International Journal of Exergy (31 papers in press)
Entropy generation due to a moving isothermal wavy surface in nanofluid
by Ahmer Mehmood, Sajid Khan, Muhammad Saleem Iqbal
Abstract: The aim of current investigation is to analyze the irreversibility phenomenon, in the presence of nanoparticles in the base fluid, in viscous flow caused by the uniform motion of a wavy plate. The utilized model for the presentation of nanofluid is the Bonjourno model in which the Brownian motion and thermophoresis effects are considered. The non-flat surface texture of the wavy plate does not allow the similarity solution to exist due to which the problem is non-similar in nature. The study of entropy generation phenomenon in such non-similar boundary layer flows is very rare in literature. An implicit finite difference scheme (the Keller-box method) is utilized to obtain the numerical solution and the results have been presented through several graphs. Impact of various controlling parameters, namely, the Brownian motion parameter, the thermophoresis parameter, wavy amplitude, Lewis number, Prandtl, and Brinkman numbers on Bejan number and entropy production number are examined. It is found that entropy production increases by increasing the concentration of nanoparticles.
Keywords: Nanofluid; entropy generation; moving wavy surface; Boungiorno model.
Enhanced exergy analysis of a bubble-pump-driven LiCl-H2O absorption air-conditioning system
by Julia Aman, Paul Henshaw, David Ting
Abstract: A thermally-driven bubble pump can replace the electrical pump in the absorption refrigeration cycle for lifting solution from the absorber to the generator and producing the required refrigerant vapor for the cooling effect. However, the lower efficiency of bubble-pump-driven absorption refrigeration cycle hinders its widespread application. The potential of a bubble-pump-driven LiCl-H2O absorption refrigeration system that can be powered by solar thermal energy or waste heat energy is discussed and analyzed in this study. The new concept of enhanced exergy analysis is integrated in the thermodynamic analyses, which quantifies the available exergy destruction of each component for overall system performance improvement. The analyses uncovered that 80% of the total exergy loss is due to each components own internal irreversibilities, whereas the remaining is through the interaction of the irreversibilities of other components in the system. The analyses revealed that though the highest exergy losses (46%) are in the absorber, priority for improvement should be given to the generator. Furthermore, the exergy losses of the condenser, the evaporator, and the solution heat exchanger are mostly unavoidable and can be reduced by improving the other components of the system.
Keywords: bubble pump; LiCl-H2O; vapor absorption refrigeration; exergy analysis; advanced exergy analysis.
Energy, Exergy and Economic Analysis for ON/OFF Cycle and VFD HVAC Cooling Systems
by Waleed M. Hamanah, Mahmoud Kassas, Ahmet Z. Sahin, Ibrahim El-Amin
Abstract: A comparison of energy, exergy rate and economic analyses for an air conditioning ON/OFF cycle and VFD HVAC systems with heat mass exchange calculation was performed. The study considered several key performance parameters including; energy consumption, energy saving, exergy destruction rate, exergy efficiency, CO2 emission, coefficient of performance (COP), and cost analysis for both HVAC systems. VFD technique significantly improves the air conditioning efficiency, while it has only a small effect on cost. However, in the presence of a VFD both the required cooling energy and the required input power decrease significantly. In addition, the total energy consumption, exergy destruction and CO2 emission are lower when a VFD HVAC is used, as compared with an ON/OFF cycle HVAC system. The total exergy destruction decreases by more than 20%, on average, when a VFD is used when compared with the case of the ON/OFF cycle. Thus, this study reveals that, when a VFD is used, the energy efficiency and exergy efficiency increase by more than 37% and 10%, respectively.
Keywords: Energy Savings; Exergy Destruction; Variable Frequency Drives VFD; ON/OFF Cycle; Heating; Ventilation; and Air Conditioning (HVAC).
Exergetic evaluation of a conceptual design for hydrogen production and seawater desalination using an advanced nuclear reactor as energy source.
by Daniel González Rodríguez, Fernando Roberto De Andrade Lima, Carlos Alberto Brayner De Oliveira Lira, Carlos Rafael García Hernández
Abstract: In this work, a computational model to develop the conceptual design for hydrogen production and seawater desalination based on a modular nuclear reactor as an energy source is presented. The 4-step Cu-Cl process is used to produce hydrogen coupled to the GT-MHR nuclear system through a Brayton cycle for the electrical energy generation. A fraction of the thermal energy from the GT-MHR system is used to reach and maintain the temperature requirements in the Cu-Cl process. The rejected heat from the oxy-decomposition reaction is used to desalinate seawater through a multi-stage process flash. It is employed a chemical process simulator in order to develop a computational model of the proposed system. The global energy and exergy efficiencies of the proposal are 32.47% and 52.20% respectively, producing 0.2190 kg/s of hydrogen and desalinating 4.9492 kg/s of seawater. It is made an estimate of the cost of hydrogen produced using HEEP
Keywords: nuclear hydrogen production; exergy; energy; efficiency; seawater desalination; cost estimative.
Sustainable management and conservation of resources for different wheat production processes; Cumulative Exergy Consumption Approach
by Hasan Yildizhan, Morteza Taki
Abstract: Inputs in crop production process can be defined as energy resources. All the inputs used in agricultural production can be renewable or not. One of the new methods for evaluate the exergy-energy and share of each input on total output, is Cumulative Exergy Consumption (CEXC) analysis. So, the CExC approach ensures that crop production processes can evaluate in the context of sustainable management and conservation of resources. Wheat is produced by using various methods and energy inputs. So, the amount of energy sources and the output yield vary according to each wheat production process. In this research, wheat production processes in two different cultivation methods (dry and wet) was investigated by CEXC approach. Cumulative Degree of Perfection (CDP) calculated 2.9 and 6.48 for wet and dry wheat production, respectively. The Renewability Indicator (RI) in this research were obtained 0.65 and 0.84 for wet and dry wheat production, respectively. In this research, electricity and diesel fuel had the highest consumption in all wheat production process. For a new case, it was assumed that the electricity and diesel fuel are produced by solar energy and biodiesel, respectively. In the new case, the CDP factor of wet and dry wheat production were 16.70 and 13.92 and RI values were 0.94 and 0.92, respectively.
Keywords: Iran; Wheat production; Cumulative exergy consumption; Sustainable agriculture; Renewable energy.
Examination of the liquefaction system for used different cryogenics in terms of thermodynamic analysis
by Arif Karabuga, Zafer Utlu, Resat Selbas
Abstract: The purpose of this study is to determine the parameters affecting the exergy efficiency of the cryogenic liquefaction unit integrated into a real cryogenic air separation unit. Cryogenic liquefaction is one of the basic processes between liquefaction methods. In addition to this process, absorption and membrane are used in methods. The main difference in the selection of these methods is the desired purity rates. Cryogenes are defined as fluids used in cryogenic cooling. In this study, five different cryogenes in the air were investigated. The energy and exergy analysis of the liquefaction unit for each cryogen was made. As a result of the study, the highest COPactual value was obtained with 0.3105 hydrogen fluid and the highest COPrev value with 0.8551 oxygen. Exergy of the system was found as 0.48 with hydrogen.
Keywords: Cryogenic liquefaction; Cryogenics; Energy and exergy analyses.
Exergy, exergoeconomic and environmental analysis of diesel engine operating with EGR rate
by Eduardo José Cidade Cavalcanti
Abstract: This research presents the effects of exhaust gas recirculation (EGR) and load on a diesel engine. The operational conditions of diesel engine were different loads (5-30 kW) with increment of 5 kW and EGR rate (0-10%) with increment of 2.5 %. The engine was supplied with blend of diesel and 7% of biodiesel. The exergetic, exergoeconomic and environmental analysis were investigated in order to evaluated the cost and pollutant emissions of electricity. The results reveal that the load increases the exergetic efficiency, exergy destruction, fuel cost rate and reduces the specific power cost and relative cost difference. In addition, the EGR rate decreases the exergetic efficiency and increases exergy destruction, fuel cost rate, relative cost difference and specific power cost. At low load, the specific total pollution damage is predominant, then the higher EGR rate is desired. At high load, reduction of performance is significant with EGR rate, and total pollution damage loses significance, then the lower EGR rate is desired. Therefore, the maximum load and EGR rate of 2.5% are the best condition under the exergoeconomic and environmental point of view.
Keywords: diesel engine; exergy; exergoeconomy; environmental analysis; EGR; load; emissions; biodiesel; exergy destruction.
Exergy Surface Shaping and Thermodynamic Flow Control of Electro-Mechanical-Thermal Systems
by Wayne Weaver, Rush Robinett, David Wilson
Abstract: This paper extends the concepts and tools of Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) for electro-mechanical (EM) systems to Exergy Surface Shaping and Thermodynamic Flow Control (ESSTFC) for electro-mechanical-thermal (EMT) systems (i.e., irreversible work processes with heat and mass flows). For this paper, Extended Irreversible Thermodynamics will be utilized to produce consistent thermal equations of motion that directly include the exergy destruction terms. A simplified EMT system that models the EMT dynamics of a Navy ship equipped with a railgun is used to demonstrate the application of ESSTFC for designing high performance, stable nonlinear controllers for EMT systems.
Keywords: Electro-Mechanical-Thermal Modeling; Hamiltonian Surface; Pulse Power Load.
Thermodynamic analysis of a biomass gasifier driven combined power and ejector absorption refrigeration (CPER) system
by Mohd Parvez
Abstract: This paper provides the thermodynamic study of an advanced power, cooling and refrigeration system which derives the required energy from biomass gasification and waste heat recovery operated ejector absorption refrigeration system. The system deploys refrigerants such as R-141b and lithium bromide water mixture as the working fluids which eventually generates the cooling and refrigeration simultaneously with stack gases. First and second law efficiencies are calculated to determine the effects of the crucial thermodynamic properties on turbine inlet temperature to heat recovery steam generator, turbine inlet pressure, evaporator temperature, change in biomass materials and then exergy destruction of each components of the system. It is observed that both first and second law efficiencies of the system decreases with increase in turbine inlet pressure but rises considerably with the increase in turbine inlet temperature. It is further observed that both the efficiencies rises with the employment of an ejector and absorption refrigeration by approximately 6.22% and 3.21% as compared to combined power cycle. Exergy analysis presented in this paper will gives a new dimension to the future researches in terms of reduced environmental impact and energy conservation.
Keywords: biomass gasification; combustion; exergy destruction; ejector; vapor absorption.
Exergoeconomic Optimization of an Air Cooled Heat Exchanger with Copper Oxide Additives
by Nader Javani
Abstract: In the current study, the effect of suspended CuO nanoparticles in a fluid on the exergoeconomic and thermoeconomic properties of an air cooled heat exchanger (ACHE) is investigated. Multi-objective particle swarm optimization algorithm is employed for this purpose. Nine design parameters are selected and two sets of objective functions including the exergy efficiency versus total annual cost (exergoeconomic optimization) and effectiveness versus total annual cost (thermoeconomic optimization) are taken into account. In each case, the results are compared with the base fluid which has no nanoparticles. Results show that nanoparticles have not a meaningful effect on the exergoeconomic improvement of ACHE while a significant improvement is observed for the thermoeconomic optimization. It is also shown that adding CuO nanoparticle into the base fluid for a specified effectiveness, decreases the heat exchanger total annual cost (TAC). If a fixed annual cost is considered, the base fluid mixed with nanoparticles will increase the heat exchanger effectiveness. A value of 9.5% improvement in effectiveness is found for the nanoparticle additives compared with the base fluid for a fixed value of 140$ total annual cost. On the other hand, 20.7% improvement in total annual cost is obtained for the nanoparticle additives compared to the base fluid for the same effectiveness of the 0.7.
Keywords: Air cooled heat exchanger; Exergy efficiency; Exergoeconomics; Nanoparticle; Optimization.
Thermodynamic assessment of the use of alternative metabolic energy resources on work performance efficiency of spontaneous rat myometrium contractions
by Gulnihal Selay Varicioglu, Sinem Ethemoglu, Ali Bahadir Olcay, Bayram Yilmaz, Mustafa Ozilgen
Abstract: Uterine smooth muscles (myometrium) are employed during labour to expel fetus (infant) out of the uterus. Exergy efficiency of the rat myometrium muscle contractions were assessed with the data collected in organ bath experiments in Krebs solutions. The major energy source, glucose, of the Krebs solution was substituted with sucrose, sodium pyruvate and calcium and lactate to assess the effect of the metabolic energy source on the exergy efficiency of work performance. Force versus time graphs were correlated with the work done during the contractions. Muscle contraction exergy efficiency was calculated as the ratio of work done by a muscle strip to the total exergy supplied. Exergy efficiency of the contractions was the highest, 36.7 %, when lactate was the metabolic energy source and it was followed by 35.3 % when pyruvate was the metabolic energy source. Exergy efficiencies of the cases with glucose and sucrose were 34.1 % and 23.5 %, respectively. The findings of this study may open way to further studies which may eventually help women give birth to babies with less pain by increasing exergy efficiency of the process.
Keywords: Myometrium; muscle work performance; exergy efficiency; energy source.
Energy, Exergy and Exergoeconomic Analyses of a Solar Refrigeration Cycle Using Nanofluid
by Hossein Asgharian, Ehsan Baniasadi, C. Ozgur Colpan
Abstract: In this paper, energy, exergy and exergoeconomic analyses of a solar absorption refrigeration cycle with energy storage are conducted. In this cycle, nanofluid is used as the heat transfer fluid (HTF) in a flat plate collector to improve the performance of the cycle. Based on the results of the analyses, the type of nanofluid and working conditions that lead to lower cost of cooling effect and higher COP and exergy efficiency of the cycle are found. The results show that utilization of CuO and Al2O3 nanofluids with 5% volume fraction increases the COP of the solar cycle by 17.98% and 14.51%, respectively, whereas the exergy-based cost rate of cooling decreases by 10.25% and 5.48%, respectively. Utilization the CuO nanofluid as the HTF is found to be more favorable for improving the performance of the cycle and decreasing the exergy-based cost of cooling.
Keywords: Solar absorption refrigeration cycle; Exergoeconomic analysis; Exergy efficiency; Cooling effect; Nanofluid; Energy storage.
Energy, exergy and exergoeconomic analysis of high temperature short time milk pasteurization plant
by Gurjeet Singh, Gurjeet Singh, P.J. Singh, P.J. Singh, V.V. Tyagi, V.V. Tyagi, P. Barnwal, P. Barnwal, A.K. Pandey, A.K. Pandey
Abstract: India produces 19.54% of the total annual milk production of the entire world (819 MT) with a yearly rise of 3.6%. However, a gloomy picture is portrayed by its limited processing capabilities (35%) which are responsible for its meager share (0.68%) in world trade. The motivation for the present work emerges from the fact that specific manufacturing cost of pasteurised milk as well as cost rate of exergy destruction in production of pasteurised milk in a dairy food processing plant had not been determined in any of the studies performed in the past. Therefore, present work concentrates primarily upon exergoeconomic evaluation of High-Temperature Short-Time Milk Pasteurisation Plant so as to achieve cost optimization and enhancement of overall profitability in the existing milk plant setup. Further, exergy gauge registered an exergy efficiency of 68.84%, with an exergy improvement potential of 48.14%, accompanied by specific exergy destruction of 32.21 kJ/kg of pasteurised skim milk. The thermoeconomic analysis revealed that specific manufacturing cost of pasteurised skim milk was calculated to be 2.75 R/kg along with cumulative cost rate of exergy destruction amounting to Rs. 14266.88 R/H. The high and low values of exergoeconomic factor magnify the role of capital investment and thermodynamic inefficiencies respectively. The former was reported to be most significant in case of holding coil (62.45%), heat exchanger (49.25%) and regeneration-1(20.18%), whereas the latter was diagnosed to be prominent in pumping and cream separation unit. Additionally, the total operating cost rate was estimated to be highest for the subunits regeneration-2 (6108.20 R/H) followed by a heating section (2153.63 R/H) and final chiller (2000.28 R/H) of dairy food processing plant.
Keywords: Energy; exergoeconomic; exergy; milk processing; milk pasteurization plant.
ENTROPY ANALYSIS FOR THERMALLY DISTURBED THIN FILMS
by Bekir Sami Yilbas, Saad Bin Mansoor
Abstract: Entropy generation rate during phonon transport across consecutively placed two thin films is examined. The films are thermal disturbed via setting the temperature differential at the edges. The Boltzmann transport equation is introduced to model the micro/nano scale heat transfer across the films. Thermal resistance is incorporated at the edges and at the interface of the films to model the boundary scattering. Thermodynamic irreversibility in association with the entropy generation rate is formulated in the films while adopting the phonon intensity distribution. The thermal conductivity predictions are validated incorporating the previous data. It is demonstrated that the thermal conductivity data predicted and obtained from the experiments are in good agreement. The phonon scattering at the film edges and at the interface results in temperature jump in these regions. As the film thickness reduces, the entropy generation rate becomes large, which is related to the thermodynamic irreversibility caused by temperature jump. The entropy generation rate predicted through the Fourier heating model remains significantly larger than that obtained from the phonon radiative transport model, which is more pronounced for the small film thicknesses
Keywords: Phonon transport; thin films; entropy generation; boundary scattering.
Exergy-based parallel between steam- and combined-cycle power plant configurations burning blast furnace gas
by Gustavo Bonolo De Campos, Cleverson Bringhenti, Jesuino Takachi Tomita
Abstract: This manuscript provides an exergy-based parallel between combined- and steam-cycle power plant configurations burning blast furnace gas. The combined cycle was based on a currently operational power plant located in Rio de Janeiro, Brazil. The steam cycle was created by replacing the gas turbines for steam generators that handled the same amount of fuel. The results show that the combined cycle achieved a 21.25% higher exergy efficiency, although emitting twice as much nitrogen oxide. The combined cycle generated 52.08% less steam while wasting 78.86% less exergy, which indicated that steam generators benefit from a higher amount of excess air. The gas turbine combustion chamber high exergy efficiency indicates that burning low-grade fuels is beneficial for reducing the intrinsic waste of chemical reactions. However, the compression process required prior to combustion undermines this benefit. Ultimately, this manuscript provides a comparison between two options to avail blast furnace gas.
Keywords: exergy; combined cycle; steam cycle; power plant; blast furnace gas; coke oven gas; steel mill; exergy efficiency; exergy waste ratio; emissions.
Exergy Analysis of a Natural Gas Fuelled Gas Turbine Based Cogeneration Cycle
by Yildiz Koc, Ozkan Kose, Huseyin Yagli
Abstract: In this paper, the monthly based annual performance of a natural gas fuelled gas turbine based cogeneration cycle was analysed. The performance analysis of the system was investigated in three steps. First, the real system parameters like temperature, pressure and power production were measured during a year. The measured parameters were compared with theoretical calculations. After which exergy based annual analysis of the system was performed for both system components and the overall system. Finally, the exergy analysis of the maximum and minimum power generated months (December and February) were compared with each other to show differences between the endpoints. As a result of the study, during the year, the maximum thermal and exergy efficiency of the simple gas turbine was calculated as 36.45% and 50.50% for the real case and 43.82% and 60.70% for the theoretical case, respectively. Moreover, the maximum thermal and exergy efficiency of the cogeneration system was determined as 79.00% and 94.19% for the real case and 83.92% and 91.64% for the theoretical case.
Keywords: Gas turbine; cogeneration cycle; real and theoretical comparison; annual analysis; performance analysis; exergy.
Towards a better understanding of energy systems using emergy-based exergoeconoenvironmental analysis
by Mortaza Aghbashlo, Marc A. Rosen
Abstract: This paper introduces 'emergy-based exergoeconoenvironmental analysis', a new methodology for improved understanding of energy systems through simultaneous consideration of thermodynamic, financial, and ecological criteria. A new parameter called exergetic ecological emergy/financial emergy ratio is first introduced. This parameter is then used for deriving emergy-based exergoeconoenvironmental balances for an energy system by combining it with exergy cost concepts. The exergetic ecological emergy/financial emergy ratio for all exergy streams of the system is determined using the SPECO approach. The developed approach is applied to a simple cogeneration system of power and steam to demonstrate its general applicability and robustness. The outcomes of the developed method herein are assessed in comparison with those of emergy-based exergoeconomic and exergoenvironmental methods. Overall, the highest total exergetic ecological emergy/financial emergy ratio (13.0841 sej/sej) is observed in the heat-recovery steam generator (HRSG) followed by the air preheater (APH) (10.0379 sej/sej). Even though both emergy-based exergoeconomic and exergoenvironmental methods give the improvement priority first for the combustion chamber (CC), the heat-recovery steam generator is suggested by emergy-based exergoeconoenvironmental analysis. Generally, the hybrid framework developed here appears to be a promising complement to available exergy-based techniques for systematically developing thermodynamically, financially, and ecologically conscious energy systems.
Keywords: emergy; exergoeconoenvironmental analysis; specific exergy costing; exergy cost.
Exergy analysis and assessment of performance criteria for compressed air energy storage concepts
by Friederike Kaiser, Uwe Krüger
Abstract: Compressed air energy storage (CAES) systems provide power reserve to compensate for intermittent renewable electric energy. The compressed air is stored to drive an open gas turbine. Enthalpy is close to zero at ambient air temperatures, which implies low storage efficiencies of the CAES open gas turbine cycle. Thus, in this project, the characterisation of CAES concepts based on exergy in contrast to enthalpy is discussed. The CAES energy efficiency defined as ηcaes = Wel,G / (Wel,M + Qfuel), resulting in approximately 42% for Huntorf and 54% for McIntosh, is unsuitable for characterizing CAES as an electrical energy storage. Instead, an alternative round trip energy efficiency ηrt4 is presented. An exergy-based counterpart is deemed ideal to evaluate storage properties of CAES. Calculations emphasize the efficient generation characteristics of fuel-driven CAES (e.g., McIntosh with 82% fuel efficiency of the turbine process as compared to a Carnot value of 75%).
Keywords: compressed air energy storage; CAES; Huntorf; energy storage efficiency; exergy; steady state thermodynamics; performance criteria; comparison.
Enhanced exergetic analysis of an olive oil refining plant: evaluation of the first and second level of exergy destructions
by Elif Bozoglan, Zafer Erbay, Arif Hepbasli, Huseyin Gunerhan
Abstract: Enhanced exergy analysis is built up as a novel modality to specify the origins of irreversibilities and to concentrate substantial improvement potential of components. The scope of this paper is to apply the enhanced exergy analysis to an olive oil refinery plant operated in Izmir, Turkey, that is conducted for the first time to agree the first level (endogenous/exogenous) and the second level (combination of the endogenous/exogenous and unavoidable/avoidable parts studied before) of destructions for exposing substantial efficiencies. Results showed that the components in the plant mostly have endogenous exergy destructions. Besides, the distillation unit has the highest endogenous exergy destruction value of 150.9 kW as the avoidable and unavoidable endogenous sections are 76.85 and 74.08 kW, respectively. Furthermore, the shell and tube economiser has the highest modified (enhanced) exergetic efficiency of 99.9% while the modified performances of plate-heat exchanger and pump (VII) are calculated as 73% and 71.24%, respectively.
Keywords: enhanced exergy; olive oil refining plant; endogenous; exogenous; modified exergetic efficiency.
Energetic and exergetic investigations of an innovative heat recovery exhaust system using a double acting type Stirling engine based on theoretical analysis
by Houda Hachem, Ramla Gheith, Fethi Aloui, Sébastien Delprat, Sébastien Paganelli
Abstract: This study aims to predict the feasibility and the performances of an innovative recovery system. It couples a double acting Stirling engine to the exhaust hot gas of internal combustion engines drive shaft. The behaviour of a micro-cogeneration system using Stirling engine is investigated. Referring to previous energetic analyses, exergetic model is set up in order to quantify the exergy destruction and efficiencies in each part of the recovery exhaust system. The repartition of the exergy fluxes in each part are determined and represented in Grassmann diagram. Possible solutions to improve the overall exergy efficiency of the micro-cogeneration unit were proposed. The performance of the Stirling engine was evaluated under different operating conditions. Effects of certain parameters including charge pressure, rotational speed, hot exhaust gas temperature and cooling water temperature are systematically studied. The effect of hot-side and cold-side exchange surfaces on the power and efficiency of the Stirling engine as well as on the efficiency of the global micro-cogeneration unit is investigated. The performance of the Stirling engine using three different working fluids: nitrogen N2, helium He and hydrogen H2 is estimated. Results can be useful for scientists and engineers to design an appropriate and efficient micro-cogeneration unit.
Keywords: micro-cogeneration system; double acting Stirling engine; exhaust gas; exergy destruction; exergy efficiency.
Perspective on the ontological ramifications of the 2nd law of thermodynamics
by Yunus Çengel
Abstract: Mass and energy are conserved quantities and are associated with the 1st law of thermodynamics, while entropy and exergy are non-conserved quantities and are associated with the 2nd law. The physical universe as we know it consists of matter and energy, including dark matter and dark energy. As conserved quantities, mass and energy fit into the description of physical entities, but entropy and exergy do not since entropy can be created and exergy can be destroyed. Thus, unlike mass and energy, the properties entropy and exergy are not physical entities although they are closely related to the physical entities mass and energy. Therefore, the 2nd law deals with quantities that are of a different kind of existence - a universe in which things come into existence out of nothing and go out of existence into nothing - and points to a form of existence that is beyond the physical universe we are familiar with. Extensions are made to other non-material entities such as physical laws, force, free will and life, and parallels are drawn with the glitter of light reflected off diamond. This paper is intended to stimulate discussion on non-conserved quantities like entropy and exergy with philosophical ramifications on existence.
Keywords: second law; thermodynamics; entropy; exergy; philosophy; ontology; existence; laws of physics; non-conserved quantities.
Special Issue on: GCGW2018 Exergetic Solutions for Better Performance
Comparative Thermodynamic Performance Assessment of Two-Stage Cycle for Various Refrigerants
by Fatih Yilmaz, Murat ÖZTURK, Resat SELBAS
Abstract: In this paper, the thermodynamic performance evaluations of the two-stage cooling cycle are investigated comparatively for different refrigerants under the same operating conditions. Due to their environmentally friendly properties, CO2, R600, R600a, R161, and R134a are selected as the refrigerants. The change in energy performance coefficient (COPen) and exergy performance coefficient (COPex) of the defined cycle are investigated according to the various indicators, such as reference temperature, gas cooler outlet temperature and pressure. Results are shown that, at the evaporator temperature of -5 oC and the gas cooler outlet temperature of 40 oC , the COPen of the cooling cycle are 1.644, 1.603, 1.452, 2.0356 and 1.928 for the refrigerants CO2, R600, R600a, R161 and R134a, respectively. Furthermore, COPex of the cycle are computed as 25.94%, 15.57%, 14.07%, 19.73% and 18.68% for the same refrigerants in the same order. In addition, the overall exergy destruction rate of the cooling cycle for CO2 refrigerant is calculated as 145.69 kW.
Keywords: CO2; energy; exergy; cooling; refrigerants.
Energy, Exergy and Thermoeconomic Analyses of Biomass and Solar Powered Organic Rankine Cycles
by Özüm Çallı, C. Ozgur Colpan, Huseyin Gunerhan
Abstract: In this paper, energy, exergy and thermoeconomic analyses of three different integrated systems consisting of an organic Rankine cycle (ORC) are presented. These systems differ from each other in terms of the energy technology providing the heat transfer to the ORC. For this purpose, biomass burner, parabolic trough solar collector (PTSC), and a combination of those are used. For analyses, numerous control volumes surrounding the system components are first formed. Then, applying energy, exergy and thermoeconomic balance equations around these control volumes, the thermodynamic properties of each state, work and heat transfer interactions, and exergy and cost per unit of exergy are calculated. As a result of these analyses, the electrical and exergy efficiencies of the system, as well as the specific cost of the electricity (per unit of exergy) are found. The effects of biomass type and solar irradiation on the performance and cost are assessed. The energy and exergy-based performance and electricity cost of these systems are also compared with each other for the baseline conditions and different number of PTSCs. The results show that biomass-based ORC system yields the highest electrical (10.61%) and exergetic efficiencies (9.18%) and the lowest cost (30.37 $/GJ). In addition, the system having PTSC and biomass burner is thermoeconomically advantageous when this system has 4 or fewer collectors compared to the solar based ORC system having 12 collectors.
Keywords: Organic Rankine cycle; energy; exergy; thermoeconomic; renewable energy.
Thermoeconomic assessment of a solar based ejector absorption cooling system with thermal energy storage: A case study for al-Jofra city in Libya
by Salem Yosaf, Hasan Ozcan
Abstract: Libya lying in one of the warmest regions in the world, a continuous cooling is required for domestic and industrial needs. In this study, a concentrated solar photovoltaic energy (CSPV) based ejector absorption refrigeration cycle (EARC) is evaluated using thermodynamic and thermoeconomic tools for a house requiring ~3.4 kW peak cooling in Libya. The solar data of Al-Jofra city is utilized to operate the CSPV system that produce enough heating and electricity for the refrigeration cycle generator and the thermal energy storage, as well as the system circulation pumps. The thermal energy storage medium uses Therminol as the heat storage fluid to utilize the system when there is no solar energy input. The overall COP and exergy efficiencies of the system at peak times are 0.82 and 32%, respectively. Cooling cost flow rate of the overall system is found to be around $0.22 per hour at generator temperatures above 100⁰C without thermal energy storage, while it is determined to be as high as $0.29 per hour with storage. Even though the system present high cooling costs due to high investment costs for the CSPV equipment, almost 6.58 tons of annual CO2 emissions can be prevented with this renewable based cooling system when replaced with conventional vapor compression refrigeration systems.
Keywords: Clean Cooling; Absorption Refrigeration; Ejector; Concentrated Solar Photovoltaics; Thermoeconomics.
Energetic and Exegetic Analysis of A Novel Multi-Generation System Using Solar Power Tower
by Muhammad ABID, Victor Adebayo, Victor Adebayo, Ugur Atikol, Ugur Atikol
Abstract: In this study, energy and exergy analyses are conducted on a multi-generation system driven by renewable energy source. The system produces power, domestic hot water and cooling as output by means of a gas cycle, a steam cycle, a double-effect absorption chiller and two domestic hot water heaters. The parametric study is carried out so as to examine the result of varying some operating conditions such as ambient temperature and irradiation from the sun on the effectiveness of the system. The solar multi-generation system is seen to have an energetic efficiency of 55.94% and an exergetic efficiency of 29.23%, while the COP (en) of the double-effect absorption chiller is determined to be 1.253 and the exegetic efficiency of the absorption chiller is 0.3762. The exergy destruction assessment for some components of the system shows that the receiver of the solar power tower is the component with the highest exergy destruction rate. Increasing the evaporator temperature of the absorption chiller is seen to raise the COP (en) of the chiller.
Keywords: Energetic; exergetic; multi-generation; double-effect absorption chiller; solar energy.
Conventional and advanced exergy analyses of an air-conditioning system in a subway station
by Hua Yin, Huafang Guo, Zhihua Tang, Junyan Yu, Haiyang Lu
Abstract: Air-conditioning systems in subway stations consume a large amount of energy. In this study, conventional and advanced exergy analyses were carried out to determine the energy-saving potential of an air-conditioning system in a subway station. Results show that air handling unit (AHU) should be improved for the highest values of relative irreversibility (RI) with conventional exergy analysis, whereas the compressor should have the highest improvement priority for the largest avoidable exergy destruction with advanced exergy analysis. Moreover, influences of compressor efficiency, condensation temperature, and evaporation temperature on avoidable exergy destruction of the air-conditioning system were also investigated. According to the findings, compressor efficiency significantly influences the systems total avoidable exergy destruction. The lower the compressor efficiency, the more rapidly the avoidable exergy destruction of the compressor increases. Furthermore, the avoidable exergy destruction of condenser, compressor, cooling tower (CT), and cooling water pump (CWP) increases with the rise of the condensation temperature, whereas that of the evaporator, throttling valve (TV), condenser, compressor, CT, and CWP decreases with the rise of the evaporation temperature.
Keywords: conventional and advanced exergy analyses; air-conditioning system; subway station.
Increasing exergy efficiency of a coal-fired thermal power plant via feedwater-heating repowering application
by Mustafa Zeki Yilmazoglu, Altug Alp Erdogan
Abstract: This study presents an exergetic comparison when feedwater-heating repowering method is used in a coal fired thermal power plant. Design data for Soma A thermal power plant was used to calculate the exergetic efficiency before repowering. Secondly, the exergetic efficiency calculations were repeated for thermal power plant after feedwater-heating repowering method. It was found that exergy destruction in combustion chamber (boiler) decreased from 84% to 66%. However, exergy destruction for the combustion chamber of gas turbine was found to be 15%. Total exergy destruction increased from 54.4 MW to 69 MW. However, total exergy destruction per installed capacity decreased from 2.3 MW/MWel to 1.99 MW/MWel. In addition, exergetic efficiencies for the designed and repowered cycles were found to be 31% and 34%, respectively. In conclusion, the feedwater-heating repowering method can increase the exergetic efficiency of the coal fired thermal power plants.
Keywords: Repowering; exergy; feedwater heating; thermal power plant; exergetic efficiency.
Exergetic Performance of Building Attached Photovoltaic Power Plant: A Case Study for an Olive Oil Production Corporation
by Elif Bozoglan, Mete Cubukcu, Eylem SAGLAM, A. Evren Ogutcen
Abstract: It is known that solar energy is among the most available and sustainable renewable sources of energy. Nowadays, there has been a gradual increase in the use of solar energy in the generation of electricity for industrial purposes. This study utilized energy and exergy analyses to assess the performance of a building attached photovoltaic plant (BAPV), installed on the roof of an olive oil manufacturing company situated in Izmir, Turkey. The plant has been reported to have a capacity of 701.2 kWp, and was designed as a grid connected model. Strings having a total of 21 monocrystalline solar modules constitute the BAPV system. These monocrystalline solar modules are more efficient in electricity production, compared to the polycrystalline ones. Prior to conducting analysis on exergetic performance, data were collected from Sunny Portal. These included data on total insolation of solar energy, panel surface temperature, ambient temperature, electricity production, etc. In 2017, energy and exergy efficiencies, exergy destructions and sustainability indexes were determined as a function of ambient temperature. The plant was found to have an exergy efficiency around 12.49-15.76%. Also, it was discovered that the sustainability indexes of the BAPV plant were in the region of 1.14-1.19. The module plane and the electricity produced, recorded annual solar irradiation of 1561.32 kWh/ (m2y) and 878.29 MWh/y, respectively. As a result of the values, this study recorded a mean annual electricity specific yield of 1252.55 kWh/kWp and performance ratio of 81.86 %.
Keywords: Solar energy; building attached photovoltaic power system; exergetic efficiency; exergetic destruction; sustainability index; electricity yield analysis.
Energy, Exergy, Exergoeconomic, and Exergoenvironmental study of a parabolic trough collector using a converging-diverging receiver tube.
by Eric Chekwube Okonkwo, Tahir Abdul Hussain RATLAMWALA, Muhammad ABID
Abstract: This study presents a novel energy, exergy, exergoeconomic and exergoenvironmental analysis of a parabolic trough solar collector operating with a converging-diverging absorber tube design. The collector is modeled thermally after the experimental results of the Sandia National Laboratory LS-2 collector test using the engineering equation solver. The results of the analysis show that the converging-diverging geometry obtained a mean enhancement in thermal efficiency of 1.13% and 0.49% in exergetic efficiency when compared to the conventional absorber tube. The optical losses with 24.5% accounted for the highest source of exergetic losses while the exergy destruction due to heat transfer between the sun and the absorber accounted for 59.7% at inlet temperatures of 350 K. The exergoeconomic study shows that the cost rate of exergy destruction is seen to decrease from 3.4 - 0.35 $/hr as the inlet temperature increases from 323-650 K. The environmental study yielded an exergoenvironmental impact factor of 0.31 with the values of 2.61, 0.82 and 1.22 for the exergoenvironmental impact coefficient, impact index and impact improvement respectively.
Keywords: parabolic trough collector; converging-diverging; energy; exergy; exergy destruction; exergy loss; exergoeconomic; exergoenvironmental; thermal efficiency; heat transfer.
First and second law analyses of wastewater cooled condenser for a refrigeration system
by Ibrahim Karacayli, Lutfiye Altay, Arif Hepbasli
Abstract: In this study, a vapor compression refrigeration (VCR) system with a wastewater (WW) cooled condenser at a temperature range of 27 29 oC was designed. The cooling capacity of the system using R134a as the refrigerant was 1.09 kW. The condenser consisted of a coaxial heat exchanger with a capacity of 1 kW. This paper dealt with energy and exergy analyses of the VCR system using WW, as a heat sink. Experiments were performed in order to evaluate the energetic and exergetic performances of the wastewater-cooled condenser (WWC) and the overall system. The convective heat transfer coefficient of WW and refrigerant in the condenser, overall heat transfer coefficient of the WWC, total amount of heat removed by WW, amount of cooling effect, coefficient of performance (COP), exergy destruction rate, and second law efficiencies of the WWC and VCR system were calculated under different WW temperatures and flowrates. Increasing volumetric flowrate of WW from 200 L/h to 400 L/h caused 4.4% improvement in COP, 12.0% reduction in exergy destruction, and 10.3% increase in exergy efficiency.
Keywords: wastewater; refrigeration; energy; exergy; coefficient of performance; second law efficiency.
Special Issue on: IEEES-10 Exergetic Modelling of Advanced Energy Systems
Exergetic Approach to Determine Optimum Insulation Thickness for Cooling Applications with Life cycle Integrated Economic Analysis
by Emin Acikkalp, Süheyla Yerel Kandemir, Onder Altuntas, T. Hikmet Karakoc
Abstract: Optimum insulation thickness for building walls is investigated using a new method called as Combined economic and environmental methods (CEEM). In this method, environmental costs are integrated in the fuel and insulation material costs and in this way, it is possible to consider both of economic and environmental aspects. Environmental cost of carbon dioxide, fuel and insulation materials are added to their cost and total annual cost for the system is calculated and results are investigated according to insulation thickness. In this paper, optimum insulation thickness with life cycle integrated economic analysis in terms of exergy approach is defined. Rockwool and glasswool are chosen as insulation materials and calculations were made for Bilecik located in Marmara region in Turkey. Optimum points are found for CEEM, economic approach and environmental approach and they are compared with each other.
Keywords: Insulation thickness; life cycle integrated economic analysis; energy consumption.