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A thermodynamic model is proposed to study the exergetic content of incident solar radiation reaching on the Earth’s surface which can be used to produce work through a dually cascaded thermodynamic cycle. The “topping” cycle is an ad hoc engine created by nature that connects the outer shell of the terrestrial atmosphere (which is in equilibrium with the extraterrestrial solar radiation) to the collector of a solar heat engine operating on the Earth’s surface. The work produced by the topping cycle is dissipated in form of scattering, absorption, heat, movement of air masses (wind), etc. The “bottoming” cycle is a heat engine operating between the collector and surrounding temperatures, and delivers useful work. It is shown that the maximum work extractable from this system as exergy is obtained when both cycles operate reversibly. An expression for this maximum work, which represents the exergy of incident solar radiation on the Earth’s surface, is proposed. The application of the present model is illustrated and validated by calculating the exergy of solar radiation based on some measurements. The results obtained by the present model are compared to the ones obtained through other models available in the open literature. [ABSTRACT FROM AUTHOR]

Abstract In the current study, a novel hybridized system for vehicle applications is proposed, analyzed thermodynamically through energy and exergy approaches and evaluated through energy and exergy efficiencies. The current system comprises gas turbine set running on compressed natural gas (CNG), Li-ion battery, CNG tank, two generators, electric motor, power control unit (PCU), thermoelectric generator (TEG), organic Rankine cycle (ORC) and an absorption chiller system (ACS). The overall energy and exergy efficiencies of the proposed system are found to be 38% and 34% respectively at net output power of 63.6 kW from the turbine set. The maximum exergy destruction rate is found in the combustion chamber followed by the TEG unit. For a detailed analysis of the proposed system, a comprehensive parametric study is further carried out to detect the effect of varying the operating and ambient conditions on the system performance. [ABSTRACT FROM AUTHOR]

In the current study, a combined steam and gas turbine system integrated with solar system is studied thermodynamically. In addition, an electrolyzer is added to the integrated system for hydrogen production which makes the current system more environmental friendly and sustainable. This system is then evaluated by employing thermodynamic analysis to obtain both energetic and exergetic efficiencies. The parametric studies are also conducted to investigate the effects of varying operating conditions and state properties on both energy and exergy efficiencies. The present results show that while gas turbine can generate 312 MW directly, 151.72 MW power is generated by steam turbine using solar collectors and exhausted gases recovered from the gas turbine. Furthermore, by adding electrolyzer to the integrated system, a total of 131.3 g/s (472.68 kg/h) hydrogen is generated by using excess electricity which leads to more sustainability system. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive steady state modelling and thermodynamic analysis of Direct Urea Solid Oxide Fuel Cell integrated with Gas Turbine power cycle (DU-SOFC/GT). The use of urea as direct fuel mitigates public health and safety risks associated with the use of hydrogen and ammonia. The integration scheme in this study covers both oxygen ion-conducting solid oxide fuel cells (SOFC-O) and hydrogen proton-conducting solid oxide fuel cells (SOFC-H). Parametric case studies are carried out to investigate the effects of design and operating parameters on the overall performance of the system. The results reveal that the fuel cell exhibited the highest level of exergy destruction among other system components. Furthermore, the SOFC-O based system offers better overall performance than that with the SOFC-H option mainly due to the detrimental reverse water-gas shift reaction at the SOFC anode as well as the unique configuration of the system. [ABSTRACT FROM AUTHOR]

This paper presents a thermodynamic analysis of a steam reformer coupled with a combined power plant to produce hydrogen from steam and hydrocarbon fuel. In the analysis, the steam reformer uses glycerol as a fuel and produces hydrogen for high temperature proton exchange fuel cells in which the catalyst is tolerant to the amount of carbon monoxide. The results show that increasing the steam to glycerol ratio increases the hydrogen production. However, it decreases the overall efficiency of the system because of the high heat input requirement to the system. Numerous operating conditions and plant parameters are varied and their effects on the overall energy and exergy efficiencies of the system are studied. An optimization study is performed in order to find the optimal system parameters for better performance. [ABSTRACT FROM AUTHOR]

The dissociation of gaseous hydrogen sulphide (H 2 S) into its components is an energy intensive process. The process is studied in this paper with respect to the thermodynamic limits. The band gap of the catalyst and the nature of the solar radiation limit the proportion of incoming radiation that may be used for the reaction. The intensity of the incoming radiation and the reactor temperature are varied and the performance is studied. The exergy efficiency is determined as a function of the quantum efficiency of the photochemical process, and the catalyst band gap. It is shown that an optimum case exergy efficiency of up to 28% can be achieved for the process. With the current status of technology, an exergy efficiency value in the region of 0.4–1% is calculated, with a short-term improvement potential of up to 10%. Hydrogen sulfide has high energy content, but is not widely used due to its impact on environmental pollution. The proposed process in this paper is attractive as it allows that energy to be utilized, while degrading the highly toxic gas into less harmful products. [ABSTRACT FROM AUTHOR]

Abstract: The exergetic efficiency of the thermal management system (TMS) in hybrid electric vehicles (HEVs) has great importance since the supply of available energy onboard is limited, and that the efficiency is closely tied to the overall environmental impact of the vehicle. Thus, it is imperative to have a good understanding of the thermodynamic irreversibilities and environmental impact associated with the system and its components. In this paper, exergoenvironmental analysis is conducted on hybrid electric vehicle thermal management systems. In the exergy analysis part, the balance equations are written for each system component of the TMS to determine exergy destruction rates and exergy efficiencies of the system and its individual components. In the environmental analysis part, a life cycle assessment (LCA) is carried out (using Eco-indicator 99 points) and environmental impact correlations are created in order to obtain the environmental impact of each relevant system components and input and output streams. Consequently, exergoenvironmental variables are calculated, and exergoenvironmental evaluation is performed to determine the most environmentally friendly system components and provide information about trends and possibilities for design improvements. Based on the analysis, it is found that the electric battery has the highest environmental impact in the system due to the copper used in the anodes and gold used in the integrated circuits which accounts for over 40% and 26% of the overall impact respectively. [Copyright &y& Elsevier]

Abstract: In the present study, an integrated system is proposed and thermodynamically analyzed to reduce greenhouse gas (GHG) emissions while improving overall system performance. The integrated system is comprised of a supercritical carbon dioxide (CO2) Rankine cycle cascaded by an Organic (R600) Rankine cycle, an electrolyzer, and a heat recovery system. It is designed to utilize a medium-to-high temperature geothermal energy source for power and hydrogen production, and thermal energy utilization for space heating. Therefore, parametric studies for the supercritical CO2 cycle, the Organic (R600) cycle, and the overall system are conducted. In addition, the effect of various operational conditions, such as geothermal source, ambient and cooling water temperatures on the performance of each cycle and the integrated system, is illustrated. It is found that increasing geothermal source temperature results in slight increases of the exergetic efficiency of the overall system. The energy efficiencies of the CO2 and Organic Rankine cycles do not considerably vary with source temperature changes. The decay of the cooling water temperature leads to a decrease in the overall system exergetic efficiency. The system configuration, which is introduced, is capable of producing about 180 kg/h for the geothermal source of mass flow rate of 40 kg/s and a temperature of 473 K. [Copyright &y& Elsevier]

SUMMARY In this paper, a novel integrated solar photovoltaic thermal absorption desalination system for freshwater and cooling production is proposed and analyzed thermodynamically. Ammonia-water pair is considered as a working fluid for the absorption system. Effect of average solar radiation for different months, time period of solar radiation availability in Abu Dhabi, salinity of seawater, and temperature of the seawater on energetic and exergetic COPs, production rate of freshwater, and overall performance of the system are investigated under different operating conditions. It is found that energetic and exergetic COPs, production rate of freshwater, energetic and exergetic utilization factors, and performance ratios vary greatly from one month to another because of the dynamic variation in solar radiation and its time of availability. The highest amount of freshwater is produced in the month of July as calculated to be 152 kg/h for a collector area of 100 m2 and solar power of 4.8 kW. The highest energetic and exergetic COPs and utilization factors are also obtained for the month of July. Moreover, the highest performance ratio is found to be 0.056 as obtained in the month of July when solar radiation intensity is highest as available for more than half of a day. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper performs a thermodynamic analysis of a modified dual photo-electrochemical cell for water electrolysis, previously developed by Grätzel. In a typical Grätzel cell, a semi-transparent photo-electrode is used in conjunction with a dye photo-sensitized cell to generate a bias voltage necessary to overcome the inherent over-potentials caused by irreversibilities within the cell. The modified method implements hybrid photo-catalysis instead of heterogeneous catalysis. In the hybrid photo-catalysis approach, both homogeneous and heterogeneous photo-catalysts are used to enhance the speed of the water splitting reaction and to widen the portion of the solar radiation spectrum for the process. The dual cell consists of two tandem units. The first unit is a photo-electrolysis cell exposed to solar radiation (at both cathodic and anodic sides) via a transparent window, whereas the second unit is a dye-sensitized solar cell, which assists the photo-electrolysis cell. In the cathodic solution, there are dissolved Brewer-type supra-molecular complexes for photo-catalytic water reduction to generate hydrogen. They absorb solar radiation in the upper visible spectrum and dislocate multiple electrons at the active center. The complexes accept electrons donated from a GaP-based semi-transparent photo-cathode. The remaining un-absorbed radiation (mainly in the infrared range) crosses the semitransparent counter-electrode and the back glass. It is absorbed by a solar thermal collector for enhancing the solar radiation utilization by co-generating low-grade heat. The tandem cell with hybrid photo-catalysis has promising potential of improved solar radiation utilization. This paper analyzes the system efficiency and shows that 4% energy efficiency can be obtained for hydrogen generation. About 20% of the incident solar spectrum can be captured by the cell and used for hydrogen generation. Around 60% of solar radiation is recovered in the form of heat on a flat plate solar thermal collector placed behind the cell. The influence of catalyst concentration and pH also is studied. The device forms a four-gap solar absorber system, which is coupled to a cogeneration sub-system for heating, so the solar energy utilization is maximized. The four-gap system absorbs photons at 1.6, 2.1, 2.3, and 2.7 eV and generates five reversible potentials of 0.42, 0.9, 1.6, 2.1, and 2.3 V. Based on the predicted results, the reaction rate appears to be enhanced with respect to other solar electrolysis cells (such as photo-electrolyzers and a dual photo-electrochemical cell) because homogeneous catalysis enhances the electrode kinetics. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, a comprehensive thermodynamic analysis of the triple-effect absorption-refrigeration system using ammonia-water solution is carried out in order to investigate the effect of different operating conditions on the coefficient of performance (COPs) and rate of heat input to the system. It is found that both energetic and exergetic COPs vary from 0.31 to 1.867 and 0.165 to 0.964, respectively, as the inlet temperature to the high-temperature generator (HTG), cooling load, and concentration of the strong solution are increased, while the rate of heat input varies from 65.5 to 71.5%. Moreover, increase in the mixture exit temperature from the HTG, concentration of the weak solution, and mass flow rate result in the variation of energetic and exergetic COPs from 2.49 to 0.68 and 1.0 to 0.23, respectively, which results in the change of rate of heat input from 7.1 to 28.5 kW. When the outdoor temperature is increased, the exergetic COP varies from 0.43 to 1.23. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new seawater electrolysis technique to produce hydrogen is developed and analysed thermodynamically. Although hydrogen production occurs at high columbic efficiency, it causes a localized pH change. It leads to a higher cell voltage and solid deposition as significant challenges of seawater electrolysis. In this regard, the anolyte feed after oxygen evolution to the cathode compartment for hydrogen production is examined. The study aims to prevent the occurrence of a large pH difference on the cathode and anode in the electrolysis of a neutral solution if sufficient OH− ions are permeated through the membrane. The cell performance is evaluated with an anion exchange membrane for separation of the anode and cathode compartments. An inexpensive and efficient molybdenum-oxo catalyst with a turn-over frequency of 1200 is examined for the hydrogen evolving reaction. The flow rate and current density are parametrically studied to determine the effects on both bulk and surface precipitate formation. The effect of electrolyte circulation on the amount of precipitation is predicted based on a mass transfer approach. The mixing electrolyte volume and electrolyte flow rate are found to be significant parameters as they affect cathodic precipitation. [Copyright &y& Elsevier]

Abstract: In this paper, a parametric study of the triple effect absorption cooling system (TEACS) integrated with solar photo-voltaic/thermal (PV/T), geothermal, and Linde–Hampson cycle is conducted. The effect of different operating parameters on the COPs, ratio ‘n’, amount of hydrogen gas pre-cooled, amount of hydrogen liquefied, and utilization factor of the integrated system are studied. It is found that when mass flow rate of air increases the energetic and exergetic COPs decrease in an exponential form from 2.6 to 1.9, and 0.4 to 0.3, respectively. The amounts of hydrogen gas pre-cooled and hydrogen liquefied decrease from 0.39 kg/s to 0.32 kg/s and 0.082 kg/s and 0.066 kg/s, respectively with increase in mass flow rate of air. Moreover, the amounts of hydrogen gas pre-cooled and hydrogen liquefied decrease from 0.42 to 0.27, and 0.088 to 0.066, respectively with increase in mass flow rate of geothermal. In addition, energetic and exergetic utilization factors of integrated system decrease from 0.059 to 0.037, and 0.21 and 0.13, respectively with increase in mass flow rate of geothermal. [Copyright &y& Elsevier]

Abstract: In this paper, the recovered heat is examined for cabin cooling for ejector and absorption cooling cycles. Energy and exergy analyses are conducted to study the role of various design parameters on the cooling capacity. Waste heat from the battery pack, as well from exhaust gases in the Internal Combustion Engine (ICE) mode, are the inputs for the boiler and generator. In a city driving mode, waste heat of 15.4 kW will be available. Results show that transferring this waste heat to the boiler in the ejector cooling system leads to a cooling effect of 7.23 kW, with energetic and exergetic Coefficients of Performance (COPs) of 0.48 and 0.2 respectively. In the absorption cycle, the energetic COP of the system is 0.53 with a coolant capacity of 7.93 kW. Results also show that, for the electric mode, the cooling capacity is lower than 2 kW, which is insufficient to provide cooling. While recovered heat from Hybrid Electric Vehicles (HEV) can be used for vehicle cabin cooling by both ejector and absorption systems, the analysis shows that the latter system has a better coefficient of performance and cooling capacity than the ejector system. [Copyright &y& Elsevier]

Abstract: Combined cycles use the exhaust gases released from a Gas Turbine (GT). Approximately 30–40% of the turbine shaft work is typically used to drive the Compressor. The present study analyzes a system that couples a Wind Turbine (WT) with a combined cycle. It demonstrates how a WT can be used to supply power to the Compressor in the GT cycle and pump fluid through a reheat Rankine cycle, in order to increase the overall power output. Three different configurations are discussed, namely high penetration, low penetration and wind power addition. In the case of a low electricity demand and high penetration configuration, extra wind power is used to compress air which can then be used in the low penetration configuration. During a high load demand, all the wind power is used to drive the pump and compressor and if required additional compressed air is supplied by a storage unit. The analysis shows that increasing the combustion temperature reduces the critical velocity and mass flow rate. Increases in wind speed reduce both energy and exergy efficiency of the overall system. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a novel integrated geothermal based binary multi-stage power generating and quadruple effect absorption system (QEAS) for cooling, heating, power and hot water production. Parametric studies are undertaken and the effects of some operating conditions such as geothermal temperature, geothermal mass flow rate, concentration of ammonia–water vapor, temperature of inlet stream to the very high temperature generator (VHTG), and pressure of the first turbine on the outputs of the system are investigated. It is found that increasing geothermal source temperature and concentration of ammonia in vapor leaving VHTG results in improved performance of the overall system. Moreover, it is found that the best results are obtained for the temperature of 383K of the strong solution inlet to the VHTG (state 14). In addition, an increase in the operating pressure of the first-stage turbine from 3000kPa to 3600kPa increases the power generation from 76.4kW to 87kW, respectively. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a novel integrated geothermal absorption system for hydrogen liquefaction, power and cooling productions. The effect of geothermal, ambient temperature and concentration of ammonia-water vapor on the system outputs and efficiencies are studied through energy and exergy analyses. It is found that both energetic and exergetic coefficient of performances (COPs), and amounts of hydrogen gas pre-cooled and liquefied decrease with increase in the mass flow rate of geothermal water. Moreover, increasing the temperature of geothermal source degrades the performance of the quadruple effect absorption system (QEAS), but at the same time it affects the liquefaction production rate of hydrogen gas in a positive way. However, an increase in ambient temperature has a negative effect on the liquefaction rate of hydrogen gas produced as it decreases from 0.2 kg/s to 0.05 kg/s. Moreover, an increase in the concentration of the ammonia-water vapor results in an increase in the amount of hydrogen gas liquefied from 0.07 kg/s to 0.11 kg/s. [Copyright &y& Elsevier]

Abstract: This paper reports a thermodynamic analysis of filling a fuel tank with compressed gaseous hydrogen. The analysis is based on energy and exergy methods. A parametric study is performed to investigate the effect of initial conditions on the exergy destruction and exergy efficiency of filling processes. The transient filling process is studied to determine the temperature and pressure changes inside the storage tank during filling. [Copyright &y& Elsevier]

Abstract: In this study, a comprehensive performance analysis of a transportation system powered by a PEM fuel cell engine system is conducted thermodynamically both through energy and exergy approaches. This system includes system components such as a compressor, humidifiers, pressure regulator, cooling system and the fuel cell stack. The polarization curves are studied in the modeling and compared with the actual data taken from the literature works before proceeding to the performance modeling. The system performance is investigated through parametric studies on energy, exergy and work output values by changing operating temperature, operating pressure, membrane thickness, anode stoichiometry, cathode stoichiometry, humidity, reference temperature and reference pressure. The results show that the exergy efficiency increases with increase of temperature from 323 to 353 K by about 8%, pressure from 2.5 to 4 atm by about 5%, humidity from 97% to 80% by about 10%, and reference state temperature from 253 to 323 K by about 3%, respectively. In addition, the exergy efficiency increases with decrease of membrane thickness from 0.02 to 0.005 mm by about 9%, anode stoichiometry from 3 to 1.1 by about 1%, and cathode stoichiometry from 3 to 1.1 by about 35% respectively. [Copyright &y& Elsevier]

SUMMARY The present study deals with a comprehensive thermodynamic modeling of a combined heat and power (CHP) system in a paper mill, which provides 50 MW of electric power and 100 ton h−1 saturated steam at 13 bars. This CHP plant is composed of air compressor, combustion chamber (CC), Air Preheater, Gas Turbine (GT) and a Heat Recovery Heat Exchanger. The design parameters of this cycle are compressor pressure ratio ( rAC), compressor isentropic efficiency ( ηAC), GT isentropic efficiency ( ηGT), CC inlet temperature ( T3), and turbine inlet temperature ( T4). In the multi-objective optimization three objective functions, including CHP exergy efficiency, total cost rate of the system products, and CO2 emission of the whole plant, are considered. The exergoenvironmental objective function is minimized whereas power plant exergy efficiency is maximized using a Genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost is performed. The results show that at the lower exergetic efficiency, in which the weight of exergoenvironmental objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of the Pareto Frontier with the lower weight of exergoenvironmental objective. In addition, with increasing exergy efficiency, the purchase cost of equipment in the plant is increased as the cost rate of the plant increases. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This study is basically composed of two sections. In the first section, a CFD analysis is used to provide a better insight to molten carbonate fuel cell operation and performance characteristics at very high current densities. Therefore, a mathematical model is developed by employing mass and momentum conservation, electrochemical reaction mechanisms and electric charges. The model results are then compared with the available data for an MCFC unit, and a good agreement is observed. In addition, the model is applied to predict the unit cell behaviour at various operating pressures, temperatures, and cathode gas stoichiometric ratios. In the second section, a thermodynamic model is utilized to examine energy efficiency, exergy efficiency and entropy generation of the MCFC. At low current densities, no considerable difference in output voltage and power is observed; however, for greater values of current densities, the difference is not negligible. If the molten carbonate fuel cell is to operate at current densities smaller than 2500Am−2, there is no point to pressurize the system. If the fuel cell operates at pressures greater than atmospheric pressure, the unit cell cost could be minimized. In addition, various partial pressure ratios at the cathode side demonstrated nearly the same effect on the performance of the fuel cell. With a 60K change in operating temperature, almost 10% improvement in energy and exergy efficiencies is obtained. Both efficiencies initially increase at lower current densities and then reach their maximum values and ultimately decrease with the increase of current density. By elevating the pressure, both energy and exergy efficiencies of the cell enhance. In addition, higher operating pressure and temperature decrease the unit cell entropy generation. [Copyright &y& Elsevier]

Abstract: In this paper, an integrated process of steam biomass gasification and a solid oxide fuel cell (SOFC) is investigated energetically to evaluate both electrical and energy efficiencies. This system is conceptualized as a combined system, based on steam biomass gasification and with a high temperature, pressurized SOFC. The SOFC system uses hydrogen obtained from steam sawdust gasification. Due to the utilization of the hydrogen content of steam in the reforming and shift reaction stages, the system efficiencies reach appreciable levels. This study essentially investigates the utilization of steam biomass gasification derived hydrogen that was produced from an earlier work in a system combines gasifier and SOFC to perform multi-duties (power and heat). A thermodynamic model is developed to explore a combination of steam biomass gasification, which produces 70–75 g of hydrogen/kg of biomass to fuel a planar SOFC, and generate both heat and power. Furthermore, processes are emerged in the system to increase the hydrogen yield by further processing the rest of gasification products: carbon monoxide, methane, char and tar. The conceptualized scheme combines SOFC operates at 1000 K and 1.2 bar and gasifier scheme based on steam biomass gasification which operates close to the atmospheric pressure, a temperature range of 1023–1423 K and a steam-biomass ratio of 0.8 kmol/kmol. A parametric study is also performed to evaluate the effect of various parameters such as hydrogen yield, air flow rate etc. on the system performance. The results show that SOFC with an efficiency of 50.3% operates in a good fit with the steam biomass gasification module with an efficiency, based on hydrogen yield, of 55.3%, and the overall system then works efficiently with an electric efficiency of ∼82%. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogen production from biomass gasification needs to be improved through investigation of the operating parameters and thermodynamic efficiencies (energy and exergy). A comprehensive study is conducted to predict H2 production with a gasifier using a quantity of 14.5kg/s from biomass (wood sawdust) and an amount of 6.3kg/s of steam at 500K and evaluate system performance through energy and exergy efficiencies for hydrogen production from biomass. The gasification process takes place in a temperature range of 950–1500K and steam–biomass ratio of 0.17–0.51. The results indicate that an improvement in exergy efficiency from 33 to 37% is possible during hydrogen production only. It becomes more sensitive if the temperature goes beyond 1000K. In this regard, the exergy efficiency increases from 42 to 47% when all of the product gases are taken in consideration and from 47 to 52% when all of the products from the gasification process are taken in consideration. Over a range of gasifier temperatures, the gasification ratio is 97–105g H2/kg of biomass while hydrogen yield reaches 1.5kg/s for the studied biomass. [ABSTRACT FROM AUTHOR]

Abstract: An investigation is reported of the thermodynamic performance of the gasification process followed by the steam-methane reforming (SMR) and shift reactions for producing hydrogen from oil palm shell, one of the most common biomass resources. Energy and exergy efficiencies are determined for each component in this system. A process simulation tool is used for assessing the indirectly heated Battelle Columbus Laboratory (BCL) gasifier, which is included with the decomposition reactor to produce syngas for producing hydrogen. A simplified model is presented here for biomass gasification based on chemical equilibrium considerations, with the Gibbs free energy minimization approach. The gasifier with the decomposition reactor is observed to be one of the most critical components of a biomass gasification system, and is modeled to control the produced syngas yield. Also various thermodynamic efficiencies, namely energy, exergy and cold gas efficiencies are evaluated which may be useful for the design, optimization and modification of hydrogen production and other related processes. [Copyright &y& Elsevier]

Abstract: For a given set of operating conditions, the hydrogen production from biomass gasification can be improved through optimization of the operating parameters and efficiencies. The present approach can predict hydrogen production via biomass gasification in a range of 10–32kg/s from biomass (sawdust wood). The biomass is introduced to a gasifier at an operating temperature range of 1000–1500K. Also, 4.5kg/s of steam at 500K is used as gasification medium. Results indicate that improvement in hydrogen production from biomass steam gasification depending on the amount of steam and quantity of biomass feeding to the gasifier as well the operating temperature. Over the range of feeding biomass, the hydrogen yield reaches 80–130g H2/kg biomass while in the operating temperature examined, the hydrogen yield reaches 80g H2/kg biomass. On mole basis it is found that, in the first range of H2 varies from 51 to 63% in the studied range of feeding biomass in existing 4.5kg/s from steam while H2 gets to 51–53% in existing of 6.3kg/s from steam. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate the performance of a newly proposed power and heating system using proton-conducting solid oxide fuel-cell (SOFC-H+) for vehicular applications and its optimization for the best possible performance in terms of power output and efficiency. We also study heat recovery option here to improve the performance. Taking this into account, we calculate the exergy efficiency as 60–75% as a function of the air stoichiometry. Also, we show that by allocating optimal volumes to the main components it is possible to maximize the system''s volumetric power output. The optimal allocation is quantified by the ratio of stack''s volume versus the overall system volume. Both system configuration and performance depend on the optimization objective that may aim to obtain either maximum power density (or useful space on-board) or maximum efficiency (or driving range). If the optimization is performed for a maximum efficiency, the stack occupies about 75% of the total system volume, but the compactness is reduced by about 40% with respect to the maximum power density design. [Copyright &y& Elsevier]

Abstract: In this paper, energy and exergy analyses for a 1.2kWp Nexa PEM fuel cell unit in a solar-based hydrogen production system is undertaken to investigate the performance of the system for different operating conditions using experimental setup and thermodynamic model. From the model results, it is found that there are reductions in energy and exergy efficiencies (about 14%) with increase in current density. These are consistent with the experimental data for the same operating conditions. A parametric study on the system and its parameters is undertaken to investigate the changes in the efficiencies for variations in temperature, pressure and anode stoichiometry. The energy and exergy efficiencies increase with pressure by 23% and 15%, respectively. No noticeable changes are observed in energy and exergy efficiencies with increase in temperature. The energy and exergy efficiencies decrease with increase in anode stoichiometry by 17% and 14%, respectively. These observations are reported for the given range of current density as 0.047–0.4A/cm2. The results and analyses show that the PEM fuel-cell system has lower exergy efficiencies than the corresponding energy efficiencies due to the irreversibilities that are not considered by energy analysis. In comparison with experimental data, the model is accurate in predicting the performance of the proposed fuel-cell system. The parametric and multivariable analyses show that the option of selecting appropriate set of conditions plays a significant role in improving performance of existing fuel-cell systems. [Copyright &y& Elsevier]

Abstract: This paper examines the exergetic performance of a high-temperature solid oxide fuel cell (SOFC) combined with a conventional recuperative gas turbine (GT) plant. Individual models are developed for each component, specifically for SOFC and a combustor that is located downstream of the cell stack. The exergy destruction and efficiency of each component are derived and presented. Furthermore, the overall system is analyzed and its exergy efficiency, as well as exergy destruction, is computed. An assessment of the cycle is performed for an actual system and the results for certain operating conditions are compared with past published results. The comparisons provide useful verification of the thermal simulations in the present work. Further outcomes indicate that increasing the turbine inlet temperature (TIT) results in decreasing the exergy and thermal efficiencies of the cycle, whereas it improves the total specific power output. Also, an increase in either TIT or compression ratio (r p) leads to a higher rate of exergy destruction of the plant. A comparison between the GT–SOFC plant and a traditional GT cycle, based on identical operating conditions, is also made. The superior performance of a GT–SOFC, in terms of thermal and exergy efficiencies, over a traditional GT cycle is evident: 26.6% and 27.8% better exergetic and energetic performance, respectively, than a traditional GT plant. In this case, the exergy and thermal efficiencies of the integrated cycle become as high as 57.9% and 60.6%, respectively, at the optimum compression ratio. [Copyright &y& Elsevier]

Abstract: This study deals with the energy and exergy analysis of a molten carbonate fuel cell hybrid system to determine the efficiencies, irreversibilities and performance of the system. The analysis includes the operation of each component of the system by mass, energy and exergy balance equations. A parametric study is performed to examine the effect of varying operating pressure, temperature and current density on the performance of the system. Furthermore, thermodynamic irreversibilities in each component of the system are determined. An overall energy efficiency of 57.4%, exergy efficiency of 56.2%, bottoming cycle energy efficiency of 24.7% and stack energy efficiency of 43.4% are achieved. The results demonstrate that increasing the stack pressure decreases the overpotential losses and, therefore, increases the stack efficiency. However, this increase is limited by the remaining operating conditions and the material selection of the stack. The fuel cell and the other components in which chemical reactions occur, show the highest exergy destruction in this system. The compressor and turbine on the other hand, have the lowest entropy generation and, thus, the lowest exergy destruction. [Copyright &y& Elsevier]

Abstract: This study examines the performance of a high-temperature solid oxide fuel cell combined with a conventional recuperative gas turbine (GT–SOFC) plant, as well as the irreversibility within the system. Individual models are developed for each component, through applications of the first and second laws of thermodynamics. The overall system performance is then analyzed by employing individual models and further applying thermodynamic laws for the entire cycle, to evaluate the thermal efficiency and entropy production of the plant. The results of an assessment of the cycle for certain operating conditions are compared against those available in the literature. The comparisons provide useful verification of the thermodynamic simulations in the present work. The comparisons provide useful verification of the thermal simulations in the present work. Further outcomes indicate that increasing the turbine inlet temperature results in decreasing the thermal efficiency of the cycle, whereas it improves the net specific power output. Moreover, an increase in either the turbine inlet temperature or compression ratio leads to a higher rate of entropy generation within the plant. It was found that the combustor and SOFC contribute predominantly to the total irreversibility of the system. About 60% of the irreversibility takes place in the following components at typical operating conditions: 31.4% in the combustor and 27.9% in the SOFC. A comparison between the GT–SOFC plant and a traditional GT cycle, based on identical operating conditions, is also made. Although the irreversibility of a modern plant is higher than that of a conventional cycle, the superior performance of a GT–SOFC, in terms of thermal efficiency and environmental impact (lower CO2 emissions), over a traditional GT cycle is evident. It has about 27.8% higher efficiency than a traditional GT plant. In this case, the thermal efficiency of the integrated cycle becomes as high as 60.6% at the optimum compression ratio. [Copyright &y& Elsevier]

Abstract: This article investigates the entropy production of condensation of a vapor in the presence of a non-condensable gas in a counter-current baffled shell and one-pass tube condenser. The non-dimensional entropy number is derived with respect to heat exchange between the bulk fluid and condensate, as well as heat exchange between the condensate and coolant. Numerical results show that heat transfer from the condensate to the coolant has a dominant role in generating entropy. For example, at an air mass flow rate of 330kg/h, 93.4% of the total entropy generation is due to this source. The resultant profiles during the condensation process indicate that a higher air mass flow rate leads to a lower rate of entropy production. For example, as the air mass flow rate increases from 330kg/h to 660kg/h and 990kg/h, the total entropy generation decreases from 976J/sK to 904 and 857.2J/sK, respectively. By introducing a new parameter called the condensation effectiveness, a correlation is also developed for predictions of the entropy number, and an illustrative example is presented. [Copyright &y& Elsevier]

An exergoeconomic analysis of glycol cold thermal energy storage (CTES) is reported. Glycol CTES is an application of sensible heat storage where the temperature of a storage material changes in order to store cold energy, usually generated from electricity when its cost is low. Exergoeconomic analysis combines thermodynamic analysis based on the first and second laws with principles of economics, mostly cost accounting. Exergy analysis accounts for energy quality and irreversibilities, and provides more meaningful and useful information than energy analysis about efficiency and losses. A storage tank with a capacity of 350 000 kg is considered for this investigation and a water solution based on ethylene glycol is used as the storage medium. Several thermodynamic system factors are analysed, such as change in storage temperature, coefficient of performance (COP) of the chiller, heat losses from the storage tank, and the mass flow rates. Simulation results indicate that the system exergy efficiency is much less (∼45%) than the energy efficiency. The average exergy efficiency of the storage tank is determined to be 35% and the average energy efficiency 80%. The system exergy efficiency is determined to be 30% and 40% at 45 and 25°C ambient temperatures, respectively. The chiller COP is observed to be strongly related to storage temperature, and to vary approximately between 2.4 and 5.8 at a 35°C ambient temperature. As ambient temperature decreases, COP increases. The exergoeconomic analysis indicates that the ratio of exergy-based thermodynamic loss to capital cost of the glycol CTES ranges from 0.00233 to 0.00225 kW $-1 at a 35°C reference environment temperature, and from 0.00235 to 0.00227 kW $-1 at a 25°C reference environment temperature. The reference environment temperature affects significantly exergy destruction and efficiency, e.g. a 10°C change in ambient temperature causes a 37.5% change in exergy efficiency. This result implies that cold energy is more valuable at higher ambient temperatures. Heat loss from the storage tank exhibits a mild dependence on ambient temperature, e.g. a 10°C increase in ambient temperature causes a heat loss increase of 7.1%. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper we deal with the effects of varying reference temperature on the exergy efficiencies of one- and two-stage crude oil distillation units. Such units essentially consist of the crude oil heating furnace, the distillation column and a network of heat exchangers. Since the exergy efficiency is a key parameter to see how well the system is performing, we undertake a study on the influence of the reference temperature on such efficiencies. In this regard, a commercial software package, SimSci/PRO II program is used for the calculations. The results show that increasing reference temperature decreases the exergy efficiency in both one- and two-stage crude oil distillation systems and also increases the difference between the exergy efficiencies of both systems. Therefore, the exergy losses increase in the crude oil distillation systems. [Copyright &y& Elsevier]

Energy and exergy analyses are investigated for cogeneration-based district energy systems. In the analyses, exergy methods, in addition to the more conventional energy analysis, are employed to evaluate overall and component efficiencies and to identify and assess thermodynamic losses. Exergy analysis provides an enhanced understanding of the characteristics of energy systems and can assist design and improvement efforts. A case study is presented to highlight the importance of district energy systems and to illustrate how exergy analysis can be efficiently and effectively applied to such systems to determine system and component efficiencies. The results should assist in the enhancement of both cogeneration-based district energy systems and simulation techniques for building energy systems. [ABSTRACT FROM AUTHOR]

In this paper we present a new model for thermodynamic analysis, in terms of exergy, of a drying process. Exergy efficiencies are derived as functions of heat and mass transfer parameters. An illustrative example is considered to verify the present model and to illustrate the applicability of the model to actual drying processes at different drying air temperatures, specific exergies of drying air, exergy differences of inlet and outlet products, product weights, moisture contents of drying air, and humidity ratios of drying air. As a result, this work is intended not only to demonstrate the usefulness of exergy analysis in thermodynamic assessments of drying processes, but also to provide insights into their performances and efficiencies. It is believed that the present model should be useful to people seeking (i) to optimize the design of drying systems and their components and (ii) to identify appropriate applications and optimal configurations for drying systems. [Copyright &y& Elsevier]

A thermodynamic analysis of the fluidized bed drying process of large particles is performed to optimize the input and output conditions. Energy and exergy models were used for the study. The effects of the hydrodynamic and thermodynamic conditions such as the inlet air temperature, the fluidization velocity and the initial moisture content on the energy efficiency and the exergy efficiency were analyzed. The analysis was carried out using two different materials, wheat and corn. It was observed that the thermodynamic efficiency of the fluidized bed dryer was the lowest at the end of the drying process in conjunction with the moisture removal rate. The inlet air temperature has a strong effect on thermodynamic efficiency for wheat, but for corn, where the diffusion coefficient depends on the temperature and the moisture content of particles, an increase in the drying air temperature did not result in an increase of the efficiency. Furthermore, the energy and exergy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the particles. A good agreement was achieved between the model predictions and the available experimental results. [Copyright &y& Elsevier]

Describes the usefulness of exergy analysis in providing insights into the behavior and performance of thermal energy storage (TES) systems. Consideration of thermodynamics in TES evaluation; Importance of temperature in TES evaluations; Status of aquifer systems, stratified storages and cold TES; Use of exergy methods in optimization and design.

Some of the more significant thermodynamic methods to improve the efficiency of coal-based electricity generation technologies are surveyed and examined, focusing on minor practical improvements that can be undertaken with limited effort and cost. Two categories of methods are examined. The first is efficiency-improvement techniques such as better maintenance and control, application of exergy and related analysis methods, and use of computer-based simulation, analysis, optimization, and design. The second category includes efficiency-improvement measures for devices, including steam generators, condensers, reheaters, and regenerative feedwater heaters. A case study is presented. It is concluded, for coal-fired electricity generation plants, that (i) many useful techniques exist (especially exergy analysis) and should be used for identifying and designing efficiency improvements, and (ii) the many possible measures to improve efficiency should be weighed against other factors and where appropriate implemented. Where larger efficiency increases are sought, improvements applicable over longer time frames and of a broader nature should be investigated. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we undertake a comprehensive study to meet the building heating/cooling and power demand through a sustainable operation. We integrated polymer electrolyte membrane fuel cell (PEMFC) system and triple effect absorption refrigeration system (TEARS) for space cooling/heating and water heating applications in buildings. The analysis is carried out to observe the effects of different operating conditions on the efficiency of the fuel cell, output of the fuel cell and TEARS, and the utilization factor of the system. It is found that the efficiency, the utilization factor, and change in temperature of hot water increases from 36% to 48.8%, 49% to 86%, and 14K to 23K, respectively when the temperature of the cell is increased for different cooling loads and membrane thicknesses. In addition, the increase in membrane thickness affected the efficiency, the utilization factor, and change in temperature of hot water in a negative way and they were found to be decreasing from 47.3% to 42%, 85% to 49%, and 23K to 12K, respectively for different cooling loads. The water supplied to the house is obtained from a geothermal water source which makes the system more sustainable. [Copyright &y& Elsevier]

Abstract: This paper examines the performance of a new Marnoch heat engine, which uses dry air and a pneumatic piston assembly to convert thermal energy to electricity. The system has unique capabilities of operating over temperature differentials less than 100 K. Unlike a common Stirling engine, the heat exchangers and piston assembly are not co-located, which is beneficial for positioning of heat exchangers in various configurations. This paper presents an operational laboratory-scale, proof-of-concept Marnoch heat engine (MHE), including its performance and power generation capabilities. It also presents a thermodynamic analysis of the system. Based on the MHE results, component modifications are made to improve its performance. The configuration has an efficiency of about thirty percent of a Carnot heat engine operating in the temperature range between 272 K and 372 K. Experimental data is acquired to provide verification of the predictive model, as well as demonstration of the MHE’s capabilities for efficient generation of electricity from waste heat sources. [Copyright &y& Elsevier]

Abstract: In this paper, a method is proposed for reforming fuels to hydrogen using solar energy at distributed locations (industrial sites, residential and commercial buildings fed with natural gas, remote settlements supplied by propane etc). In order to harness solar energy a solar concentrator is used to generate high temperature heat to reform fuels to hydrogen. A typical fuel such as natural gas, propane, methanol, or an atypical fuel such as ammonia or urea can be transported to distributed locations via gas networks or other means. The thermodynamic analysis of the process shows the general reformation reactions for NH3, CH4 and C3H8 as the input fuel by comparison through operational fuel cost and CO2 mitigation indices. Through a cost analysis, cost reduction indices show fuel-usage cost reductions of 10.5%, 22.1%, and 22.2% respectively for the reformation of ammonia, methane, and propane. CO2 mitigation indices show fuel-usage CO2 mitigations of 22.1% and 22.3% for methane and propane respectively, where ammonia reformation eliminates CO2 emission at the fuel-usage stage. The option of reforming ammonia is examined in further detail as proposed cycles for solar energy capture are considered. A mismatch of specific heats from the solar dish is observed between incoming and outgoing streams, allowing a power production system to be included for a more complete energy capture. Further investigation revealed the most advantageous system with a direct expansion turbine being considered rather than an external power cycle such as Brayton or Rankine type cycles. Also, an energy efficiency of approximately 93% is achievable within the reformation cycle. [Copyright &y& Elsevier]

Abstract: In this paper, an ammonia–water based Rankine cycle is thermodynamically analyzed for renewable-based power production, e.g. solar, geothermal, biomass, oceanic-thermal, and nuclear as well as industrial waste heat. Due to the nature of the ammonia–water mixture, changes in its concentration allow thermodynamic cycles to adapt to fluctuations in renewable energy sources, which is an important advantage with respect to other working fluids. The non-linearity of the working fluid’s behaviour imposes that each cycle must be optimized based upon several parameters. A model has been developed to optimize the thermodynamic cycle for maximum power output and carry out a parametric study. The lowest temperature state of the system is fixed, and three other parameters are variables of study, namely, maximum system temperature, ammonia concentration and energy ratio, which is a newly introduced parameter. Energy ratio indicates the relative position of the expansion state and is defined in terms of enthalpies. The study is conducted over a concentration range of 0–0.5, the maximum temperature studied varies between 75°C and 350°C for extreme cases, and the energy ratio from saturated liquid to superheated vapour. As a result, the optimal expansion energy ratio is predicted. The cycle efficiencies are drastically affected by the concentrations and temperatures. Depending on the source temperature, the cycle energy efficiency varies between 5% and 35% representing up to 65% of the Carnot limit. The optimal energy ratio has been determined for several concentrations and reported graphically. [ABSTRACT FROM AUTHOR]

In this paper, a novel industrial waste heat recovery based cogeneration is proposed for the combined production of power and refrigeration. The system is an integration of Rank me power cycle and absorption refrigeration cycle. A thermodynamic analysis through energy and exergy is employed, and a comprehensive parametric study is performed to investigate the effects of exhaust gas inlet temperature, pinch-point, and gas composition on energy efficiency, power-to-cold ratio, and exergy efficiency of the cogeneration cycle and exergy destruction in each component. The variation in specific heat with exhaust gas composition and temperature is accounted in the analysis for further discussion. The first-law efficiency decreases while power-to-cold ratio and exergy efficiency increase with increasing exhaust gas inlet temperature. The parameters, such as power-to-cold ratio and second-law efficiency, decrease while first-law efficiency increases with increasing pinch-point. Exergy efficiency significantly varies with gas composition and oxygen content of the exhaust gas. Approximating the exhaust gas as air and the air standard analysis leads to either underestimation or overestimation of cogeneration cycle peiformance on exergy point of view. Exergy analysis indicates that ,naximu,n exergy is destroyed during the steam generation process; which represents around 40% of the total exergy destruction in the overall system. The exergy destruction in each component of the system varies significantly with exhaust gas inlet temperature and pinchpoint. The present analysis contributes further information on the role of composition, exhaust gas temperature, and pinch-point influence on the performance of a waste heat recovery based cogeneration system from an exergy point of view. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the performance of a combined industrial molten carbonate fuel cell (MCFC) system, including a turbo expander, which was recently installed by Enbridge Inc. in Toronto, Canada. It entails a comprehensive thermodynamic analysis regarding energy and exergy calculations, subject to varying operating conditions. Furthermore, a simplified and novel method is used for a cost analysis to assess the amortization of the system. The results from the base case study suggest that an overall energy efficiency as high as 60% is achievable while fuel cell stack energy and exergy efficiencies of 50.6% and 49.3%, respectively, are reached. The cost analysis indicates that the amortization of the system may take up to 15 years of operational time, depending on the price of electricity and natural gas. However, carbon offsets may make a paramount contribution to the overall savings and economic viability of future combined MCFC systems. [Copyright &y& Elsevier]