h, volumes of high-pressure S-CO2 storage tank are 314,387.51 m3 and 287,982.91 m3 for System-CP and System-VP, respectively. Thereby, the energy storage density (ESD) of System-CP and System-VP are 0.24 kW·h/m3 and 0.26 kW·h/m3, respectively. Meanwhile, the total capital cost (TCC) is $477.84 × 106 for System-CP, and $437.41 × 106 for System-VP, and the corresponding payback period (PBP) are 14.76 years and 12.39 years respectively. Further, the effect of key parameters on systems performance is revealed. The results show that with the decrease of slip-pressure range decreases, RTE, TCC and the volume of storage tanks increase linearly.

Impact of collector aspect ratio on the energy and exergy efficiency of a louvered fin solar air heater

Solar air heaters have huge applications in renewable energy utilization segments concerning the issues of space heating, drying, and ventilation systems. Performance prediction of such systems largely depends upon the design of the collector itself. The present study has highlighted the influence of various aspect ratios of the collector on the thermal and exergy performance of louvered finned solar or air heaters. In this context, an experimental analysis has been carried out to compare the performance of LFSAH with conventional PSAH. These results show that an increase in aspect ratios enhances thermal efficiencies of heat transfer and the systems. An aspect ratio of 4:1 showed the maximum thermal efficiencies as 81.63 % for LFSAH and 68.13 % for PSAH. On the other hand, at larger mass flow rates, the exergetic efficiency of LFSAH becomes lower owing to the larger friction and exergy losses and sometimes even lower than that of PSAH. The novelties of the present study are in emphasizing the importance of aspect ratio in optimizing solar air heater design and providing relevant insight for better energy use.

Development of a geothermal-driven multi-output scheme for electricity, cooling, and hydrogen production: Techno-economic assessment and genetic algorithm-based optimization

This study aims to develop an environmentally friendly multi-energy system for sustainable production of electricity, cooling and hydrogen. The study introduces a pioneering geothermal-based system, integrating an ejector refrigeration cycle, a dual-loop organic Rankine cycle, and a hydrogen production unit with proton exchange membrane electrolyzers. The study provides a thorough analysis of the system's energy and exergy performance, as well as its economic feasibility. Through sensitivity and parametric analyses, the research identifies key parameters that significantly influence system performance. The system's innovative design promises minimal environmental impact while delivering multifaceted performance: generating 1.38 MW of electricity, supplying 436 kW of cooling load, and producing 5.39 kg/h of hydrogen. In the exergy analysis, Evaporator1 is identified as the primary contributor to exergy loss, representing 34 % of the total exergy destruction. This is followed by the electrolysis unit, the condenser, and the ejector refrigeration cycle, which contribute 18 %, 14 %, and 12 %, respectively. The system achieves optimal efficiency at an organic Rankine cycle turbine1 inlet temperature of 387 K, yielding a power generation of 885.4 kW and an exergy efficiency of 26.7 %. Beyond this temperature, any further increase leads to a decline in power output due to operational disturbances. A multi-criteria optimization using genetic algorithm is applied, resulting in an optimized system with a cost rate of 18.13 $/h and an exergy efficiency of 38.96 %.