Applied Thermal Engineering (13594311)
Green vehicles, particularly Fuel Cell Vehicles (FCVs), offer a promising solution to environmental challenges. One of the major obstacles for FCVs is starting the Polymer Electrolyte Membrane (PEM) fuel cell stacks in subfreezing temperatures, where the water produced by chemical reactions can freeze and hinder the cold-start process. Preheating the inlet air to the stack up to 80 °C is an effective approach to overcome this issue. However, conventional heating systems, such as electric heaters, are unable to heat the air quickly enough. This paper introduces a novel heating method to enhance the cold-start capability of FCVs. The proposed solution involves integrating vortex tubes, which are simple and cost-effective, with the vehicle's existing compressor. This system not only preheats the inlet air to the stacks but also provides warm air for the passengers simultaneously. By developing a 3D-CFD model of the vortex tube, the results demonstrate that the system can preheat the inlet air to the stacks from −30 °C to 80 °C and the air entering the passenger compartment from −30 °C to nearly 37 °C in just about 5 s. In comparison, conventional heating systems require over 600 s (10 min) to achieve the same temperature rise. © 2024
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
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
Baharlou-Houreh N.,
Masaeli N.,
Afshari, E.,
Mohammadzadeh K. International Journal of Numerical Methods for Heat and Fluid Flow (09615539)(12)
Purpose: This paper aims to investigate the effect of partially blocking the cathode channel with the stair arrangement of obstacles on the performance of a proton exchange membrane fuel cell. Design/methodology/approach: A numerical study is conducted by developing a three-dimensional computational fluid dynamics model. Findings: As the angle of the stair arrangement increases, the performance of the fuel cell is reduced and the pressure drop is decreased. The use of four stair obstacles with an angle of 0.17° leads to higher power density and a lower pressure drop compared to the case with three rectangular obstacles of the same size and maximum height. The use of four stair obstacles with an angle of 0.34° results in higher power density and lower pressure drop compared to the case with two rectangular obstacles of the same size and maximum height. Originality/value: Using the stair arrangement of obstacles as an innovation of the present work, in addition to improving the fuel cell’s performance, creates a lower pressure drop than the simple arrangement of obstacles. © 2023, Emerald Publishing Limited.
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
Energy Conversion and Management (01968904)258
One of the proposed methods to improve the performance of a proton exchange membrane fuel cell is using metal foam within the channels. Here, we performed a 3D numerical simulation and studied the effect of structural properties of metal foam on the system performance. Also, we used artificial neural network to predict three criteria, i.e., maximum temperature, temperature uniformity index, and pressure drop, together with Genetic Algorithm for system optimization. Obtained results indicate that using metal foam can improve the temperature uniformity in the cell, so that maximum temperature and temperature uniformity index are decreased about 1.785 K and 0.7 K, respectively, while resultant increase in overall pressure drop of the system is only about 4.4%. The same amount of maximum temperature reduction is possible by increasing the flow rate; however, this scheme puts 60% more pressure drop upon the system. Moreover, we compared the performance of air- and water-cooling systems and found that for a given pressure drop, the maximum temperature as well as temperature uniform index of an air-cooling system is lower than that of a water-cooling system, while for the same system parasitic power, a system with water coolant has more uniform temperature distribution with lower maximum temperature. © 2022 Elsevier Ltd
International Communications in Heat and Mass Transfer (07351933)
Dry gas inhalation can harm the mucous layer of the respiratory tract. For mechanically ventilated patients the inhalation gas must get humidified before inspiration due to the preservation matter of thickness and wetness of the mucus layer. In this study, an air-to-air planar membrane humidifier is replaced instead the bubble humidifier for ventilators. Comprehensive numerically investigation is performed for a mechanical ventilation system for 8 ml/kg tidal volume. Studies are performed to specify the effects of the respiratory rate, wet gas inlet temperature, flow rate and humidity and cell numbers of membrane humidifier. Results show that increasing the body weight and the respiratory rate decreases the humidifier performance due to the addition of tidal volume. More wet gas flow rate and humidity achieve more performance and wet gas temperature in the most effective variable on the delivery air parameters. By increasing the humidifier cell number at the fixed tidal volume and wet gas flow rate performance increases. A multicell membrane humidifier exhibits lower pressure drop and wider rang coverage of tidal volumes. Studied membrane humidifier can provide up to 1900 ml/inspiration with an 8-cell membrane humidifier for tracheal intubation. © 2022 Elsevier Ltd
Medicine in Novel Technology and Devices (25900935)
Medical humidifier is one of the vital instruments for a respiratory patient in hospital, which is used to humidify the required oxygen for respiratory patients. The conventional type of humidifier, bubble humidifier, has some technical problems, including the need to drain condensed water and a lack of accurate control of air or oxygen required by the patient. In contrast, Membrane humidifier has exciting advantages, including the simplicity of the system, the absence of moving parts, very low noise, and the ability to control temperature and humidity. In this study, three configurations, including parallel, cross, and serpentine of a single module of a membrane humidifier according to the person's weight and breathing rate (the range of 10–28 SLPM) are numerically investigated. For validation of numerical models, a membrane humidifier experimental setup test is used. The obtained results indicated that the crossflow configuration for membrane humidifier has a minimum Dew Point Approach Temperature (DPAT) (2
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 Energy and Environmental Engineering (20089163)(2)
A dynamic model for polymer electrolyte membrane (PEM) fuel cell with pin-type flow field with bean-shaped pins is presented to comprehensively investigate the performance of the fuel cell against the operating conditions (temperature, pressure, relative humidity, and stoichiometric flow ratio). A three-dimensional and multi-component numerical model, employing pin-type flow field with bean-shaped pins at the cathode side, is introduced to investigate the transient behavior of fuel cell. Governing equations including the mass, momentum, species, charge, and energy conservation coupled with electrochemical kinetics are solved. The post-processing associated results consist of species concentration and current density distributions in addition to velocity distributions; along with different pin-type flow field patterns, a detailed insight is provided into the transport phenomena within the PEM fuel cell. The results indicated that utilizing pin-type flow field can improve transportation of oxygen into the catalyst layer leading to an increase in the current density average value. Also, the transient time of a fuel cell is about few seconds; the start-up process of the PEM fuel cell is very quick. © 2021, The Author(s), under exclusive licence to Islamic Azad University.
Applied Thermal Engineering (13594311)196
Inhalation gas humidification is a kind of major matter for patients using mechanical ventilation systems due to the necessity of keeping mucus layer at the suitable thickness and wetness. The performance of membrane humidifier with partially blocked gas channels, is investigated in this study. Three types of membrane humidifier channel arrangement, including a normal, wet channel with obstacles, and similar ones in both channels (wet and dry) are studied under various mass flow rates and temperatures. Flanged obstacles improve the thermal efficiency of the humidifier so that in this case the outlet dry air temperature can be increased about 4°by using 10 obstacles in both channels but they increase the pressure drop noticeably. PEC is calculated as a dimensionless parameter to compare the performance enhancement with pressure drop increment, simultaneously. Higher water recovery rate (WRR) and dew point temperatures at the dry side channel outlet, indicate the higher humidifier performance. At all mass flow rates, presence of obstacles improves the performance of the humidifier by increasing the dew point temperature and water recovery rate (WRR). Overall, the presence of obstacles on both channels amplifies the overall performance of the membrane humidifier in almost all cases. © 2021 Elsevier Ltd
Amirkabir Journal of Mechanical Engineering (20086032)53(9)pp. 1153-4924
The heat pipes are usually simulated by using a two phase model and a model describing the phase-change process. The computational costs of the two-phase approaches are relatively high and the model generally needs small-size time steps, which leads to a long simulation run times in the order of several days. In the present study, a variable conductance heat pipe is simulated by using a set of single-phase fluid flow models. It is shown that the proposed approach needs to a simulation time in the order of minutes that considerably facilitates the parametric study process of the variable conductance heat pipe. The effect of heat rate, sink temperature, mass of non-condensable gas, vapor radius, and wick porosity on the performance of variable conductance heat pipe are investigated. For the considered variable conductance heat pipe, the obtained numerical results indicate that sink temperature has the greatest effect on distributions of average wall temperature, overall heat transfer coefficient, the active length of condenser, and its average temperature. By increasing the sink temperature of 10 K, the active length of condenser is increased about 48 mm and average wall temperature is increased about 6.4 K. © 2021, Amirkabir University of Technology. All rights reserved.
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
A suitable cooling flow field design for proton exchange membrane fuel cell (PEMFC) improves the cell's net generated power, besides achieving steady cell performance and a longer lifespan. The innovation in this work lies in the simultaneous simulation of electrochemical and cooling models while accounting for both thermal and electrical contact resistance between the gas diffusion layer and bipolar plates. In this study, flow field designs including straight parallel channels (Case A), straight parallel channels filled with metal foam (Case B), multi-channel serpentine (Case C), novel serpentine channels (Case D), and integrated metal foam (Case E) used for both gas channels and cooling channels are numerically simulated. Results show that the highest uniformity of temperature in the catalyst layer-gas diffusion layer interface is obtained in Case D, which has the largest pressure drop compared to Cases B, C, and E. However, due to the uniform distribution of reactant flows, the maximum temperature observed in the catalyst layer of this flow field was the lowest compared to the rest of the cases. Furthermore, the maximum power density of 0.75 Wcm−2 was observed in Case D at a corresponding voltage of 0.6 V, which reduced when the effect of high pressure drop was taken into account. Following the conclusion of the simulation and analysis, Case D displayed the best cooling performance while Case E produced the maximum net power output. © 2021 Elsevier Ltd
Journal Of Thermal Analysis And Calorimetry (13886150)(4)
Thermal management of proton-exchange membrane (PEM) fuel cell has an important effect on the overall cell performance. In this paper, metal foams as flow field are used to render more uniform temperature, gaseous reactants and current density distribution and also to reduce the mass and the cost of machining of flow-field channels and to enhance the performance of the PEM fuel cell. A 3-D model is considered and a set of equations including continuity, momentum, species, energy, and charge together with electrochemical kinetics are developed and numerically solved. A comparison is made between the PEM cell with metal foam and parallel channel as flow-field gas distributor. The results show that utilization of metal foam as flow field leads to increase in the reactant gas transfer and current density, and the current density distribution improves. The maximum temperature in the cell with metal foam is lower than conventional cell, and temperature distribution is more uniform within the cell. At low and middle current densities, the cell with metal foam has better performance than conventional channel due to lower temperature and lower ohmic resistance and this cell is more efficient at high current density due to lower mass transport losses. Furthermore, metal foam with high permeability provides a more uniform distribution of reactant gases with low pressure loss. © 2019, Akadémiai Kiadó, Budapest, Hungary.
Ghaedamini M.,
Baharlou-Houreh N.,
Afshari, E.,
Shokouhmand H.,
Ahmaditaba A.H. Applied Thermal Engineering (13594311)
In this work, a membrane heat and moisture exchanger (MHME) with partially blocked channels is fabricated and tested at isothermal condition. There are eight rectangular baffles in each wet side channel with the height of 1.5 mm (75% of channel height). Dew point approach temperature (DPAT) is the main performance evaluation criterion of the MHME. The experimental parametric study of the blocked MHME shows that the performance of the MHME improves with increase of dry side inlet relative humidity (RH) and decrease of operating temperature. At higher RHs of dry side inlet, the MHME performance at different temperatures approaches each other. In different operating conditions, counter flow configuration shows better performance than the parallel flow. When the volumetric flow rates of wet side and dry side inlets are kept constant, increase of operating pressure causes the performance deterioration. When the pressure increases from 1 to 2.5 bar, DPAT in temperature of 30 °C increases by 6.68°, while in temperature of 60 °C increases by only 1.43°. It is also deduced that the water concentration difference between the wet side and dry side is the main driving force of mass transfer. © 2020 Elsevier Ltd
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
International Journal of Energy Research (1099114X)44(7)pp. 5730-5748
Improvement in the cooling system performance by making the temperature distribution uniform is an essential part in design of polymer electrolyte membrane fuel cells. In this paper, we proposed to use water-CuO nanofluid as the coolant fluid and to fill the flow field in the cooling plates of the fuel cell stack by metal foam. We numerically investigated the effect of using nanofluid at different porosities, pore sizes, and thicknesses of metal foam, on the thermal performance of polymer electrolyte membrane fuel cell. The accuracy of present computations is increased by applying a three-dimensional modeling based on finite-volume method, a variable thermal heat flux as the thermal boundary condition, and a two-phase approach to obtain the distribution of nanoparticles volume fraction. The obtained results indicated that at low Reynolds numbers, the role of nanoparticles in improvement of temperature uniformity is more dominant. Moreover, metal foam can reduce the maximum temperature for about 16.5 K and make the temperature distribution uniform in the cooling channel, whereas increase in the pressure drop is not considerable. © 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 Numerical Methods for Heat and Fluid Flow (09615539)(1)
Purpose: In this paper, a single module of cross-flow membrane humidifier is evaluated as a three-dimensional multiphase model. The purpose of this paper is to analyze the effect of volume flow rate, dry temperature, dew point wet temperature and porosity of gas diffusion layer on the humidifier performance. Design/methodology/approach: In this study, one set of coupled equations are continuity, momentum, species and energy conservation is considered. The numerical code is benchmarked by the comparison of numerical results with experimental data of Hwang et al. Findings: The results reveal that the transfer rate of water vapor and dew point approach temperature (DPAT) increase by increasing the volume flow rate. Also, it is found that the water recovery ratio (WRR) and relative humidity (RH) decrease with increasing volume flow rate. In addition, all mixed results decrease with increasing dry side temperature especially at high volume flow rates and this trend in high volume flow rates is more sensible. Although the transfer rate of water vapor and DPAT increases with increasing the wet inlet temperature, WRR and RH reduce. Increasing dew point temperature effect is more sensible at the wet side is compared with the dry side. The humidification performance will be enhanced with increasing diffusion layer porosity by increasing the wet inlet dew point temperature, but has no meaningful effect on other operating parameters. The pressure drop along humidifier gas channels increases with rising flow rate, consequently, the required power of membrane humidifier will enhance. Originality/value: According to previous studies, the three-dimensional numerical multiphase model of cross-flow membrane humidifier has not been developed. © 2019, Emerald Publishing Limited.
Jamalabadi M.Y.A.,
Ghasemi M.,
Alamian R.,
Afshari, E.,
Wongwises S. Applied Sciences (Switzerland) (20763417)(17)
The fuel cell is an electrochemical energy converter that directly converts the chemical energy of the fuel into electrical current and heat. The fuel cell has been able to identify itself as a source of clean energy over the past few decades. In order to achieve the durability and stability of fuel cells, many parameters should be considered and evaluated Therefore, in this study, a single-channel high-temperature polymer exchange membrane fuel cell (HT-PEMFC) has been numerically simulated in three-dimensional, isothermal and single-phase approach. The distribution of the hydrogen and oxygen concentrations, as well as water in the anode and cathode, are shown; then the effect of different parameters of the operating pressure, the gas diffusion layer porosity, the electrical conductivity of the gas diffusion layer, the ionic conductivity of the membrane and the membrane thickness are investigated and evaluated on the fuel cell performance. The results showed that the pressure drop in the cathode channel was higher than the anode channel, so that the pressure drop in the cathode channel was higher than 9 bars but, in the anode channel was equal to 2 bars. By examining the species concentration, it was observed that their concentration at the entrance was higher and at the output was reduced due to participation in the reaction and consumption. Also, with increasing the operating pressure, the electrical conductivity of the gas diffusion layer and ionic conduction of the membrane, the performance of the fuel cell is improved. © 2019 by the authors.
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 Electrochemical Energy Conversion and Storage (23816872)(3)
In this research, cooling of polymer membrane fuel cells by nanofluids is numerically studied. Single-phase homogeneous technique is used to evaluate thermophysical properties of the water/Al2O3 nanofluid as a function of temperature and nanoparticle concentration. Four cooling plates together with four various fluids (with different nanoparticle concentrations) are considered for cooling fuel cells. The impact of geometry, Reynolds number, and concentration is investigated on some imperative parameters such as surface temperature uniformity and pressure drop. The results reveal that, among different cooling plates, the multipass serpentine flow field has the best performance. It is also proved that the use of nanofluid, in general, enhances the cooling process and significantly improves those parameters directly affecting the fuel cell performance and efficiency. By increasing the nanoparticle concentration by 0.006, the temperature uniformity index will decrease about 13%, the minimum and maximum temperature difference at the cooling plate surface will decrease about 13%, and the pressure drop will increase about 35%. Nanofluids can improve thermal characteristics of cooling systems and consequently enhance the efficiency and durability of fuel cells. Copyright © 2019 by ASME.
Physica Scripta (00318949)94(6)
Operating temperature is one of the most important parameters affecting the performance of polymer electrolyte membrane (PEM) fuel cells. The cooling system of a PEM fuel cell maintains the temperature of the fuel cell stack at a specific value and removes the heat generated in the cell. This paper presents 3D numerical simulation of a water-cooled PEM fuel cell cooling system, with a metal foam insert instead of traditional cooling channels. We explore the possibility of using metal foams for thermal management of fuel cells. We consider the turbulent flow of the coolant through the porous medium and investigate the effect of metal foam properties, including porosity and pore size, on the performance of the cooling system. The Brinkman-Darcy-Forchheimer equation is employed to analyze the flow field in the porous medium and the k - ϵ model is utilized for turbulence studies. The numerical results indicate that, at a specific Reynolds number, by increasing the porosity and the pore size of the metal foam, the pressure drop decreases, while the maximum temperature difference occurs in the cooling plate. The temperature uniformity index also increases. The latter result indicates that the temperature distribution in the cooling plate becomes more uniform. The obtained results of present study are in good agreement with available experimental and analytical data, confirming that the presented computational fluid dynamics modeling using the selected turbulence model can accurately predict the flow field parameters in the cooling channels of PEM fuel cells. © 2019 IOP Publishing 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.
Journal of Cleaner Production (09596526)
The performance of a proton exchange membrane fuel cell (PEMEC) depends on appropriate design of the flow field, particularly at the cathode side of PEMEC. Uniform distribution of the parameters such as current density, temperature, and pressure, along with proper management of water and heat, enhances overall performance and durability of PEMFC. In this study, we proposed a comprehensive 3D multiphase CFD model of a PEMFC with a new flow field pattern at the cathode side. Honeycomb flow field is composed of a regular pattern of hexagonal pins which are categorized in pin-type flow fields. The behavior of such a field is numerically analyzed by solving a set of continuity, momentum, energy, species and electrochemical equations. The obtained results revealed that maximum pressure-drop across the cathode gas channel are 762 Pa, while the pressure and temperature distributions are uniform at the gas diffusion layer (GDL)-catalyst layer (CL) interface. Also, the results indicated that water content is less than 14 in the membrane, reducing the possibility of water flooding in the CL. It was also found that the possibility of hotspots and flooding phenomena in PEMFC decrease by increasing the uniformity of temperature, pressure, and oxygen mass fraction distributions. © 2019 Elsevier Ltd
Energy Sources, Part A: Recovery, Utilization and Environmental Effects (15567036)(12)
A necessary requirement for polymer electrolyte membrane fuel cell (PEMFC) performance is providing sufficient water content in the membrane. The bubble humidifier is the simplest and inexpensive method for PEMFC humidification. In this study, a prototype of bubble humidifier is designed, fabricated, and tested. The effects of water temperature in the reservoir, water level inside the reservoir and inlet air flow on the humidifier performance are investigated. The results show that the outlet air relative humidity decreases (about 6% - 11%) with an increase in the inlet air flow rate from 1 m3 h−1 to 3 m3 h−1 at four different water temperatures. The increase in the water temperature and water level inside the reservoir lead to the better humidifier performance. At the water temperature of 20°C, increasing water level from 5 cm to 7.5 cm has a significant effect on humidifier performance but increasing water level from 7.5 cm to 15 cm does not offer any advantage. © 2018, © 2018 Taylor & Francis Group, LLC.
International Journal of Engineering, Transactions B: Applications (1728144X)31(5)pp. 812-819
The performance of proton-exchange membrane fuel cell cooling system using coolant flow channels enhanced with baffles was numerically investigated. To do this, the maximum temperature of the cooling plate, temperature uniformity and also pressure drop along the flow channels were compared for different cases associated with number of baffles and their dimensions inside the channels. The governing equations by the finite-volume approach in three dimensions were solved. Numerical results indicate that the baffle-restricted cooling flow channels, generally improved the performance of the fuel cell in such a way that a reduced maximum temperature of the cell and a better temperature uniformity in the cooling plates were determined. As the pressure drop increases by incorporating the baffles inside the coolant flow channels, one needs to compromise between the improvement of cooling system performance and the total pressure drop. © 2018 Materials and Energy Research Center. All Rights Reserved.
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
Chinese Journal of Chemical Engineering (10049541)25(10)pp. 1352-1359
The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis (CHFS) system to enhance the heat transfer and minimize the required length of the heat exchanger. For this purpose, numerous numerical simulations are performed to investigate performance of the system with porous media. First, the numerical simulation for the heat exchanger in CHFS system is validated by experimental data. Then, porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness, based on the minimum required length of the heat exchanger. Finally, by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate, the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed. The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%. The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness. Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions. © 2017 Elsevier B.V.
Energy (18736785)118pp. 705-715
In the present work, the performance of proton exchange membrane fuel cells is studied for three cases; A fuel cell with two parallel flow channels (model A), locally baffle restricted flow channels (model B), and metal foam as a flow distributor (model C). The fully coupled thermal-electrochemical equations are numerically solved in three dimensions, based on the macroscopic, single-domain, and finite-volume approaches. While having no significant effect on temperature distribution, the existence of baffles inside flow channels results in more oxygen penetration into gas diffusion and catalyst layers at the cathode side of the cell. This improves the chemical reaction rate, current density and cell performance. Using metal foam increases oxygen concentration and current density at the cathode catalyst surface, and improves the uniformity of their distributions. Furthermore, a more uniform temperature distribution is achieved, when compared with the other cases. For the considered dimensions, it is observed that decreasing the flow channel depth results to an increase in current density and also in pressure drop along channels (models A and C). Moreover, increasing metal foam porosity can increase the current density value and decrease pressure drop in model C, while it has nearly no effects on temperature distribution. © 2016 Elsevier Ltd
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
Journal of the Energy Institute (17460220)90(5)pp. 752-763
This paper concerns with numerical modeling of fluid flow through a zigzag-shaped channel to be used as the cooling plate for polymer electrolyte membrane fuel cells. In general, large scale PEM fuel cells are cooled by liquid water flows through coolant flow channels, and the shape of these channels has a key role in the cooling performance. We perform a three-dimensional numerical simulation to obtain the flow field and heat transfer rate in square area cooling plates. The performance of zigzag flow channels is evaluated in terms of maximum surface temperature, temperature uniformity and pressure drop. The results indicate that in the zigzag channels model, maximum surface temperature, surface temperature difference and temperature uniformity index, respectively, reduce about 5%, 23%, and 8% with respect to straight channels model. Hence, the cooling performance of fuel cells can be improved by implementing the zigzag channels model as the coolant fluid distributors, although the coolant pressure drop is higher than straight channels in this model. © 2016 Energy Institute
International Journal of Hydrogen Energy (03603199)41(3)pp. 1902-1912
This paper deals with the usage of metal foams in coolant flow field of bipolar or cooling plates in PEMFC stack rather than conventional machined channel designs. A three-dimensional model is employed to simulate the fluid flow and heat transfer in cooling plates and the capabilities of four different coolant flow field designs, include one parallel, two serpentine and one metal foam porous media field, are investigated and compared based on the maximum surface temperature, uniformity of temperature and the pressure drop. The numerical results indicated that a model with the porous flow field made by metal foam is the best choice for reducing the surface temperature difference, maximum surface temperature and average surface temperature, among the studied models. Furthermore, due to its high permeable coefficient, the coolant pressure drop is very low in this model. Consequently, this model can be well-used as a coolant fluid distributor to improve the PEM fuel cell performance. © 2015 Hydrogen Energy Publications, LLC.
Modern Physics Letters B (02179849)30(16)
In PEM fuel cells, during electrochemical generation of electricity more than half of the chemical energy of hydrogen is converted to heat. This heat of reactions, if not exhausted properly, would impair the performance and durability of the cell. In general, large scale PEM fuel cells are cooled by liquid water that circulates through coolant flow channels formed in bipolar plates or in dedicated cooling plates. In this paper, a numerical method has been presented to study cooling and temperature distribution of a polymer membrane fuel cell stack. The heat flux on the cooling plate is variable. A three-dimensional model of fluid flow and heat transfer in cooling plates with 15 cm × 15 cm square area is considered and the performances of four different coolant flow field designs, parallel field and serpentine fields are compared in terms of maximum surface temperature, temperature uniformity and pressure drop characteristics. By comparing the results in two cases, the constant and variable heat flux, it is observed that applying constant heat flux instead of variable heat flux which is actually occurring in the fuel cells is not an accurate assumption. The numerical results indicated that the straight flow field model has temperature uniformity index and almost the same temperature difference with the serpentine models, while its pressure drop is less than all of the serpentine models. Another important advantage of this model is the much easier design and building than the spiral models. © 2016 World Scientific Publishing Company.
Applied Thermal Engineering (13594311)99pp. 373-382
This paper concerns with modeling nanofluid boundary layer flow in the presence of a magneto hydrodynamic field over a horizontal permeable stretching flat plate using artificial neural network. The flow is generated due to the linear stretch of the sheet. The governing PDEs are transformed into ODEs and numerically solved using a double precision Euler's procedure. We studied numerically the effects of injection or suction from the surface, the volume fraction of nanoparticles, the viscous dissipation, and the magnetic parameter on the skin friction factor, Nusselt number and hydraulic and thermal boundary layer thicknesses. The results show that both the friction factor and Nusselt number increase as the volume fraction of nanoparticles increases. Moreover, the magnetic field increases the friction factor while reduces the Nusselt number. By a multilayer neural network model, we also calculated the skin friction factor and Nusselt number with respect to the aforementioned effective parameters. The model is able to compute the test data set with mean relative errors of 0.19% and 0.36% for the friction factor and Nusselt number, respectively. This means the applied neural network model can accurately predict the output results. © 2016 Elsevier Ltd. All rights reserved.
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.
International Journal of Engineering, Transactions B: Applications (1728144X)(5)
The purpose of present study is to investigate the dynamic response of two conventional types of solid oxide fuel cells to the inlet air mass flow rate variation. A dynamic compartmental model based on CFD principles is developed for two typical planar and tubular SOFC designs. The model accounts for transport processes (heat and mass transfer), diffusion processes, electrochemical processes, anode and cathode activation and ohmic polarizations, among others. Using developed model, the dynamic response of the cell to the step change of the air feed stream conditions is investigated. The results show an almost slow electrical response of the cell to the air mass flow rate step variation which is estimated to be about one hour. Moreover, it can be concluded that the effect of the inlet air flow conditions on a tubular solid oxide fuel cell performance is more noticeable than its effects on a planar SOFC. However, the electrical response time of the tubular type SOFC is calculated about ten times more than the planar type. © 2015, Materials and Energy Research Center. All rights reserved.
International Journal of Modern Physics C (01291831)(6)
A membrane humidifier with porous media flow field (metal foam) can provide more water transfer, low manufacturing complexity and low cost in comparison with the conventional humidifier. In this study, a two-dimensional numerical model is developed to investigate the performance of the humidifier with porous metal foam. The results indicate that the dew point increases with a decrease in the permeability, but at permeabilities lower than 10-8 the pressure drop increases extremely. At all ranges of pressures, temperatures and flow rates of humidifier inlet, the pressure drop in humidifier with porous media flow field is only about 0.5 kPa higher than that of the conventional humidifier, which is not significant and it can be ignored. An increase in the pressure at dry side inlet and wet side inlet of the humidifier results in a better humidifier performance. Humidifier performs better at high flow rates and temperatures of humidifier wet side inlet. At all ranges of pressures, flow rates and temperatures humidifier with porous metal foam indicates better performance. © 2015 World Scientific Publishing Company.
International Journal of Hydrogen Energy (03603199)(23)
In this study, the anodic recirculation system (ARS) based on ejector technology in polymer electrolyte membrane PEM fuel cell is studied with employing a theoretical model. A practical method is presented for selecting or designing the ejector in an ARS, that offers the best selection or design. A comprehensive parametric study is performed on the design parameters of a PEM fuel cell stack and an ARS ejector. Four geometrical parameters consist of cell active area, cell number, nozzle throat diameter, and mixing chamber diameter in the design of ARS are intended. The effect of each contributes to the overall system performance parameters is studied. In this parametric study, the correlation between stack design parameters and ejector design parameters are studied. Eventually, based on the results, two dimensionless parameters are useful in the design process are proposed. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
International Journal of Modern Physics B (02179792)(16)
In this study, we propose a configuration of partially blocked oxidant channel with baffle plate(s) transversely inserted in the cathode channel and their effect on the oxygen transport and fuel cell performance is investigated. In order to investigate the effects of the selected shape, size and the number of baffles on the oxygen transport in the gas diffusion layer (GDL) and fuel cell performance a numerical modeling is carried out in 27 cases. With the consideration of both maximum oxygen concentration in the GDL and reasonable pressure drop criterions, the results indicate that in all cases, an increase in baffle height is more effective than an increase in number of baffle plates. Also, installing many large rectangular baffles seem quite appropriate, but when there is restriction in securing pressure in fuel cell, installing the semicircle baffle is better than the rectangular one. © 2014 World Scientific Publishing Company.
Applied Thermal Engineering (13594311)71(1)pp. 410-418
In this study, a CFD model is adopted for investigating the effects of the four important ejector geometry parameters: the primary nozzle exit position (NXP), the mixing tube length (Lm), the diffuser length (L d), and the diffuser divergence angle (θ) on its performance in the PEM fuel cell system. This model is developed and calibrated by actual experimental data, and is then applied to create 141 different ejector geometries which are tested under different working conditions. It is found that the optimum NXP not only is proportional to the mixing section throat diameter, but also increases as the primary flow pressure rises. The ejector performance is very sensitive to the mixing tube length while the entrainment ratio can vary up to 27% by change in the mixing tube length. The influence of θ and Ld on the entrainment ratio is evident and there is a maximal deviation of the entrainment ratio of 14% when θ and Ld vary from 2° to 8° and 6Dm to 24Dm, respectively. To make sure the correlation of all geometric parameters on the ejector performance, the artificial neural network and genetic algorithm are applied in obtaining the best geometric. © 2014 Elsevier Ltd. All rights reserved.
Energy Conversion and Management (01968904)
Using metal foam as flow distributor in membrane humidifier for proton exchange membrane (PEM) fuel cell system has some unique characteristics like more water transfer, low manufacturing complexity and low cost compared to the conventional flow channel plate. Metal foam can be applied at wet side or dry side or both sides of a humidifier. The three-dimensional CFD models are developed to investigate the performance of the above mentioned meanwhile compare them with the conventional humidifier. This model consists of a set of coupled equations including conservations of mass, momentum, species and energy for all regions of the humidifier. The results indicate that with the metal foam installed at wet side and both sides, water recovery ratio and dew point at dry side outlet are more than that of the conventional humidifier, indicating a better humidifier performance; while using metal foam at dry side has no positive effect on humidifier performance. At dry side mass flow rates higher than 10 mgr/s pressure drop in humidifier containing metal foam at wet side is lower than that of the conventional humidifier. As the mass flow rate increases from 9 to 15 mgr/s humidifier containing metal foam at wet side has better performance, while at mass flow rates lower than 9 mgr/s, the humidifier containing metal foam at both sides has better performance. At dry side inlet temperatures lower than 303 K, humidifier containing metal foam at wet side has better performance and at temperatures higher than 303 K, humidifier containing metal foam at both sides has better performance. © 2014 Elsevier Ltd. All rights reserved.
Heat and Mass Transfer/Waerme- und Stoffuebertragung (14321181)(11-12)
A two dimensional, two-phase non-isothermal electrochemical-transport using a fully coupled numerical model is developed to investigate heat transfer and water phase change effects on temperature distribution in a PEM fuel cell. The multiphase mixture is used formulation for the two phase transport process and developed model is treated as a single domain. This process leads to a single set of conservation equations consisting of continuity, momentum, species, potential and energy for all regions of cell. The results indicate that heat release due to condensation of water vapor affects the temperature distribution. When the relative humidity of the cathode is low, phase change would have a small effect on the maximum temperature that appears at the cell inlet, but it has higher effect on temperature variation further down stream towards the exit of cathode channel and its GDL. Under full-humidity conditions, the cell temperature at all regions of cell increases due to the phase change that starts to appear at the inlet, but the maximum effect of phase change occurs further up stream in cathode channel and its GDL. Also, vapor-phase diffusion which provides a new mechanism for heat removal from the cell, affects the cell temperature distribution. © 2010 Springer-Verlag.
Energy Conversion and Management (01968904)(4)
A two-dimensional, non-isothermal, electrochemical-transport using a fully coupled numerical model is developed for a proton exchange membrane fuel cell to investigate simultaneous water, heat transport phenomena and their effects on cell performance. The multiphase mixture formulation for the two-phase transport process is used, and developed model is treated as a single domain. This process is leading to a single set of conservation equations consisting of continuity, momentum, species, potential and energy for all regions of cell. The result indicates that flooding of porous cathode reduces the rate of oxygen transport to the cathode catalyst layer and causes an increase in cathode polarization. Also, flooding could effect current density distribution, where a slight abrupt change occurs in the slope of the local current density curve. The amount and location of condensation in the GDL cathode is directly related to the cell temperature, where the temperature difference predicted by this model is about 3.7 °C at 0.6 V. The maximum temperature occurs near the inlet and at interface between membrane/catalyst layers at cathode side where major heat generation takes place. The results are validated with experimental data available that are in good agreement. © 2009 Elsevier Ltd.
Journal of Power Sources (03787753)(1)
A two-phase non-isothermal model is developed to explore the interaction between heat and water transport phenomena in a PEM fuel cell. The numerical model is a two-dimensional simulation of the two-phase flow using multiphase mixture formulation in a single-domain approach. For this purpose, a comparison between non-isothermal and isothermal fuel cell models for inlet oxidant streams at different humidity levels is made. Numerical results reveal that the temperature distribution would affect the water transport through liquid saturation amount generated and its location, where at the voltage of 0.55 V, the maximum temperature difference is 3.7 °C. At low relative humidity of cathode, the average liquid saturation is higher and the liquid free space is smaller for the isothermal compared with the non-isothermal model. When the inlet cathode is fully humidified, the phase change will appear at the full face of cathode GDL layer, whereas the maximum liquid saturation is higher for the isothermal model. Also, heat release due to condensation of water vapor and vapor-phase diffusion which provide a mechanism for heat removal from the cell, affect the temperature distribution. Instead in the two-phase zone, water transport via vapor-phase diffusion due to the temperature gradient. The results are in good agreement with the previous theoretical works done, and validated by the available experimental data. © 2009 Elsevier B.V. All rights reserved.
American Journal of Applied Sciences (15543641)(1)
In this study a two-phases, single-domain and non-isothermal model of a Proton Exchange Membrane (PEM) fuel cell has been studied to investigate thermal management effects on fuel cell performance. A set of governing equations, conservation of mass, momentum, species, energy and charge for gas diffusion layers, catalyst layers and the membrane regions are considered. These equations are solved numerically in a single domain, using finite-volume-based computational fluid dynamics technique. Also the effects of four critical parameters that are thermal conductivity of gas diffusion layer, relative humidity, operating temperature and current density on the PEM fuel cell performance is investigated. In low operating temperatures the resistance within the membrane increases and this could cause rapid decrease in potential. High operating temperature would also reduce transport losses and it would lead to increase in electrochemical reaction rate. This could virtually result in decreasing the cell potential due to an increasing water vapor partial pressure and the membrane water dehydration. Another significant result is that the temperature distribution in GDL is almost linear but within membrane is highly non-linear. However at low current density the temperature across all regions of the cell dose not change significantly. The cell potential increases with relative humidity and improved hydration which reduces ohmic losses. Also the temperature within the cell is much higher with reduced GDL thermal conductivities. The numerical model which is developed is validated with published experimental data and the results are in good agreement. © 2009 Science Publications.
ECS Transactions (19386737)(1 PART 2)
The purpose of this paper is to present a control volume based numerical model for simulation of fuel/air flow, electrodes, and electrolyte components of a single tubular solid oxide fuel cell. The SOFC uses a mixture of H 2, CO, CO2, and H2O (vapor) components (pre-reformed methane gas) as fuel. The developed model determines the effect of fuel and air mass flux on local EMF, state variables (pressure, temperature and species concentration) and cell performance. In addition, the effect of fuel hydrogen concentration on output characteristics of fuel cell is investigated If we consider a pure hydrogen fuel, we will have maximum Nerenst potential and power generation. While the hydrogen goes through the channel and is being consumed, vapor is introduced into the flow and hydrogen concentration is reduced along the flow direction. Therefore, the local Nernst potential decreases. For mixed fuel, output parameters are function of fuel molar composition. In general, this model shows how output parameters of the SOFC can be controlled and adjusted by inlet fuel and air mass flow rate as well as hydrogen concentration of the fuel. Finally the numerical study is validated by experimental results such as polarization curve and power density. © The Electrochemical Society.
Most of the weight of the proton exchange membrane (PEM) fuel cell stack is in the bipolar plates. The main function of bipolar plates is uniform distribution of gas reactants as well as distribution of cooling fluid (water or air) inside the fuel cell. Therefore, the plate design and the characteristics of the gas and cooling channels inside them are essential to the operation of the PEM. Although reactive gas channels and cooling channels perform separately, there are many similarities between them. For example, gas channels should be designed so that distribution of reactive gases on the electrode surfaces is uniform. Also, cooling channels should be designed so that temperature distribution inside the fuel cell is uniform. Further, pressure drop of reactive gases inside the gas channels and the fluid inside the cooling channels must be minimal. In this chapter, initially the characteristics, functions and making materials of bipolar plates along with the to make channels inside of them are investigated. Afterwards, gas channels, cooling channels and effects of the shape and size of channels on the PEM fuel cell performance are studied. Finally, different configurations of gas and cooling channel with emphasizing on the new configurations of these channel are researched simultaneously. © 2022 Elsevier Inc. All rights reserved.
The ultra-fast charging capability, distinct properties, fine performance and high capacity of nickel cadmium (Ni-Cd) and nickel metal hydride (Ni-MH) batteries along with their limited weight and size are very attractive for use in many applications including cordless and portable devices, emergency and standby power, telecommunication equipments, photovoltaic systems, electric vehicle, satellite and space craft and power plant supporting equipments. However, the limitation on their temperature requires a detail thermal analysis of these batteries. Thermal behavior of batteries are effected by their boundary conditions, type and construction, and more importantly by their chemical reaction. The purpose of this study is to investigate the effect of temperature on thermal behavior of the Ni-Cd and Ni-MH batteries. The governing equation is the transient and non-linear differential energy equation subjected to non linear radiation boundary conditions and source term. To solve the transient and non-linear governing differential energy equation a control volume based finite difference code is utilized. In formulation of the governing differential energy equation, the Ni-Cd and Ni-MH properties (K, C, ρ) are not constant and the chemical characteristic of the Ni-Cd and Ni-MH batteries, source term, vary with location and time. Calculated thermal characteristic of each battery is then compared to experimental results. The result shows that Ni-MH battery is thermally more suitable for space application and satellite. Copyright © 2004 by ASME.
Work production systems cannot convert all input energy into useful work, and in these systems, always a part of the input energy is rejected to the environment in the form of heat. Therefore, the efficiency of work production systems is limited. In these systems, one of the limiting factors of the work production rate is the disposal of the produced heat during the process. The lack of proper heat dissipation increases the temperature of the system and its various parts of damages. Cooling system is an inseparable part of work production systems. The cooling system can be very simple (a natural circulation air-cooling system) or very complex (a nuclear facility cooling system). Simple cooling systems are usually used for low energy production rates (a few watts) and complex systems for high production rates (several hundred megawatts). The polymer electrolyte membrane (PEM) fuel cell is not excluded from this issue. In addition to the production of electric power, heat is produced in the PEM fuel cell, which is even slightly more than the production power. Therefore, one of the most important challenges that affects the use of this fuel cell is the issue of heat removal from the cell and heat management in it, which is done by a cooling system. © 2023 Elsevier Inc. All rights reserved.
