International Journal of Exergy (55 papers in press)
Exergy-based analysis of irreversibilities for heat pump working fluids and cycle layouts
by Benjamin Zühlsdorf, Jonas Kjær Jensen, Brian Elmegaard
Abstract: The use of zeotropic mixtures in well-designed heat pump cycles enables considerable performance improvements. Temperature glide matching of the heat exchange processes and recovery of expansion losses by internal heat exchange decrease the exergy destruction and yield higher cycle performances. A case study for supply to district heating is presented, indicating increases in COP from 4.3 for a pure fluid in a standard cycle to 5.2 for a zeotropic mixture in a cycle with optimized internal heat exchange. As these improvement potentials are difficult to quantify by conventional and advanced exergy analysis, a new approach was suggested. For deriving a meaningful benchmark for cycle optimization, the exergy destruction was distinguished into a contribution describing the irreversibilities from the respective components operating with an ideal working fluid and cycle design and another contribution resulting from the cycle and working fluid being non-ideal. In addition, the exergy destruction was related to the COP, enabling an intuitive interpretation of the exergy-based analyses.
Keywords: Cycle design; exergy; exergy destruction; heat pump; irreversibility; Lorenz cycle; refrigerant; temperature glide matching; working fluid; zeotropic mixtures.
Exergetic evaluation and optimisation of a novel integrated energy conversion system including thermoelectric generators
by Muhammad Zesshan Malik, Farayi Musharavati, Morteza Saadat-Targhi, Shoaib Khanmohammadi, Hadi Genceli
Abstract: A comprehensive thermodynamic study of a solar integrated energy system consisted of a solar flat plate collector, an organic Rankine cycle, a thermoelectric generator, and a proton exchange membrane electrolyzer is undertaken to generate power and hydrogen. The Matlab and Engineering Equation Solver softwares are linked, and various optimization scenarios are investigated. The results of computational analysis indicate that with adding a thermoelectric generator unit in the system about 14 kW of energy in the form of electricity can be obtained from the waste heat of condenser. Various optimization schemes with exergy efficiency, exergy destruction rate, as well as hourly hydrogen generation as optimization targets are considered. The optimization results comparison between base case and optimum design shows that exergetic efficiency improves by about 2.3% and rate of exergy destruction decrease by about 0.791 MW.
Keywords: Electrolysis; exergy efficiency; heat recovery; thermoelectric generator; TEG.
Exergy analysis of vapour compression-absorption two stage refrigeration cycle
by Canan Cimsit, Ilhan Tekin Ozturk
Abstract: In this work, the exergy analysis of vapour compression-absorption two stage refrigeration cycle has been performed. To improve the performance of the cycle, it is possible to reduce the total damage by focusing on the parts that cause high exergy damage. Therefore, the detailed exergy analysis has been made for different operating conditions (generator temperature, condenser temperature and intermediate pressure) of the cycle. The exergy destruction rates each component were calculated and compared. The performance coefficient (COPcyclegen) increases as the intermediate pressure increases. Maximum value of the exergy efficiency is obtained at the intermediate pressure of 516.015 kPa. With this cycle, it is possible to refrigeration down by using alternative energy sources. Also, environmentally friendly is refrigeration system because environmentally safe fluids are used in this cycle.
Keywords: Refrigeration; Absorption; Two stage refrigeration; Energy; Exergy.
Experimental study and exergy analysis of three-fluid tubular heat exchanger with nanofluids
by Tarikayehu Amanuel, Manish Mishra
Abstract: The present study addresses numerical and experimental approaches for exergy analysis of three-fluid tubular heat exchanger with Al2O3-water nanofluids. The goal is to assess the exergetic performance of employing nanofluids through a three-fluid heat exchanger. A Single-phase approach has been implemented to conduct numerical analysis in ANSYS fluent workbench v.17.2, commercial CFD package. Experiments were also conducted to investigate the effects of varying flow rates, flow arrangements, and nanoparticle volume concentrations on the overall performance of the exchanger under study.
Reynolds number in the range 2500 - 10,000 and volume concentration of nanoparticles in the range 0 - 3% have been considered to study their effects. Besides, four flow arrangements (parallel, parallel-counter, counter-parallel, and counter) have been considered for numerical and experimental studies. The numerical investigation results revealed that increasing flow rate and addition of nanoparticles resulted in a reduction of exergy loss of the system. However, a non-monotonic variation of exergy loss with Reynolds number has been observed from experimental results. The experimental results also showed a significant deviation from the numerical ones, mainly due to the uncertainties in experimental measurements and equipment accuracy. At a maximum Re=10,000, a drop in exergy loss by 23.7% for parallel, 11.56% for parallel-counter, 10.6% for counter-parallel, and 25.8% for counter flow arrangements by varying ? from 0% to 3%. Furthermore, minimum exergy loss for all the flow arrangements was found at ?=3% and Re=4500.
Keywords: Exergy; Experimental; Numerical; Three-fluid heat exchanger; Nanofluid.
Comparative Study of Three Modified sCO2 Brayton Recompression Cycles Based on Energy and Exergy Analysis with GA Optimization
by Chunlei Li, Qitai Eri
Abstract: As a novel supercritical CO2 (sCO2) power cycle, the recompression cycle has gained a lot of attention. Various modifications of the recompression cycle have been put forward. However, comparative studies are still required to determine whether these modifications are necessary. In this paper, three common modifications (reheating, partial cooling, reheated partial cooling) are analyzed and compared with the original recompression cycle from the exergetic perspective. Thermodynamic states are calculated based on the recuperator effectiveness. The genetic algorithm (GA) is used to calculate the split ratio, reheating pressure and pre-cooling pressure. The results show that the thermal efficiencies are: 40.01%, 40.44%, 39.88% and 41.63%. The exergy efficiencies are: 55.49%, 56.07%, 55.27% and 57.69%. They reveal that the modification of reheating or partial cooling alone fail to produce great improvement, but the combination of the two can. Furthermore, the results of a parametric study indicate that the conclusion are not limited to specific parameters. In most cases, a roughly 23% improvement is observed. An explanation can be given from the analysis of the exergy loss distribution and T-s diagrams, which reveal that the reheated partial cooling modification enhances the positive effects of both reheating and partial cooling, thereby achieving greater improvement.
Keywords: sCO2 Brayton Cycle; Recompression cycle; Exergy analysis; Genetic algorithm optimization.
Enhanced Exergetic Evaluation of Regenerative and Recuperative Coal-Fired Power Plant
by Oguz Arslan, Merve Senturk Acar
Abstract: The coal-fired power generation systems are still in use and have a large rate in electricity generation for countries such as Turkey. In this regard, it is an important issue to take into account the relevance of coal generation, to achieve greater operating efficiencies, and to reduce costs and environmental impacts. From this point of view, combustion, which is the most exergy destructive process, should be handled in detail for potential improvement. In this study, Seyitomer coal-fired power plant was analyzed by the enhanced exergy method. In this regard, enhanced exergy analysis of coal combustion was introduced first by defining ideal and unavoidable conditions. The real conditions of the plant were obtained by measurements. As conclusion, an improvement potential of approximately 33.11% was determined for the overall system. The highest avoidable exergy destruction was determined in the boiler group with 29.46%. The endogenous part of this destruction was calculated as 6.77% where the exogenous part was approximately 22.69%. The improvement potential of the boiler group was determined as approximately 19.09%. The second highest avoidable exergy destruction was determined as the turbine group with approximately 16.35%. The endogenous part of this destruction was calculated as approximately 5.70% where the exogenous part was 10.65%.
Keywords: Coal combustion; Enhanced Exergy; Power plant; Recuperation; Regeneration.
A detailed thermodynamic assessment and exergetic performance analysis of an industrial-scale orange juice production plant
by Zeinab Khorasani Zadeh, Farshid Nasiri, Khadijeh Faraji Mahyari
Abstract: In the present work, detailed exergy analysis was conducted on an industrial-scale orange juice production plant located in the north-west part of Iran. The plant consisted of four main lines including steam generation, above-zero refrigeration, mixing and pasteurization lines. The overall rate of destructed exergy in the whole plant was 17.7 MW. The majority (76.2 %) of it was observed in the steam generation in which boiler & compressor had the highest contribution (12073.09 kW /89%) in exergy destruction. In the above-zero refrigeration line, the ice-water tank possessed the highest exergy destruction (2802.36 kW) accounted for 71 % of total exergy destruction, which could be improved by thermal insulation. The mixing and pasteurization lines had the lowest overall exergy destruction (1.5 %). The exergetic efficiencies of all the pumps were in a poor range that strongly are suggested to employ the Variable Speed Drive.
Keywords: Above-zero refrigeration; Exergy analysis; Exergy destruction; Exergy efficiency; Mixing and pasteurization; Steam generator.
Energy and entropy generation analysis of hydrological cycle in tropical regions
by Saumyakanta Mishra, Bishnu N. Mahapatra, Sudhansu S Sahoo, Auroshish Rout
Abstract: The hydrological cycle has been presented in a thermodynamic framework in this paper. The energy and the entropy studies of processes involved in the cycle have been carried out assuming that the hydrologic cycle acts as an actual Rankine cycle and the atmosphere consists of water only. The effect of the irreversibilities and the generation of entropy due to these irreversibilities are also taken into account. The net work of the cycle which is used for atmospheric circulation (mesoscale convective circulation) has been quantified for both the reversible and the irreversible processes. At a given set of operating conditions, the net work outputs and the efficiencies are evaluated for both reversible and irreversible cycles and both these determined values of the reversible cycle are found to be greater than those of the irreversible one. The efficiency value is found to vary from 0.028 to 0.068 when the difference in hot and cold temperatures varies from 10
Keywords: Hydrological cycle; Rankine Cycle; Energy analysis; Entropy analysis; Irreversibilities.
Multi-Objective Optimization of Solar-Driven Combined Stirling Engine/LNG Burned Micro Gas Turbine based on Exergy and Energy Analysis
by Mojtaba Babaelahi, Hamed Jafari
Abstract: An appropriate method for electric power generation is one of the challenges that has been investigated by many researchers in recent years. Due to the limited resources available for fossil fuels, access to new resources and methods for power generation is critical. For the selection of these new resources, various indicators such as efficiency, production cost, and fuel consumption are significant. In this paper, a 200 kW Capstone microturbine is considered a base model and a Stirling engine. Solar energy and LNG fuel have been used as the system's hot source. To power generation in the Stirling engine, the exhaust heat of the Capstone microturbine and the cold exergy of the LNG evaporation has been used as the hot and cold source. For the evaluation of the proposed system, energy analysis and exergy methods have been used. The effect of using solar energy on the fuel consumption, and the effects of ambient temperature, the pressure ratio across the compressor, the temperature of the heat sink in the Stirling engine on the exergy and energy efficiency are examined. The results show that thermal efficiency improves from 34% (base cycle) to 38% and the exergy efficiency from 35% (base cycle) to about 43% in the proposed cycle. Also, the results showed that by increasing the comparison ratio and inlet temperature of the turbine, the exergy and energy efficiencies are increased. Finally, to find the optimal design point, multi-objective optimization was accomplished to reach the maximum efficiency through the particle swarm optimization (PSO) procedure. The results of the optimization showed that the exergy and energy efficiencies are increased by 6.42% and 15.92 %, respectively, compared to the base case.
Keywords: Solar; Micro-gas-turbine; Stirling Engine; LNG; Exergy; Optimization.
Exergy based sustainability analysis of a dual fluid hybrid photovoltaic/thermal (PV/T) solar collector
by Hasila Jarimi, Devrim Aydin, Adnan Ibrahim, Ahmad Fazlizan, Ahmad Afif Safwan, Kamaruzzaman Sopian
Abstract: This paper aims to investigate the exergetic sustainability index (SI) of a dual-fluid PV/T type solar collector that integrates both air and water into the same solar collector. The contribution of the exergy efficiency of each of the dual fluid PV/T collectors components to the overall sustainability of the whole system was analyzed. A theoretical approach based on an experimentally validated numerical model was employed. The results show that, the SI of the PV component of the dual fluid PV/T system is in general higher than the solar thermal component by approximately 9% since it is higher in quality. When evaluated under three different climatic conditions, the contribution of the thermal component as a cooling medium to the PV is only prominent in hot climates with SI higher by 4% compared to the stand-alone PV system. For the cool and cold temperate climates, the difference is less than 0.1%.
Keywords: Exergy; Sustainability; dual fluid; hybrid photovoltaic thermal; solar thermal.
Energy and Exergy Parameters of Low-Temperature Solar Thermal Energy Storage Systems: Empirical Estimation and Optimization
by Babatunde O. Adetifa, Ademola K. Aremu
Abstract: This study presents the energy and exergy analyses of three low-temperature solar thermal energy storage (STES) systems. These STESs were of the same design but, contained different heat storage materials (benzoic acid, stearic acid, and palm olein) evaluated during heat charging and discharging periods. The energy and exergy inputs and outputs were analysed and factored to estimate of the efficiencies during heat charging, while the energy and exergy drop during heat discharge were also estimated. The energy and exergy outputs were optimised using a set constraint employed on Design-Expert 11 software. The energy and exergy outputs ranged between 25.89-95.96 W and 13.15-52.37 W, respectively, depending on the type of heat storage materials used. Under optimized conditions, the energy and exergy outputs increased to 117.1-202.7 W and 81.2-107.5 W, respectively. The STESs were found to have a positive and significant effect on the energy and exergy efficiencies and on the energy and exergy drop. The quantity of water heated only affected the energy and exergy drop. This paper reveals that the energy and exergy parameters of a solar thermal system can be optimised by the integration of a STES.
Keywords: Heat storage material; Energy; Exergy; Solar cooker; Design-Expert; Water heating.
Exergy Analysis of Petrol Engine Accommodated Nanoparticle in the Lubricant System
by Esam Jassim
Abstract: An energy and exergy analysis of a four stroke Spark Ignition Engine operated with nano-lubricant is experimentally investigated to assess the environment-engine energy interaction. The warm-up period and the influence of mixing nanoparticle with the lubricant on the exergy rate at various volume fractions VOF are also reported. It was observed that the engine warm-up period is dropped up to 40% when nano-lubricant is employed. The results also showed that presence of nanoparticles in the lubricant would double the exergy potential of the engine. Energy and Exergy efficiency are both augmented when nanocopper is mixed with the lubricant.
Keywords: Exergy; ICE; Lubricant; Nanoparticle; Exergy Destruction Rate.
Thermodynamics analysis of biomass fired brick drying process
by Aziz Dogru, Emre Camcioglu, Onder Ozgener, Leyla Ozgener
Abstract: For drying the bricks used in the construction sector in Turkey is estimated that the need to power of 460MW. Moreover, the estimated energy consumption and produced brick are 2,680,400MWh/ year and 5 million ton per year, respectively. Due to increasing global warming and climate change, the amount of energy consumed per year for drying decreases. As the outdoor temperature increases, the amount of energy supplied for drying the brick will be reduced. This study was carried out because of this high energy consumption during drying process in brick production sector. According to the case study, energy and exergy analyses of a brick factory with an annual production capacity of 150,000 tons in Manisa were conducted using real operating data. The drying system was analyzed according to ambient temperature (0-20
Keywords: thermodynamics; exergy.
An Exergy Analysis of a Concentric Tube Heat Exchanger using hBN-Water Nanofluids
by NESE BUDAK ZIYADANOGULLARI, Suleyman PERCIN
Abstract: This study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel- and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest Exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 7532) for parallel flow operation at 152 W. The exergy loss of water at the highest Reynolds number (Re = 7532) for parallel flow operation increased by 14.7%, 23.8% and 48.6% for hBN-water concentrations of 0.01%, 0.1% and 1% respectively. Exergy loss of water at the highest Reynold number (Re =7532) for counter flow operation increased by 9.23%, 15.3% and 27.1% for hBN-water concentrations of 0.01%, 0.1% and 1% respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).
Keywords: hexagonal boron nitride–water nanofluid; concentric tube heat exchanger; exergy efficiency; exergy loss; pump power.
Energy, exergy, and exergo-economic analyses of a novel three-generation system to produce power, heat, and distilled water
by Malihe Pashapour, Samad Jafarmadar, Shahram Khalilarya
Abstract: In this study, energy, exergy, and exergo-economic analyses were conducted for a new system producing power, heat, and distilled water. First, the waste heat of a gas turbine was recovered by a heat recovery steam generator, and then by an organic Rankine cycle. Simultaneously, a geothermal energy resource was utilized for re-heating the organic fluid to increase the power and efficiency of the ORC. Moreover, this system encompasses a reverse osmosis desalination unit to produce freshwater. Feed-water is heated in the condenser before it enters into the desalination unit; hence, specific power consumption of the high-pressure pump reduces by 43.52%. Exergy efficiency of the system was estimated to be 53.86%, where was 5% higher than basic mode (i.e., with no desalination unit and re-heating). The exergo-economic factor was 12.14%, suggesting that exergy destruction accounts for a high proportion of costs.
Keywords: Energy; Exergy; Exergo-economic; Gas turbine; Organic Rankine cycle; Heat recovery; Re-heating; Geothermal energy; RO desalination.
ENERGY AND EXERGY ANALYSES OF EXPERIMENTAL COMPRESSED AIR VEHICLE PROTOTYPE WITH HEATING ELEMENT
by Reza Alizade Evrin, Ibrahim Dincer
Abstract: In this study, a new automobile powering system comprising of compressed air as a source of energy and as a non-polluting fuel is developed and tested. A working prototype for the pneumatic vehicle is developed at the Ontario Tech University, Oshawa and its performance is investigated. The compresssed air vehicle consists of a novel powering option integrated with a heating element prototype. The study introduces for the first time a compressed air vehicle prototype with 4 air mototrs powering the wheels. In addition, the compressed air exiting the motors is recovered for a second exapnsion to provide electrical power that heats the air before being recovered. The ACE dynamometer is used for investigating the performance of the developed prototype. The energy efficiency for the prototype is found to be 59.5%. Also, the exergy efficiency is 51.0%. The prototype driving range is calculated to be 128 km with 300 liters of air at a pressure of 350 bar. The maximum shaft work generated is measured as 20.84 kW.
Keywords: Compressed air vehicle; prototype; energy; exergy; efficiency;.
Exergetic Evaluation and Optimization of Primary Methane Steam Reformer (PMSR)
by Anthony Hamzah, Raden Cik Awang, Sri Haryati, Muhammad Djoni Bustan
Abstract: It is widely accepted that exergy diagnosis on reactor often overlooks the intrinsic reaction and physico-chemical factors in the reactor itself. In this work, these factors are included to analyze their influence on the exergetic performances of the primary steam reformer (PMSR). Thermal and steam to carbon (S/C) ratio sensitivity assessment was performed to obtain the optimal operating conditions of the reactor. Aside of the conventional exergetic analysis, physical-chemical exergy destruction ratio was also introduced to determine the most dominant irreversibility in the system. Results of numerical simulation showed that higher temperature increases hydrogen production and at the same S/C ratio, decreases chemically-driven exergy destruction. The exception applied on very low S/C (around 2) and very high temperature (880-900 oC), where significant physico-thermally-driven exergy destruction was observed. On the other hand, excessive steam lead to more exergy losses, while the exergy destruction was kept at minimal and more chemically-driven.
Keywords: exergy analysis; hydrogen production; steam reforming; physical-chemical exergy destruction ratio.
EXERGOECONOMIC AND EXERGOENVIRONMENTAL ASSESSMENT OF A PV/T ASSISTED WASTEWATER SOURCE HEAT PUMP SYSTEM FOR A SUSTAINABLE FUTURE
by Mustafa Araz, Arif Hepbasli, Huseyin Gunerhan
Abstract: In this paper, the exergetic, exergoeconomical and exergoenvironmental performances of a photovoltaic/thermal (PV/T) assisted wastewater source heat pump (WWSHP) system were investigated. In the first part of the study, the data gathered from the experiment conducted in the heating mode were used for the exergetic analysis while some performance indicators, such as exergy destruction, exergy efficiency, relative irreversibility and improvement potential of each component, were obtained. After that, economic and environmental life cycle analyses (LCA) were conducted to get the cost and environmental impact data related to every component of the system. Finally, the results of exergy analysis were combined with those of economic and environmental analyses by using exergoeconomic and exergoenvironmental methods. The highest relative irreversibility among all the components occurred in the PV/T unit, followed by the compressor. The functional exergy efficiencies of the WWSHP and whole system were found to be 0.10 and 0.15, respectively. The exergoeconomic factors of the condenser and wastewater heat exchanger (WWHE) were determined to be considerably high among all the components, which indicated that the main driver of the cost associated with them was related to investment costs. On the other hand, the highest exergy loss per unit price was due to the PV/T system. Exergoeconomic factors for each equipment and the entire system tended to decrease with increasing yearly working period and decreasing interest rate. The same trend was also observed in the specific cost of exergetic product. Exergy destruction related environmental impacts was found to be the major element in almost all of the components and therefore its reduction should be the main focus on exergoenvironmental performance improvements.
Keywords: waste heat; wastewater source heat pump; PV/T; exergoeconomic analysis; exergoenvironmental analysis.
Exergy analysis and exergoeconomic assessment of trigeneration system: a case study
by Ana Livia Leite, Dos Santos , Alvaro Ochoa, Paula Michima
Abstract: An energetic and exergetic analysis based on the first and second thermodynamic Laws, and an exergoeconomic assessment by the SPECO method was applied to a trigeneration system. Two LiBr/H2O absorption chillers and a diesel combustion engine integrate the trigeneration system. The system was proposed to meet the energy demands of a resort in Piau
Keywords: Trigeneration; absorption chiller; diesel engine; energy and exergy efficiency; exergetic cost.
Exergetic design and optimization of LNG cold energy utilization system for dual-fuel main engine of a container ship
by Yao Shouguang, Zhang Zijing, Huang Haiqi, Feng Guozeng, Xu Jinjin
Abstract: In this paper, a 9200TEU container LNG fuel-powered ship is used as a prototype ship, and combined with the cooling load requirements of on-board cold storage, desalination and air conditioning, a LNG cold energy cascade comprehensive utilization system scheme is proposed. On the basis of system simulation analysis, the initial plan is optimized in terms of system process arrangement and power cycle working medium selection, and two optimized design system plans are determined. Based on the genetic algorithm, the global parameter optimization of the determined scheme is further carried out, and the annual net income and the initial investment cost of the two optimization design system schemes are analyzed. The results showed that the optimized exergy efficiency of the LNG cold energy full power utilization system proposed in this paper reaches 54.69%, which has the best cold energy utilization efficiency; and the optimized LNG cold energy cascade comprehensive utilization system scheme has the optimized exergy efficiency as 50.13%, but it has the best economic benefits.
Keywords: LNG vaporization cold energy; cascade utilization; container ship; exergy analysis.
Performance assessment of a solar tower assisted combined cycle power plant using supercritical carbon dioxide as a heat transfer fluid
by MUHAMMAD KHAN, MUHAMMAD ABID, M.I. YAN, TAHIR RATLAMWALA, ISHRAT MUBEEN
Abstract: The aim of the present research is to investigate the detailed exergo-environmental analysis of solar-assisted power and hydrogen production system in addition to the energetic and exergetic analysis. The proposed system consists of five sub-systems (heliostat field, solar tower, gas cycle, steam cycle and an electrolyzer). Mathematical model is developed using engineering equation solver (EES) to investigate the integrated system according to the thermodynamic point of view and parametric study is conducted to access the impact of key parameters on the overall performance of the integrated system. The results reveal that thermal efficiency of the receiver is noticed to be 72%, whereas, 42% is observed for the power cycle. The integrated first and second law efficiencies of power plant are 20.93% and 22.51%, accordingly. Exergo-environmental impact index decreases to 33.66% by increasing direct normal irradiation which is considered to be a favorable indicator for the environment, while exergo-environmental impact improvement and exergetic sustainability index increases by 55% and 33.6%, respectively. The net power output and rate of hydrogen production are found to be maximum at a pressure ratio of 10 and a gradual reduction is observed at elevated pressure ratios. Single objective optimization of the system reveals that the optimized overall efficiency of the system is 23.42%.
Keywords: s-CO2; Exergo-environmental; Sustainability; Heliostat; hydrogen;.
A constructal view of prefractal dendritic flow networks using an exergy analysis
by Antonio F. Miguel
Abstract: Evidence supports the interpretation that natural dendritic networks are described by fractal theory. It is recognized that the fractal description alone is not a complete description of nature of space filling. This study addresses the fundamental question of what the size of dendritic flow networks should be, in order to perform with the least irreversibilities, in addition to what fractal features-based pattern should have. Optimal shapes of symmetric and asymmetric networks for viscous flow and diffusion with junction loss effects are analyzed based on exergy minimization rate. Global size constraints included in the analysis are the volume and surface area. The optimal sizes of the flow networks are obtained, and prefractal dimensions that characterize these networks are computed. It is shown that the prefractal dimensions depend on both flow properties and space constraints. The physics link between prefractal regularity and optimal flow performance is clear presented.
Keywords: exergy analysis; prefractal dimension; constructal law; dendritic flow networks; scale factor; homothety ratio.
THERMODYNAMIC ANALYSIS OF A BINARY GEOTHERMAL POWER PLANT
by Zekeriya Ozcan, Ozgur Ekici
Abstract: In the frame of this study, performance of a geothermal power plant located in Germencik/Turkey is evaluated both from thermodynamic and economic perspectives. First and second law efficiencies of the plant are calculated to be 4.82% and 25.7% respectively. On plant level, it is found out that brine re-injection process is primarily responsible of exergy losses (21.9%). At organic Rankine cycles of examined plant, major sources of exergy losses are turbines and pumps (25.44%), heat exchangers (21.78%) and condensers (10.8%). In order to achieve more realistic conditions with modelling environment, thermal losses from heat exchangers are calculated and found to be around 444 kW. This amount corresponds to 0.27% of total heat transfer value during heat exchanging processes. After the thermodynamic analysis, case studies are conducted to evaluate the applicability of water-cooled condensers instead of the existing air-cooled condenser systems. Results indicate that it is possible to reduce the initial capital investment around 20% with such an application by using factorial cost estimation techniques. It is also demonstrated that it might be possible to further increase the exergetic efficiency of this hypothetical water-cooled condensers by increasing the rejection temperature and subsequently decrease the initial capital investment by 1.4%. An additional benefit of such an application would be a decline of the heat release to the environment, which is pointed out as a serious environmental issue in several studies for agricultural areas of Germencik.
Keywords: Binary Geothermal Power Plant; Plant Analysis; Exergy Flows; Heat Transfer; Factorial Cost Estimation Method.
Overall efficiency analysis of an innovative load-following nuclear power plant thermal energy storage coupled cycle
by Mohamed Ali, Ahmed K. Alkaabi, Saeed A. Alameri, Yacine Addad
Abstract: An innovative-coupled nuclear power plant (NPP) system is investigated in the present study. The system, proposed herein, is intended to have a better ability to follow the grid demand, hence, overcoming the current variable load limitations of existing NPPs systems. In the present design, the concept of integrating a thermal energy storage (TES) as an active component in the NPP system is evaluated. In this proposed design layout, the phase change material (PCM)-based TES is planned to have a dual role in acting as; a simple heat exchanger between the primary and secondary loops when the grid power demand exactly matches the one generated by the high temperature reactor, while it is mostly acting as storage or energy supplement source to account for the daily fluctuating energy demand. To assess the feasibility of the TES integration for different thermodynamic cycles, the efficiency of the overall coupled system is examined by computing the energy and exergy balances at the plant main components (turbines, compressors, pumps condensers, and heat exchangers) for two designs of the power generation process: Rankine and supercritical carbon dioxide (SCO2) Brayton cycles. The obtained results confirm that, as expected, around 50% of the exergy is lost during plant operation in the reactor core. Most importantly, it also reveals that the losses in the TES are actually in the same order as the ones in the remaining components (i.e. turbines, condensers, and pumps) which are much smaller (<10%) than the reactor core losses. SCO2 Brayton cycle with regenerator is found more efficient than Rankine cycle and overall efficiency can reach 50% using high effectiveness and high efficient components.
Keywords: Exergy; Energy; Thermal Energy Storage; Nuclear Power Plant.
Comprehensive investigation of using n-butanol/gasoline blends in a port-fuel injection spark-ignition engine
by Murat Kadir Yesilyurt, Hayri Yaman
Abstract: In this study, butanol was examined mixing with gasoline at different ratios (Bu0, Bu5, Bu10, Bu20, and Bu30) in a single-cylinder, four-stroke, PFI SI engine for monitoring engine characteristics at various loads to perform thermodynamic analyses. It can be reported that the maximum efficiencies were calculated at the highest load for tested fuels. Accordingly, the maximum thermal efficiencies were computed to be between 35.85-40.60% meanwhile corresponding exergetic efficiency results were found to be between 33.33-37.85% for tested fuel samples. In addition, the maximum SIN values were achieved between 1.500-1.609.
Keywords: Butanol; Economic; Emissions; Exergy; Higher alcohol; Performance; Sustainability.
DEVELOPMENT OF EMPIRICAL MODELS FOR ESTIMATION DIFFUSE SOLAR RADIATION EXERGY IN TURKEY
by Nurullah Arslanoglu
Abstract: In this study, exergy of diffuse solar radiation is estimated using empirical models. Long-term meteorological data (1983-2005) consisting of monthly mean diffuse solar radiation for 7 selected stations were available from from NASA Langley Research Center. Empirical models were developed by correlating diffuse solar radiation exergy in terms of relative sunshine period. Three different regression models (Linear, quadratic, cubic) are presented to predict diffuse solar radiation exergy. The empirical models performance is determined with the most frequently utilized statistical methods. The performance ranking of the models is carried out by using the global performance indicator method (GPI). The maximum diffuse solar radiation exergy value (53 MJ/m2year) belongs to Adana for selected provinces . Quadratic type is the best predictive method for Bursa, Ankara, Adana, Gaziantep provinces located in Turkey, and Igdir and Trabzon regions are excellently predicted by Cubic type. Linear type is then used for the best prediction of the Izmir city of Turkey. Consequently, The empirical models obtained in this study can successfully predict diffuse solar radiation exergy. Therefore, it is easy to apply for other places with similar climatic conditions all over the world. In this way, it will be possible to design solar systems correctly by scientists and industrialists.
Keywords: Diffuse solar radiation; exergy; empirical models; clearness index; sunshine period.
Exergy Analysis of a HDH-VCR Cycle for Water and Air Conditioning
by Tangellapalli Srinivas
Abstract: The fresh water and space conditioning are the human needs for the comfort living. Humidification dehumidification vapour compression refrigeration (HDH-VCR) cycle for combined portable water and air conditioning (A/C) has been studied with exergy approach. HDH-VCR cycle has been studied with thermodynamic exergy approach for efficient operation of the cycle. The focused options in this work are dehumidification with normal water (HDH), dehumidification with chilled water (HDH-VCR 1) and dehumidification with VCR (HDH-VCR 2). The exergy losses of the components are compared for these three units. As per the exergy analysis, HDH-VCR 2 has been highlighted with higher exergy efficiency compared to the others.
Keywords: air conditioning; HDH-VCR; exergy; psychrometry; second law of thermodynamics.
Maximization of Energy and Exergy Efficiencies for a Sustainable Thermoelectric Cooling System by applying Genetic Algorithm
by JITENDRA MOHAN GIRI, Pawan Kumar Singh Nain
Abstract: The efficient thermal management of thermoelectric cooler (TEC) as a sustainable cooling technology is important. The energy loss, electrical power requirement, and irreversibility of the TEC system need to be minimized. Hence, the loss of energy and energy quality (exergy) are two significant points of concern. Thus, energy and exergy efficiency can be used as the key indicators to optimize TECs performance. Through this work, authors separately optimized TEC energy efficiency (?I) and exergy efficiency (?II) considering thermoelectric elements geometry and electric current by using the genetic algorithm (GA). The effects of electrical contact resistance and thermal resistance are considered in the mathematical model of this work. Unlike previously reported works, the authors have used junction temperatures different from surface temperatures at the respective cold and hot sides of TEC. This study reveals that maximum energy and exergy efficiencies are obtainable at the same values of electric current, length, and cross-sectional area of thermoelectric elements. It is significant as these identical optimum design variables assert maximum ?I and ?II. At cold surface temperature (Tc) of 20?, the maximum energy efficiency of 4.11 and the maximum exergy efficiency of 0.0715 are obtained. Exergy efficiency can be used as the basis to choose TEC since it assures better energy quality and connects with sustainable development. The genetic algorithm optimization result is validated through ANSYS
Keywords: thermoelectric cooler; energy efficiency; exergy efficiency; genetic algorithm; optimization; finite-element simulation.
EXERGETIC PERFORMANCE ANALYSIS OF HIGH PRESSURE AIR SYSTEMS ON SHIPS
by Asim Sinan KARAKURT, Ibrahim OZSARI, Veysi BASHAN
Abstract: Energy consumption, energy/exergy efficiency, and being more ecologically issues are among the most scientifically researched topics today. These three important aspects also attract attention to ships that have many high energy consumption systems. One of the highly energy consumed system in ships is high pressure start air systems with relatively have high capacity consuming compressors. In this study, energy and exergy analyses are made to optimize the use of a ship high pressure air system according to performance outputs such as power consumption, exergy destruction, and ecological coefficient of performance (ECOP). Exergy destructions caused by the power consumed by the main compressors and the improper use of the air stored at high pressures are calculated. And also, the ECOP criterion was used to compare 3 different models according to the first and second laws of Thermodynamics. The general results obtained from the analysis are as follows. The power consumption of models are 1530, 1283, and 1276 kW (38%, 31%, and 31%); the exergy destruction values are nearly 250, 471, and 450 kW (21%, 40%, and 39%); ECOP values are 6.15, 2.72, and 2.84 (53%, 23%, and 24%), respectively. Moreover, the effects of different sea water temperature, ambient temperature, and isentropic efficiencies of compressors on the power consumption, exergy destruction, and ECOP values are presented.
Keywords: Air storage; ECOP; Exergy analysis; Ship compressed air system.
Why brain functions may deteriorate with aging: A thermodynamic evaluation
by Cennet Yildiz, Mustafa Özilgen
Abstract: Loss of the brain functions with ageing is related to decrease of its oxygen utilization in the literature. Although we have much more limited data obtained with the brain, when compared with the muscles, at the present level of our knowledge, we may say that the loss of ageing damage to the brain functions may be caused by the brain work performance caused by deterioration of the energy generation capacity of the mitochondria and work performance ability of the warned out ion pumps upon ageing. Thermodynamic assessment points the muscle work performance as the place to look at. Nature has equipped the muscle cells with healing capability, in terms of fixing the damage to the mitochondria or multiplying their numbers. If the same natural healing technologies may be implemented to the brain cells, ageing damage to the brain cells may be at least partly recovered.
Keywords: Ageing in the brain; mitochondrial energy; entropy generation; Gibbs free energy utilization; ion pumps; work performance efficiency.
Thermodynamic analysis of a new multi-generation plant based on the waste heat from the cement industry for improved energy management
by Mehmet Altinkaynak, Murat Ozturk, Ali Kemal Yakut
Abstract: In this paper, the hydrogen production and liquefaction option by utilizing the waste heat from the raw material preheating sub-unit of cement facility are investigated thermodynamically. The gas turbine plant and Rankine cycle are chosen to generate power and, also in order to generate hydrogen, a part of the produced power is used for PEM electrolysis. In these conditions, the hydrogen generation from analyzed integrated plant is computed as 0.028 kg/s. The energetic and exergetic effectiveness of Brayton and Rankine cycles integrated with the waste heat recovery process in the cement facility are computed as 58.24% and 42.17%, respectively, for the chosen working condition. It is also asserted that increasing the input temperature of gas turbine depended on the cyclone gas temperature increases the exergy efficiency of investigated system.
Keywords: Waste heat; cement facility; energy; exergy; efficiency; hydrogen production and liquefaction.
Development of exergy maps as a tool for assessing solar energy potential in Iraq
by Abdul Hadi Khalifa, Fadhil Kareem
Abstract: This work aims to develop three sets of maps for solar intensity and the exergy efficiency of the solar and PV systems for Iraqi cities. The first is for the global solar radiation that falls on a horizontal surface; the second is solar exergy efficiency. In contrast, the third set is for the exergy efficiency of a 20 kW hybrid-connected PV system installed at the Middle Technical University's presidency, Iraq- Baghdad. The development of the solar exergy and the exergy efficiency map sets are based Petela model; the model equations were programmed depending on the Iraqi weather data and solved using the Engineering Equation Solver (EES) software. Meteonorm package was used to collect the weather data for 48 sites inside and outside Iraq to cover this country's entire area. From the weather data and the theoretical model, it is found that: The average daily global solar intensity in January is varied from 275 to 375 W/m2, while it is varied from 530 to 710 W/m2 in July. The western regions of Iraq, which are often desert lands, suffer from the low intensity of solar radiation due to the dusty weather that characterizes this region. The solar exergy is 70 to 138 W/ m2 in January, and this range in July is 260 to 330 W/ m2. The higher average exergy efficiency ranges from 15 to 19.3 % in the winter, while the lower is 7.5 to 13.8% in the summer. Finally, the site at lower latitudes has more global solar radiation. On the other hand, higher latitudes have more exergy efficiency than those for the sites at lower latitudes.
Keywords: Solar radiation; Solar exergy; PV exergy efficiency; Exergy maps.
EXERGY ANALYSIS OF A NATURAL GAS COMBINED CYCLE POWER PLANT: A CASE STUDY
by Gabriel Marques Pinto, Christian Jeremi Rodriguez Coronado, Tulio Augusto Zucareli De Souza, Eudes Muller D’Oliveira Santos
Abstract: This work performs energetic and exergetic analysis of a CCPP, by using a full-scope simulator, which faithfully reproduces the operation of a real Brazilian CCPP. The analyses are performed for design and off-design conditions. The results present, for the design condition, a power generated of 820.6 MW, a first law efficiency of 51.54% and a second law efficiency of 49.32%. The equipment responsible for the main irreversibilities were: the combustion chamber (70.24%), gas turbine (10.75%) and heat recovery steam generator (7.37%). In the off-design scenario, the first and second law efficiencies were decreased by 2.65% and 2.54%, respectively.
Keywords: Combined cycle; Exergy; Efficiency; Exergy destruction rate.
Exergoeconomic analysis of a solar CCHP with partially porous material filled collector
by Navid Tonekaboni, Hesamoddin Salarian, Majid Eshagh Nimvari, Jahanfar Khaleginia
Abstract: In this research, a parabolic solar collector is analyzed in solar combined cooling, heating and power cycle by adding porous materials in five stages are investigated. This research focus on use of flat plate collectors in solar CCHP. Following this study, the exergoeconomic analysis of the system was performed for financial analysis and calculation of the payback period. The average enhancement of collectors efficiency and solar CCHP cycle using porous media is 16% and 11% respectively. By using flat solar collector fully filled porous media, the cost of the cogeneration cycle reduces up to 38% in comparison with other CCHP.
Keywords: Solar collector; exergoeconomic; porous materials; partially porous; payback period.
Special Issue on: IEEES-12 Exergetic Solutions for Better Environment
AN EXPERIMENTAL STUDY ON GAS-TO-LIQUIDS (GTL) AND BIOGAS DUAL FUEL OPERATION OF A DIESEL ENGINE
by Saket Verma, L.M. Das, S.C. Kaushik
Abstract: In the present configuration, GTL replaces diesel, and biogas is used as gaseous fuel in the Dual Fuel (DF) operations. The effects of this substitution have been evaluated from the perspectives of second-law of thermodynamics. The results are compared with the diesel single-fuel, GTL single-fuel and GTL-biogas DF operations. Also, engine out emissions have been compared to understand the environmental impact of these fuel combinations. The results show that DF operation offers up to 80% pilot liquid fuel replacement by biogas, however, some reductions in energy and exergy efficiencies are observed.
Keywords: Biogas; Diesel; Dual fuel; Exergy; GTL; Irreversibility; Renewable fuels.
Numerical Analysis of a Hybrid Thermal Energy Storage System Using Thermochemical and Phase Change Material for Constant, Low Temperature Applications
by Swaraj Kumar B, James Varghese, Stiben Paul
Abstract: A novel hybrid energy storage method is proposed in this paper to overcome high temperature levels at the start of the reaction in thermochemical energy storage, which causes this technology to be unsuitable for constant temperature applications. This numerical study shows that the hybrid storage system with thermochemical material and phase change material is a promising method in the field of low temperature thermal energy storage. The melting temperature of the PCM and the flow rate of the heat transfer fluid must be chosen carefully to enhance the performance of the system.
Keywords: Hybrid thermal energy storage; Thermochemical Energy storage; Packed bed reactor.
Thermo-hydraulic and Exergy Analysis of Parabolic Trough Collector with Wire Matrix Turbulator: An Experimental Investigation
by Varun K, Arunachala Chandavar
Abstract: The present energy crisis due to the exhaustion of fossil fuels, global warming, the surging gap between energy supply and demand, high electricity price, etc. has paved a path to harness renewable energy resources effectively. Among various sources, due to enormous potential and implicit superiority, solar thermal energy has been proved to be the best solution for the energy crisis. As an outcome, the oldest and prevailing solar concentrating technology i.e. parabolic trough collector (PTC) is being used extensively. However, the majority of studies are numerical as its receiver is subjected to highly non-uniform concentrated heat flux (circumferentially). Further, the outdoor testing is a laborious task due to the transient operating condition. Hence a novel method having a combination of differential heating, analytical model, and SOLTRACE
Keywords: Parabolic trough collector; Non-uniform heat flux; SOLTRACE®; Wire matrix; Performance evaluation criterion; Exergy enhancement ratio.
Design and comparative analysis of a geothermal energy supported plant for tri-generation purposes
by Nejat Tukenmez, Fatih Yilmaz, Murat Ozturk
Abstract: In this study, two geothermal-based energy systems that provide beneficial outputs of hydrogen, electricity and hot-water are proposed. In this study, two thermoelectric generators are included in the second system, unlike the first system, proposed to analyze the impact of thermoelectric generators on plant performance. For comprehensive thermodynamic and performance analysis of the proposed systems, the proposed systems are modeled according to thermodynamic equilibrium equations. The parametric works are performed to address the impact of different system indicators affecting the useful outputs and performance of the modeled systems. In addition, the performance evaluation of the modeled systems is conducted in comparison with several working fluids. The energetic and exergetic efficiencies of the designed first cycle are 40.4% and 31.57%, while the energetic and exergetic efficiencies of the suggested second cycle are found as 49.36% and 41.79%. The hydrogen generation realized by both proposed systems per unit time is 0.001196 kg/s.
Keywords: Energy; Exergy; Geothermal Energy; Thermodynamic Analysis; Thermoelectric Generator.
Potential energy optimisation in a domestic air to water heat pump
by Stephen Tangwe, Kanzumba Kusakana
Abstract: The study focused on the determination of the coefficient of performance (COP) and exergy losses of a 1.2 kW, 150 L add-on air to water heat pump (AWHP). It further justifies opportunity to optimise both the exergy losses and COPs of the system. Adequate sensors were installed at precise locations within the AWHP. Specific controlled hot water of 150, 50 and 100 L were drawn off from the AWHP during the morning, afternoon and evening for a full year. The results depicted that the average week-day COP, electrical and thermal energy consumed was 3.420, 3.478 kWh and 11.896 kWh, respectively. The associated exergy loss rate at the evaporator, compressor, condenser and expansion valve was 11.63, 41.89, 18.90 and 27.58%, respectively. The results of the experiments and in conjunction with the energy and exergy analyses, demonstrate potential opportunities of improving the efficiency of the AWHP.
Keywords: Air to water heat pump (AWHP) ; Coefficient of performance (COP); Exergy analysis method; Energy analysis method; Enthalpy.
A sustainable PV-powered energy retrofit modeling to achieve net ZEB in churches: A simulation study for San Marcello Al Corso
by Mohammad Mohammadzadeh, Navid Hadifar, Bahareh Mohammadzadeh
Abstract: This interdisciplinary study proposes practical modifications for achieving net-zero energy building (net ZEB) in historical churches while all the values of the church have been recognized and preserved. The church studied from structural, mechanical, and electrical perspectives. A 40.7% rise in energy efficiency and a 12% rise in exergy efficiency are observed after applying modifications. The concept of net ZEB has been accomplished in the church. A 98% balance in annual energy exchange is reached between the on-site and the utility grid power generation by applying the net metering method.
Keywords: energy retrofit; PV system; net-zero energy building (net ZEB); net metering; sustainability; horizontal air curtain; exergy analysis.
Exergy analyses of a tunnel furnace and a tunnel dryer
by Gurhan Tahtali, Hayati Olgun, Mustafa Gunes, Arif Hepbasli
Abstract: The main objective of this study is to comprehensively perform exergy analysis of the tunnel furnace and the tunnel dryer, which was selected as the control volume and involved in a brick production line. The analysis was based on the real data measured over one year period at a working brick factory with a daily production capacity of 392 tons fired bricks. Energy and exergy efficiencies of the control volume were obtained to be 76.46% and 12.90% for dead state values of 25 ?C and 1.013 atm, respectively.
Keywords: brick factory; tunnel furnace; tunnel dryer; energy and exergy analysis.
Influence of boundary conditions on the exergetic performance of the combination of a Thermal Energy Storage System and an Organic Rankine Cycle
by Andreas König-Haagen, Dieter Brüggemann
Abstract: The combination of a high-temperature packed bed Thermal Energy Storage (TES) with an Organic Rankine Cycle (ORC) named ORCTES is analyzed and optimized numerically for different boundary conditions from an exergetic point of view. The temperature dependency of all relevant material properties is taken into account. Characteristic curves from literature are used to model the ORC. Pressure and heat losses as well as convection, diffusion and radiation in the packed bed are included in the TES model. To identify the optimization potential and interactions in the system, a detailed exergetic evaluation method is applied. For one set of boundary conditions, an optimization is performed and compared with a previous publication. These two cases refer to the highest and lowest overall exergetic efficiency in the non-optimized case. Interestingly, the effect of physical aspects on the exergetic efficiency can be higher or lower for the TES itself compared to the effect on the overall system and these effects strongly depend on the boundary conditions. The optimization raised the exergetic overall efficiency from 36.1 % to 43.4 % and from 7.6 % to 28.0 %.
Keywords: Exergy; Detailed Analysis; Optimization; Thermal Energy Storage; Organic Rankine Cycle;.
Thermo-environmental analysis and performance comparison of solar assisted single to multi-generation systems
by Muhammad Khan, MUHAMMAD ABID, Mi Yan, Tahir Ratlamwala
Abstract: In the present study, a novel multi-generation system producing electricity, heating, cooling, thermal energy storage and hydrogen is investigated according to the thermodynamic and environmental point of views. The purpose of the present work is to thermodynamically examine and evaluate the performance of solar-aided multi-generation system. Different operating parameters are varied to assess the performance of the integrated multigenerational system. The results of the study illustrate that overall energy and exergy efficiency of the proposed integrated system is 51.62% and 53.45%, respectively while, hydrogen production rate is observed to be 0.00742 kg/s.
Keywords: Heliostat; multi-generation; overall energy; exergy; exergo-environmental; hydrogen.
Exergy analysis of a biogas-diesel fuelled dual fuel engine
by Feroskhan M, Sreekanth Manavalla, Saleel Ismail
Abstract: This work presents the exergy analysis of a biogas-diesel dual fuel engine for various operating loads and flow rates using simulated biogas. The engine is operated with pure methane and raw biogas with variable CH4:CO2 ratios to assess the effects of carbon dioxide extraction, termed as methane enrichment. Addition of biogas reduces exergy destruction and improved exergy efficiency vis-
Keywords: Biogas; Dual fuel; Exergy; Exergy efficiency; Exergy destruction.
Exergy and CO2 emission analysis of rotary hearth furnace-electric arc furnace routes of steelmaking
by Binay Kumar, Gour Gopal Roy, Prodip Kumar Sen
Abstract: Model-based analysis of exergy and CO2 emission of an emerging steelmaking process through rotary hearth furnace-electric arc furnace (RHF-EAF) system has been studied. Exergy indices of two RHF based processes yielding either iron nugget (ITmk3 process) or DRI (FASTMET process), operating with EAF are found to be either superior or comparable to conventional steelmaking (BF-BOF) process. Net CO2 emissions through RHF-EAF processes are found to be comparable to emissions from BF-BOF process. Considerable improvement in main-product exergy efficiency and CO2 emission are observed on utilisation of RHF off-gases to in-house power generation.
Keywords: Exergy analysis; CO2 emission; Emerging routes of steelmaking; RHF-EAF process; BF-BOF process.
Influence of Orifice in Entropy Generation and Exergy Analysis under transient condition for Large Diameter Natural Circulation Loops
by Elton Dylan Nazareth, Arunachala U. Chandavar, Rajat A. Chandavar
Abstract: Stable power generation is of concern due to instability in NCL. The entropy generation analysis in a 38.89 mm diameter loop identified the flow reversals by a drop in its value after a peak. Orifice plates and operating procedures lead to a change in threshold value. During unsteady state, the least entropy generation was observed with ? = 0.77. At higher power, constant power generation is possible with low orifice as it exhibits better exergy efficiency. The entropy generated due to friction was negligible compared to that by heat transfer
Keywords: Natural circulation systems; single phase; instantaneous entropy generation; instability; orifice; large-diameter loop; exergy analysis.
Comparative Exergetic, Economic and Exergoeconomic analysis of a hybrid cascade refrigeration system using ammonia-propane, propane-propylene and isobutane-propane refrigerant pairs
by Kaushalendra Kumar Singh, Rajesh Kumar, Anjana Gupta
Abstract: In the present study a comparative exergetic, economic and exergoeconomic analysis is done on a hybrid cascade refrigeration system using ammonia-propane, propane-propylene and isobutane-propane refrigerant pairs. Overall system cost rate, component-wise exergy destruction rates, exergetic efficiencies and exergoeconomic factors are investigated for the three refrigerant pairs at thermodynamic optimal operating conditions. The study concludes that ammonia-propane is the best refrigerant pair with maximum exergetic efficiency of 24.83% and minimum total cost rate of 564469 $/yr, whereas isobutane-propane is thermodynamically superior, but economically inferior than propane-propylene refrigerant pair.
Keywords: Cascade refrigeration system; Optimization; Exergy and Economic; Comparative analysis; Exergoeconomic factor; Natural refrigerants.
Special Issue on: ECOS 2019 Progress in Exergy Analysis of Energy Systems
Exergy Analysis of Novel Integrated Systems Based on MHD Generators
by Hossein Sheykhlou, Samad Jafarmadar, Rogayieh Abbasgholi Rezaei
Abstract: The present work concerns with the thermodynamic analysis of novel opened and closed Magneto Hydrodynamic Organic Rankine Cycles (MHD-ORCs). In this regard, the thermodynamic simulation of the integrated systems with the assumption of the constant stream velocity in the MHD generator has been performed. The impact of MHD input temperature, the electrode surface area, the plasma velocity, and the compressor isentropic efficiency on the overall performance of the combined cycles have been investigated. Moreover, exergy and thermal efficiencies of opened and closed MHD based cycles have been calculated and achieved in optimal points as follows; 66.15 %, 71.67%, 49.21 %, and 39.77%, respectively.
Keywords: Magneto Hydrodynamic Organic Rankine cycle; MHD generator; Coal combustion; Exergy Efficiency; Thermal Efficiency.
Study on combustion irreversibility in turbocharged spark-ignition engines
by Caio Henrique Rufino, Alessandro José Truta Beserra De Lima, Fazal-Um-Min Allah, Janito Vaqueiro Ferreira, Waldyr Luiz Ribeiro Gallo
Abstract: The direct injection (DI) and turbocharging strategies are recently adopted for spark ignition (SI) engines in order to achieve better fuel economy and lower pollutant emissions. A comprehensive analysis is required in order to evaluate the effects of aforementioned strategies on in-cylinder combustion processes. The second law analysis is a proficient thermodynamic tool which is used for identifying irreversibilities and exploring the possibilities of thermal systems optimization. The present work aims at carrying out an exergetic analysis of a downsized turbocharged DISI engine. The engine is fuelled with E10 (gasoline with 10% of ethanol content) while experimental data is acquired for different engine operating conditions. The exergetic analysis identified the combustion irreversibilities. Moreover, a comparison between second law analyses of a previously analysed port fuel injection (PFI) naturally aspirated SI engine and turbocharged DI SI engine is also presented. The study concluded with the potential benefits and drawbacks of newly adopted strategies for SI engines.
Keywords: Direct-injection; Turbocharging; Spark ignition; Irreversibility; Exergy.
Exergy and environmental analysis of black liquor upgrading gasification in an integrated kraft pulp and ammonia production plant
by Meire Ellen Gorete Ribeiro Domingos, Daniel Florez-Orrego, Moises Teles Dos Santos, Hector Velasquez, Silvio De Oliveira Junior
Abstract: The black liquor is a byproduct of the kraft pulping process that contains more than half of the exergy content in the total woody biomass fed to the digester, representing a key supply of renewable energy to the pulping process. In this work, the conventional scenario of the black liquor use (i.e. concentration and combustion) is compared with the black liquor upgrading (via) gasification process for ammonia production in terms of economics, exergy efficiency and environmental impact. The combined energy integration and exergy analysis is used to identify the potential improvements that may remain hidden to the energy analysis alone, namely, the determination and mitigation of the process irreversibility. As a result, the exergy efficiencies of the conventional and the integrated cases average 40% and 42%, respectively, whereas the overall emission balance varies from 1.97 to -0.69 tCO2/tPulp, respectively. The negative CO2 emissions indicate the environmental benefits of the proposed integrated process compared to the conventional kraft pulp mill.
Keywords: Entrained flow gasifier; Black liquor; kraft pulp; Exergy; Ammonia; Environmental impact; Renewability; Decarbonization; Energy integration; Fertilizers.
Measurement of interior thermal environment of a passive solar house in an urban area in Japan and analysis of time-series variation of human body exergy balance
by Hideo Asada
Abstract: The purpose of this study was to know what kind of time-series variation of interior thermal environment was appeared in the passive solar house as a consequence of installed some passive methods, heating equipment and residents adaptive behaviour acquired through their own lifestyle and accumulated experience and to reveal what time-series variation of human body exergy balance were appeared as a consequence for living in a passive solar house. To know this, we had done a measurement on interior thermal environment of the passive solar house in urban area of Tokyo after 6 years have passed from constructed and had done analysis on time-series variation pattern of human body exergy. As a result, a unique interior thermal environment fluctuation pattern reflecting adaptive behaviour of the residents were formed in the passive house, and the time-series variation patterns of a human body exergy balance created by specific interior thermal environment in winter and summer were explicitly shown and discussed.
Keywords: passive solar house; measurement; indoor thermal environment; passive solar house; urban area; analysis of time series variation; human body exergy balance; adaptive behavior; lifestyle; accumulated experience; time series variation pattern; unsteady state; radiant heating; natural ventilation; human body exergy consumption.
A thermodynamic explanation of the function of bifurcated structures in nature and in engineered artefacts
by Enrico Sciubba
Abstract: Why do bifurcated structures appear in nature? Both in living and non-living systems, the construction of a bifurcation requires some energy input, and in view of the economic principle of nature, this must be justified by a compensating gain for the resulting evolved structure. The most celebrated attempt to a theory of such phenomena is Bejans Constructal Theory, based on a generalization of the Hess-Murray law, first derived in 1903 by the Swiss biologist Walther Rudolf Hess. In spite of the great success of CT, some questions remain unanswered: Given that the purpose of bifurcations is to transport material and immaterial flows, what underlying principle governs the radius ratio between successive branches, the diameter/length ratio and the splitting angle? How do the prevailing boundary conditions influence the onset of bifurcations? This paper presents a novel thermodynamic model based on the assumption that the driving force behind the emergence of a bifurcated structure is its exergy cost. The model may be considered an extension and a completion of the Hess-Murray law: an extension, because it measures the advantage of branched structures with respect to their non-branched counterparts in terms of exergy instead of energy; a completion, because it includes the formation exergy, neglected by previous theories. Since exergy is a homogeneous and rigorous measure of the investment necessary to operate the transport, it seems natural to consider as the fuel required for this transport both the exergy equivalent of the work done to overcome friction and the material exergy embodied in the structure. The model proposed in this paper leads to a quantification of this primary exergy cost. The ubiquity of branched structures seems to suggest that they consume less exergy to perform the same task (transferring mass or energy), and thus can better exploit the resources available in their immediate surroundings, and the numerical results presented here confirm this intuition. The same principle ought to guide the design of artificial bifurcated structures or networks: more effective delivery of material and immaterial fluxes, milder mechanical and thermal gradients, higher power/volume and power/surface ratios
Keywords: Bifurcated Flows; Exergy Analysis; Hess-Murray Law; Constructal Theory.
Electrified District Heating Networks: A Thermo-Economic Optimisation Based on Exergy and Energy Analyses
by Getnet Tadesse Ayele, Mohamed Tahar Mabrouk, Pierrick Haurant, Björn Laumert, Bruno Lacarrière, Massimo Santarelli
Abstract: This paper presents a thermo-economic optimisation of an electrified district heating network consisting of wind power plant, gas-fired combined heat and power plant and heat pumps. The load flow problem of the resulting multi-energy system is formulated by considering all physical and operating parameters in both of the electricity and heat distribution networks. First, energy and exergy analyses are applied to identify and isolate lossy branches of a meshed heating network. This is followed by the optimal placement of heat pumps. Finally, supply and return temperatures are optimised. Particle Swarm Optimisation technique is implemented in order to find the best place of heat pumps, their economical dispatch and optimal temperature profile of the district heating network. Results show that up to 59.12% of the distribution heat loss and 9.37% of the operating cost can be saved by following a step-by-step methodology discussed in this paper.
Keywords: Combined heat and power (CHP) plants; District heating network (DHN); Electrified district heating network; Energy hubs; Exergy; Heat pumps; Lossy branch identification; Multi-energy systems; Optimal placement; Particle swarm optimisation; Thermo-economic optimisation.
Eco-credit system to incentivize the recycling of waste electric and electronic equipment based on a thermodynamic approach
by Alicia Valero, Ricardo Magdalena, Guiomar Calvo, Sonia Ascaso, Fernando Círez, Abel Ortegof
Abstract: The use of electric and electronic equipment has been increasing dramatically in the last years and entails an important amount of waste containing many valuable metals which could constitute an important source of raw materials if appropriately recycled. In this paper, an expression has been developed to value waste of electric and electronic equipment that are sent by users to an appropriate recycling plant. The user obtains in turn eco-credits, which can be later exchanged through different incentives. The eco-credit expression is based on the raw material content of the given device, assessed through an indicator called thermodynamic rarity, which rates minerals according to their scarcity in the crust and the energy required to mine and refine them. Additionally, the state of the device, lifetime and recyclability of the materials are considered in the equation. The expression has been applied as a case study to a working tablet and a LED lamp.
Keywords: Raw Materials; Reuse; Recycling; Exergy; Eco-credits; Rarity; WEEE.
Exergy analysis of a thermostatic heat pump drying system with adjustable bypass air ratios
by Qiuyuan Qin, Lan Tang
Abstract: Drying is the best method to preserve products, but it will consume large amounts of energy. In this paper, a new heat pump drying system is designed, the wet cotton cloth is selected as drying material and the exergy analyses for the main components and the whole system are carried out. The results show that the maximum exergy loss always occurs in the compressor. Both the drying air temperature (DAT) and bypass air ratio (BAR) affect the exergy efficiency of the whole system and components. For the whole system and main components, the optimal BAR at 35?, 40?, 45? are always 40%, 0% and 60% respectively. Under a higher DAT, both the dehumidification ability of the evaporator and its exergy efficiency are reduced by the excess air mass flow rate. Through the exergy analysis, some improvement measures for the exergy efficiency are put forward.
Keywords: Exergy Analysis; Heat Pump Drying; Drying air Temperature; Bypass Air Ratio.