International Journal of Exergy (29 papers in press)
Functional exergy efficiency of an air heat recovery exchanger under varying environmental temperature
by Vytautas Martinaitis, Giedre Streckiene, Darius Biekša, Giedrius Šiupšinskas, Juozas Bielskus
Abstract: The ventilation heat recovery exchanger (HRE) for low energy buildings is becoming one of the important heat transformers in the HVAC systems. The purpose of this paper is to develop the possibilities of exergy analysis for the HRE, when the reference temperature (RT) is variable. The method was prepared through consideration of the exergy flow direction changes, when variable RT was placed below, above and across the operating temperature of working fluids. By using the coenthalpy diagrams, there were obtained three functional exergy efficiencies which had greater sensitivity than universal exergy efficiency. The prepared solution allows the reliable using of the ubiquitous thermodynamic (exergy) analysis for energy chain in the HVAC systems. This methodology may be developed for other heat exchangers with different mass flows, operated in temperatures close to the environment temperature. The results could have a practical application for designing the HVAC systems and implementing their exergy optimum operation controls.
Keywords: HVAC systems; exergy analysis; functional exergy efficiency; ventilation heat recovery exchanger; coenthalpy.
Thermo-ecological performance analysis of a double-reheat Rankine cycle steam turbine system (RCSTS) with open and close feed water heaters
by Guven Gonca
Abstract: This study presents the exergetic and thermo-ecological performance optimization of a Rankine cycle steam turbine system (RCSTS) consisting of three turbines, one open feed water heater (OFWH) and two closed feed water heaters (CFWHs). In this study, different performance characteristics such as effective power, effective power density, exergy efficiency, exergy destruction and ecological coefficient of performance (ECOP) are used to investigate and optimize the system performance. The effects of condenser pressure, OFWH pressure and reheat pressures on the performance characteristics of the system have been examined by considering the irreversibilities and system properties. The results showed that the component pressures considerably affect the system performance. Therefore, they should be optimized to obtain maximum performance characteristics.
Keywords: Steam turbine; Rankine cycle; Thermo-ecological optimization; Power density; ECOP; Exergy.
The mode of interaction of the constituents of a microbial system determines the attainable exergy utilization
by Mustafa Özilgen, Bahar Değerli
Abstract: The typical text book definition of exergy is the maximum work that this system can produce if it is brought to thermal, mechanical and chemical equilibrium with its surroundings via reversible processes. In microbial systems, this ability depends on the interaction, e.g., collaboration, competition or antagonism, between the constituents of the system. Leavening of dough with mixed cultures of microorganisms is a typical example, where the constituents of a system may present different modes of interaction depending on the temperature and their relative amounts. Data pertinent to ten cases of leavening at two different temperatures and six different inoculum ratio of Saccharomyces cerevisiae and Lactobacillus plantarum were proceesed to relate the microbiological and the exergy efficiency optima. The maximum carbon dioxide production, expansion work, and dough volume increase were found to coinside with the case where the system achieved the highest exergy utilization and the highest CO2 production.
Keywords: Exergy efficiency; constituents of the system; ability of resource utilization; sour dough leavening.
Aircraft Fuel System Energy and Exergy Analysis under Hot Day Conditions
by Muhammet Yilanli, Onder Altuntas, Emin Acikkalp, T.Hikmet Karakoc
Abstract: In this paper, energy and exergy analysis of the fuel system is performed to investigate the variation of flow and heat energies of fuel. Thermal balance, formed by many different components of aircraft systems by means of heat management, has been significantly affected by aircraft performance. For that reason, thermal management of the fuel system in the aircraft has a significant indication concerning energy and exergy flow. The results indicate that the rate of energy transfer, which is occurred in the fuel system components throughout flight is respectively 42% for low pressure heat exchanger, 23% for high pressure heat exchanger and 22% for low pressure fuel pump and finally 13% for the high pressure fuel pump. In addition to that; during the flight the exergy destruction rate in the fuel system, in proportion to flight phases, is 51% during climbing phase, 21% during the acceleration phase, 14% during the idle position and 7% during both cruise and descent phase.
Keywords: energy analysis; exergy analysis; thermal management; aircraft fuel system.
Analysis of Effect of Construction Parameters on Energetic and Exergetic Efficiency of Induction Air Heaters
by Umit UNVER, Alper KELESOGLU, Ahmet YUKSEL, Halil Murat UNVER, Fikret YUKSEL
Abstract: The use of induction heating systems in different areas is increasing every day and the energy efficiency of induction heaters became an important issue. Thus, this study is concerned with the energy and exergy efficiency analysis of a novel air heater that operates with induction principle. The aim of this paper is investigation of the energy and the exergy efficiency augmentation of the new K-1 induction air heater prototype. Energy and exergy performance of the K-1 prototype of induction air heater was analysed and compared with the previous K-0 prototype. The analyses were performed with experimental study and with CFD simulation. The improvement of the flow geometry leaded to reduce the natural convection and the radiation heat losses 61.5 W and 115.5 W respectively. The new design boosted the energy efficiency up to 22.98%. The exergy efficiency of the K-1 was calculated to be around 11.5 % max. The CFD simulation results showed that energy efficiency increases linearly with the inlet velocity increment. A 1 m/s increase in the inlet velocity yields 3.1% and 0.06% augmentation in the energy and the exergy efficiency respectively. On the other hand, the inlet temperature increase negatively affects the energy and the actual exergy efficiencies. It was concluded that the induction air heaters would be more efficient and competitive with the appropriate flow field enhancements.
The improvement of the flow geometry leaded to reduce the natural convection and the radiation heat losses 61.5 W and 115.5 W respectively. The new design boosted the energy efficiency up to 22.98%. The exergy efficiency of the K-1 was calculated to be around 11.5 % max. The CFD simulation results showed that energy efficiency increases linearly with the inlet velocity increment. A 1 m/s increase in the inlet velocity yields 3.1% and 0.06% augmentation in the energy and the exergy efficiency respectively. On the other hand, the inlet temperature increase negatively affects the energy and the actual exergy efficiencies. It was concluded that the induction air heaters would be more efficient and competitive with the appropriate flow field enhancements.
Keywords: air heating; induction air heater; energy analysis; exergy analysis; thermal efficiency; exergetic efficiency.
Energy and Exergy Analysis of Advanced Absorption Power Cycles using Salt-Water Mixtures as Working Fluids
by Hasan Ozcan, Salem Yosaf
Abstract: In advanced absorption power cycles (AAPCs), a jet ejector is installed at the absorber inlet and serves for two main functions; it assists pressure recovery, and improves the mixing between the weak solution and the vapor coming from the turbine. These effects enhance the absorption of the vapor into the solution resulting in a better performing power cycle. The influence of the jet ejector on the energy and exergy efficiencies of an AAPC is evaluated, and the thermodynamic efficiencies of the AAPC are compared to those of conventional absorption power cycle (APCS) using three different working fluids, namely ammonia-water solution (NH3-H2O) , lithium bromide-water solution (LiBr-H2O), and lithium chloride-water solution (LiCl-H2O). Five cases are studied that represent the improvement in the AAPCS efficiencies as results of jet ejector integration in the cycle. Some parametric studies are performed comparatively by taking into account both power cycle configurations. Results of parametric studies depict that LiCl-H2O exhibits the highest energy and exergy efficiencies used in AAPC.
Keywords: Absorption power cycle; advanced absorption power cycle; Jet ejector; LiBr-water; NH3-water; LiCl-water; energy; exergy.
Evaluation of Cogeneration Plant with Steam and Electricity Production based on Thermoeconomic and Exergoenvironmental Analyses
by Eduardo Jose Cidade Cavalcanti
Abstract: A cogenerative system which produces 83.6 MW of steam and 119 MW of electricity was evaluated. The exergoeconomic and exergo environmental approach were carried out in order to calculate the cost rate and environmental impact per exergy unit of both products. The Specific Exergy Costing (SPECO) approach was used in balance. The specific cost rate of steam and electricity are 66.6 $/GJ and 62.8 $/GJ, respectively. And the specific environmental impact rate of steam and electricity are 15545 mPt/GJ and 14350 mPt/GJ, respectively. The results reveal that the combustor chamber has the most exergy destruction and higher cost rate of exergy destruction in both analyses. The higher total cost rate and environmental impact were in the gas turbine and the superheater, respectively. The lower exergoeconomic factor and exergoenvironmental factor was in the combustor. In addition, the effect of air environmental temperature at products (electricity and steam) was evaluated. The outcomes were the increase of air temperature, reduce the electrical power and exergetic efficiency. The increase of air temperature, increase the specific cost rate of electricity and steam. And the increase of air temperature, increase the specific environmental impact rate of electricity and steam.
Keywords: Cogeneration; exergoeconomy; steam; exergoenvironmental analyses; eco-indicator 99.
Energy-Exergy-Economic (E3) Analysis of Stand-Alone Solar Thermal Cogeneration Power Plant
by K.S. Reddy
Abstract: Concentrating solar power (CSP) based solar cogeneration plants are more energy efficient compared to single purpose power plants. In this paper, energy, exergy and economic analysis have been carried out for the stand-alone solar thermal co-generation power plant (SASTCPP), which is based on Rankine cycle. Both direct and indirect steam generation is adopted for the comparative E3 analysis. To achieve high energy efficiency, back pressure steam turbine with regenerative feed water heating is incorporated in power block. Reference cogeneration power plant has a capacity of 50 MWth. Levelized cost of electricity (LCOE) associated to SASTCPP is calculated with three different cost allocation approach direct, equivalent fuel consumption, and exergy approach. The observed exergy efficiency (33 to 35%) is comparatively less than energy efficiency (62 to 70 %) and the maximum exergy destruction takes place within the solar field. Minimum LCOE calculated as Indian rupees (INR) 5.46 with direct steam generation.
Keywords: concentrating solar power; energy-exergy-economic analysis; levelized cost of electricity; solar thermal cogeneration power plant; direct steam generation.
Thermodynamic optimization of rectangular and elliptical microchannels with nanofluids
by Bouthayna Khlifi, Brahim Kalech, Mourad Bouterra, Afif Cafsi
Abstract: In this paper, the thermodynamic optimization of laminar flow in rectangular and elliptical microchannels subjected to low or high heat flux is analytically studied. Two mathematical models are developed, by incorporating the aspect ratio term, to evaluate entropy generation numbers. Two relations for calculating the conductivity and the viscosity of CuO-water nanofluids, based on experimental data from literature, are proposed. An entropy generation analysis is proposed to optimize the geometry of the microchannel (aspect ratio, shape) and the working fluid (type of nanofluid, nanoparticles concentration, thermophysical properties) for each heat flux condition. It has been revealed that at low heat flux, using water as working fluid flowing inside microchannels with aspect ratio ε=1 is more efficient from the standpoint of thermodynamic criteria. However, at high heat flux, it is more advisable to use microchannels with the smallest possible aspect ratio containing CuO-water nanofluids with higher conductivity and higher nanoparticles concentration. For the two cases of heat flux values, the rectangular microchannel reaches the minimum value of total entropy generation number compared to the elliptical microchannel.
Keywords: Thermodynamic performance; entropy generation; irreversibilities; rectangular microchannel; elliptical microchannel; aspect ratio; nanofluids; thermophysical properties ; Nusselt number; Poiseuille number.
Novel pinch point method based exergetic optimization of subcritical organic Rankine cycle for waste heat recovery
by Jahar Sarkar
Abstract: New pinch point design methodology for subcritical organic Rankine cycle is proposed to predict pinch point locations in both evaporator and condenser, and optimize working fluid mass flow rate to get maximum heat recovery and exergetic efficiency for given heat source and heat sink conditions. Selected working fluids have been compared based on various performance parameters for various heat source conditions. The present method seems to be better than previous pinch point design methods as it optimize the cycle by considering both source and sink. At optimum operation, ammonia is best in terms of lower mass flow rate and turbine size, toluene is best in terms of lowest heat exchanger size and cost, whereas, R-1233zd and isopentane are best in terms of higher power output and heat recovery, exergy and entrancy efficiencies. Contour plots are presented as well to select optimum design parameters for available heat source and sink.
Keywords: Waste heat recovery; Organic Rankine Cycle; Pinch point temperature difference; Exergetic efficiency; Irreversibility; Entrancy efficiency.
Exergy Quantification for a variable capacity solar absorption system
by Sanjeev Anand, Ankush Gupta
Abstract: The comparative analysis of ETC based double-effect vapour absorption system having different cooling capacities (i.e., 10 TR, 5TR and 2 TR) based on mathematical and numerical modeling has been carried out and the findings obtained revealed that the highest COP is obtained for 2 TR system when compared to 5 TR and 10 TR systems for same varying conditions. The impact of evaporator along with absorber as well as condenser temperature variation on theperformance of the system has also been assessed. The solution heat exchanger shows the highest physical irreversibility while absorber shows a maximum of chemical irreversibility. The 2TR, 5TR and 10TR capacity systems can control the release of 4.2, 10.5 and 21 tons/year respectively of CO2,0.504, 0.1261 and 0.252 tons/year respectively of SO2 and 0.031, 0.077 and 0.15 tons/year respectively of NO(Nitric oxide) in to the atmosphere.
Keywords: Vapour Absorption system; COP; Double-effect; Exergy analysis; Exergy efficiency; Evacuated Tube Collector (ETC); Harmful Gases.
An Alternative Derivation of Second Law Results to Better Relate Derivation to Practical Exergy Analysis
by Indranil Brahma
Abstract: A general and physically intuitive alternative to the classical macroscopic derivation of second law results is proposed, in order to better relate the derivation to practical exergy analysis. This connection is missing from the classical macroscopic presentation of the second law because results are derived from imaginary reversible processes occurring within heat engines operating between infinite temperature reservoirs. These specific processes and devices are absent in practical problems. In contrast, the proposed derivation is applicable to any arbitrary control volume across which heat and/or work interactions occur. The finite control volume is discretized into infinitesimally small elements. So called Interface Equations are developed at the interfaces of these elements, utilizing the second law statement that heat transfer occurs from higher to lower temperature. Terms from the interface equations are then rearranged at each element to show that that ds>dQ/T for the overall control volume. All other second law formulations follow from this result. Reversible processes have been mathematically defined using the interface equations. This is useful in understanding irreversibilities and entropy generation in terms of spatial non-uniformities in temperature distribution. The derivation is short enough that it can possibly supplement the classical presentation, rather than replace it in introductory texts.
Keywords: Second Law; Derivation,Reversibility; Heat Engine; Clausius Inequality; Entropy; Entropy Generation; Exergy.
Performance Analyses and Optimization of the Joule-Brayton Cycle via the Mean Cycle Pressure (MCP) Criterion
by A. Sinan Karakurt, Bahri Sahin
Abstract: Within the scope of developing a new method to optimize the use of economic and ecological thermal systems, a comparative study was conducted by means of different compression ratios and temperature ratios according to Mean Cycle Pressure (MCP) criterion for the simple Joule-Brayton cycle. The results, when compared with the other performance criterias results in the literature, show that the thermal efficiency and network at maximum MCP condition are approximately 1-2% more and 12-13% times less than other criteria, respectively. Moreover, the thermal efficiency that corresponds to the maximum MCP condition is nearly 15% more than the maximum network condition, and the network at the maximum MCP and maximum thermal efficiency conditions are equal. Thus, MCP criterion will give more useful and realistic information in terms of designing more efficient and smaller thermal systems.
Keywords: Exergy Density; Joule-Brayton Cycle; Mean Cycle Pressure.
Application of Exergetic Methods in the Analysis of Different Purifying Techniques
by Alexsandr Smirnykh
Abstract: This article provides the rationale for applying an exergetic method when evaluating the thermodynamics of column-rectification apparatuses, while reviewing the operating profiles of typical purifying columns and purifying columns with stripping modules operating under atmospheric pressure, vacuum, and with mechanical vapor recompression. Graphical representations of the purifying columns exergy balance are provided as GrassmannSzargut diagrams. The exergy balance data showed that the total value of exergy loss is comparable between conventional purifying columns and those equipped with a stripping module (30.94% and 30.78% efficiency, respectively); moreover, exergy loss is lower in systems where the components operate under a vacuum (31.33% efficiency). For purifying columns that operate using mechanical vapor recompression, their exergetic efficiency is highest (32.6%), which indicates that the thermodynamic precision of system being studied increases when a heat pump is used as the primary source of high-grade energy supply in the column apparatus.
Keywords: ethanol; distillation; rectification; heat pump; purifying column; exergy; Grassmann–Szargut diagram.
SOLAR RADIATION EXERGY AND QUALITY PERFORMANCE FOR IRAQ AND TURKEY
by Hayder Noori Mohammed, M. Pinar Mengüç
Abstract: The present study is conducted with two primary objectives: First, a new formulation for the maximum efficiency of the solar radiation conversion is developed by considering the radiative energy transfer between two surfaces at different temperatures for a constant volume system. Second, a new methodology is introduced for estimating the exergy value of the monthly average daily horizontal global radiation, including many parameters, such as monthly average daily value of the horizontal extraterrestrial radiation, the number of sunny hours, the day length, the mean temperature and the mean wind velocity. Seven statistical parameters are used to validate the accuracy of all models. The results of the two new models are found to be more reliable than the results obtained from other models. This study, which was conducted for four locations in Iraq and Turkey. The findings would help in predicting the maximum availability of solar radiation based on weather parameters.
Keywords: Solar radiation; Solar radiation exergy; Empirical models.
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.
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);.
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.