International Journal of Exergy (33 papers in press)
Exergy Analysis and Optimization of Naphtha Reforming Process with Uncertainty
by Asadullah Akram, Iftikhar Ahmad, Arshad Chughtai, Manabu Kano
Abstract: Naphtha reforming is an energy-intensive process, and thus it requires a highly energy efficient design for making it feasible and sustainable. In general, exergy analysis has been used to realize energy efficient processes. However, conventional exergy analysis methods face the challenge of coping with the effect of process uncertainty. In this work, we proposed a novel framework which incorporates the concepts of uncertainty analysis and optimization in the conventional exergy analysis. The proposed framework was realized as a MATLAB-based algorithm which connects with an Aspen PLUS model of the naphtha reforming process, extracts process information, and calculates the process exergy efficiency. Then a statistical model, i.e., random forests (RF), combined with a bootstrap filter is used to analyze the effect of process uncertainty on the exergy efficiency. Finally, an optimization method is devised by combining genetic algorithm (GA) with artificial neural networks (ANN). The MATLAB-based system is supported by an extensive database of standard chemical exergies of elements. The algorithm can be customized for any model simulated in the Aspen PLUS environment, and the database of standard chemical exergies can be updated by users according to the new process requirements.
Keywords: Exergy analysis; Naphtha reforming process; Uncertainty quantification; Bootstrap filter; Genetic algorithm (GA).
Energy, Exergy and Environmental Analyses of Hydrogen Production Process by Ethanol Steam Reforming Incorporated to Sugar and Alcohol Mill
by Wendell Lamas, José Silveira
Abstract: This work aims to perform the thermodynamic, economic, and ecological studies of incorporation of hydrogen production process by ethanol steam reforming considering data from a sugar and alcohol mill, which produces near of 62.9 kg of sugar and 42.8 L of alcohol for each tonne of sugar-cane. A technical analysis of the actual process of ethanol production is performed before an analysis of the same plant with hydrogen production process incorporated. After that, an engineering economic analysis is developed to allocate the production costs of new conﬁguration proposed, such as cost of sugar production, cost of ethanol production, and cost of hydrogen production. Finally, the effects on pollutants emissions with a view on incorporation of the new process for hydrogen production in that plant are determined.
Keywords: co-generation system; energy exploitation; hydrogen production; sugar and alcohol industry; sugar-cane bagasse.
Cooling Air Energy Recovery in Portable Air Compressor: An Exergoeconomic Analysis
by Vanderson Pinto, Wendell Lamas
Abstract: This study aims to optimise the cooling system of a portable air compressor in order to obtain a lower power consumption of its drive motor that, for this type of compressor, uses an internal combustion engine in Diesel cycle. This proposal will be achieved through reduction in power consumption in the axial fan used in cooling system. The analysis methodology starts with system modelling. This ﬁrst stage pass through the thermodynamic modelling of compressor element and fan selection by comparison between fan manufacturer curves and experimental ones. After that, functional tests provide a way to validate the modelling and fan selection through experimental practices. At last, exergoeconomic analysis provides a cost estimation for products associate, also its exergetic production cost. Selecting a commercial fan-based more accurate according to cooling system data provided indicates that it is possible to reduce the ventilator power consumption, 21.5 % for this case study. Based on the results of this study there is a reduction of 2.58 % in fuel consumption (motor running at 2,200 rpm), keeping the air ﬂow in the cooling system indicating that the fan could be changed so that compressor to increase its energy efﬁciency and therefore operating costs of the equipment as it is directly reﬂected in spending on fuel.
Keywords: Energy Efficiency; Exergetic Production Cost; Fan Selection; Heat Exchangers; Physical Optimisation; Water Heaters.
Thermoeconomic Diagnosis of an Air-Cooled Air Conditioning System
by Yungpil Yoo, Hoo-Suk Oh, Cuneyt Uysal, Ho-Young Kwak
Abstract: In this study, diagnosis of a 120-kW air-cooled air conditioning system under faulty conditions was performed using a thermoeconomic method called modified productive structure analysis. Unit cost of cooling capacity for the system and lost cost flow rate for each component were calculated based on data obtained by using a simulator for the cases of pre-fixed faulty and normal operating conditions. The relative malfunction (RMF) and the relative difference in the lost cost flow rate between real operation and normal operation (RDLC) were found to be effective indicators for the identification of malfunction components. Calculation results revealed that malfunction due to fouling at the condenser and evaporator, compressor valve leakage, the superheating in the suction line and refrigerant undercharge,whose fault levels by the percent degradation induced in the cooling capacity are 3.4%,10.5%,15.1%, 3.5% and 4.1%, respectively, can be identified. Unit cost of the cooling capacity of the system increases when malfunction occurs at any component in the air conditioning system.
Keywords: air conditioning units; thermoeconomic diagnosis; malfunction; fault indicators.
Entropy generation minimization in a moving porous pipe under magnetic field effect
by Saima Ijaz, Muhammad Mushtaq, Sufian Munawar, Najma Saleem
Abstract: The second-law aspect of an electrically conducting thermal boundary-layer flow inside a permeable pipe moving along its axis under Joule heating effect is considered here. The governing equations are normalized by suitable similarity transformations and solved analytically. An expression for average entropy number is obtained by integrating entropy number over the entire fluid volume for various cross-sections. Graphical illustrations of spatial distributions of total and average entropy of the system, the Bejan number, isotherms and heat transfer rate are imparted against different parameters of interest. The ranges of variables are reported for which entropy production is minimum. It is shown that the pipe moving with small Reynolds number needs small injection velocity to minimize entropy production in the system.
Keywords: Viscous flow; permeable pipe; entropy generation minimization EGM; Joule heating.
Thermodynamic analysis of the human body in different climate regions of Turkey to determine the comfort conditions with exergy method
by Firat EKINCI, Mehmet BİLGİLİ
Abstract: Thermodynamic analysis of human body is studied to determine the thermal comfort conditions. In this context, exergy and energy analysis in the air conditioning of buildings is necessary for efficient use of energy. Thermodynamic analysis of human body is carried out for seven different climate regions of Turkey based on the use of meteorological parameters such as minimum and maximum and average monthly temperatures, atmospheric pressure and average relative humidity by implementing energy and exergy analysis. Human body, which is the subject of this study, was in the light activity level quantified as 58.2 W/m2. Analysis results have indicated that the major energy loss with 39.28 W/m2 is due to heat transfer with radiation, convection and conduction. Furthermore, the energy loss rates by water vapor diffusion from the skin, respiration, temperature difference and sweating were determined as 11.13 W/m2, 4.29 W/m2, 0.73 W/m2 and 0.02 W/m2, respectively. The maximum exergy consumption rate by the human body was 2.33 W/m2 for the cold and semi dry - less humid climate region (CR-7), while the minimum exergy consumption rate was obtained as 0.91 W/m2 for the hot and semi dry climate region (CR-1). Information presented in this study is expected to contribute to the design of air conditioning systems in order to choose more efficient energy systems.
Keywords: Human body; energy loss; entropy generation; exergy consumption; exergy efficiency.
Energy and exergy analyses of an integrated iron and steelmaking process
by Zhang Qi, Xu Jin, Zhao Xiaoyu, Wang Yujie
Abstract: As a material- and energy-intensive industry, the iron and steel industry faces challenges in energy saving and emission reduction. The energy efficiency of the iron and steel manufacturing process (ISMP) can be improved through comprehensive analysis and assessment. Thus, this study proposes a hybrid energy and exergy flow analysis model at the process and system levels. This model is established in a typical ISMP in China. The energy and exergy flows are graphically mapped out by performing calculations. The possibility of improving the thermodynamic efficiency of the entire system is evaluated by obtaining the efficiencies and losses of the energy and exergy for all sub-processes. Results indicate that the energy efficiencies of the sub-processes in the ISMP vary between 77.71% and 98.36%, whereas the two kinds of exergy efficiencies vary between 46.49% and 92.80%, and between 18.76% and 89.82%. These findings suggest that the sintering process must be improved significantly by technologies such as heat recovery and preheating mixture, and that the blast furnace iron making process incurs the maximum exergy loss. The overall energy and exergy efficiencies can be improved by adopting waste heat technologies. An integrated evaluation of the energy and exergy can be conducted to improve their efficiencies and consequently achieve energy conservation.
Keywords: Iron and steel manufacturing process; Energy; Exergy; Energy conservation.
Experimental and numerical investigation of a triple-dish solar concentrator A thermal and exergy study
by Evangelos Bellos, Sasa Pavlovic, Darko Vasiljević, Velimir Stefanovic, Christos Tzivanidis
Abstract: The objective of this study is to investigate an innovative concentrating collector experimentally and numerically. This solar collector has three dish reflectors and a spiral-coil absorber. This configuration is innovative, combining a compact design which can be manufactured with low cost. The numerical analysis is performed with SolidWorks Flow Simulation. The developed model in SolidWorks is validated with the obtained experimental results and after this step, the solar collector is examined energetically and exergetically under various operating temperatures. According to the final results, the system can reach a thermal efficiency close to 32%, a relatively low value which is explained by the low reflectance of the experimental setup. The system exergetic efficiency reaches up to 8.3%, for inlet temperature close to 90oC. The detailed exergetic analysis proved the low exergy efficiency is explained by the high optical exergy loss and the high exergy destruction between sun and receiver.
Keywords: Triple dish reflector; thermal analysis; exergy analysis; SolidWorks Flow Simulation.
Entropy Generation and Irreversibility Analysis of a Compressible Gas Flow inside a Two- Dimensional Uniform Microchannel
by Khaleel Al Khasawneh
Abstract: The entropy generation for steady, compressible gas flow inside two-dimensional rectangular microchannel at slip flow regime with constant walls temperature has been investigated. The obtained solutions of the flow field are used to evaluate the entropy generation, Bejan number and irreversibility ratio inside the microchannel. Finally, the influence of Knudsen number, Brinkman number, aspect ratio, and pressure ratio on entropy generation rate and irreversibility were presented.
Keywords: Rectangular microchannel; Irreversibility; Entropy generation; Compressible gas flow; Slip flow; Bejan number.
Exergy Analysis and Optimization Study of Eliminating Negative Effects of Electrical Load Variations in Steam Power Plants
by Behnam Roshanzadeh, Hossein Ahmadi-Danesh-Ashtiani
Abstract: Energy consumption is increasing rapidly in the world, and sustainable development has been considered as one of the main goals for the countries. Existence of strong connection between permanent energy supply and sustainable development is undeniable, and power plants are known as the main source of energy supply in the world. In this paper, energetic and exergetic analyses of a steam power plant are performed, and the effect of electrical load variations on energy and exergy efficiencies is studied. Load may decrease due to environmental considerations or operation of the power plant during the night, but the results show that lowering the load has negative effects on energy and exergy efficiencies, specific fuel consumption and CO2 production per unit of power. Moreover, exergy analysis reveals that turbines control valves play a considerable role in exergy destruction of the power plant. Based on these results, an optimization is proposed which makes the efficiencies, specific fuel consumption and carbon dioxide production per unit of power almost independent from the load variations.
Keywords: Energy; Exergy; Specific Fuel Consumption; CO2 production; Fossil fuels; Sustainable development.
Investigation of the component exergy efficiencies of a two stage vapour compression cycle
by Sertac Samed Seyitoglu, Ali KILICARSLAN
Abstract: The exergy efficiencies of the components (compressor I and II, condenser, evaporator and flash tank) of a two stage vapor compression refrigeration cycle were analyzed with respect to evaporator and condenser temperatures for various refrigerants such a R1234ze, R1234yf, R236fa, R227ea and R134a. In the analysis, a computer program was improved by means of Engineering Equation Solver (EES). The exergy efficiencies of components such as evaporator, condenser, flash tank and compressor I increased while the exergy efficiency of compressor II decreased for the refrigerants used in the cycle for the evaporator temperatures ranging -15
Keywords: Vapor compression refrigeration; two-stage; exergy efficiency; R1234ze; R1234yf; R236fa; R227ea; R134a.
Exergy Approach for Advancing Sustainability of a Biomass Boiler
by Marc Compton, Behnaz Rezaie, Marc Rosen
Abstract: An exergy analysis of the district energy plant at University of Idaho, Moscow, Idaho, USA is presented. Exergy flows through the components of the steam cycle, specifically through the biomass boiler, are quantified to identify major sources of exergy destruction in the district heating system. A mathematical model is developed to determine the sources of exergy destruction using measurements taken at each state of the steam cycle. It is found that the largest sources of exergy destruction occur in the boiler and furnace at 35% and 33% of the overall exergy losses, respectively, followed by the heating equipment on campus at 5.7% and the pressure reducer at 3.5%. Parametric studies reveal that decreasing steam pressure levels through the boiler to reduce exergy destruction in the pressure reducer result in increased exergy destruction rates in the boiler. Increasing boiler steam pressure levels instead reduces exergy destruction in the boiler but has negligible effects on the overall exergy efficiency of the complete cycle. This indicates that the pressure reducer is limiting potential improvements in the boiler exergy efficiency.
Keywords: biomass boiler; wood chips; environmental impact; sustainability; district energy; exergy analysis; exergy efficiency; energy plant.
RADIATIVE ENERGY AND EXERGY ANALYSES OF SPECTRALLY- SELECTIVE SURFACES FOR CSP SYSTEMS
by Hayder Noori Mohammed, M. Pinar Mengüç
Abstract: This work presents a new methodology for spectral radiative energy and radiative exergy calculations to evaluate the performances of concentrated solar power (CSP) systems. Spectral radiative properties and the operating temperature of selective surfaces, along with the temperature of the environment, are taken into account in CSP analyses. Here, first the fundamental quantities needed for the spectral radiative energy and radiative exergy analyses are introduced. Then, the two approaches were used to assess the spectral performance of five selective coatings. One approach considered two blackbodies for the temperatures of the sun and surface absorber. The second approach was based on the data obtained from direct solar spectral radiation. The spectral analysis is performed in the wavelength range of 250 nm to 20,000 nm, while thermal analysis is carried out for the temperature range of 325 K to 800 K. NREL 6A coating was found to result in the highest radiative energy and radiative exergy for both efficiencies and gains, and the best thermal stability compared to the other coatings.
Keywords: Concentrating solar power systems; Selective coating; Spectral radiative energy analysis; Spectral radiative exergy analysis.
An advanced exergy analysis based on the dysfunction and malfunction methodology for a combined cycle power plant: a mexican case study
by Rodolfo Herrera, Federico Mendez
Abstract: The present work studies the irreversibilities and inefficiencies of a combined power plant. The analysis predicts the malfunction and dysfunction distributions for a typical system located in Mexico. The study was conducted by first performing the energy balances of the system using the first law of thermodynamics. The concept of exergetic unit cost was then used to calculate the corresponding exergy destruction of the plant. And finally, structural theory and symbolic thermoeconomic analysis for constructing the malfunction and dysfunction conditions of the plant, showing clearly that for the combined cycle the irreversibilities are basically increased through the dysfunctions. It is important to note that the classic references on thermoeconomic analysis of combined cycles and for the knowledge of the authors, there are no works in the specialized literature that determine the distributions of malfunctions and dysfunctions for the current configuration of the combined cycle: two gas turbines and one turbine steam. The most frequently studied situation is for those systems where only one gas turbine and one steam turbine are operating and hence the importance and relevance of the present study. With the evaluation of the malfunction-dysfunction matrix (intrinsic and extrinsic irreversibilities), the propagation of the irreversibilities through the combined cycle is shown. The previous analysis shows the following results: the total increment of the irreversibility for the present cycle is 19879.33 kW, which represents about 3.5% of the fuel exergy required taking into account data of design; and the subsystems with the greatest dysfunctions correspond to both gas compressors.
Keywords: Thermoeconomic diagnosis; exergy; cycle power; irreversibility; efficiency.
Energy and exergy analyses of oxy-fuel combustion power plants with chemical looping air separation
by Shiyi Chen, Ahsanullah Soomro, Jun Hu, Wenguo Xiang
Abstract: Conventional cryogenic air separation unit imposes significant energy penalty in oxy-fuel combustion power plants. This paper describes and compares different integrated chemical looping air separation (CLAS) systems in three oxy-fuel combustion power plant configurations. The results reveal that this type of oxy-fuel combustion technology displays a higher energy efficiency than other systems such as post-combustion and oxy-fuel combustion with cryogenic air separation. Energy analysis reveals that the arrangement of a steam generation system based on a conventional pulverized coal power plant is more suitable and efficient for oxy-fuel combustion power plants with integrated CLAS technology. Thus, a power generation efficiency of 41.6% can be achieved. However, CO2 compression imposes an additional energy penalty of ~4%, resulting in a net power efficiency of 37.6%. On the other hand, exergy analysis reveals that the most significant exergy destruction portion of the system occurs in the combustion process. CO2 compression also imposes large exergy destruction. Finally, we concluded that the exergy destruction could be alleviated by reasonable arrangement of the heat exchangers.
Keywords: Chemical looping air separation; Oxy-fuel combustion; CO2 capture; Exergy analysis; Power plant.
Thermoeconomic analysis and multi-objective optimization of MED-TVC and MED-TVC.FH systems using ABC algorithm
by Davood Beyralvand, Mahmood Yaghoubi
Abstract: In this study, 4E analysis for feasible integrated systems for cogeneration of fresh water were investigated. Steam generation provided by a steam boiler, designed to supply the thermal heat requirements of MED-TVC & MED-TVC.FH systems. Parametric analysis is made to determine CO2 emission rate, gain output ratio, exergy destruction rate and special heat rate for each system. By using Artificial Bee Colony algorithm, systems were optimized for maximum exergy efficiency and minimum cost of the produced distilled water. The results showed that by selecting final optimum solutions, the distillated water cost reduced by 18.1% and 28.8% for MED-TVC and MED-TVC.FH systems respectively. Also exergy efficiency increased from 3.2% and 4.04% in the base case to 3.63% and 4.47% for MED-TVC and MED-TVC.FH respectively in the optimum case. The system with feed water preheater, has more exergy efficiency and less CO2 emission, also the cost of distilled water reduced by 7.86%.
Keywords: 4E analysis; MED-TVC; MED-TVC.FH; CO2 emission; Exergoeconomic; Multi objective optimization; Artificial Bee Colony algorithm; TRR method.
ENTROPY GENERATION BEHAVIOR OF THE LEAN AND OBESE RATS SHOWS THE EFFECT OF THE DIET ON THE WASTED LIFE SPAN WORK
by Selcen Semerciöz, Bayram Yılmaz, Mustafa Özilgen
Abstract: Thermodynamic analyses of the experimental data obtained from the literature showed that the obese Zucker rats may generate 22,092 kJ/ K of entropy when fed soybean oil diet and 38,718 kJ/ K of entropy when fed with butter fat in their 803 days of life span. Their lean counterparts may generate 15,314 kJ/ K of entropy when fed with soybean oil diet and 47,657 kJ/K of entropy and when fed with butter fat diet in their 1,067 days of life span. The lean Zucker rats fed with butter fat oil diet had the highest, 92 %, while the obese Zucker rats fed with soybean oil diet had the lowest, 72 %, wasted life-time work potential. A fraction of the exergy of the nutrient up take is utilized for work performance, meanwhile metabolic heat and entropy is generated. Although entropy generation is regarded as the indicator of the inefficient work performance by a system, work performance is also the prerequisite of entropy generation; e.g., it may not be generated in the case of zero work performance. The lean rats have about 32 % longer life span than their obese counterparts, therefore have the ability of generating more entropy in their longer life span. Obese Zucker rats fed with butter fat diet performed approximately 48 % more total physical work and generated 48 % more muscular heat through their life span than the lean rats fed with soybean oil diet. Obese rats fed with butter fat diet do not have enough metabolic capacity to process all the nutrients they ate, therefore a fraction of the chemical exergy of their diet is stored in their adipose tissue as fat. Both the obese and lean Zucker rats fed either with butter fat or soybean oil diets did not have significantly different second law or exergy efficiencies. The reason for this result was considering fat stored in the adipose tissue as an inert material and not converting it into work. In a dynamic case, where fat is synthesized, stored and broken down later to provide energy for the daily activities, this result would be substantially different.
Keywords: Obese rats; exergy balance; lifespan entropy; muscle work performance; lost work potential.
Exergetic Performance Assessment of Solar Driven Combined CO2 Power and Refrigeration System
by Onder Kizilkan
Abstract: The scope of this study is to assess a solar driven combined power-refrigeration system working with carbon dioxide (CO2) through energy and exergy. The system consists of a supercritical Brayton cycle, a transcritical organic Rankine cycle, and a subcritical vapor compression refrigeration cycle. All three subsystems operate with carbon dioxide as the working fluid thanks to its zero-ozone depleting potential and negligible global warming potential. In addition, it is a sustainable working fluid. The combined systems heat energy demand is supplied by using parabolic trough solar collector system. Heat energy demand of organic Rankine cycle is supplied by the rejected heat of supercritical Brayton Cycle; while the refrigeration cycle is driven by the power generated from the organic Rankine cycle. The results show that the energy efficiencies of the Brayton and organic Rankine cycles are found to be 12.9% and 4.47%, respectively, while the performance coefficient of the refrigeration cycle is determined to be 3.35. The energy efficiency of the overall system is determined to be 20.89 %; while the exergy efficiency of the overall system is determined to be 12.95%. The exergy destruction rate of the whole system is calculated as 4891 kW.
Keywords: Solar energy; Combined power-refrigeration system; CO2; Parabolic trough solar collector.
COMPREHENSIVE ENERGY AND EXERGY ANALYSIS ON OPTIMAL DESIGN PARAMETERS OF RECUPERATIVE SUPERCRITICAL CO2 POWER CYCLE
by Veysi Bashan, Emrah Gumus
Abstract: This paper focuses mainly on the supercritical carbon dioxide (s-CO2) cycles performance as regards from the aspect of thermodynamic point of view. Detailed analyses have been performed by considering; the effects of compressor inlet temperature and pressure, turbine inlet temperature, compressor outlet pressure, recuperator pinch temperature and pressure drop. Turbine and compressor efficiencies on cyclic performance were investigated and the results have been given. Exergy efficiency and exergy destruction ratios have been provided with respect to compressor inlet temperature variation. Exergy efficiency decreased when compressor inlet temperature increased. Results show that an optimum input pressure value for high cycle efficiency should be a value between 75 bar and 90 bar. In addition, the pressure ratio should be between 2.5 and 3 in order to have high cycle efficiency and high output power. The effect of the increase in turbine efficiency is more important than compressor efficiency.
Keywords: Brayton cycle; Supercritical; s-CO2; Thermodynamic analysis; Exergy
Exergy Analysis of a Target Drone Engine: An Experimental Study for TRS18
by Emre Aydin, Onder Turan, Ramazan Kose
Abstract: This article examines exergetic performance of an experimental TRS18 turbojet engine build in Anadolu University Faculty of Aeronautics and Astronautics Test-Cell Laboratory. In the analysis, engine performance parameters (pressure, temperature, fuel and airflow, thrust force) taken from the test-cell measurement devices. At the end of the work, total exergy efficiency of the target drone engine is obtained to be 42%. For TRS18 exergy destruction rate 0.872 MW in the combustor due to physical and chemical exergy destruction. For maximum exergy destruction rate is obtained to be 0.872 MW in the combustor due to physical and chemical exergy destruction, while it is 1.21 MW for the total for the engine. Improvement rates (IP) for combustion chamber, compressor and turbine are calculated to be 0.34 MW, 0.0025 MW and 0.007MW, respectively. As a conclusion, it is expected that results from this study can be useful to future design, research and experimental works related to small turbojets, auxiliary power units and target drone power systems.
Keywords: Turbojet; TRS18; exergy; missiles; propulsion; target drone; auxiliary power unit
Performance Analysis of an Industrial Steam Power Plant with Varying Loads
by Mehmet Tontu, Mehmet Bilgili, Besir Sahin
Abstract: In this study, energy and exergy analyses of a coal-fired steam power plant with 660-MW capacity were conducted to define the system performance. Analyses were performed with three different rates of operating loads such as 100%, 70% and 40%. Influences of three different loads on the exergy destructions were investigated for all plant components, for example, boiler, turbines, heaters, condensers and pumps. In addition, the exergy efficiency of each component and the overall thermal efficiency of the steam power plant were computed. Heat addition in boilers, heat rejection in condensers, heat transfer in heaters, exergy destructions of all plant components (boiler, turbines, heaters, condensers and pumps), overall thermal and exergy efficiencies of the plant were evaluated in detail. The first-law efficiencies of thermal power plant were determined to be 41.5%, 39.7% and 36.4% % at three different loading capacities such as 100%, 70% and 40% respectively. The second-law efficiencies of thermal power plant were calculated to be 39.1%, 37.4% and 34.3% at loading capacities of 100%, 70% and 40% respectively. According to the obtained results, energy losses mainly happen in the condenser and exergy destructions mainly take place in the boiler. It is found that if the exergy destructions are reduced, the power plant efficiencies are positively affected.
Keywords: Coal-fired power plant; energy efficiency; energy and exergy analysis; exergy destruction; operating load.
Special Issue on: IEEES-9 Exergetic Dimensions of Energy Systems
Entropy generation analysis of multilayer PCM slabs integrated with fins
by Mustafa Asker, Ersin Alptekin, Mehmet Akif Ezan, Hadi Ganjehsarabi
Abstract: In this study, the utilization of composite phase change materials (PCMs) slabs with fins in a thermal energy storage (TES) system is numerically analyzed. The storage system consists of three PCM layers at different melting temperatures. First, the predicted results are verified against the analytical solution that is taken from literature. Afterwards, the influence of the design parameters such as fin length and fin spacing on the time for complete melting of the multi-layer TES are examined. Custom field functions are integrated into the ANSYS-FLUENT software to assess the local and volume averaged entropy generation within the system. The results show that at constant fin spacing, that increasing fin length from 20 mm to 80 mm enhances the melting rate up to 50% rnIn addition, when the fin spacing is doubled, the elapsed time for complete melting decreased about 37%. Moreover, the fin arrangement has a considerable effect on entropy generation.
Keywords: CFD; Entropy generation; Finned wall; Multi-layer PCM slab.
Natural rubber - nanodiamond films for the minimisation of losses in dielectric energy harvesters
by Alexandra Shakun, Essi Sarlin, Jyrki Vuorinen
Abstract: Dielectric elastomer generators (DEGs) belong to the new and promising class of devices harvesting energy from ambient sources, e.g. ocean waves. However, the efficiency and energy output of the existing DEG prototypes are often limited, for example, by high material-related losses of the utilized dielectric elastomers. Therefore, despite of the recent advances in the DEG research, minimisation of losses of elastomeric material for DEG application is still in demand. The present study focuses on the material-related losses of natural rubber (NR) and shows the possibility to decrease the low frequency losses by the addition of nanodiamonds. The post-treatment of the films, namely leaching and acetone extraction, allows reducing the losses even more by almost 25% for NR. Moreover, acetone treatment results in a positive effect on the mechanical properties of the samples, as well as reduced viscous losses and improved stress relaxation behaviour.
Keywords: DEG; dielectric elastomer generator; natural rubber latex; nanodiamonds; dielectric spectroscopy.
Exergoeconomic optimization of basic and regenerative triple-evaporator combined power and refrigeration cycles
by Hadi Ghaebi, Hadi Rostamzadeh, Keivan Mostoufi, Mohammad Ebadollahi, Majid Amidpour
Abstract: This paper deals with reconstruction of conventional combined cooling and power (CCCP) cycle for producing simultaneous power and cooling for triple applications of freezing, refrigeration and air-conditioning. For this purpose, three evaporators with different temperature levels are added to the CCCP cycle in parallel, using ejector among them. The proposed systems are integrated from organic Rankine cycles (ORCs) and an ejector refrigeration cycle (ERC). To show the feasibility of the proposed systems, energy, exergy and exergoeconomic analysis of the proposed system are carried out. It is found that among all components, vapor generator accounts for the largest contribution of exergy destruction. In addition, single- and multi-objective optimizations of the proposed systems are conducted, using genetic algorithm (GA). The results of optimization revealed that the thermal efficiency of the basic triple-evaporator CCP (B-TECCP) and regenerative TECCP (R-TECCP) systems can be improved by 7.48% and 6.23%, respectively, whereas the exergy efficiency of the proposed systems is enhanced by 10.83% and 6.84%, respectively. In addition, the sum unit cost of product (SUCP) of system is also decreased by 11.88% and 15.19% for B-TECCP and R-TECCP systems, respectively, through this optimization mode. At last, a comprehensive parametric study is performed to give more information from operating conditions of the proposed systems for designers. It is observed that the thermal efficiency can be increased by increasing the turbine expansion ratio (TER) and evaporators temperature or decreasing condenser temperature, whereas the exergy efficiency can be increased by increasing the TER, evaporator(I) temperature and condenser temperature or decreasing vapor generator temperature. Also, it is concluded that the cost of system can be decreased by increasing the TER and condenser temperature or decreasing evaporators temperatures.
Keywords: Triple-evaporator; Cogeneration; Thermodynamic analysis; Thermoeconomic analysis; Optimization; Genetic algorithm (GA);.
Energetic and exergetic comparative analysis of advanced vapor compression cycles for cooling applications using alternative refrigerants
by Mohammed Gadalla
Abstract: In this paper, advanced single stage as well as multi stage systems of Vapour Compression Refrigeration Cycles (VCRCs) for cooling applications are presented with detailed comparative analyses under different operating conditions and a constant cooling load of one ton refrigeration; 3.52 kW. Different types of refrigerants such as R404A, R134A, R22, and R410A are used as working fluids in different cycle configurations. The refrigerants were selected due to their thermodynamic properties, their ability to work with common compressor models, low cost and different cooling application ranges. The study involves energetic and exergetic COPs analyses for each cycle as a key indicator for the overall cycle performance. Unlike the conventional energy analysis, the exergy analysis of the system is considered as a complementary tool that helps the designer in making better judgment on the overall system performance and efficiency as it considers the external factors such as the ambient conditions that always affect considerably the cycle performance. The influence of the dedicated mechanical subcooling system as well as the liquid-vapor heat exchanger on the different vapor compression refrigeration cycle configurations is additionally investigated. The results of the parametric analyses show that the subcooling systems has a great impact on the overall energetic and exergetic COPs of the advanced vapor compression refrigeration cycles as it increases the cooling capacity and reduces the power consumed by the compressor. The results of the paper conclude the best configuration with the highest performance, lowest total exergy destruction and the recommended refrigerant that can be utilized in the cycle within the required operating conditions. Finally, the obtained results due to different operating conditions and environmental effects are presented and considered to be used as effective and complimentary tools for developers and researchers during the design stage.
Keywords: Advanced VCRCs; Subcooling heat exchangers; Energetic COP; Exergetic COP; Exergy analysis; Exergy destruction; Alternative refrigerants.
Energy and exergy analyses of a solar air heater with wire mesh-covered absorber plate
by Atilla G. Devecioğlu, Vedat Oruç, Zafer Tuncer
Abstract: Thermodynamic analysis on a novel design of solar air heater having absorber plate covered with copper wire mesh was investigated in this study. The newly-designed collector was tested for various air flow rates and tilt angles of collector, and then the results were compared for the case without wire mesh. The experimental study was carried out for mass flow rates of 0.030 and 0.055 kg/s as well as collector tilt angles of 25
Keywords: Solar air heater; wire mesh; exergy; thermal efficiency.
Comparative Energy and Exergy Studies of Combined CO2 Brayton-Organic Rankine Cycle Integrated with Solar Tower Plant
by Abdullah AlZahrani, Ibrahim Dincer
Abstract: The present study investigates the performance of a combined cycle power plant used as a power block for solar tower (central receiver) system. The combined power cycle employs a supercritical carbon dioxide (S-CO2) Brayton cycle as a topping cycle and an Organic Rankine Cycle (ORC) as bottoming cycle. A solar concentrating system consists of a central receiver, and a heliostat field provides thermal power to the combined cycle. To evaluate the system performance, a thermodynamic analysis is conducted through energy and exergy approaches for each subsystem and hence evaluation of its overall energy and exergy efficiencies. Furthermore, the energy and exergy efficiencies of the integrated system are parametrically studied under different operating conditions. The features of using CO2 as a working fluid in a Brayton cycle are elaborated in the context of high temperature solar tower technologies. Moreover, the opportunity of recovering the topping cycle low-grade heat is investigated, and an n-butane based ORC is, in this regard, proposed as a bottoming cycle. The integrated solar plant with a combined cycle and a solar tower is modeled, and the conceptual feasibility of the integration of the S-CO2 Brayton cycle with ORC is illustrated.
Keywords: Solar tower; Carbon dioxide; Brayton cycle; ORC; Energy and Exergy analysis; integrated power system.
Exergo-economic Analysis of Parabolic Trough Integrated Cogeneration Power Plant
by K.S. Reddy
Abstract: Cogeneration plant produces heat and electricity simultaneously, and have a great potential towards best use of primary energy resources as compared to other plants, which produces heat and electricity separately. Parabolic trough integrated cogeneration power plant (PTICPP) is one of the attractive alternatives to utilizing solar energy in an efficient manner. The economically viable PTICPP could bring an opportunity for its utilization at large scale. Therefore, estimation of levelised cost of electricity (LCE) is done by two different rational cost apportionment method namely; lost-kilowatt and exergy method. To achieve the objective of this paper, a reference PTICPP having a capacity of 20 MWe and 61.94 MWth is designed, and comprehensive thermal performance of reference plant is analyzed at the variable amount of irradiation. In Indian climatic condition, the minimum estimated LCE are 0.127 $/kWh and 0.114 $/kWh respectively by lost-kilowatt and exergy method.
Keywords: Parabolic trough integrated cogeneration power plant; direct steam generation; exergo-economics; levelized cost of electricity.
An experimental investigation of biodiesel-biogas dual-fuel engine based on energy and exergy analysis
by SAKET VERMA, S.C. Kaushik, L.M. Das
Abstract: Pursuit of a green transportation fuel has intensified the efforts not only to explore various renewable fuels but also to improve present IC engine technologies for their effective utilization. Such improvements are possible through careful examination and comparison of various processes involved in the system (IC engine) based on their abilities to deliver the output. Therefore, in the present work, exergy analysis based on second-law of thermodynamics has been implemented to study the biodiesel-biogas dual fuel (DF) operation of compression ignition (CI) engine. This experimental DF operation has been studied with biodiesel (Jatropha curcas) as pilot fuel to ignite the main fuel (biogas-75% CH4 by volume), which was inducted as premixed charge with air in the combustion chamber. Experiments have been performed at constant engine speed of 1500 rpm with varying engine loads and optimized injection timings for both diesel and DF modes. The results indicate that DF operation at low load condition show poor performance and emission characteristics, however, not significant variations were observed between diesel-DF and biodiesel-DF operations. At 23% of engine load, exergy efficiencies were found to be 8.53% and 8.4% for diesel-DF and biodiesel-DF operations respectively; compared to 12.57% for pure diesel operation. Nevertheless, at higher loads, exergetic performances of DF operations were significantly improved. At full engine load, exergy efficiencies were found to be 24.4% and 23.3% for diesel-DF and biodiesel-DF operations respectively; compared to 28.42% for pure diesel operation. Furthermore, NOx emissions from DF operations were significantly reduced compared to that with diesel operation. During the entire run of the experimentations, engine was found to be running smoothly with biodiesel-biogas DF operations.
Keywords: Dual fuel; Biogas; Biodiesel; Exergy; Irreversibility.
Thermodynamic Analysis of Sensible Thermal Energy Storage in Water Filled PET Bottles
by Dogan Erdemir, Necdet Altuntop
Abstract: This study presents an experimental investigation of thermodynamic performance of the sensible thermal energy storage in water filled PET bottles. Heating of the indoor sports hall with solar energy have been researched experimentally. Sports hall is 1,500 m^2 and 15,000 m^3. There are two 160 m^2 solar air collectors on the one side of the building. 5,120 pieces 1.5-liter water filled PET bottles are used in thermal energy storage unit. Total storage volume is 7.680 m^3. These bottles are kept in an insulated tank. Energy charging period is between 7:00 and 17:00, while the energy discharging period is between 17:00 and 22:00. Performance of the sensible thermal energy storage in water filled PET bottles has been examined thermodynamically for October and November. Result indicates that how exergy analysis supplied more realistic and significant assessment than energy analysis. The overall energy and exergy efficiencies have been calculated as 79.85% and 51.89% for October and 69,95% and 46.26% for November, respectively. At the end of study, it has been found that using water filled PET bottles as storage medium in solar energy heating systems is a convenient method. Because, the use of water filled PET bottles do not require an extra heat exchanger between hot air coming from solar collector and water which is storage medium. PET bottles behave as the capsule of storage material.
Keywords: Sensible thermal energy storage; Solar heating; PET bottle.
Second law analysis of wildfire evolution under wind and slope effect
by Elisa Guelpa, Vittorio Verda
Abstract: Despite wildfire behavior has been largely studied during last decades, many issues still remain in the evaluation of fire behaviour in the prediction of its evolution. In this paper, a second law analysis is applied to grassfire evolution. The system is studied through a full physical numerical model, with the aim of collecting data to perform the analysis. The study is conducted considering different wind speed and terrain slope, whichg the driving forces that most affect forest fire evolution. The aim is to analyse possible relations between the quantities driving the fire evolution and the entropy generated during the process.
Keywords: Second law analysis; forest fire; wildfire modeling; entropy generation; WFDS;.
One-Dimensional exergy analysis of an unglazed low-cost PhotoVoltaic/Thermal (PVT) solar collector
by Francesco Calise, Rafal Damian Figaj, Laura Vanoli
Abstract: In this paper a one-dimensional finite-volume model of a low-cost unglazed flat-plate PhotoVoltaic/Thermal (PVT) solar collector is presented. Mass, energy and exergy balances are performed on each finite-volume of the computational domain, discretized along the flow direction. Experimental and numerical data are compared. Exergy destruction rate and exergetic efficiency are evaluated for each element of the computational domain. In addition, the effect of the main design/operation parameters on the collector exergetic performance is also investigated. The comparison between experimental and numerical data in terms of PVT outlet temperature shows an absolute error and a standard deviation of -1.06
Keywords: PhotoVoltaic/Thermal (PVT) collector; finite-volume model; one dimensional; experimental; exergy analysis; parametric analysis.
Increasing engine efficiency at part load with the exhaust valve control: A simplified modelling approach
by Ante Kozina, Gojmir Radica, Sandro Nižetić
Abstract: In this study, a new, innovative system based on variable regulation of the exhaust valves in the gasoline engine was described and analyzed. The efficiency of spark ignited engines decreases during partial load compared to full load, due to increased losses in the exchange of working medium, precisely, loss of suction. To solve this problem, most of manufacturers use variable control of the intake valves, based on the Miller or Atkinson cycle. The basic principle of the proposed system is to partly or completely remove regulatory inlet restrictor during the inlet stroke, the engine draws in the maximum amount of air so that the pumping losses are minimal. During the compression stroke an exhaust valve is open to release the excess air which is the difference between the maximum amount for the full load and the amount needed for the desired loading.The simplified model of the new system has been developed and a comparison was made between the standard engine, regulated with a valve on the intake system, and an engine which is regulated by dual opening of the exhaust valves. Research was carried out on the model of a four cylinder Otto engine with direct injection into the cylinder.The main results showed a significant improvement over the standard engine with a fixed intake and exhaust geometry.Specific consumption is reduced between 3.83% and 4.23%, and losses of cylinder gases exchange have decreased between 85% and 87%.
Keywords: engine efficiency; exhaust valve control; cylinder gas exchange; gasoline engine.