International Journal of Exergy (22 papers in press)
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 and optimization of a biomass energy based combined system for multigeneration
by Nejat Tukenmez, Yunus Emre Yuksel, Murat Ozturk
Abstract: In this study, an integrated energy plant is designed for multi-generation and a parametric study is performed for integrated energy plant design. At the same time, optimization studies of integrated energy plant with parametric assessment are carried out. The energetic and exergetic performances of integrated system have been computed as 51.28% and 46.67%. Thermodynamic analysis data show that some parameters in the system are more effective on system efficiency and cost than other parameters. By using parametric study, these parameters are determined as biomass flow rate, gas turbine inlet temperature, gas turbine inlet pressure and air compressor compression ratio. These parameters are used as the decision variable in the optimization study. Optimal points of the integrated energy system are shown on the Pareto front.
Keywords: biomass gasification; multigeneration; energy; exergy; optimization.
Experimental exergoeconomic performance assessment of a wastewater source heat pump system
by Mustafa Araz, Arif Hepbasli, Huseyin Gunerhan
Abstract: This study aims at experimentally analyzing and assessing the performance of a wastewater source heat pump system (WWSHP) in cooling mode, which was installed at Yasar University, Izmir, Turkey through exergetic and thermoeconomic (exergoeconomic) analysis methods. Within this context, first, conventional exergy analysis was performed based on the actual experimental data, where exergy efficiencies, destructions and relative irreversibilities of each element were determined to indicate improvements. Then, these results were combined with the cost data of the system to make exergoeconomic analysis. Functional exergy efficiencies of the entire system and the WWSHP were obtained to be 7.56% and 11.77%, respectively. The compressor had the biggest relative irreversibility, which was followed by the fan-coil. The exergoeconomic factor values of the condenser, WW heat exchanger (WWHE) and fan-coil unit were lower than 0.5, indicating that the exergy destruction costs associated with these components were higher than the capital investments.
Keywords: wastewater; wastewater source heat pumps; waste to energy; exergy; thermoeconomic; exergoeconomic.
Exergy Analysis of Heating Options for Buildings in the Pacific Northwest
by Heather Dillon, Rachel Dzombak, Chrissi Antonopoulos
Abstract: A framework for quantifying environmental impact in future energy codes is explored based on exergy analysis. An example exergy analysis is performed that quantifies the environmental impact of electric resistance heating with exergetic efficiency of only 13% compared to 30% and 40% for air source and ground source heat pumps. This provides motivation for removing electric resistance as a space heating option in future energy codes in the Northwest.
Keywords: exergy; building energy codes; exergy policy; sustainability.
Exergetic optimization of twin screw expanders
by Hormoz Abolhasani, Mahdi Moghimi, Mahmood Ebrahimi
Abstract: Limited access to energy resources, air pollution and its subsequent detriments to Ozone layer have accentuated the importance of green industry for recovering exergy from high-pressure flow to generate clean electrical power. Due to low maintenance costs, usage in two-phase fluids and longer lifespan, the twin screw expanders (TSE) have attracted great attention though there is still much to be done to improve their performance. The complexity of computing in screw machines, as well as the time consuming of their simulation throughout the entire design space by the computational fluid dynamics (CFD), requires the use of other complementary tools to optimize the performance of these types of machines. In this paper, based on laboratory model specification and experimental data a TSE model was simulated and validated using CFD. Consequently, by helping design of experiments (DOE) a CFD alternative model is obtained called surrogate-based modeling (SBM) and the effect of three main geometric parameters on the expanders exergy efficiency were investigated in entire design space. Finally, a more efficient TSE with 86% exergy efficiency was obtained by using multi-objective genetic algorithm in the shortest time.
Keywords: Exergy efficiency; Surrogate-based modeling; Twin screw expander; Design of experiments.
Performance simulation of a double-reheat Rankine cycle mercury turbine system based on exergy
by GÜVEN GONCA, İbrahim Genç
Abstract: In this paper, a thermo-ecologic performance investgation of a Rankine cycle mercury turbine system (RCMTS) operating with natural gas and consisting of three turbines, one open feed mercury heater (OFMH) and two closed feed mercury heaters (CFMHs) is comprehensively performed. The most known performance characteristics such as net power (NP), net power density (NPD), exergy efficiency (EXEF), exergy destruction (EXED) and ecological coefficient of performance (ECOP) are used to investigate and optimize the system performance. The effects of condenser and boiler temperatures, the first and second reheat stage temperatures, temperature of the extracted mercury from the LPMT (Low pressure mercury turbine) on the performance properties of the system have been investigated. The results indicated that the component pressures and stage temperatures noticeably affect the performance characteristics of the mercury turbine system.
Keywords: Mercury turbine; Optimization; Reheated Rankine cycle; ECOP; Exergy; ANN Model.
Experimental Investigation of Phase Change Material Utilization Inside the Horizontal Mantled Hot Water Tank
by Dogan Erdemir, Necdet Altuntop
Abstract: The main objective of this study is to experimentally investigate the effect of placing phase change material (PCM) inside the horizontal mantled hot water tank on thermal energy storage (TES) performance. Six cylindrical paraffin tubes made of glass of 1 liter were placed inside the mantled hot water tank storage tank side by side vertically, respectively. At the end of this study, it was found that using paraffin inside the hot water tank increased the TES capacity and amount of hot water obtained from the tank. The amount of obtained hot water didnt increase proportionally with the increase of the amount of paraffin, as the volume of the tank was constant. Because the amount of hot water in the tank decreased with increasing the amount of paraffin. The stored energy in the paraffin wasnt transferred to the water efficiently. In order to obtain the highest volume of hot water, 4 tubes paraffin should be placed inside the tank. Discharging period duration could be increased 17 minutes with 4 tubes paraffin. Each added 1-liter paraffin reduced the temperature in the tank by nearly 1
Keywords: Horizontal mantled hot water tank; Phase change material; Paraffin; Solar domestic hot water system.
Energy and Exergy Analyses of Chemical Looping Combustion based 660 MWe Supercritical Coal Fired Power Plant
by Gajanan Dattarao Surywanshi, B. Basant Kumar Pillai, Venkata Suresh Patnaikuni, Ramsagar Vooradi, Sarath Babu Anne
Abstract: Coal still remains to be the major resource for power production in many countries. Supercritical (SupC) steam generated coal-fired power plants (CFPP) are found to be superior to subcritical steam generated plants in terms of the overall plant efficiency. Chemical looping combustion (CLC), which is an indirect combustion between fuel and air, is an innovative, inherent CO2 capture and recent technology for power production. In this study, two cases - conventional SupC CFPP without CO2 capture and CLC based SupC CFPP for high-ash Indian coal have been simulated. Detailed energy and exergy analyses are conducted for both the cases and compared. The study shows that CLC based capture technology has less energy penalty with Fe2O3 oxygen carrier and little energy gain with CuO and NiO carriers compared to conventional plant without CO2 capture. This study demonstrates the superiority of CLC based SupC CFPP for CO2 capture over the conventional plant.
Keywords: Supercritical power plant; Chemical looping combustion; Energy analysis; Exergy analysis; High ash coal.
Human body exergy consumption in the thermal environment of shelter gymnasium in winter
by Koichi Isawa
Abstract: This study attempts to evaluate the thermal stress in the winter shelter gymnasium in terms of human body exergy balance analysis. The human bodys exergy consumption rate was quantitatively analysed, revealing that the total human exergy consumption differs depending on the difference in heat insulation performance of the evacuation gymnasium. Integrated exergy consumption after 30 days is 15.7 MJ/m2 for an existing outer skin with no heating, 14.4 MJ/m2 for an existing outer skin with radiant heating, and 12.5 MJ/m2 for a modified outer shell with no heating It decreased to 9.6 MJ/m2 in the rehabilitating envelope with radiant heating. In the case of existing hulls, accumulation of thermal stress was found to be greater than in the case of renovation hulls.
Keywords: natural disaster; community shelter; gymnasium; indoor thermal environment; thermal stress; human body; thermal adaptation; physiological adaptation; exergy; Numerical analysis.; unsteady state; passive system; building envelope; active system; heating system.
Exergy and Energy analysis of a biogas-fueled micro-tubular flame fuel cell
by Milad Nasrzad, Samad Jafarmadar, Parisa Mojaver
Abstract: In the present study, a combination of 60% CH
Keywords: Energy; Exergy; Biogas; Partial oxidation; Micro-tubular flame fuel cell; Equivalence ratio.
Entropy analysis of 3D MHD nanofluid flow over a linearly stretching surface
by Muhammad Nazim Tufail, Adnan Saeed Butt, Asif Ali
Abstract: A numerical study of three dimensional magnetohydrodynamic flow of nanofluid over a surface stretching linearly in two directions is carried out. The problem is analyzed from first and second law of thermodynamics point of view. Suitable similarity transformations are employed to obtain nonlinear ordinary differential equations from the partial differential equations that govern the considered problem. The shooting technique with fourth fifth order Runge Kutta method is utilized to solve the converted equations. The effects of pertinent parameters on velocity and temperature profiles as well as on entropy generation are discussed briefly using graphs.
Keywords: Buongiorno model; Brownian motion; thermophoresis; entropy generation; magnetic field.
Exergy analysis of the valorization of rice straw for energy purposes with a life cycle approach. Rice production in Cuba
by Edelvy Bravo, Ralf Kiran Schulz, Osvaldo Romero Romero, Eduardo Lopez Bastida, Yenima Martinez Castro, Alberto E. Calvo Gonzalez, Leonor Patricia Guereca Hernandez
Abstract: In this paper the Exergy analysis methodology is used to analyze four alternatives for the valorization of rice straw for energy purposes in Cuba. The exergy input and output of the product (%), the exergy destroyed (MJ) and the exergetic efficiency (%) are calculated. The exergetic efficiency increases in the three alternatives where rice straw is valorized for energetic purposes. In alternative 4, where it is considered the production of biomethane (to replace 60% of the diesel fuel for harvesting and transportation of products) and electricity via biogas, the exergetic efficiency reaches values of 66.6%. The exergy flow contained in the product increases from 13.2% to 21.9%. The increase in exergy flow in the final product also represents a reduction in greenhouse gas emissions as emissions are avoided by generating the same amount of electricity in a thermal power plant. Alternative 4 also achieves the highest sustainability index (2.994). The cumulative exergy consumption in greenhouse gases (CExCGEI), a new indicator that considers the accumulated exergy that is destroyed in greenhouse gases, is proposed.
Keywords: Exergy; Wastes; Rice straw; Biogas; Sustainability; Renewable energy.
Cleaner production of purified terephthalic and isophthalic acids through exergy analysis
by Ali Ghannadzadeh, Majid Sadeqzadeh
Abstract: The purified terephthalic and isophthalic acids production process was improved through the exergy analysis approach demonstrated here. The overall exergy losses and low-exergy-efficient units were first identified and presented using visualized exergetic flowsheets. Recommendations were then proposed to reduce losses based on the main cause(s) of irreversibility. Three out of the five constituent blocks contained the highest exergy losses. The oxidation block was the main player where it was suggested that using several reactors in series with gradually decreasing temperatures could lower losses. The product refining block had the second largest irreversibilities, where improving coolers performance were recommended. The crude terephthalic acid crystallization block was the third largest loss producer (1,547 kJ/kg), where isothermal and isobaric mixing in the Solvent Dehydrator was suggested to reduce losses. The approach used in this work can be adapted to improve the energy footprint of other chemical processes.
Keywords: sustainability; irreversibilities; purified terephthalic acid; purified isophthalic acid; process design; exergy; energy efficiency; visualized exergetic flowsheets.
Energy and exergy analyses of dual refrigerant system for liquefaction of natural gas
by Morteza Saadat-Taraghi, Shoaib Khanmohammadi
Abstract: Present study proceeds thermodynamic modeling, and analysis of dual refrigerant system for liquefaction of natural gas (LNG) that is one of the most important technologies in producing LNG. Using energy equations pressure, quality, enthalpy, entropy of natural gas and two refrigerants i.e. methane and propane is specified. The effects of different cycle variables on the thermodynamic performance especially the coefficient of performance (COP) is studied. Using the second law of thermodynamic for the system components, the exergy destruction rates has been found. The exergy analysis results show that heat exchanger I (HX I), heat exchanger II (HX II) and turbine have the highest exergy destruction rate. Furthermore, results indicate that the total exergy destruction rate of studied cycle for generation of 1 kg/s LNG is 2996 kW. Moreover, energy and exergy analysis shows that important parameters such as propane mass flow rate has different effects on the COP and exergy destruction rate.
Keywords: LNG, Liquefaction, COP, exergy destruction, dual refrigerant precooling mixed
Tumor Cells and Life Expectancy: an Exergy Approach
by Izabela Henriques, Silvio de Oliveira Junior
Abstract: The relation between energy and life has been under discussion for a long time and recently the concept of exergy is also being applied to analyze living organisms. In the present work, the rate of living theory and exergy analysis are gathered in order to assess the effects of cancer on life expectancy. Herein, an exergy model of a cancer cell metabolism is proposed taking into account the changes in the metabolic paths of the tumor. The results indicate a threefold increase in the rate of exergy metabolism of a cancer cell, in comparison to a healthy one. Moreover, per mole of glucose, a cancer cell obtains 8.9 moles of ATP against 32 synthetized by a healthy one. However, because of the increase in the rate of glucose uptake, the metabolic routes of the tumor are less efficient but are faster, being able to fulfill the needs of the proliferating cells. The analysis of a generic tumor progression indicates that, in the absence of treatment, the survival time would be around 3 years. Furthermore, in case of complete removal of the tumor, every six months living with the disease would lead to a reduction of almost four years in life expectancy.
Keywords: exergy destruction; metabolism; cancer; life expectancy.
Interpreting Exergy Analysis as applied to Spray Drying Systems
by Perry Johnson, Timothy Langrish
Abstract: The comparison of different energy recovery systems employed on a spray dryer is challenging. This work compares two cases with a base case of a dryer alone, to identify any available improvements and interpretation of the factors used within exergy analysis, for system-wide optimisation. While exergy analysis results indicate natural gas boiler systems (Case 1) are superior to compressor-driven recovery systems (Case 2) (13% better evaporation efficiency), this paper demonstrates the significant potential to improve either system, and that dryers are one of the limiting units within the process (38% exergy improvement potential). The improvement potential for both cases is quite high (~90% of total added exergy), particularly as the inlet gas temperature increases. This paper demonstrates a method of simplifying exergy analysis to make it more accessible to engineers as a tool for optimising thermal and non-thermal systems that include a dryer as a significant part of the system.
Keywords: Energy; Exergy; Analysis; Dryer; Vapour Recompression; Optimisation; Efficiency; Effectiveness; Drying; Exergy analysis
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) was 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.
An evaluation of multi-effect desalination with a thermal vapour compression system in terms of thermo-economics
by Mehmet Tontu, Besir Sahin, Mehmet Bilgili
Abstract: In this study, a multi-effect distillation system (MED-TVC) that is presently in use in a thermal power plant was analysed. The operating data of an existing MED-TVC (2,000 m3/day) desalination process were used for thepresent analysis. The analysis of the considered system was performed based on the energy, exergy and thermoeconomic approach. Also, the effect of operating plant load, seawater temperatures and upper brine temperatures on the performance of the desalination plant was investigated. The gain output ratio and exergy efficiency increased with increasing production load and seawater temperature. When the production load and seawater temperatures were 100% and 33°C, respectively, the gain output ratio and exergy efficiency obtained was 7.73 and 2% respectively. The results showed that the steam ejector was responsible for about 45% of the total exergy destruction. The unit product cost of the distilled water at the full load was calculated by 1.7 $/m3.
Keywords: brine temperature; desalination; energy; exergy destruction; exergy efficiency; gain output ratio; multi-effect; sea water temperature; thermo economic analysis; thermal power plant; thermal vapour compression.
Energy and exergy analyses of using natural gas compressor station waste heat for cogeneration power and fresh water
by Mahdi Deymi-Dashtebayaz, Amir Ebrahimi-Fizik, Sajjad Valipour-Namanlo
Abstract: In this paper, a thermodynamic simulation is developed based on energy and exergy analysis for evaluating the features in the proposed cycle including combined power generation, water distillation and natural gas cooling cycle. The Faruj NGCS in Iran is selected as a case study to evaluate the proposed cycle. Based on exergy analysis, in the MSF distillation cycle, consisting of HRS, HRJS and brine heater, the exergy destruction rate of the HRS unit with 25 flashing stages is obtained 71%. Moreover, the results show that the proposed cycle is able to produce 9,000 m3/day distilled water from 30,000 m3/day brine water. Also, 2.1 MW electricity is generated by steam turbine. Moreover, the waste heat potential of all NGCSs in Iran, in order to produce distilled water, is investigated. Finally, economic analysis based on net present value (NPV), internal rate of return (IRR) and payback period indicators have been performed.
Keywords: natural gas compressor station; NGCS; exergy; economic analysis; multi-stage flash desalination; multi-stage flashing; MSF; waste heat recovery.
Energy and exergy evaluations of catalytic dry reforming of methane for syngas production in fixed-bed reactors
by Reiyu Chein, Wen-Huai Hsu
Abstract: The energy and exergy characteristics of dry reforming of methane (DRM) were numerically studied in this study in a tubular fixed-bed reactor under heat supply from uniform temperature furnace or uniform wall heat flux. Variations in enthalpy, entropy and exergy were computed based on non-equilibrium thermodynamics for chemical reactions. The heat supply, heat of chemical reaction and entropy generation due to irreversibility were the sources that caused changes in enthalpy, entropy and exergy between the reactor inlet and outlet. Based on the simulated results it was found that the chemical reaction is the most dominant factor for entropy generation. It was also found that exergy at reactor outlet depends on the heat supply and a minimum value can be found due to contribution variations from the gas species involved in DRM.
Keywords: syngas; dry reforming of methane; DRM; uniform temperature furnace; uniform wall heat flux; chemical energy and exergy efficiencies.
Exergetic performance analysis of heat pumps: two alternative approaches
by Henrik Holmberg, Timo Laukkanen
Abstract: This paper evaluates the performance of a compressor driven and an absorption heat pump on the basis of exergy analysis using two different approaches. Approach 1 is based on the calculation of the effective heat absorbing and emitting temperatures and the entropy generation rate. Approach 2 is based on the commonly used exergy analysis where the real ambient temperature is used. The main goal is to analyse how these two approaches differ from each other. Approach 1 gives the exact improvement potential (Wreal - Wreal) of the heat pump while Approach 2 underestimates it. The average flow temperature also approximates the correct improvement potential with sufficient accuracy when temperature change of the flow is relatively small. Both approaches can be used when performances of heat pumps are compared. Both approaches also give a more realistic view of the performance than the commonly used COP, especially regarding the absorption heat pump.
Keywords: rational ratio; exergy efficiency; irreversibility rate; coefficient of performance; COP; absorption heat pump; compressor driven heat pump.
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.