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Applied Energy (03062619)
Borehole thermal energy storage systems are emerging as a promising technology for storing intermittent renewable thermal energy sources. BTES systems utilize the underground as a thermal reservoir, where heat is stored during periods of excess energy production and retrieved when needed. This enables these systems to address the challenge of matching the supply of renewable energy with the demand for heating and cooling in buildings. This approach not only enhances the efficiency of renewable energy systems but also contributes to reducing greenhouse gas emissions and reliance on fossil fuels. This study introduces a novel approach to literature analysis in the BTES field by employing bibliometric and qualitative analysis tools, including SciMAT, VOSviewer, and NVivo, providing a systematic alternative to traditional manual review methods. The goal is to identify key publications, summarize their findings, and track the evolution of research directions over time, enhancing the understanding of the field. The paper is structured into six sections. The first section provides an overview of analytical and numerical models used to simulate the performance of BTES systems. The second section discusses the differences between traditional literature review methods and those employing bibliometric and qualitative analysis tools, highlighting their respective limitations and benefits. Additionally, it compares studies that have analyzed the BTES field using traditional review methods, explaining why a literature review with bibliometric and qualitative analysis tools is necessary and what advantages they offer. The third section outlines the research structure and employs bibliometric metrics to identify significant publications in the BTES field, while the fourth section uses SciMAT, VOSViewer, and NVivo to create scientific maps and networks of keywords, documents, publication sources, and active countries, revealing major research themes and influential publications. The fifth section organizes BTES publications into seven groups, reviewing selected studies within each to highlight recent developments, while the final section evaluates the dispersion of these studies to pinpoint well-researched areas as well as areas that require further exploration within the BTES field. The study highlights a growing interest in BTES research and identifies gaps in areas such as regulatory frameworks, market status, environmental impacts, and integration with smart energy systems. It also emphasizes the need to further investigate the thermal effects of groundwater, grout, ground thermal properties, and ground temperature imbalances on BTES system performance, underscoring the importance of continued research to address challenges and advance the development of BTES systems. © 2025 Elsevier Ltd
International Journal of Hydrogen Energy (03603199)
To decrease carbon emissions in energy production systems, a new system has been introduced and investigated that utilizes solid oxide fuel cells (SOFC), a closed Bryton cycle (CBC), and a carbon dioxide capture unit (CCU). An extensive mathematical model has been created to evaluate the thermodynamic efficiency of this combined system. Findings show that the exergy efficiencies of the separate components, including SOFC and SOFC-CBC, are 39% and 79%, respectively, and the integrated system exhibits a total cost rate of 109.3 $/hr. The system is equipped with a CO2 capture unit, allowing it to efficiently separate the carbon dioxide produced during combustion and store it in a designated tank. The system is designed to effectively absorb 90% of carbon dioxide, successfully separating an impressive 221.94 kg/h. The exergy analysis of the system reveals that the afterburner has the greatest exergy destruction. Therefore, this component has the potential for system improvement from a thermodynamic perspective. Furthermore, a comprehensive study on the influence of the system's key parameters has been conducted to understand the system's performance. Maximum efficiency is realized when the SOFC functions at a temperature of 600 K with a fuel utilization ratio of 3.7. © 2025
Journal of Thermophysics and Heat Transfer (08878722) (1)
In general, for installing multilayer insulation (MLI) blankets on curved spacecraft equipment, creating a pattern that has multiple sectors is necessary because of the impossibility of establishing a single piece of MLI. The sector area of the MLI contains numerous seams and sewing. Therefore, prediction of overall performance or effective emittance is not simply possible, and they need to be tested in some experimental ways. The aim of the current research is to present a methodology for determining the conductivity between layers in both nonsewing and sewing regions of MLI to correctly estimate the effective emittance coefficient and the thermal behavior of MLI. Firstly, by conducting two experimental tests, both sewn and nonsewn square MLIs’ effective emittance coefficients are computed. In the second step, the conductive thermal coupling coefficients of nonsewing and sewing regions are determined as 1.615 and 1.95 W∕)m2 . K) respectively, utilizing experimental data. In the third step, a spherical geometry fuel tank is selected as a case study, and these coefficients are utilized in the simulation process of an MLI tank. Finally, the overall effective emittance coefficient of that tank is determined. The results indicate that the effective emittance is reduced by about 8%. © 2024 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Parvanian A.M. ,
Baniasadi, E. ,
Lalpour A. ,
Lalpour, N. ,
Abanades S. Fuel (00162361)
This study explores the enhanced efficiency of solar-driven redox reactions using ceria foams coated with Ca-doped lanthanum manganite (LCM) perovskite, focusing on sustainable fuel production. The effects of substrate pore density (10, 30 ppi) and coating thickness (3 and 6 perovskite layers) were investigated. The LCM perovskite was synthesized and uniformly coated onto porous ceria substrates, as confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dual-scale porous structure of ceria enhanced the coating's effectiveness and reactivity, with coating thicknesses ranging from 75-140 μm (three layers) to 100–400 μm (six layers). Thermogravimetric analysis (TGA) showed superior reduction extents for LCM-coated ceria samples, with O2 production up to 131 µmol/g, compared to 55 µmol/g for pure ceria. This led to a 20–40 % increase in total fuel production, with CO yields up to 141 µmol/g versus 98 µmol/g for pure ceria. Performance stability for CO2 and H2O splitting was confirmed through fifteen consecutive cycles in a high-temperature solar reactor. Solar thermochemical cycling tests showed that LCM-coated ceria foams produced up to 244 µmol/g CO, with a peak CO production rate of 6.22 mL·min-1·g-1, during reduction at 1450 °C and oxidation under pure CO2 below 900 °C. However, pure ceria exhibited faster oxidation kinetics. This research underscores the importance of material design and optimization in improving solar thermochemical processes for large-scale solar fuel production. © 2025 Elsevier Ltd
Baniasadi, E. ,
Rezk A. ,
Batista, Luciano ,
Tola, Tetenayet Bekele ,
Alaswad, Abed Energy Conversion and Management (01968904)
This study develops and optimises a renewable-driven hybrid refrigeration system to enhance food preservation in off-grid rural areas. The system integrates solar photovoltaic, solar thermal collectors, wind energy, and battery storage to provide a sustainable, cost-effective cooling solution. A comprehensive techno-economic analysis was conducted using Ethiopia as a case study to evaluate system performance, cost-effectiveness, and market feasibility. The optimised system meets 22.42 kW of thermal power demand and 2.82 kW of electrical power demand, reducing daily operational costs from $100 to $86.2. Optimisation improved system efficiency by increasing photovoltaic panels to 15, reducing battery storage from 11 to 7 units, and optimising solar collector area to 322 m2. The length of underground thermal storage piping was reduced to 1366 m, enhancing thermal efficiency. The system achieved near off-grid operation, with grid dependency reduced from 9.3 W to 3.2 W and auxiliary heater reliance below 1 % of total demand. A business model incorporating subscription-based and lease-to-buy financing supports adoption by smallholder farmers and cooperatives, with a five-year payback period. Survey results indicate that 90 % of farmers lack cooling facilities, while 48 % of cooperatives favour government incentives. The system's environmental benefits include zero on-site (operational) CO2 emissions and eco-friendly refrigerants. This research demonstrates the feasibility of hybrid renewable energy integration in sustainable cold storage, reducing post-harvest losses and enhancing food supply chains in off-grid communities. Sensitivity analysis against inter-annual resource variability and ± 20 % capital-cost dispersion confirms the robustness of the optimised configuration. © 2025 The Author(s)
Journal of Energy Storage (2352152X)
This study employs the finite line source (FLS) method, a fully analytical model, to evaluate thermal interactions, heat loss, and heat storage rates of borehole thermal energy storage (BTES) systems. The proposed model provides rapid and accurate simulations, in contrast with existing methodologies that rely on time-consuming numerical models. The model first assesses the temperature distribution within and around the boundaries of the BTES. Using the determined temperatures, Fourier's law is applied to calculate heat losses, and the principle of energy conservation is used to determine the thermal energy stored within the BTES. To account for variations in heat exchange rates among boreholes and over time, the FLS solution is superposed both spatially and temporally, and a specific load aggregation technique is employed to reduce computational cost. Further computational efficiency is achieved by approximating the error function required for the FLS solution with a Gaussian Q-function and by using hierarchical agglomerative clustering to categorize boreholes with similar temperatures and heat exchange rates. The proposed method is validated through several case scenarios of increasing complexity and compared against the publicly known duct ground storage (DST) model and simulations conducted using COMSOL software. The results demonstrate the effectiveness of the FLS method in assessing thermal interactions, heat loss, and heat storage rates of different BTES configurations with regular or irregular borehole arrangements, as well as various series-parallel connections. It is also observed that approximating the FLS solution and categorizing boreholes into groups can significantly reduce calculation time, depending on the size and complexity of the problem. An application of the proposed method is also presented, wherein the borehole spacing and length of a BTES are optimized to minimize heat losses and maximize heat storage over time. A grid independence analysis revealed that most inaccuracies of the proposed method occur during the early operational stages, particularly in the evaluation of heat storage rates. These inaccuracies can be mitigated by increasing the radial, axial, and angular segments around boreholes and refining time intervals. Alternatively, inaccuracies can be reduced by evaluating heat storage rates by subtracting heat loss rates from heat exchange rates, similar to the approach used in the DST model. © 2025
Process Safety and Environmental Protection (09575820)
In this study, four different cooling techniques with a variety type of coolant for a commercial photovoltaic-thermal collector have been simulated optically and thermally by using the discrete ordinate radiation model (DO) and compared in a hot climate. These methods include a cooling channel with lateral inlet and outlet (case II), a cooling channel with uniquely designed fins (case III), a channel with circular inlet and many elliptical outlets patterns (case IV), and a specific pattern of copper tubes containing water beneath the solar module (case V), in comparison with a standard PV module (case I). The cooling fluids utilized in this research consist of dry air, moist air with relative humidity of 20 %, 40 %, and 60 %, and water in an active cooling method. The results indicate that using fins and copper pipes reduces the temperature, respectively, by 12 °C and 23 °C, leading to 4.10 % and 7.92 % improvement in electrical efficiency, which corresponds to a power improvement of 4.12 % and 7.98 % in cases III and V. In comparison, in cases II and IV, temperature reductions were only 6.5 °C and 9 °C, respectively, leading to a smaller improvement in efficiency of 2.20 % and 4.10 % in both scenarios where no fins are present. Consequently, the shape of the inlet and outlet, along with the distribution of air inside the channel, influences the cooling performance of the solar module significantly. It is observed that in cases II, III, and IV, by increasing the relative humidity of the incoming air to 60 % with an inlet velocity of 1 m/s, the electrical efficiency improves approximately 4.21 %, 5.5 %, and 4.91 %, respectively, compared to Case I. © 2024 The Institution of Chemical Engineers
International Journal of Hydrogen Energy (03603199)
In this paper, a three-dimensional numerical model is developed for an anion exchange membrane electrolyser cell (AEMEC) with a double serpentine flow field pattern. The focus on the AEMEC is due to its benefits, including the solid membrane, inexpensive catalysts and membrane, and high stability. The effect of important operating parameters, i.e. cell temperature and cathode pressure, on the performance of the electrolyser is numerically modeled by considering different causes of performance degradation. The polarization curve, uniformity index, and the distribution of the hydrogen concentration, current density, temperature, and pressure in different operating conditions are presented. By increasing the operating temperature and decreasing the cathode pressure, the voltage of the elctrolyser decreases. Due to the higher concentration of water at the inlet of the cathode channel, more hydrogen is produced, and the current density is higher. The maximum current density and hydrogen concentrations are [Formula presented] and [Formula presented], respectively, when the operating condition is set to the temperature of 343 K, the pressure of 1 bar, and the cell voltage of 1.85 V. © 2023 Hydrogen Energy Publications LLC
Case Studies in Thermal Engineering (2214157X)
The increasing carbon footprint associated with conventional cooling methods underscores the urgent need for sustainable alternatives. This study investigates the economic and environmental advantages of various solar-thermal cooling systems, with a focus on optimizing their performance across different climate conditions. Employing a multi-objective approach, the research emphasizes exergy-economic indices to optimize selected cycles. The analysis covers multiple refrigeration technologies, including liquid absorption, solid adsorption, and solid desiccant cycles. Results indicate that the liquid absorption cycle performs optimally in hot, arid climates, reducing the payback period to approximately 8 years when optimized. In hot and humid regions, the solid desiccant cycle proves most effective due to its superior humidity control, yielding a payback period of 5.3 years. For cold and mountainous areas, the solid adsorption cycle is preferred, with a payback period of 13.5 years, while moderate and humid climates benefit from the solid desiccant cycle for both cooling and humidity regulation. The exergy-economic factors for the solar refrigeration systems across semi-arid, hot and arid, hot and humid, cold and mountainous, and moderate and humid climates are 0.758, 0.602, 0.698, 0.74, and 0.575, respectively. © 2024 The Authors
Steel production is a highly energy-intensive industry, responsible for significant greenhouse gas emissions. Electrification of this sector is challenging, making green hydrogen technology a promising alternative. This research performs a thermodynamic analysis of green hydrogen production for steel manufacturing using the direct reduction method. Four solid oxide electrolyzer (SOE) modules replace the traditional reformer to produce 2.88 kg/s of hydrogen gas, serving as a reducing agent for iron pellets to yield 30 kg/s of molten steel. These modules are powered by 37,801 photovoltaic units. Additionally, a thermal storage system utilizing 1342 tons of steel slag stores waste heat from Electric Arc Furnace (EAF) exhaust gases. This stored energy preheats iron scraps charged into the EAF, reducing energy consumption by 5 %. A life cycle assessment, conducted using open LCA software, reveals that the global warming potential (GWP) for the entire process, with a capacity of 30 kg/s, equates to 93 kg of CO2. The study also assesses other environmental impacts such as acidification potential, ozone formation, fine particle formation, and human toxicity. Results indicate that the EAF significantly contributes to global warming and fine particle formation, while the direct reduction process notably impacts ozone formation and acidification potential. © 2024 The Authors
Baniasadi, E. ,
Rezk A. ,
Tola, Yetenayet Bekele ,
Alaswad, Abed ,
Imran, Muhammad Energy Conversion and Management (01968904)
This study presents a new method for sustainable cooling systems using a hybrid refrigeration system powered by hybrid renewable energy sources. The system comprises a modular unit of vertical wind turbines integrated with bio-photovoltaic films to provide sustainable energy. The hybrid refrigeration system combines evaporative and solar thermal-driven adsorption cooling systems. In addition, a finite volume of soil is proposed for thermal energy storage. Experimental data inform the development of a digital twin for an integrated system, soil thermophysical characteristics, wind turbine performance, and technical specifications for other system components. This sustainable cooling package is cost-effective and space-efficient, particularly in remote or off-grid locations. Notably, the evaporative cooler and chilled water coil contribute to a cooling effect of 20.4 kW, and solar power generation reaches 12.38 kW at an intensity of 1053 W/m2. The annual electrical output averages 1.7 kW at a wind speed of 3.5 m/s. Under best conditions, wind power can surge to 7.99 kW at 9.88 m/s. The ratio of power generated by wind to solar energy ranges from 1.1 to 1.3. The system effectively meets a peak thermal energy demand of approximately 74 GJ/month, facilitated by solar collectors, underground thermal storage, and a renewable energy-fed auxiliary heater. This study paves the way for future techno-economic optimisation and advancements in sustainable energy solutions for remote cold storage facilities. © 2024 The Author(s)
International Journal of Hydrogen Energy (03603199)
Due to the widespread use of multi-generation systems utilizing renewable energy sources and the growing global demand for such systems from both economic and environmental considerations, numerous researchers have focused on the design and evaluation of their performance. To this end, this research presents a biomass-based multi-generation system with an innovative and practical design that can generate electricity, heat, and hydrogen. This system includes a modified gas turbine cycle, a supercritical CO2 (SCO2) cycle, a transcritical CO2 (TCO2) cycle, a proton exchange membrane (PEM) electrolyzer, and a PEM fuel cell unit. This study aims to evaluate the impact of various biomass sources (paper, wood, paddy husk, and municipal solid waste) on the system performance. The proposed system has been analyzed using the first and second laws of thermodynamics. This system uses the maximum capacity to produce power, heat and hydrogen. A fuel cell unit has been used to consume hydrogen and generate more electricity. In the basic mode, the system has energy and exergy efficiencies of 47.89% and 32.26%, respectively, and can produce 2.74 kg/h of hydrogen. The biomass fuel consumption rate within the system is 0.055 kg/s. The overall exergy destruction of the system amounts to 1240 kW, with the biomass boiler and the condenser being the components that experience the greatest exergy destruction, registering values of 535.5 kW and 432.3 kW, respectively. Notably, employing municipal waste as biomass increases the system's exergy efficiency to 33.16%. © 2024
Applied Thermal Engineering (13594311)
In this paper, the performance of solar-thermal cooling systems for air conditioning application is investigated in different climates of Iran. Diverse climate types are considered which makes the results applicable to other countries. Available commercial refrigeration cycles that are capable of integration with solar-thermal collector systems including the closed liquid absorption cycle, closed solid adsorption cycle, and desiccant cycle are studied. First, a solar and climatic map is proposed and the representative cities have been selected for each climate. Then, the climate parameters related to each region are extracted to create an hourly database. Also, the cooling load of a reference building is modeled based on the climate database, each refrigeration cycle is simulated using thermodynamic equations, and the dynamic model is generalized daily for the hot season in each city. In the last step, each cooling system is examined using an exergy-economic analysis, and technical and economic indicators are compared. The results show that the most suitable solar-thermal refrigeration cycle that can be installed in the central plateau and semi-arid areas of Iran is the closed-cycle liquid absorption system. The annual average exergy-economic factor and the annual solar fraction in this cycle are 0.7578 and 0.57, respectively. In the southern coastal areas, due to the high humidity and air temperature in summer, the solid desiccant refrigeration system with an exergy-economic factor of 0.6978 and a solar fraction of 0.2416 is preferred. The suitable solar-thermal refrigeration cycle in the cold and mountainous regions of Iran is a solid adsorption system with a silica gel absorber. The annual solar fraction and average annual exergy-economic factor in this cycle are 0.5158 and 0.7394. Also, in northern moderate regions, the solid adsorption refrigeration system with an average annual exergy-economic factor of 0.409 and average exergy efficiency of 0.12 is comparatively beneficial. © 2023 Elsevier Ltd
Applied Energy (03062619)
An external membrane humidifier (MH) is widely used to control humidity and temperature in a polymer electrolyte membrane (PEM) fuel cell. The arrangement of flow channels highly affects the performance of the humidifier. Although the modified arrangement of flow channels in MHs affects the enhancement of heat and mass transfer, the pressure drop inside the channels also changes by varying the arrangement of flow channels. Therefore, by defining the performance evaluation criteria (PEC), the simultaneous impacts of heat and mass transfer along with pressure drop can be examined. Larger PEC indicates higher heat and moisture transfer rates with lower pressure drop, i.e. higher performance. In this study, three MHs with finned channels, serpentine channels, and simple parallel ones are fabricated and tested to compare their performance based on dew point approach temperature (DPAT), water recovery ratio (WRR), and PEC. The results demonstrate that the PEC of finned-channel and serpentine-channel MHs is greater than 1 for all flow rates on the WS and DS, indicating the improved performance of both MHs. At low flow rates of WS and DS, the PEC of the serpentine-channel MH is much larger than that of the finned-channel MH. By enhancing the flow rate, the PEC of these two MHs approaches each other. At high flow rates of WS and DS, the pressure drop of the serpentine-channel MH is much larger than that of the finned-channel one. The pressure drops of these two MHs approach each other by decreasing the flow rate. Therefore, it is better to use the serpentine flow arrangement at low flow rates and to utilize the finned-channel configuration at high flow rates. © 2023 Elsevier Ltd
Green Energy and Resources (29497205) (4)
Energy storage is a crucial solution for the intermittency and instability of renewable energy. Carnot batteries, a novel electrical energy storage technology, promise to address the challenges of renewable electrical energy storage worldwide. Rankine-based Carnot batteries, which are geographically unconstrained and effectively store energy at low temperatures, have attracted considerable attention in recent years. In this study, a mathematical model was developed, and a multi-objective optimization with power-to-power-efficiency, exergy efficiency, and levelized cost of storage was performed. Moreover, the investment cost and exergy loss of the optimized system components were investigated in detail and analyzed. The results showed that the optimal power-to-power-efficiency, exergy efficiency, and levelized cost of the storage system can be achieved at 60.3%, 33%, and 0.373 $/kWh based on single-objective optimization, and the operating parameters of the proposed system are different. Therefore, there is a strong trade-off relationship between the three objective functions mentioned above. Under the same weighting for the two approaches, they are 25.8%, 23%, and 0.437 $/kWh, and 39.3%, 29.1%, and 0.549 $/kWh, respectively. Furthermore, this study observed that the exergy destruction in the charge mode was nearly 95 kW larger than that in the discharge mode, and the exergy destruction of the throttle valve was the largest at 95.83 kW, accounting for 28.32%. The expander was the component with the highest cost (35.84% of the total cost) in the proposed system, followed by the compressor. © 2023 The Author(s)
Applied Thermal Engineering (13594311)
This study proposes a serpentine flow field to enhance the performance of a membrane-based water and heat exchanger (MWHE) to employ in polymer electrolyte membrane fuel cells. Two MWHEs (serpentine and parallel-flow channels) are numerically simulated and compared in terms of water vapor transmission rate (WVTR), water recovery ratio (WRR), temperature and dew point at the outlet of the dry side, and the dew point approach temperature (DPAT). For all mass flow rates at the dry and wet inlets, the outlet temperature of the dry side and the dew point at the dry side outlet of the MWHE with serpentine channels are higher compared to the one with parallel channels. Using serpentine channels, compared to simple parallel channels, the WRR is enhanced by 8.5 % to 20 % and the DPAT is diminished by 4 % to 13.6 % for a range of mass flow rates on the wet side. At higher wet-side flow rates, the use of serpentine arrangement has a more significant influence on WRR and DPAT. In both MWHEs, an increase in the dry side mass flow rate leads to a reduction in heat and water transfer rates and an increment in the wet side mass flow rate, resulting in a reduction in the DPAT and WRR. Enhancing the operating pressure has a negative impact on the performance of the MWHE. By changing the operating pressure from 100 to 150 kPa, WRR is reduced by 18.1 % and DPAT is enhanced by 10.2 %. © 2022 Elsevier Ltd
International Journal of Hydrogen Energy (03603199) (62)
Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively. © 2022 Hydrogen Energy Publications LLC
International Journal of Hydrogen Energy (03603199) (95)
In this paper, the electrochemical performance and temperature distribution of a polymer electrolyte membrane water electrolyzer (PEMWE) are studied using a numerical model. The effect of three important parameters including operating pressure, operating temperature, and thickness of the membrane on the thermal and electrochemical performance of the electrolyzer are investigated. The results of numerical modeling are verified against experimental data. Higher temperature is observed over the anode because the exothermic process at the anode is dominant in PEMWE. By increasing the operating temperature and decreasing the operating pressure, the temperature distribution is more uniform and the performance of the electrolyzer improves. By increasing temperature from 333 K to 353 K, the mean temperature difference decreases by 4.5%. In addition, by increasing membrane thickness from 127μm to 254μm, the mean temperature difference of the electrolyzer cell increases by 0.18 K, and the voltage of the electrolyzer increases by about 3.63%. © 2022 Hydrogen Energy Publications LLC
International Journal of Hydrogen Energy (03603199) (47)
This paper investigates the performance of a hydrogen refueling system that consists of a polymer electrolyte membrane electrolyzer integrated with photovoltaic arrays, and an electrochemical compressor to increase the hydrogen pressure. The energetic and exergetic performance of the hydrogen refueling station is analyzed at different working conditions. The exergy cost of hydrogen production is studied in three different case scenarios; that consist of i) off-grid station with the photovoltaic system and a battery bank to supply the required electric power, ii) on-grid station but the required power is supplied by the electric grid only when solar energy is not available and iii) on-grid station without energy storage. The efficiency of the station significantly increases when the electric grid empowers the system. The maximum energy and exergy efficiencies of the photovoltaic system at solar irradiation of 850 W m-2 are 13.57% and 14.51%, respectively. The exergy cost of hydrogen production in the on-grid station with energy storage is almost 30% higher than the off-grid station. Moreover, the exergy cost of hydrogen in the on-grid station without energy storage is almost 4 times higher than the off-grid station and the energy and exergy efficiencies are considerably higher. © 2021 Hydrogen Energy Publications LLC
International Journal of Energy Research (0363907X) (7)
Fluid flow manifold plays a significant role in the performance of a fuel cell stack because it affects the pressure drop, reactants distribution uniformity and flow losses, significantly. In this study, the flow distribution and the pressure drop in the gas channels including the inlet and outlet manifolds, with U- and Z-type arrangements, of a 10-cell PEM fuel cell stack are analyzed at anode and cathode sides and the effects of inlet reactant stoichiometry and manifold hydraulic diameter on the pressure drop are investigated. Furthermore, the effect of relative humidity of oxidants on the pressure drop of cathode are investigated. The results indicate that increase of the manifold hydraulic diameter leads to decrease of the pressure drop and a more uniform flow distribution at the cathode side when air is used as oxidant while utilization of humidified oxidant results in increase of pressure drop. It is demonstrated that for the inlet stoichiometry of 2 and U type manifold arrangement when the relative humidity increases from 25% to 75%, the pressure drop increases by 60.12% and 116.14% for oxygen and air, respectively. It is concluded that there is not a significant difference in pressure drop of U- and Z-type arrangements when oxygen is used as oxidant. When air is used as oxidant, the effect of manifold type arrangement is more significant than other cases, and increase of the stoichiometry ratio from 1.25 to 2.5 leads to increase of pressure drop by 527.3%. © 2020 John Wiley & Sons Ltd
Journal of Energy Storage (2352152X)
This paper investigates a single cell proton exchange membrane based electrochemical hydrogen compressor for hydrogen storage purposes. This work applies a three-dimensional numerical model based on single-domain method in order to simulate the thermal and electrochemical kinetics of the electrochemical cell. The design parameters including operating temperature, pressure, the thickness and porosity of the gas diffusion layer, and channel dimension affect the electrochemical hydrogen compression cell performance. The results show that the performance of the cell improves by increasing the operating temperature at high current density, but it has a negligible effect within the activation region. Increase of pressure from 1 bar to 20 bar at the current density of 5000 A m−2 reduces the overall cell voltage by almost 24% and the cell performance deteriorates. The results indicate that increase of gas diffusion layer thickness from 0.2 to 0.5 mm has a negative effect on the performance of electrochemical cell. Moreover, a comparison between different gas diffusion layer porosities shows no significant effect on the polarization curve due to the high permeability of hydrogen. Furthermore, the required voltage will be grown in the range of 87.84 -70.61 mV by varying the channel rib in the range of 0.5 -1 mm. © 2020 Elsevier Ltd
International Journal of Hydrogen Energy (03603199) (60)
Electrochemical hydrogen compression (EHC) is a promising alternative to conventional compressors for hydrogen storage at high pressure, because it has a simple structure, low cost of hydrogen delivery, and high efficiency. In this study, the performance of an EHC is evaluated using a three-dimensional numerical model and finite volume method. The results of numerical analysis for a single cell of EHC are extended to a full stack of EHC. In addition, exergy and exergoeconomic analyses are carried out based on the numerical data. The effects of operating temperature, pressure, and gas diffusion layer (GDL) thickness on the energy and exergy efficiencies and the exergy cost of hydrogen are examined. The motivation of this study is to examine the performance of the EHC at different working conditions and also to determine the exergy cost of hydrogen. The results reveal that the energy and exergy efficiency of EHC stack improve by almost 3.1% when operating temperature increases from 363 K to 393 K and the exergy cost of hydrogen decreases by 0.5% at current density of 5000 A m−2. It is concluded that energy and exergy efficiency of EHC stack decrease by 25% and 5.4% when the cathode pressure increases from 1 bar to 30 bar, respectively. Moreover, it is realized that the GDL thickness has a considerable effect on the EHC performance. The exergy cost of hydrogen decreases by 53% when the GDL thickness decreases from 0.5 mm to 0.2 mm at current density of 5000 A m−2. © 2020 Hydrogen Energy Publications LLC
International Journal of Hydrogen Energy (03603199) (14)
Anodic fuel recirculation system has a significant role on the parasitic power of proton exchange membrane fuel cell (PEMFC). In this paper, different fuel supply systems for a PEMFC including a mechanical compressor, an ejector and an electrochemical pump are evaluated. Furthermore, the performances of ejector and electrochemical pump are studied at different operating conditions including operating temperature of 333 K–353 K, operating pressure of 2 bar–4 bar, relative humidity of 20%–100%, stack cells number from 150 to 400 and PEMFC active area of 0.03 m 2 –0.1 m 2 . The results reveal that higher temperature of PEMFC leads to lower power consumption of the electrochemical pump, because activation over-potential of electrochemical pump decreases at higher temperatures. Moreover, higher operating temperature and pressure of PEMFC leads to higher stoichiometric ratio and hydrogen recirculation ratio because the motive flow energy in ejector enhances. In addition, the recirculation ratio and hydrogen stoichiometric ratio increase, almost linearly, with increase of anodic relative humidity. Utilization of mechanical compressor leads to lower system efficiency than other fuel recirculating devices due to more power consumption. Utilization of electrochemical pump in anodic recirculation system is a promising alternative to ejector due to lower noise level, better controllability and wide range of operating conditions. © 2019 Hydrogen Energy Publications LLC
Journal of Energy Storage (2352152X)
Phase Change Materials (PCM) have been widely used in different applications. PCM is recognized as one of the most promising materials to store solar thermal energy in the form of latent heat. Utilization of PCMs for solar energy storage compensates for the intermittent characteristic of this energy source. Mathematical modeling and numerical simulation of solar energy storage systems provide useful information for researchers to design and perform experiments with a considerable saving in time and investment. This paper is focused on modeling and simulation of PCM based systems that are used in different solar energy storage applications. A thorough literature review is performed to investigate and compare the results and accuracy of different mathematical models, numerical methods and thermodynamic analysis of using different PCMs in different solar systems. Moreover, the potential research areas in numerical simulations and thermodynamic analysis of solar systems based on PCMs are determined considering the existing gaps in the literature. Although the main idea of using PCMs is storing thermal energy for different applications, PCMs can be used for other purposes such as cooling photovoltaic panels. Past studies have shown that utilization of PCMs in photovoltaic panels can improve the performance of panels by decreasing the average panel temperature by 9.7%. The results of simulations also showed that for each climate a specific PCM with a melting temperature should be used to reach the most uniform temperature distribution. © 2018 Elsevier Ltd
International Journal of Exergy (17428297) (1)
In this paper, energy, exergy and exergoeconomic analyses of a solar absorption refrigeration cycle with energy storage are conducted. In this cycle, nanofluid is used as the heat transfer fluid (HTF) in a flat plate collector to improve the performance of the cycle. Based on the results of the analyses, the type of nanofluid and working conditions that lead to lower cost of cooling effect and higher COP and exergy efficiency of the cycle are found. The results show that utilisation of CuO and Al2O3 nanofluids with 5% volume fraction increases the COP of the solar cycle by 17.98% and 14.51%, respectively, whereas the exergy-based cost rate of cooling decreases by 10.25% and 5.48%, respectively. Utilisation of the CuO nanofluid as the HTF is found to be more favourable for improving the performance of the cycle and decreasing the exergy-based cost of cooling. © 2019 Inderscience Enterprises Ltd.
Applied Thermal Engineering (13594311)
Cold energy storage during the off-peak hours to supply the cooling demand during the peak hours leads to reduction of the chiller size and energy expenses. In this paper, the performance of an ice bank system based on spherical capsules is experimentally analyzed and the effects of different parameters are investigated using a numerical model. The numerical simulation is performed for optimum design of the energy storage system and the results of numerical simulation are validated against the experimental data. Moreover, temperature distribution inside the ice bank is evaluated, experimentally and numerically, and heat transfer rate from the spherical capsules wall and the liquid fraction inside these spherical capsules are determined using numerical simulations during the charge and discharge processes. The results indicate that utilization of two inlets for heat transfer fluid (HTF) leads to decrease of charging time by 11 min and increase of the efficiency by 37%. Moreover, the best efficiency during the charge and discharge modes are 77% and 51% using 0.04 kg/s mass flow rate, respectively. Furthermore, the results showed that when the capacity of the system increases by increase of spherical capsules from 60 to 120, the system efficiency during the charge and discharge processes increase by 26% and 23%, respectively. © 2018 Elsevier Ltd
Mesforoush H. ,
Pakmanesh, M.R. ,
Esfandiary, H. ,
Asghari, S. ,
Baniasadi, E. Cryogenics (00112275)
Multi-layer insulation (MLI) blankets are one of the main components of satellite thermal control system. The past studies have considered infinite heat transfer coefficient in modeling the MLI shields due to the use of reflective thin films such as aluminized Kapton (Polyimide Film Developed by DuPont Company) or aluminized PET (Polyethylene Terephthalate) in MLI shields. Therefore, equal temperature was considered on two sides of a shield and the effect of thermal resistance has been ignored in the total thermal resistance. In the present study, the effects of thermal conductivity of thin film and shield thickness are analyzed. For this purpose, numerical analyses are performed on three types of blankets that are made of Kapton, PET and null shields. The results indicate that the difference in effective emittance of Kapton and PET blanket is 17% to 2% from the thinnest film to the thickest film, respectively. In order to confirm the numerical results, the effective emittance of two types of MLI blankets made of Kapton and PET films is measured under identical conditions. It is concluded that the Kapton blanket has lower effective emittance than PET. © 2019 Elsevier Ltd
Energy Conversion and Management (01968904)
Absorption chiller systems are advantageous to vapor compression cooling systems due to capability of utilizing low-grade heat sources such as waste heat from industries, renewable energies, and generated heat by fuel cell. The main issue in absorption cooling system is the low cycle coefficient of performance (COP) that can be addressed by integrated ejector-absorption cooling systems. In this study, an integrated system of proton exchange membrane (PEM) fuel cell that thermally drives an ejector-absorption refrigeration cycle is proposed. The effects of generator temperature, condenser pressure, evaporator pressure, and inlet fuel mass flow rate to the fuel cell on the ejector entrainment ratio (ϕ) and COP are evaluated. Moreover, the performance of the integrated system is evaluated at different geometrical and operating conditions of PEM fuel cell. The results reveal that the ϕ and COP parameters increase up to 18.51% and 48% by increasing the generator temperature from 70 °C to 100 °C, respectively. At higher inlet mass flow rate of fuel to the reformer, the cooling capacity and the system COP improve. Furthermore, the maximum value of ϕ and COP are 0.39 and 0.77, respectively, at the best operating condition of the PEM fuel cell, i.e. the current density of 0.75 A/cm2. It is also concluded that the system overall energy efficiency at temperature of 80 °C and the current density of 0.5, 0.6, 0.75, and 0.85 A/cm2 are 43%, 39%, 35%, 32%, and 37%, respectively. Moreover, the COP of absorption chiller with ejector at the operating pressure of 1 bar and the temperature of 80 °C for PEM fuel cell is 6.7% higher than conventional absorption chiller. © 2019 Elsevier Ltd
Journal Of Thermal Analysis And Calorimetry (13886150) (3)
The performance of a proton exchange membrane electrolyzer cell directly depends on the arrangement of flow field in bipolar plates (BPs). The design of flow field in BPs should be in a way that a uniform distribution of flow is achieved; in this regard, a three-dimensional model of a new flow field arrangement with a cross section of 64 cm2 is proposed and the distribution of current density, temperature, and pressure drop is investigated. A numerical model is carried out at the steady-state, single-phase, and non-isothermal condition based on finite volume control method. The continuity, momentum, species, energy and electric charge balance equations together with electrochemical kinetics relations in different regions of PEM electrolyzer are solved in a single-domain model. The results of numerical model are compared against experimental data, and an acceptable agreement is observed at low and medium currents densities. The results reveal that the spiral flow field yields a uniform distribution of produced hydrogen and current density. Moreover, the proposed flow field design leads to a uniform distribution of temperature through the channel path. The availability of water and current density at vertical paths of the flow field are higher. © 2018, Akadémiai Kiadó, Budapest, Hungary.
Electrochimica Acta (00134686)
The arrangement of flow field in a proton exchange membrane electrolyzer cell (PEMEC) plays a significant role on distribution of reactants over the active area of electro-catalyst and transfer of products toward the outlet of PEMEC. In this paper, the performance of a PEMEC with metal foam as flow distributer is investigated and compared with two common flow fields. A numerical analysis is conducted based on a three-dimensional model of an electrolyzer with parallel pattern flow field (model A), double path serpentine flow field (model B), parallel flow field and metal foam as a flow distributor (model C), and a simple channel that is filled with metal foam (model D). The performance of four different models are compared to each other in terms of current density, temperature, hydrogen mass fraction and pressure drop distribution. The current density for model A, model B, model C, and model D at voltage of 1.55 V are 0.3, 0.41, 0.43 and 0.44 A/cm2, respectively. The results indicate that model D has the best performance in comparison with other models in terms of pressure drop and uniformity of hydrogen mass fraction and temperature. There is no significant difference between models B, C, and D in terms of current density, but the pressure drop in the model B, model C and model D are 736, 9.72, and 4.917 kPa, respectively. It is concluded that utilization of metal foams has advantages such as high electrical conductivity and low weight, and an appropriate foam permeability should be selected to optimize the pressure drop. © 2018 Elsevier Ltd
International Journal of Hydrogen Energy (03603199) (42)
Hydrogen recirculation loop in the fuel supply system of a proton exchange membrane (PEM) fuel cell increases the fuel consumption efficiency and maintains moisture within the cell. Conventional recirculation systems utilize mechanical compressors with high power consumption or ejectors that are sensitive to any deviation from the optimum operating conditions. In this paper, an electrochemical pump is analyzed in the hydrogen recirculation loop of a PEM fuel cell and it is compared with two conventional systems, i.e. ejector and mechanical compressor, in terms of system efficiency. The results reveal that the efficiency of the integrated system with a mechanical compressor is lower than two other systems at any working current density due to higher power consumption. Moreover, the efficiency of hydrogen recirculation system with electrochemical pump is close to the system with ejector at low current density. However, at high current density, efficiency of ejector is relatively higher than electrochemical pump because PEM fuel cell has higher parasitic power that can be compensated using ejector in the anodic recirculation system. © 2018 Hydrogen Energy Publications LLC
International Journal of Hydrogen Energy (03603199) (11)
This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants. © 2017 Hydrogen Energy Publications LLC
Electrochimica Acta (00134686)
This paper presents a comparison between five flow field patterns including parallel, single path serpentine (1-path), dual path serpentine (2-path), triple path serpentine (3-path) and quadruple path serpentine (4-path) with 25 cm2 active area to identify the pattern with the best performance in terms of distribution of molar fraction of produced hydrogen, current density, temperature and pressure drop. This is a three-dimensional (3-D) numerical analysis for different flow fields based on finite volume method at steady state, single phase and non-isothermal conditions. The results of the numerical analysis are in good agreement with experimental data. The results reveal that serpentine flow field provides better distribution of current density and temperature in comparison with parallel configuration. At voltage of 1.6 V, the current density for 1-path, 2-path, 3-path, and 4-path patterns are almost 0.28, 0.19, 0.13, and 0.10 A/cm2 higher than parallel pattern, respectively. Also, for 1-path, 2-path, 3-path, and 4-path patterns, the hydrogen mole fraction at outlet of anode channel are 0.0034, 0.0028, 0.0023 and 0.0021, respectively. The results indicate that the 2-path pattern is relatively advantageous in terms of pressure drop, distribution of current density and hydrogen molar fraction. © 2018 Elsevier Ltd
International Journal of Hydrogen Energy (03603199) (9)
In this study, the effect of clamping pressure on the performance of a proton exchange membrane fuel cell (PEMFC) is investigated for three different widths of channel. The deformation of gas diffusion layer (GDL) due to clamping pressure is modeled using a finite element method, and the results are applied as inputs to a CFD model. The CFD analysis is based on finite volume method in non-isothermal condition. Also, a comparison is made between three cases to identify the geometry that has the best performance. The distribution of temperature, current density and mole fraction of oxygen are investigated for the geometry with best performance. The results reveal that by decreasing the width of channel, the performance of PEMFC improves due to increase of flow velocity. Also, it is found that intrusion of GDL into the gas flow channel due to assembly pressure deteriorates the PEMFC performance, while decrease of GDL thickness and GDL porosity have smaller effects. It is shown that assembly pressure has a minor effect on temperature profile in the membrane-catalyst interface at cathode side. Also, assembly pressure has a significant effect on ohmic and concentration losses of PEMFC at high current densities. © 2018 Hydrogen Energy Publications LLC
In this paper, detailed effects of operating conditions and design parameters including temperature, pressure, gas diffusion layer (GDL) thickness, membrane thickness and GDL porosity on the performance of a high temperature proton exchange membrane electrolyzer cell (PEMEC) are studied. A CFD analysis is carried out using a finite volume method based on a fully three-dimensional model. The model is verified against experimental data and the realistic effects of varying operating conditions are considered. The results indicate that decrease of operating temperature from 403 K to 373 K results in reduction of hydrogen concentration at the membrane-catalyst interface from 2.2 × 10−4 to 1.9 × 10−4 mol/m3. The temperature and hydrogen concentration under rib area of channel are relatively higher due to the accumulation of water under this area that leads to higher electrochemical rate. An increase of GDL thickness from 0.2 mm to 0.5 mm at a voltage of 1.65 V leads to reduction of current density from 0.426 A/cm2 to 0.409 A/cm2. The porosity of the GDL has no significant effect on the polarization curve. The current density of the PEMEC for a membrane thickness of 50μm at voltage of 1.6 V is 48% higher than a membrane thickness of 200μm. © 2018 Elsevier Ltd
Renewable Energy (09601481)
This paper presents a novel process for high efficiency production of hydrogen and desalination of brine water based on the concept of solar spectrum splitting. The advantage of this system is concurrent production of hydrogen and distilled water using a sustainable process at large scale. The harvested energy from the separated solar spectral bands is used to supply the required energy for high temperature steam electrolysis and a double-stage flash distillation system. The integrated solar system is designed to reduce the energy conversion deficiencies, considerably. In order to investigate the performance of this system, a process simulation code is developed. An exergy analysis is conducted and the economic feasibility of the plant is evaluated. The sensitivity of the integrated cycle performance on solar insolation, electrolyzer temperature, and pressure is analyzed, and the results indicate that utilization of concentrator cells, with a multi-band gap mirror can increase the productivity of the cycle, drastically. It is observed that hydrogen and distilled water production rate can be increased by more than 1.6 times, when the harvested solar power increases from 28 MW to 55 MW. It is concluded that the maximum energy and exergy efficiencies of the integrated solar cycle is about 45%. © 2016 Elsevier Ltd
International Gas Research Conference Proceedings (07365721)
The energy consumption, investment cost and operation cost of natural gas transmission pipelines can be optimized using the novel fabrication methods of producing higher strength and lower weight raw materials. Utilization of methods for producing steel with fine-grained structure to improve the weldability and formability characteristics of pipe material and to decrease the pipe thickness can lead to considerable saving in pipeline capital investment. An optimum design of transmission and distribution pipelines is investigated from the technical and economic aspects. The optimization method is presented to minimize the lifetime cost of natural gas transmission pipelines. All design parameters including thickness, grade, flow rate and working pressure are considered. The objective function is the total lifetime cost of a gas transmission system that includes investment and operation costs. All the technical and economic constraints are modeled as a mathematical function using a programming language. Optimization results is highly sensitive to pipeline class location and construction standards.
International Journal of Hydrogen Energy (03603199) (8)
In this study, the performance of a novel micro-combined heat and power generation system (mCHP) based on PEM fuel cell is analyzed from exergoeconomic aspect of view. The main components of the system are a 10 kW PEM fuel cell stack, a thermal energy storage tank based on phase change material, an absorption chiller, and a steam reformer that operates using natural gas. The main objective of this study is to perform an exergoeconomic evaluation on a PEM fuel cell system integrated with absorption chiller, which is designed to supply electrical energy, hot water and space cooling for a residential application. The effects of working temperature, pressure, current density, and heat source temperature of generator on the performance of the system are studied. The results reveal that besides operating pressure and temperature, fuel cell voltage can significantly affects the exergy cost of the system. It is concluded that by increasing the heat source temperature, the exergy cost of chilled water decreases and the COP of absorption chiller can be increased by more than 30%. Also, it is found that the PEM fuel cell, storage tank, and evaporator have the highest exergy destruction cost rates, respectively. © 2016 Hydrogen Energy Publications LLC
Renewable Energy (09601481)
In this study, the performance of a forced convection mixed-mode solar dryer with thermal energy storage is experimentally analyzed. The main goal was to develop an efficient and cost effective dryer that maintains drying process after sunset. The dryer mainly consists of a solar collector/absorber, drying chamber and a fan. A photovoltaic panel and battery storage are also integrated with the dryer to supply the required electrical energy. The experiments are carried out to dry fresh apricot slices at different working conditions. The effect of using phase change material to store thermal energy during daytime is analyzed. It is concluded that the performance of the solar collector is improved and the drying process is effectively extended when solar energy was not available. It is also observed that the rate of drying is almost constant along the drying chamber. The moisture pick-up efficiency and the overall thermal efficiency of the dryer are about 10% and 11%, respectively. © 2017 Elsevier Ltd
Energy Conversion and Management (01968904)
In this paper, the performance of an integrated Rankine power cycle with parabolic trough solar system and a thermal storage system is simulated based on four different nano-fluids in the solar collector system, namely CuO, SiO2, TiO2 and Al2O3. The effects of solar intensity, dead state temperature, and volume fraction of different nano-particles on the performance of the integrated cycle are studied using second law of thermodynamics. Also, the genetic algorithm is applied to optimize the net output power of the solar Rankine cycle. The solar thermal energy is stored in a two-tank system to improve the overall performance of the system when sunlight is not available. The concept of Finite Time Thermodynamics is applied for analyzing the performance of the solar collector and thermal energy storage system. This study reveals that by increasing the volume fraction of nano-particles, the exergy efficiency of the system increases. At higher dead state temperatures, the overall exergy efficiency is increased, and higher solar irradiation leads to considerable increase of the output power of the system. It is shown that among the selected nano-fluids, CuO/oil has the best performance from exergy perspective. © 2016 Elsevier Ltd. All rights reserved.
In this paper a scale-up analysis of a dual cell photo reactor based on a kinetic, radiation model and mass balance of reactants is presented. A kinetic model that includes phenomenological based parameters is developed to evaluate the reaction rate under operational conditions of a photo-reactor. The analysis is performed for six different scale-up ratios with three different constraints for each case. With a constraint of pre-determined length to diameter ratio factor, a lower enhancement in productivity can be achieved at higher light intensities. The analysis is followed by an exergoeconomic study in which two case scenarios of a hydrogen production plant with and without oxygen production for three different production capacities are considered. It reveals the maximum hydrogen exergy price of 2.2, 0.88, and 0.51kg-1 for production capacities of 1, 100, and 2000tonday-1, respectively. © 2014 Elsevier Ltd.
Engineering Applications of Computational Fluid Mechanics (19942060) (1)
In this paper, a CFD study of two types of axial-flow automotive cooling fans was conducted to investigate the effects of upstream and downstream blockage on aerodynamic performance of each fan. The realizable k-ε turbulence model was applied and simulations were performed to represent an automotive engine bay and quantify performance changes as a function of blockage distance. Modeling was performed for two fan designs: one optimized for a low flow rate, high-pressure operation; and a second optimized for high flow rate, low-pressure operation. The results show that the pressure loss caused by engine blockage increases at higher vehicle speed, and decreasing blockage distance. A new relation between blockage to fan proximity and fan performance was established. It is determined that the pressure change follows a quadratic type dependence, but the coefficients may vary, depending on fan type. The fan efficiency can be improved by taking advantage of larger blockage distances at higher speeds of the vehicle. The blockage condition causes an increase in the reverse flow near the fan interface, and a dramatic increase in radial flow. © 2013 Taylor and Francis Group LLC.
International Journal of Hydrogen Energy (03603199) (6)
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 © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Applied Catalysis A: General (0926860X)
In this paper, an experimental study of photo-catalytic water splitting with cadmium sulfide and zinc sulfide photo-catalysts is performed in a dual-cell reactor to investigate the effects of radiation intensity and photo-catalyst concentration on hydrogen and oxygen production rates. Hybridization of the photo-catalytic process is examined with multi catalysts and electric potential bias to enhance the productivity of the reactor and sustain the reaction rate. The hydrogen production of 0.41 mmol h-1 with 0.75% (v/v) ZnS is improved by almost 2 times higher than past studies due to illumination of 0.2% (v/v) CdS under 1 sun in a hybrid reactor. The productivity of the reactor is significantly enhanced at light intensities more than 1000 W m-2. The cadmium sulfide catalyst is found to be an inefficient absorbent of light energy, but it shows higher energy and exergy efficiencies compared with ZnS photo-catalysts in a light-driven water splitting process. © 2013 Elsevier B.V. All rights reserved.
International Journal of Hydrogen Energy (03603199) (22)
In this paper, an experimental study is performed for hydrogen and oxygen production by new photo-catalytic and electro-catalytic water splitting systems. An effective method for hydrogen production by solar energy without consumption of additional reactants is a hybrid system which combines photo-chemical and electro-catalytic reactions. Experiments are performed in batch and dual cell quasi-steady operation with different light intensities and zinc sulfide photo-catalyst concentrations. The photo-reactor in batch operation achieves 6 mL h-1 of hydrogen production with 3% w/v of catalyst. The hydrogen production rate corresponds to a quantum efficiency of 75% as measured through illumination of zinc sulfide suspensions in a dual cell reactor. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
International Journal of Hydrogen Energy (03603199) (14)
This paper examines the oxygen evolving reaction of water splitting under practical conditions which simulate those encountered in photo-initiated or electrochemical water oxidation processes. Most of the over-potentials are due to electrochemical processes at the anode, where oxygen evolution occurs. This paper investigates the oxygen evolving half cells for different complete systems including photoelectrochemical, photo-catalytic and electro-catalytic water splitting. An electrochemical model is developed to evaluate the over-potential losses in the oxygen evolving reaction and the effects of key parameters are analyzed. The transient diffusion of hydroxide ions through the membrane and bulk electrolyte are modeled and simulated for improved system operation. The results of the thermodynamic and electrochemical analyses show that for each water splitting configuration, there are optimal values of the operating parameters such as electrolyte concentration, current density, and membrane-electrode distance. The operating criteria of key parameters and the optimal working region of the oxygen evolving reactor are examined for assessment and optimization of a complete water splitting system. The analysis of the oxygen evolving reaction is performed for three variations of ruthenium based supramolecular complexes and molybdenum-oxo catalysts for catalytic hydrogen production. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
An exergoeconomic study of an ammonia-fed solid oxide fuel cell (SOFC) based combined system for transportation applications is presented in this paper. The relations between capital costs and thermodynamic losses for the system components are investigated. The exergoeconomic analysis includes the SOFC stack and system components, including the compressor, microturbine, pressure regulator, and heat exchangers. A parametric study is also conducted to investigate the system performance and costs of the components, depending on the operating temperature, exhaust temperature, and fuel utilization ratio. A parametric study is performed to show how the ratio of the thermodynamic loss rate to capital cost changes with operating parameters. For the devices and the overall system, some practical correlations are introduced to relate the capital cost and total exergy loss. The ratio of exergy consumption to capital cost is found to be strongly dependent on the current density and stack temperature, but less affected by the fuel utilization ratio. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
International Journal of Hydrogen Energy (03603199) (9)
In this paper, a new hybrid system for hydrogen production via solar energy is developed and analyzed. In order to decompose water into hydrogen and oxygen without the net consumption of additional reactants, a steady stream of reacting materials must be maintained in consecutive reaction processes, to avoid reactant replenishment or additional energy input to facilitate the reaction. The system comprises two reactors, which are connected through a proton conducting membrane. Oxidative and reductive quenching pathways are developed for the water reduction and oxidation reactions. Supramolecular complexes [{(bpy)2Ru(dpp)}2RhBr2] (PF 6)5 are employed as the photo-catalysts, and an external electric power supply is used to enhance the photochemical reaction. A light driven proton pump is used to increase the photochemical efficiency of both O2 and H2 production reactions. The energy and exergy efficiencies at a system level are analyzed and discussed. The maximum energy conversion of the system can be improved up to 14% by incorporating design modification that yield a corresponding 25% improvement in the exergy efficiency. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Chemical Engineering Science (00092509)
In this paper, a photocatalytic water-splitting system is designed and analyzed for continuous operation at a large pilot-plant scale. Performance of the photocatalyst and reaction system is discussed, as well as photon transfer and mass transfer limitations (in the case of liquid phase reactions). The optimization of these two processes is a main objective of this study. The system uses an external power source and two electrodes immersed in the catalyst solution to supply and transfer electrons inside two reactors to replace the need for electron acceptors and donors. A nano-filtration membrane, which is utilized to separate hydrogen and oxygen in the reactor, retains the catalyst on the cathode side while allowing passage of other species to the other half cell. A Compound Parabolic Concentrator (CPC) is presented for the sunlight-driven hydrogen production system. Energy and exergy analyses and related parametric studies are performed, and the effect of various parameters are analyzed, including catalyst concentration, flow velocity, light intensity, catalyst absorptivity, and ambient temperature. © 2012 Elsevier Ltd.
International Journal of Hydrogen Energy (03603199) (17)
In this study, both energetic and exergetic performances of a combined heat and power (CHP) system for vehicular applications are evaluated. This system proposes ammonia-fed solid oxide fuel cells based on proton conducting electrolyte (SOFC-H+) with a heat recovery option. Fuel consumption of combined fuel cell and energy storage system is investigated for several cases. The performance of the portable SOFC system is studied in a wide range of the cell's average current densities and fuel utilization ratios. Considering a heat recovery option, the system exergy efficiency is calculated to be 60-90% as a function of current density, whereas energy efficiency varies between 60 and 40%, respectively. The largest exergy destructions take place in the SOFC stack, micro-turbine, and first heat exchanger. The entropy generation rate in the CHP system shows a 25% decrease for every 100 °C increase in average operating temperature. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
International Journal of Hydrogen Energy (03603199) (17)
Today's concern regarding limited fossil fuel resources and their contribution to environmental pollution have changed the general trend to utilization of high efficiency power generation facilities like fuel cells. According to annual reducing capital cost of these utilities, their entrance to commercial level is completely expected. Hot exhaust gases of Solid Oxide Fuel Cells (SOFC) are potentially applicable in heat recovery systems. In the present research, a SOFC with the capacity of 215 kW has been combined with a recovery cycle for the sake of simultaneous of electric power, cooling load and domestic hot water demand of a hotel with 4600 m2 area. This case study has been evaluated by energy and exergy analysis regarding exergy loss and second law efficiency in each component. The effect of fuel and air flow rate and also current density as controlling parameters of fuel cell performance have been studied and visual software for energy-exergy analysis and parametric study has been developed. At the end, an economic study of simultaneous energy generation and recovery cycle in comparison with common residential power and energy systems has been done. General results show that based on fuel lower heating value, the maximum efficiency of 83 percent for simultaneous energy generation and heat recovery cycle can be achieved. This efficiency is related to typical climate condition of July in the afternoon, while all the electrical energy, cooling load and 40 percent of hot water demand could be provided by this cycle. About 49 percent of input exergy can be efficiently recovered for energy requirements of building. Generator in absorption chiller and SOFC are the most destructive components of exergy in this system. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
In this entry, photo-reactors for catalytic solar hydrogen production are introduced and explained. To be an economical environmentally benign and sustainable pathway, hydrogen should be produced from a renewable energy source, i.e., solar energy. Solar driven water splitting combines several attractive features for sustainable energy utilization. The conversion of solar energy to a type of storable energy has crucial importance. In the first part of the entry, background information is presented regarding different photo-reactor configurations for water dissociation with light energy to generate hydrogen. The photo-electrochemistry of water splitting is discussed, as well as photo-catalytic reaction mechanisms. The design and scale-up of photo-reactors for photo-catalytic water splitting are explained by classification of light-based hydrogen production systems. At the end, a new photo-catalytic energy conversion system is analyzed for continuous production of hydrogen at a pilot-plant scale. Two methods of photo-catalytic water splitting and solar methanol steam reforming are investigated as two potential solar-based methods of catalytic hydrogen production. The exergy efficiency, exergy destruction, environmental impact, and sustainability index are investigated for these systems. The light intensity is found to be one of the key parameters in design and optimization of the photo-reactors, in conjunction with light absorptivity of the catalyst. © Springer Science+Business Media New York 2013. All rights reserved.
In this paper, an exergy-economic model is developed to analyze the performance of a direct steam solar tower - steam turbine - organic Rankine cycle (ORC) power plant under different working conditions. The solar power plant is connected to a power grid, and it is integrated with a hydrogen storage system. The hydrogen storage system is composed of an electrolyser, fuel cell, steam turbine and organic Rankine cycle. When solar energy is not available, electrical power is generated by the fuel cell, steam turbine and ORC using the hydrogen produced by the electrolyzer. The analyses are made for the maximum solar irradiation that is available in the city of YAZD in Iran. The effects of the current density and operating temperature on the performance of the solid oxide electrolyzer cell (SOEC) and solid oxide fuel cell (SOFC) are investigated. The effect of solar irradiation on the energy and exergy efficiencies of the cycle is investigated. The results indicate that increase of the solar irradiation leads to an increase of the energy and exergy efficiencies of the cycle. The solar tower has the highest exergy destruction and capital investment cost. © 2022 Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2. All rights reserved.
