International Journal of Exergy (18 papers in press)

Regular Issues

• Exergetic Simulation Study of CO2 Separation by Cryogenic Distillation  
  by NANDAKISHORA Y, Ranjit. K. Sahoo, Murugan S, Sai Gu 
  Abstract: A cryogenic process for CO2 separation is developed, with exergy minimization using Aspen Plus software. The RadFrac distillation model is used for the separation of CO2 from a CO2/N2 gas mixture. The process is modified to minimize the energy penalty of CO2 separation. The comparative study is focused on energy savings, exergy losses, and economic and environmental factors. The energy penalty of the optimized process is approximately 1.049 MJ/kg-CO2 with purity and recovery of 99.9% and 98%, respectively. The exergy loss in the optimized process is approximately 14% lower than in the basic design.
  Keywords: Distillation; CO2 separation; exergy analysis; heat integration.
  
  
• Exergy Analysis In Rice Milling System Integrated With Gasifier  
  by Omil Charmyn Chatib, Armansyah Halomoan Tambunan, I. Wayan Budiastra, Mohamad Solahudin 
  Abstract: The conversion of husk to usable energy can be accomplished through gasification. Meanwhile, the integration of a gasifier into the rice milling process is beneficial to use the syngas as the energy source. Using the second law of thermodynamics, the mass, energy, and exergy balance at each stream of the system was evaluated. The results showed that a rice miller with 875 kg/h capacity could produce 250 kg/h of rice husk, which can be converted to 353.16 kg/h of producer gas. This is equivalent to 401.53 kW of exergy, higher than the required exergy of the miller.
  Keywords: Rice husk; Rice milling system; Gasifier; Energy; Exergy.
  
  
• Energy and Exergy Analyses to Enhance the Performance of Coiled-Tube Heat Exchanger by Employing Water/Al2O3 Nanofluid  
  by Esam Jassim 
  Abstract: The purpose of this research is to experimentally evaluate the degree of enhancement in the heat transfer and entropy generation when nanoparticles mix with ordinary water. Several concentrations of Al2O3 nanoparticles at various flowrates are investigated to assess the enhancement in the exchangers (NTU) and efficiency. Results illustrate that the heat exchanger performance enhances up to 27% due to presence of nanoparticles and is supplemented with the increase of the volume fraction as well as the nanofluid flowrate. Numerically speaking, the total irreversibility decreases by 47% at volume concentration of 0.5% although the frictional source augments by 27%.
  Keywords: Al2O3 nanoparticles; Coiled tube heat exchanger; Efficiency; Exergy; Nanofluid.
  
  
• Performance Investigation of a Spark Ignition Engine (SIE) Operated on Mixtures of Methane-Hydrogen and Different Liquid Fuels  
  by Guven Gonca, Ibrahim Genc 
  Abstract: This report presents the impacts of triple fuel blends composed of liquefied methane-hydrogen and benzene, gasoline, hexane, toluene, iso-octane, ethanol (ethyl alcohol) and methanol (methyl alcohol) on the specifications of performance and NO formation of a spark ignition engine (SIE). A gas fuel's mass ratio has been remained constant as 50%, mass ratio of other gas fuel has been chenged between 10 and 50%. The maximum thermal and exergy efficiencies are 37.15% and 37.31% which are observed with 50% benzene-50% hydrogen combustion and minimum values of them are 20.69% and 20.61% which are attained with 50% methanol-50% hydrogen. The peak NO is attained with 50 % benzene-50% hydrogen combustion as 5.78E-07 mol/cm3 and minimum NO is attained with 50% methane-50% hydrogen as 2.92E-9 mol/cm3.
  Keywords: Ternary fuel mixtures; liquid fuel; gas fuel; spark ignition; NO formation.
  
  
• EXERGOECONOMIC ANALYSIS OF A REVERSIBLE SOLID OXIDE CELL BASED POWER-TO-SYNGAS-TO-POWER SYSTEM  
  by Muiz Adekunle AGBAJE, Ali Volkan Akkaya 
  Abstract: Energy storage is a critical element in implementing and adopting renewable energy systems. A reversible solid oxide cell (ReSOC) system is an electrochemical energy storage system that stores and produces power. The study investigates the economic effect of the thermodynamics of a power-to-syngas-to-power system based on a reversible solid oxide cell (ReSOC) stack. This will provide insight into areas of primary importance for designing an economically feasible ReSOC system. The specific exergy cost (SPECO) approach is used for developing this thermoeconomic model, and the exergoeconomic properties in power to syngas (SOEC) and syngas to power (SOFC) modes of the ReSOC system are investigated. The results showed a capital cost rate of $9.25/h for the SOFC mode and $9.14/h for the SOEC mode of operation. The combined capital cost of the storage tanks and ReSOC stacks accounts for approximately 80% of the overall system capital costs in both operating modes. Additionally, the cost of electricity significantly influences exergoeconomic performance. The SOEC mode had a higher system exergy cost rate of $14.27 /h, and the SOFC mode had an exergoeconomic performance of 0.67. In conclusion, the exergoeconomic analysis has revealed the cost rates in the ReSOC system for both modes of operation. These results would guide in determining the most effective points of cost reduction to improve the economic performance of the ReSOC-based system.
  Keywords: Cost analysis; Energy storage; Exergoeconomics; Reversible solid oxide cell; SPECO; System analysis.
  
  
• Comparative Exergy-Based Performance Analyses and Optimisation of Combined Power Cycles  
  by Asım Sinan Karakurt 
  Abstract: The value of energy resources has grown significantly these days, making their proper and intelligent utilisation crucial. Improvements are being made to both new and existing systems to satisfy the rising energy demands and effective use of energy. Supercritical and organic Rankine power cycles (ORCs) for waste heat recovery are commonly used to create more effective and ecologically friendly systems. The article in this context analyses the effects of temperature and pressure ratios on the various objective functions of four different systems (1-Brayton, 2-Brayton-sCO2, 3-Brayton-sN2, and 4-Brayton-ORC). As a result, this study will find the optimum solutions and systems for one or more usage purposes. While System 1 can be chosen as optimum in terms of ECOP and ηII, System 4 can be chosen as the best system in terms of wnet and ηth. All systems have certain limitations relative to one another when operating at their optimum under specific parameters.
  Keywords: combine system; organic Rankine cycle; supercritical cycle.
  DOI: 10.1504/IJEX.2023.10055546
   
  
• Exergoeconomic analysis of a photovoltaic plant for different panel types  
  by FATIH AKKURT, Aysel Özselçuk 
  Abstract: In this study, exergoeconomic analyses of a 1166 kWp nominal power PV system for Polycrystalline, PERC Monocrystalline-Hulf Cut and PERC Monocrystalline panel types were carried out for the climatic conditions of Konya province in Turkey. The annual energy and exergy efficiencies were determined as 17.2% and 18.5% for PERC Monocrystalline-Half Cut, 16.8% and 18.1% for PERC Monocrystalline, 13.8% and 14.8% for Polycrystalline, respectively. The SPECO method was used for exergoeconomic analysis. The annual electricity generation costs were determined as 35, 41 and 37$/MWh while the payback periods were calculated as 48, 63 and 53 months for Polycrystalline, PERC Monocrystalline-Half Cut and PERC Monocrystalline, respectively.
  Keywords: PV system; exergy enalysis; exergoeconomic analysis; electricity generation cost; payback period.
  
  
• Energy, Exergy, Exergoeconomic Analysis of a General UAV  
  by Suha Orçun MERT, Mehmet Hakan DEMIR, Habibe DEMIR, Ceyda KOK 
  Abstract: A 3E -energy, exergy, exergoeconomic- analysis of a rotary wing UAV that is used for general purpose has been accomplished in this study. In the study a parametric investigation regarding the velocity, altitude and distance has also been investigated for identifying energy and exergy efficiency as well as exergoeconomic cost of operation. Looking at the results, while the distance increased from 0 m to 1200 m, the total energy increased up to 90000 J and the motor energy increased up to 65000 J. Parallel to this situation, energy efficiency reached 50% and exergy efficiency reached 40%. However, the exergoeconomic cost decreased from 0.0013 S/s to 0.001 S/s. While the velocity increased from 0 m/s to 14 m/s, the motor energy decreased to 10000 J and the total energy to 15000 J. As the velocity increased, the energy and exergy efficiency decreased to 20% and 15%, respectively. However, unlike energy and efficiency, the exergoeconomic cost increased as the velocity increased and was measured as approximately 0.00045 $?s. Finally, while the altitude parameter was increased from 0 m to 200 m, the total energy and motor energy increased by 20000 J and 17000 J, respectively. Contrary to this situation, while the altitude was increasing, the energy and exergy efficiencies decreased and reached up to 17% and 14%, respectively. The exergoeconomic cost increased with the speed increase and took the value of about 0.000455 $/s.
  Keywords: UAV; Energy; Exergy; Exergoeconomy; Drone; Cost; Analysis.
  
  
• Exergy and Environmental Analyses of Natural Gas and Biogas Fuels in an Internal Combustion Engine at Part Load  
  by Yasar Bulbul, Altay Arbak, Yasin Karagoz, Selman Karagoz, Tarkan Sandalci, Saban Pusat 
  Abstract: This paper presents an experimental investigation on a single-cylinder diesel engine fueled with natural gas and biogas. Biogas was obtained by mixing methane and carbon dioxide (CO2). The analyses were carried out by using the results of experiments on different fuel mixtures at constant engine power. As a result of working at partial load, the energy and exergy efficiencies of the engine were relatively low. When the results were compared by CO2 content of the fuel, it was observed that when the CO2 ratio increased, the exergy efficiency decreased. In addition, an economic analysis was performed based on the equivalent CO2 emission and the average carbon tax in the European Union. Accordingly, natural gas had the highest GWP value and tax amount. As the CO2 content in the fuel increased, the GWP (Global Warming Potential) and the carbon tax to be paid decreased.
  Keywords: Exergy analysis; Environmental analysis; Economic analysis; Biogas; Internal combustion engine.
  
  
• Performance investigation and simulation of a diesel engine operating on seven-process cycle based on energy and exergy criteria  
  by GÜVEN GONCA, Ibrahim Genc, Bahri Sahin 
  Abstract: This work investigates energetic and exergetic performances of seven-process cycle which is combination of Dual-Miller and Takemura cycles based on parametrical and grid curves. The impacts of design parameters on the maximum performance characteristics are examined. In the results, the energy (1. law) and exergy (2. law) efficiencies maximize enhance by a determined range and then they minimize with raising engine speed. Power enhances with enhancing engine speed at constant compression, Takemura cycle, equivalence and cut-off ratios. Power and efficiencies increase with raising cycle pressure ratio at constant compression, Takemura cycle, equivalence and pressure ratios. Power and efficiencies decrease with increasing exhaust temperature ratio and cut-off ratio at constant compression ratio, Takemura cycle ratio, equivalence ratio and engine speed. They enhance with increasing pressure ratio and cycle temperature ratio at constant compression ratio, Takemura cycle ratio, engine speed and cut-off ratio.
  Keywords: Takemura cycle; Dual Miller cycle; Exergy; Performance optimization; Internal combustion engines.
  
  
• Exergy Analysis and Optimization of a Hybrid Solar-Geothermal Power Plant  
  by Mahya Moghadam, Mohammad Hasan Khoshgoftar Manesh, Ana Maria Blanco Marigorta 
  Abstract: The present study aims at the Energy, Exergetic, Exergoeconomic, Exergoenvironmental analysis of a hybrid solar-geothermal power plant. In addition, the emergy-based approach based on exergoeconomic and exergoenvironmental analysis has been performed. Genetic programming and artificial neural networks have been used to generate correlations for objective functions to reduce computational time. Advanced exergy, exergoeconomic, and exergoenvironmental analyses have been done to evaluate the system better based on exogenous/endogenous and avoidable/unavoidable parts of exergy destruction. Thermodynamic simulations have been verified with high accuracy with PETROSIM software and reference data. Results analysis show that the proposed cycle produces about 59.2 MW of net power.
  Keywords: Solar; Geothermal; Exergetic; Exergoeconomic; Exergoenvironmental.
  
  
• An optimised solar-based microgrid integrated with desalination to enhance exergy sustainability  
  by Mohammadali Kiehbadroudinezhad, Adel Merabet, Homa Hosseinzadeh-Bandbafha 
  Abstract: The size of a solar microgrid system should be designed based on aspects of sustainability, such as cost, exergy, etc. This study by the division algorithm finds the optimal size with maximum reliability vs. the cumulative exergy demand. Larak Island, Iran, is used as an example of how the concept could be applied to the real world. According to the introduced optimal size, 1 m³ of freshwater generated by the solar energy system leads to an average cumulative exergy demand of 17 MJ. While integrating a diesel generator into system means, exergy demand reaches 33 MJ/m³ of freshwater.
  Keywords: solar energy; cumulative exergy demand; desalination; optimisation; reliability; division algorithm.
  DOI: 10.1504/IJEX.2023.10056723
   
  
• Entropy generation analysis of fully developed turbulent convection in a twisted elliptical duct with constant heat flux  
  by Junlin Cheng, Zizhao Wang, Huiyi Mao 
  Abstract: In this study, the entropy generation and exergy efficiency of turbulent flow through a twisted elliptical tube were investigated. The effects of the fluid properties, the aspect ratio (1.05-10.00) and the twist pitch ratio (4-200) were considered. The results indicated that the total dimensionless entropy generation increased whereas the exergy efficiency decreased as the twist pitch ratio increased. Moreover, the total dimensionless entropy generation decreased, whereas the exergy efficiency increased with an increase in the aspect ratio. The minimum total dimensionless entropy generation of 0.01 is obtained with an aspect ratio of 10.00 and a twist pitch ratio of 16.36.
  Keywords: entropy generation; exergy efficiency; turbulent flow; twisted elliptical duct; constant heat flux; geometry configuration.
  DOI: 10.1504/IJEX.2023.10056724
   
  
• Exergy analysis in an HCCI engine powered with hydrogen enriched natural gas  
  by Tawfiq Abdul-Aziz Al-Mughanam, Abdul Khaliq 
  Abstract: HCCI combustion is a very promising technology as it provides low NOx and soot formations with high efficiency. In the present investigation, the performance of turbocharged HCCI engine operated with hydrogen enriched natural gas was assessed using exergy analysis. The impact of equivalence ratio, turbocharger pressure, atmospheric temperature, and hydrogen enrichment has been ascertained on the engine's energy and exergy efficiencies. Special attention is given to identification and quantification of irreversibility of combustion and heat transfer processes using the concept of entropy generation and exergy loss. It is demonstrated that combustion and heat transfer irreversibilities in HCCI engine can be reduced from 55% to 43.4% and its power output is augmented from 31.4% to 38.4% if natural gas is replaced with 100% hydrogen. Overall, the results of second law analysis for engine under consideration show that variations of operational parameters examined have considerably affected the exergy transfer, irreversibilities and efficiencies.
  Keywords: CNG; HCCI; Hydrogen enrichment; Exergy analysis.
  DOI: 10.1504/IJEX.2023.10054172
   
  
• Work density analysis and thermoeconomic optimisation of modified Carnot cycle engine  
  by Asim Sinan Karakurt, Guven Gonca, Bahri Sahin 
  Abstract: The modified Carnot cycle, a novel thermodynamic cycle, is introduced, and the cycle's performance is analysed in order to more accurately depict the performance and design parameters of actual heat engines. Work output, thermal efficiency, and work density are all considered in conjunction during the performance analysis. In terms of maximum pressure, maximum volume, work density, thermal efficiency, and size, the results demonstrate that the modified cycle performs better than the classic Carnot cycle at simulating the real heat engine. In the performance analysis framework, a thermoeconomic optimisation has been carried out based on an objective function defined as the total cost per unit work output, which depends on an economic parameter, work density, and thermal efficiency. The findings might be used to select the modified cycle's ideal design and operation parameters, which can be applied to actual engines.
  Keywords: Carnot cycle; modified cycle; work density; performance analysis; thermoeconomic optimisation.
  DOI: 10.1504/IJEX.2023.10056733
   
  
• Thermodynamic analysis of a solar refrigeration system based on combined supercritical CO₂ power and cascaded refrigeration cycle  
  by Eydhah Almatrafi, Abdul Khaliq, Rajesh Kumar, Ahmed Bamasag, Muhammad Ehtisham Siddiqui 
  Abstract: This communication proposed a solar driven system based on supercritical CO₂ (sCO₂) power cycle integrated with cascaded refrigeration cycle (CRC) to refrigerate a thermal load of below than -40°C. The impact of varying solar irradiance (DNI), type of solar heat transfer fluid (SHTF), and the working fluid of CRC on refrigeration capacity and exergy efficiency of combined system are investigated. Results indicate helium as the most efficient SHTF with air to follow. It is shown that maximum refrigeration is produced when operating with helium as SHTF and propylene as the refrigerant for CRC. From exergetic point of view, propylene provides higher exergy efficiency; CO₂ is the one with lower, while N₂O presents intermediate results. The exergy efficiency of the system for the propylene, N₂O and CO₂ is determined as 9.64%, 8.73%, and 8.47%, respectively.
  Keywords: gaseous solar heat transfer fluids; supercritical CO₂ power cycle; cascaded refrigeration cycle; CRC; deep freezing; exergy.
  DOI: 10.1504/IJEX.2023.10056735
   
  
• Investigation of the thermal performance of cascaded latent heat thermal energy storage system based on composite phase change materials  
  by Qunli Zhang, Yimo Liu, Zhaosheng Yang, Gang Wang, Xiaoshu Lü 
  Abstract: This paper conducts thermodynamic analysis of the cascaded latent heat thermal energy storage system that is applicable to building heat storage, with focus on using the high performance composite phase change materials (CPCM). The 7.5wt. %EG/MgSO₄7H₂O-KAl(SO₄)₂12H₂O were used as PCM, the performance of cascaded system and single-stage system were compared. The results show that exergy efficiency, heat charging rate and discharging rate of the cascaded system compared with the single-stage system can be increased at most by 11.6%, 49.7%, and 9.7%, respectively. This work has important guiding significance for the applied research of the heat storage system with the CPCM.
  Keywords: phase change material; exergy efficiency; thermal storage; numerical simulation.
  DOI: 10.1504/IJEX.2023.10056359
   
  
• New insight into contradictory distillation sequence heuristics: exergoeconomic and environmental analysis  
  by Mojtaba Malayeri, Abolghasem Kazemi, G. Reza Vakili-Nezhaad 
  Abstract: This research focuses on possible sequences for the distillation of quaternary mixture to assess the performance of a system, where the general design heuristics are contradictory. In cases of contradictory heuristics, the most fitting operating scenarios for referencing each heuristic have not been explored in previous publications. The main objective of this research is to identify the most environmentally friendly and thermodynamically efficient processes, as well as to gain a better understanding of the effect of the objective function on the synthesis of separation trains, through environmental, economic and exergy analyses. To address this, 855 simulations are carried out with capital costs (CAPEX) and total annual costs (TAC) evaluations and environmental impact assessment. Global warming potential (GWP), along with exergy analysis results are also presented. The results of the current study reveal that in contrast to the heuristic criteria and recommendations, it is possible that a heuristically discouraged separation train may work very well, depending on operating conditions. It was also discovered that switching from liquid to vapour feed significantly reduces the direct sequence's superiority. Moreover, it was shown from exergy analysis that selecting the most thermodynamically efficient process does not guarantee optimal solutions in terms of economic and environmental aspects.
  Keywords: distillation; heuristics; economics; exergy; environment.
  DOI: 10.1504/IJEX.2023.10056736