International Journal of Exergy (28 papers in press)

• Consumption analysis of solid oxide fuel cells
  by Yongping Yang, Qin Yan, Rongrong Zhai, Ershu Xu 
  Abstract: The characteristics of the Solid Oxide Fuel Cell (SOFC) were introduced. The SOFC system can be divided into six sections based on the Second Law of Thermodynamics. The fuel specific consumption was taken as the primary indicator to investigate the specific consumption for each section. The Energy-flow Framework Diagram (EFD) was undertaken to modify the system, such as controlling the operating temperature, strengthening insulation and so on. It is concluded that the specific consumption of the system is about 0.19 /kWh, taking great guidelines for the system improvement.
  Keywords: solid oxide fuel cell (SOFC), exergy, specific consumption analysis, energy-flow framework diagram (EFD)
   
• Thermodynamic modeling and performance of variable- temperature heat reservoir absorption refrigeration cycle
  by Xiaoyong Qin, Lingen Chen, Fengrui Sun 
  Abstract: Finite thermal capacitance rate of heat reservoir is a common situation for practical absorption refrigeration plants. It should be considered in thermodynamic modeling and analysis for absorption refrigeration cycles. An irreversible variable-temperature heat reservoir four-temperature-level absorption refrigeration cycle model is established in this paper. The considered losses include heat resistances (heat transfer losses) between the heat reservoirs and the working fluid, internal irreversibilities due to internal dissipation of the working fluid, and the heat leakages between the heat reservoirs and the surrounding. The general relationships between the cooling load and the COP (coefficient of performance) are derived. Besides, the optimal performance characteristics between the cooling load and the COP are obtained using numerical examples. The effects of heat resistances, internal irreversibilities, heat leakages, and the thermal capacitance rates of heat reservoirs on the cycle performance are analyzed. The results obtained herein can provide some guidelines for the optimal design of practical absorption refrigerators.
  Keywords: absorption refrigerator, variable-temperature heat reservoirs, four-temperature-level, finite time thermodynamics
   
• Lifetime Exergy Consumption of Enterprise Servers
  by Christopher Hannemann, Van Carey, Amip Shah, Chandrakant Patel 
  Abstract: Several studies have recently examined the environmental impact of enterprise computing in terms of server and cooling power consumption, but such an approach fails to capture the lifecycle impacts associated with raw material extraction, manufacturing, transportation and end-of-life. This paper details the development of a lifetime exergy consumption model that captures these impacts. Material data is determined via system disassembly, and these data are aggregated with lifecycle process and energy data to obtain a more rigorous model of the overall server impact. Use of the model is demonstrated via case studies examining the effects of variance in transportation and cooling strategies. The importance of transportation modes and material mass, which are greatly affected by supply chain parameters, is shown. The impact of static and dynamic cooling within data centers is also demonstrated.
  Keywords: exergy; life-cycle assessment; servers; data center; energy efficiency; green IT; sustainable computing; environmental sustainability
   
• EXERGY ANALYSIS OF SECOND GENERATION MICRO HEAT SINKS UNDER SINGLE-PHASE AND FLOW BOILING CONDITIONS
  by Ali Kosar 
  Abstract: A parametric study of exergy efficiency was conducted to complement and follow-up a prior exergy analysis of five micro pin fin heat sinks of different spacing and shape. In particular, exergy efficiency served to probe the exergy performances of four micro pin fin heat sinks at fixed mass flow rate, fixed pressure drop, and fixed pumping power under single-phase flow conditions. The results of the exergy analysis were compared to the corresponding thermalhydraulic performance trends. Of the micro pin fin heat sinks tested, those with better heat transfer performance yielded superior exergy efficiencies in comparison to those with better thermalhydraulic performance, implying that denser configuration and flow separation-promoting geometries served to give rise to higher exergy efficiencies. In a related efficiency study, the use of R-123 in place of water as working fluid was found to enhance exergetic performance at the expense of reduced heat transfer performance. In addition to implementing a treatment typical of single-phase flow, the exergy analysis was also extended to the flow boiling of R-123 in an additional hydrofoil-based micro pin fin heat sink. It was found that exergy efficiencies decreased with mass velocity at fixed heat input, pressure drop and pumping power under flow boiling conditions. As such, exergy efficiency could be better represented using the exit mass quality. The outcome of this study also proved noteworthy in view that exergy efficiency could be made to assess both thermodynamic performance and environmental impact.
  Keywords: Micro pin fins; micro heat sinks; microscale cooling; exergy efficiency; microscale boiling
   
• Constructal entransy dissipation minimization for “volume-point” heat conduction without the premise of optimized last-order construct
  by Shuhuan Wei, Lingen Chen, Fengrrui Sun 
  Abstract: In the “volume-point” heat conduction problem with steady heat source, entransy dissipation reflects the mean temperature difference. By taking entransy dissipation as optimization objective, the high effective-conduction channel distribution has been optimized based on rectangular element, without a premise of optimized last-order construct. A more optimal construct and the limit of the equivalent thermal resistance are obtained. The conclusion shows that, in the hypothesis that the thermal current density in the high conductive link is linear, without a premise optimized last-order construct, the optimized construct with entransy dissipation minimization objective is the same as the optimized construct with maximum temperature difference minimization objective, and the mean temperature difference is 2/3 of the maximum temperature difference.
  Keywords: constructal theory, entransy, volume-point heat conduction, generalized thermodynamic optimization
   
• Influence of Soret and Dufour effects on entropy generation in transient double diffusive convection
  by Nejib Hidouri, Ammar Ben Brahim 
  Abstract: Influence of cross diffusion effects, namely Soret and Dufour effects on entropy generation in transient convective heat and mass transfer of a binary perfect gas mixture for the special case of opposing buoyancy forces with equal intensity is numerically studied. This case is of considerable importance, since it corresponds to minimum entropy generation. For moderate values of thermal Grashof number (GrT = 104), Soret and Dufour parameters induce a slight increase of entropy generation, whereas for relatively higher values of thermal Grashof number (GrT = 5x104), it was found that entropy generation exhibits oscillatory behavior where Dufour effect causes its increase while Soret effect induces its decrease. More details of the contributions of Soret and Dufour effects on entropy generation, on heat and mass transfer and on fluid flow are discussed.
  Keywords: Double diffusive convection, Entropy generation, Numerical methods, Soret effect, Dufour effect.
   
• Evolutionary Algorithm for Reversed Iterative Optimization Method Accuracy Inspection Applied for Energetic and Economic Optimization of a Pulp and Paper Mill
  by Aliasghar Mozafari 
  Abstract: “Three-link-model” Exergoeconomic methodology optimizes the design and operability of a system. Most of the conventional Exergoeconomic optimization methods are iterative in nature, and assumptions considered by Tsatsaronis for calculating the cost-optimal Exergetic efficiency and relative cost difference are applicable for them. In the present work, contrary to traditional Exergoeconomic methods a reversed method is used and since assumptions by Tsatsaronis were not applicable, new assumptions have been adopted. The iterative optimization results have been compared with evolutionary programming results in order to evaluate the present method accuracy. The strength of proposed Exergoeconomic optimization method is elucidated in a case study applied to Mazandaran wood and paper industry. Replacement of Pressure Valve and Direct Cyclone Contact Evaporation (DCCE) is proposed, while by selection of the optimum decision variable, recoverable black liquor is increased by 7% and energy consumption is decreased by 12%.
  Keywords: Evolutionary Programming, Exergoeconomic, Process System, Optimization, Reversed Iterative Optimization
   
• Application of Energy and Exergy Analyses for Efficient Energy Utilisation in the Nigerian Residential Sector
  by Ismaila Badmus, Ajiboye Osunleke 
  Abstract: This paper presents energy and exergy analyses as a useful concept in analysing true efficient energy utilisation of the Nigerian residential sector by considering energy and exergy flows in this sector for a period of 15 years - 1991 to 2005. The energy and exergy flows considered include the commercial and the ‘non-commercial’ energy sources. The most efficiently utilised energy source appears to be the Liquefied Petroleum Gas and the least efficient, Kerosene. Electricity utilisation exergy efficiency has been adversely affected by the vapour-compression air-conditioning application apart from low potential thermal energy applications. The overall utilisation energy and exergy efficiencies have been found to be 19.89% and 4.38% respectively.
  Keywords: efficiency;energy and exergy analysis;energy utilisation; residential sector; Nigeria
   
• Second Law Analysis of Compressible Flow through a Diffuser Subjected to Constant Wall Temperature
  by Mohammad Arshad, Ramazan Kahraman, Ahmet Sahin, Rached Ben-Mansour 
  Abstract: Efficient utilization of energy is primary objective in designing thermodynamic systems. Energy can be destroyed due to the intrinsic irreversibility associated within the system. Unfortunately irreversibility cannot be avoided, but it can be minimized in order to save the available energy. The minimization can be achieved if the irreversibility can be identified in the process components. Second law analysis provides a useful tool to identify the irreversibility in any thermal system. This study presents the investigation of local and total entropy generation in compressible turbulent flow through a diffuser. Air is used as the fluid. Constant temperature boundary condition is applied at the wall. Two-dimensional solution of velocity and temperature fields are obtained using the CFD code FLUENT. Distribution of entropy generation rate is investigated throughout the volume of the fluid as it flows through the diffuser. Regions of high entropy generation in the diffuser has been predicted. The desired inlet expansion angle corresponding to the minimum entropy generation at specified flow conditions is determined. The numerical analysis suggests that by successfully predicting the distribution of irreversibility in a thermal system, re-design efforts can be more carefully focused on specific regions with highest entropy generation
  Keywords: Entropy Generation, Compressible Flow, Diffuser, CFD, Constant Wall Temperature
   
• Minimum entropy generation for laminar boundary layer flow over a permeable plate
  by A. Cihat Baytaş, Adrien Réveillère 
  Abstract: A two dimensional laminar boundary layer flow over an isothermal permeable flat plate with blowing and suction has been performed as similar solution for the velocity and temperature fields. The governing fundamental equations are approximated by a system of non-linear locally similar ordinary differential equations which are solved numerically by applying the shooting iteration method along with fourth-order Runge-Kutta integration scheme. An excellent agreement was obtained between results which validates the used computer code. The utilization of the second law of thermodynamics for laminar boundary layer flow is focused on the entropy generation minimization for the optimum blowing and suction velocities on the permeable wall. The results are presented for Prandtl number, Pr from 10-2 to 102 and Brinkman number, Br, from 10-2 to 102 and the blowing/suction velocity, fw, from -1.238 to 5. The results show that the obtaining of local entropy generation maps are feasible and can supply useful knowledge for the finding of suitable blowing and suction velocities.
  Keywords: Entropy generation, Boundary layer, Similarity, Blowing, Suction, Permeable plate, Forced convection
   
• Effects of combustion efficiency on an Otto cycle
  by Osman Azmi Ozsoysal 
  Abstract: This paper explains how the combustion efficiency influence the performance of an irreversible Otto cycle under conditions of varying fuel-air ratio. The irreversibility of Otto cycle comes exclusively from the expansion and compression processes. Utilizing the combustion efficiency, heat addition process at constant volume is described as a function of fuel’s energy. It is assumed that some fraction of the fuel’s chemical energy cannot be fully released inside the engine because of incomplete combustion. Utilizing the combustion efficiency is found to be more useful to realize the cycle feasibility. The amount of released energy from the fuel into the cylinder restricts the compression ratio. The relationship between the combustion efficiency and the compression ratio and their limitations are explained. How the upper limit of compression ratio is evaluated by means of appropriate constraints for a feasible Otto cycle is shown. The valid ranges of the constraints given in literature seriously affect the feasibility of the cycle. The mathematical model developed here leads to a qualitative understanding of how engine loss can be reduced. Thermal efficiency - work curves cannot have a closed loop shape because there is a close relationship between the fuel energy, air-fuel mass ratio, combustion efficiency, maximum cycle temperature and the heat losses into the cylinder wall. If these are all omitted while heat losses are determined independently without establishing any relationship with the released fuel energy, the thermal efficiency versus work curves would just be able to have a closed loop shape.
  Keywords: Irreversible Otto cycle; Air-fuel mass ratio; Waste energy; Combustion efficiency; Fuel conversion efficiency
   
• A review on exergetic analysis and assessment of various types of engines
  by Hakan Caliskan, Mustafa Ertunc Tat, Arif Hepbasli 
  Abstract: This study presents a review on energy and exergy analysis of Otto and Diesel engines. Calculation methods of the analysis are discussed in detail. Previous studies, from 1963 to 2008, are chronologically listed and studied. The test engines have different cylinder numbers, 1 to 18, speeds 228 1/min to 5500 1/min and rated powers, 3.14 kW to 300 kW and a 19 MW of a stationary Diesel engine. Engine specifications and test bench schematics are given in tables and figures. The best exergetic efficiency is achieved with four-stroke, four-cylinder, turbocharged Diesel engines at about 30% except stationary Diesel engine. It is considered that exergetic efficiency can be higher at lower speeds between 1140 1/min to 2200 1/min.
  Keywords: energy; exergy, availability, efficiency, biodiesel, diesel, fuel, engine gasoline second law analysis
   
• Exergy analysis of a cogeneration system through artificial neural network (ANN) method
  by Yilmaz Yoru, Hikmet Karakoc, Arif Hepbasli 
  Abstract: The main objective of the present study is to apply the ANN method to a cogeneration system, located in Izmir, Turkey for exergetic evaluation purposes. The data used are based on the actual operational conditions and the results obtained from this system, which was exergetically analyzed by the authors. It consists of 3 turbines with a total capacity of 13 MW, 6 spray dryers and 2 heat exchangers. A comparison between the exergy destruction values obtained from exergy analysis calculations and the ANN method is made. Fast ANN (FANN) package (library) has been chosen as an ANN application to implement into the C++ code named CogeNNExT, which has been written and developed by the authors. From the single output of the ANN (FANN) results, the main exergy destruction rate with 60.96 MW in the exergetic analysis is obtained to be 61.001 MW with an error of 0.075%. From the 2 outputs of another ANN results, the mean input and output exergy values are found with errors of 0.438% and 2.211%, respectively.
  Keywords: cogeneration; CHP; exergy; artificial neural network; ANN; gas turbine; spray dryer; heat exchanger; artificial intelligence; AI; FANN
   
• Performance investigation of the drying of parsley in a tray dryer system
  by Ebru Hancioglu, Arif Hepbasli, Filiz Icier, Zafer Erbay, Neslihan Colak 
  Abstract: In this study, a tray dryer system for parsley drying process was analyzed using energy and exergy analysis methods for performance evaluation purposes. The drying temperatures were in the range of 40-60°C, while the drying air velocities varied from 0.5 to 1.5 m/s. The drying rate of parsley in thin layer drying was influenced mainly by the drying air temperature. The higher temperature and lower velocity was led to higher exergy and energy efficiencies. Exergy efficiencies of the system components were determined to assess their performances and to elucidate potentials for the improvement. The highest improvement potential and relative irreversibility values were obtained to be 0.685 kW and 60.69% in the drying cabinet, respectively. Exergy efficiency value for the overall system on a product/fuel basis was found to be 3.62%, while the values for specific moisture extraction rate (SMER) and specific moisture exergetic indice (SMExR) were obtained to be 0.08 and 2.47 kg/kWh, respectively.
  Keywords: Drying; Exergy analysis; Parsley; Performance assessment; Tray dryer
   
• Exergy analyses of the biochemical processes of photosynthesis
  by S. Lems, Hedzer van der Kooi, Jakob de Swaan Arons 
  Abstract: This paper gives the exergy analyses of the main biochemical processes of photosynthesis in green plants, during which sugars are synthesized with the aid of solar energy. In the light reactions, photosystem I, photosystem II, and ATP synthesis are found to operate at exergy efficiencies of 50%, 68%, and 81%, respectively, so that 48% of the exergy of utilized solar photons is converted to biochemical energy carriers (ATP and NADPH). Subsequently, in the dark reactions, a sugar like glucose is synthesized from CO2 using ATP and NADPH at an exergy efficiency of 85%, or 62-68% when including the wasteful effect of photorespiration. The overall exergy efficiency of photosynthesis is, then, determined at 31-34%. Most of the exergy losses occur in the first stages of photosynthesis: while this can be partly contributed to the absorption of solar photons, considerable additional exergy losses are associated with the initial conversion of solar to chemical energy.
  Keywords: exergy; thermodynamic; second law; efficiency; biochemical; living cell; photosynthesis; solar; photon; Calvin cycle; chloroplast; glucose.
   
• The influence of injection system characteristics on the first and second law terms in high speed DI Diesel engines with swirl combustion chamber
  by Amin Abassi, Shahram Khalilarya, Samad Jafarmadar 
  Abstract: In Diesel engine study, one of the most important parameters is combustion which is directly affected by fuel injection system characteristics. In this investigation, the influence of fuel injection system characteristics (duration of injection, injection pressure, nozzle holes diameter and number of nozzle holes) on the first and second laws of thermodynamics are analyzed in DI Diesel engines with swirl combustion chamber. The first law analysis is done by using the results of three dimensional KIVA Π code. The results show a good agreement with the experimental data. Also for the second law analysis, a home made computational code is developed. This code applies a finite difference method to discritize availability govern equations. The second law terms such as the burned fuel availability, indicated work availability, availability loss associated with the heat transfer to the walls, combustion irreversibility and entropy generation during a closed cycle are computed by this code. Behaviors of the results are a good accordance with the literature. The results represent sensitiveness of various injection system parameters on the first and second law terms. Also possibility of comparison between effects of various ways for changing the injection system parameters on engine operation is existed.
  Keywords: Internal combustion engine; Fuel injection system; First law analysis; Second law analysis; Availability; Irreversibility.
   
• Multi-Objective Optimization of Hybrid MSF-RO Desalination System Using Genetic Algorithm
  by Hassan Abdulrahim, Fuad Alasfour 
  Abstract: The purpose of this research is to perform a multi-objective optimization study for MSF-BR and hybrid MSF-RO desalination systems using genetic algorithm technique. The hybrid MSF RO desalination system has been simulated rigorously using first and second laws of thermodynamics in addition to the plant economical aspects. The MSF-BR and hybrid MSF RO desalination systems have been optimized for single, double and triple simultaneous objectives. Four objectives have been considered in this analysis; maximum distillate production, minimum product cost, maximum gain ratio and minimum exergy destruction. The multi-objective functions have been formulated using normalized weighted sum technique to aggregate different objectives together. Results showed that multi-objective optimization of MSF-BR and hybrid MSF-RO systems were successful and tend to enhance the performance of both systems. Single objective optimization on the other hand can improve one criterion at a time, while deteriorating other criteria far from its optimal value.
  Keywords: Multi objective optimization; hybrid MSF-RO; genetic algorithm; reverse osmosis; desalination system; exergy destruction; weighted sum; aggregated objectives; second law.
   
• The Influence of Ejector Component Efficiencies on Performance of Ejector Expander Refrigeration Cycle and Exergy Analysis
  by H. Kursad Ersoy, Nagihan Bilir 
  Abstract: Though a large amount of works has been conducted on ejector refrigeration cycle, the efficiency of ejector components are taken as constant in almost all existing investigations. In this study, the influence of ejector component efficiencies on performance of the ejector expansion refrigeration cycle was investigated. In the analysis, a two-phase constant area ejector flow model was used. R134a was selected as the refrigerant. In order to identify the amounts and locations of irreversibility within the components of the cycle, exergy analysis is employed. As the ejector component efficiencies increase, coefficient of performance and exergy efficiency increase. As a result, when the efficiencies of motive nozzle and diffuser are 100%, the efficiency of ejector suction nozzle increases from 20% to 100%, whereas the improvement ratio in cooling coefficient of performance and that of exergy efficiency increase at approximately 4.3 times. It was also found that as ejector component efficiencies fall, optimum ejector area ratio increases.
  Keywords: ejector; component efficiency; expansion valve; COP; exergy
   
• LASER WELDING: THE FIRST AND SECOND LAW ANALYSIS
  by Ahmet Sahin, Tahir Ayar, Bekir Yilbas 
  Abstract: Thermal efficiency analysis can be used to minimize the energy losses in laser welding. In the present study, laser welding and efficiency analysis is considered. The first and second law efficiencies for the welding process are formulated and quantified for new parameters associated with the welding geometry. These parameters include excess mass ratio, loss mass ratio, and heat loss ratio. It is found that the first and second law efficiencies improve gradually with increasing excess mass ratio. However, the first and second law efficiencies reduce with increasing loss mass ratio and heat loss ratio. Provided decrease in efficiencies with increasing heat loss ratio is gradual.
  Keywords: Laser; welding; first law and second law efficiencie; exergy
   
• Energy and exergy analyses of a spark ignition engine
  by Mohammad Ameri, Farzad Kiaahmadi, Mansour Khanaki, Mohsen . Nazoktabar 
  Abstract: In this paper, the performance of an internal combustion engine is evaluated at the steady state condition by application of energy and exergy analysis using the experimental test results. The energy and exergy balances are calculated at different engine speeds. The results show that the heat rejection of energy and exergy flow increases with increasing engine speed. The exergy efficiencies are slightly higher than the corresponding energy efficiencies. The results of this study have revealed that the most important source of the system inefficiency is the destruction of exergy by irreversible processes, mostly by the combustion. One can conclude that the use of a combined energy and exergy analysis provides better criteria for the performance assessment of a thermal system.
  Keywords: SI engine; energy analysis; exergy analysis; energy efficiency; exergy efficiency; irreversibility; performance.
   
• EXERGY ANALYSIS OF PROCESS HEATERS
  by Ahmet Sahin, Syed Zubair 
  Abstract: A second law of thermodynamics analysis is proposed to investigate the entropy generation in process heaters. The exergy destruction (availability losses) due to entropy generation as well as the exergy losses due to flue gas and radiation in process heaters is determined. The second law (exergy) efficiency in process heaters is defined. The effect of various parameters on the exergy efficiency is studied. It is found that the major portion of the exergy losses occur in the stack. It is also found that the excess air decreases the first law efficiency while the second law efficiency remains nearly constant. Although the first law efficiency is found to be in the order of 70-90%, the second law efficiency has been calculated to be low, in the range of 30 to 40%. In this regard, stack gas temperature is found to be an important parameter for improving the second law efficiency.
  Keywords: Exergy; Exergy efficiency; Process heater; Second Law of Thermodynamics.
   
• Entropy generation of laminar forced convection along the wavy surface
  by Chao-Kuang Chen, Yue-Tzu Yang, Kuei-Hao Chang 
  Abstract: In this study, Prandtl’s transposition theorem is used to stretch the ordinary coordinate system in certain direction. The wavy surface can be transferred into a calculable plane coordinate system. The governing equations of laminar forced convection along wavy surface are derived from complete Navier-Stokes equations. A simple transformation is proposed to transform the governing equations into the boundary layer equations and solved numerically by the cubic spline collocation method. Meanwhile, we derive an express for the dimensionless entropy generation equation, which takes into account both heat transfer irreversibility and fluid friction irreversibility. The distribution of both entropy generation number and Bejan number are studied. It shows that irreversibility is periodically dominated by the heat transfer and the friction in laminar forced convection.
  Keywords: Entropy generation; irreversibility; surface wavy
   
• Second law based performance analysis of seawater source cascade heat pump system: A case study
  by S.K. Tyagi 
  Abstract: This article presents the second law based analysis of a seawater source cascade heat pump system operating with two different refrigerants. The present cascade heat pump system consists of two different heat pumps attached in a way that the condenser of the first stage heat pump is the evaporator for the second heat pump and the condenser of the second heat pump is attached to the place to be heated. Based on the exergy analysis it is found that the rate of irreversibility in the evaporator is the highest while it is found to be reverse in the case of expansion valves. The rate of irreversibility for the low pressure compressor is found to be higher than that of the high pressure compressor. Similarly, the rate of irreversibility for the sea water pump is found to be more than that of the circulating water pump
  Keywords: Sea water, cascade heat pump, exergy, irreversibility, heat source
   
• Exergy Analysis of a Combined Fuel Cell and Gas Turbine Power Plant with Intercooling and Reheating
  by Greg Naterer 
  Abstract: This paper presents a comparative exergy study of the performance of various gas turbine power generation plants against a high temperature solid oxide fuel cell (SOFC). The thermodynamic performance of a conventional recuperative gas turbine (GT) power plant, combined with a SOFC, is examined. Individual models are developed for each component, specifically the SOFC, for which the exergy destruction and efficiency of each component are derived and presented. Furthermore, the overall system is analyzed and its exergy efficiency and exergy destruction are obtained. The results of an assessment of the cycle for certain operating conditions are compared against past data available in the literature. The comparisons provide useful verification of the thermodynamic simulations in the present work. Also, by extending the thermodynamic analysis, the performance of four different layouts is compared for (1) a conventional GT cycle, (2) integrated gas turbine plant with a SOFC, (3) a GT-SOFC with an intercooler (IC), and (4) a GT-SOFC-IC with a reheat SOFC. The results of the comparisons are presented in terms of thermal and exergy efficiencies, net power and exergy destruction rate, versus the compression ratio and turbine inlet temperature. It is shown that integrating a conventional GT plant with a SOFC would almost double the efficiency of the cycle. Furthermore, in contrast to a conventional GT plant where an intercooler yields a considerable system efficiency, the performance of the hybrid cycle does not show a significant improvement by adding an intercooler. The superior advantage of utilizing the reheat SOFC is further examined for other power cycles. The results indicate that the optimal efficiency of the GT-SOFC-IC with reheat SOFC occurs at a higher compression ratio. However, when designing the hybrid system, this issue would be limited by the capital costs of compressors and other equipment that becomes more expensive at higher compression ratios.
  Keywords: GT-SOFC cycle, exergy efficiency, performance, intercooler
   
• Exergy analysis of the solar thermochemical cycle for the capture of CO2 from air
  by Viktoria von Zedtwitz-Nikulshina, Vladimir Nikulshin 
  Abstract: This paper presents exergy analysis of the novel solar thermochemical cycle for CO2 capture from ambient air. The exergetic characteristics of every element are provided. The exergy balance, the degree of the thermodynamic perfection, the influence coefficient, and the exergy efficiency is determined for every element of the system. The exergy efficiency of the whole system is calculated based on the exergy efficiency of separate elements. Proposed system has rather low exergy efficiency of 4.8 %, mainly due to the primary purpose of this system to capture CO2 from ambient air and not to produce energy. Based on the exergetic analysis, possible ways of improving system performance are identified: increasing solar collector efficiency, preheating methane flow before the reforming reaction, recovering heat of the slaking process.
  Keywords: solar thermochemical cycle, CO2 capture, thermodynamic analysis, exergetic analysis, efficiency.
   
• Heat Transfer and Entropy Generation in a Two-Dimensional Orthotropic Convection Pin Fin
  by Abdul Aziz, Oluwole Makinde 
  Abstract: The paper uses a two-dimensional heat conduction model to obtain the thermal performance and entropy generation in an orthotropic pin fin used in advanced light weight heat sinks. The analytical expressions for the distribution and heat transfer rates are used to generate the thermal performance graphs that are of general applicability unlike the results for specific cases reported so far. The same information is subsequently used to generate graphs of local and total volumetric entropy generation rates in the fin. The results clearly delineate the effect of radial Biot number, fin aspect ratio, and the ratio of radial to axial thermal conductivities on temperature distribution, heat transfer rate, and local and total entropy generation rates. A procedure is discussed to illustrate the simultaneous realization of the least material and minimum entropy generation pin fin designs.
  Keywords: two-dimensional heat conduction; pin fin; orthotropic; entropy generation, least material, minimum entropy generation.
   
• Exergy analysis of conjugate heat transfer through a building block with multiple enclosed spaces
  by Mohamed Antar 
  Abstract: Exergy destruction due to heat transfer across a building block with multiple cavities is evaluated. The three modes of heat transfer were considered in this problem where conduction heat transfer occurs within the solid material of the building block whereas both natural convection and gray-body radiation occur simultaneously in the air-filled cavities. The number of cavities was varied from 1 to 6 keeping the total width unchanged to investigate its effect on the heat transfer rate, entropy generation and exergy destruction. Using more cavities with less width decreases the heat transfer rate across the block and hence provides better thermal insulation characteristics. In addition, it results in less exergy destruction. In addition, exergy destruction and heat transfer rate can be further reduced by changing the cavities layout and the radiation surface properties of the block cavity surfaces.
  Keywords: exergy analysis, heat transfer, conjugate, numerical, building block
   
• Thermodynamic and Economic Assessments of Gas Turbine Inlet Air Cooling By Evaporative Technique
  by Hasan Huseyin ERDEM 
  Abstract: In this study, the effects of gas turbine inlet air cooling by evaporative technique on work output, thermal end exergy efficiency were analyzed. These analyses are performed with the use of per unit volumetric flow which is fixed regardless of atmospheric air conditions. In addition, a simple and effective model is developed for the economic analysis of evaporative cooling. Since the duration time value of evaporative cooling affects the economic analysis as well as the numerical values of atmospheric temperature and humidity, “Evaporative Cooling Degree Day (ECDD)” containing these parameters, is defined. The daily average atmospheric condition values of one year are used for ECDD calculation. This model determines the payback period for an evaporative cooling system in a gas turbine by using evaporative cooling installation cost, additional fuel cost and electricity income. As a case study, the payback periods of two different gas turbine models are calculated for eight different regions in Turkey. Depending on the technical, economic, and environmental conditions, evaporative cooling may be suitable for the regions considered.
  Keywords: Gas turbine; Evaporative cooling; Cost analysis; Thermal efficiency; Exergy efficiency