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In this paper, for control Voltage of two chamber Microbial fuel cell, two-type PI controller and MPC controller are used. For this purpose, two compartments of the model presented by Esfandyari  et al. [1, 2] have been used to model the microbial fuel cell. Then, based on this model, a classic PI controller based on the internal model and a MPC controller was designed and implemented. Based on the designed controllers, it was adjusted by adjusting the flow rate of the substrate to changes usually introduced in turbulence, such as the concentration of input to the substrate, or the effect of the uncertainty in the parameters of the process model, such as r_max and K_s. The results show that the MPC controller has a better performance compared to the classic PI controller.
 

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There is a full connection between the electrochemical quantities of a fuel cell and the curves of the temperature and primary materials at the catalyst region. These quantities are strongly linked to the mass and heat transfer phenomena in the other regions. In the present paper, the lattice-Bolzmann method, as a microscale model with good computational capabilities in the problems such as the fuel cell, has been utilized to simulate the fluids flow and heat transfer in a two-dimensional cross section of a proton exchange membrane fuel cell including the channel, bipolar plate, gas diffusion layer and catalyst of the cathode and the electrochemical characteristics in the catalyst layer have been analyzed. By representing a method for estimation of the changes in the concentration along the channel, the serpentine arrangement has been modeled. The results reveal the essential role of the bipolar plate on the quantities at the catalyst layer.

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In this study, the geometrical changes at cathode electrode in proton exchange membrane (PEM) fuel cell has been considered by inserting baffle plates across the channel. The effects of the blockage with various gap ratios, shape, thickness and numbers of the baffle plates, and the porosity of the diffusion layer on the oxygen transport and the pressure drop across the channel length are explored. It is revealed that partially blocked oxygen channel with rectangular baffle has the most velocity and oxygen concentration in the gas diffusion layer/catalyst layer interface than that of the other shape of plates; however results in a penalty of high pressure-loss. Increasing the porosity of gas diffusion layer (GDL), baffle plate thickness and baffle number and/or reducing the gap size in order to enhance the reactant gas transport result in pressure loss. Here, among the parameters considered, the porosity of GDL, gap ratio and plate number have the most remarkable impact on the oxygen transport to GDL and variation in pressure drop.

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In this study, convergent nozzle ejector in the PEM fuel cell system is analyzed. This method can reduce the parasitic power of the fuel cell, recycle the unconsumed hydrogen to the fuel cell to increase the fuel usage efficiency, utilize the pressure potential energy of hydrogen and regulate the anode humidity with the recycle gas. For this purpose, continuity, momentum, energy and state equations are solved by numerical methods and effects of pressure drop (through the channel towards the anode), operating pressure and temperature of the fuel cell and also nozzle diameter on the ejector performance was analyzed. With decreasing of pressure drop, even in primary lower pressure, increasing of performance pressure the performance of ejector will improved. The temperature increase has no effect on the performance of the ejector itself, but has enormous effect on the fuel cell. Increasing the diameter ratio of the constant diameter zone to the nozzle diameter leads to increasing of recirculation anode line of the fuel in higher pressure.

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A novel design of multi-generation package based on the PEM fuel cell and Maisotsenko cycle is proposed and analyzed in detail. This package consists of the proton exchange membrane (PEM) fuel cell stack, novel dew point indirect evaporative cooling system (Maisotsenko cycle), heating coil, heat storage tank and the backup boiler. This package is capable of producing electricity, water and space heating as well as indirect evaporative cooling. The system performance is evaluated through the steady-state mathematical models and thermodynamic laws. Using the Matlab and EES software the results are presented in the form of Tables and Figures. Energy and exergy analyses revealed the fuel cell stack efficiency, heating and cooling cogeneration efficiency and the package multi-generation efficiency. The results indicate that, the actual output power and voltage from the PEM fuel cell stack are 3307 W and 0.6787 V, respectively.

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This paper presents a transient model for planar solid oxide fuel cells anode, which allows the simulation of steady-state performance characteristics, transient operation behavior, as well as electrochemical impedance spectra. The developed model couples the mass transport with electrochemical kinetics. The 1D Navier-Stokes conservation equations and species conservation equations are used for gas transport in the anode channel, and the linear kinetic is used for the anode electrochemistry. In order to model the electrochemical impedance, a sinusoidal excitation is imposed to system of transient equations and the obtained harmonic response is used as a base for electrochemical impedance spectra simulation. In order to solve the system of the nonlinear equations, a numerical code based on finite volume method is developed and utilized. Results show that the mass transfer in channel leads to a low frequency capacitive semicircle in the Nyquist plot. Moreover, the influence of parameters such as overvoltage, temperature, velocity and hydrogen inlet concentration on the electrochemical impedance has also been studied and the results are discussed. The simulation results are in good agreement with published data.

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The purpose of this study is thermo-economic analysis of a combined fuel cell and micro gas turbine power plant cycle for using in small scale CHP systems. Since the fuel cell is the main source of power generation in hybrid systems, in this study, complete electrochemical, thermal and thermodynamic calculations are performed to obtain more accurate results; and unlike most studies, the cell temperature is not assumed constant. The performance analysis of the hybrid system shows that increasing the pressure and air to fuel ratio, causes to loss of electrical efficiency and increase in the electricity price because of reduction in cell and turbine inlet gas temperatures. The other results of this study show that considering the economic life of the system, making use of this type of hybrid systems is economical and generates less electricity price in comparison with micro gas turbine.

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An optimum humidification of the reactant gases of proton exchange membrane (PEM) fuel cell extremely affects its performance. Here, an analytic model of a membrane humidifier for PEM fuel cell is proposed where the effect of mass flow rates, inlet temperatures and pressures are investigated. The governing equations: water transfer equation and the law of conservation of energy in whole humidifier are written, which form a Non-linear system of equations, solved through FORTRAN software. At each stage, the outlet temperatures, the water transfer rate, relative humidity and the dew point at dry side outlet are calculated and discussed. The closer the dry side outlet dew point to the wet side inlet dew point, leads to the better humidifier performance. The results show that an increase in mass flow rate at dry side inlet leads to the weaker humidifier performance; while, an increase in mass flow rate at wet side inlet leads to the better performance. An increase in the pressure at dry side inlet enhances humidifier performance; while, the pressure at wet side inlet does not affect significantly on humidifier performance. Here, preheating the dry gas is not essential and use the cooler wet gas is recommended

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In the PEM fuel cells, gas phase (air and vapour) and liquid water could simultaneously flow through the cathode Gas Diffusion Layer (GDL). On the other hand, the performance of fuel cell and the main characteristic parameters of the flow can be influenced by the interaction of these gas and liquid phases. In the present study, the main parameters of two-phase flow in the GDL such as capillary pressure, mole concentrations of gas species, gas velocity and liquid velocity have been evaluated by considering the interactional effects of the aforementioned two phases. Also, the impact of changing the value of cathode channel humidity and fuel cell temperature on the value of the mentioned parameters has been investigated. The results indicated that decreasing of relative humidity in the cathode channel causes an increase in the rate of water vaporization. Thus, this leads to a decrease in the liquid water velocity, capillary pressure gradient and saturation gradient in the GDL. Also, increasing the temperature causes an increase in the rate of water vaporization and a decrease in the gas velocity and gas pressure gradient.

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In this study, we propose a configuration of partially blocked oxidant channel with baffle plates transversely inserted in the cathode channel and effects of the fluid dynamics due to the presence or non-presence of the baffles and their effect on the fuel cell performance is investigated. A 3D model with the presence of baffle plates is considered and a set of equations (continuity, momentum, species and charge together with electrochemical kinetics) in the form of single domain is developed and solved numerically. The baffles block the main flow in the cathode channel and force more reactant gases to turn to the GDL. This fact implies an enhancement of the oxygen flux at the GDL and catalyst surface, especially at the position beneath the location of the baffle plates. An increase in the number of baffles contribute to the reactant gas transport to GDL with more uniform distribution of gas in the GDL and catalyst layer, specially in high current densities, where it leads to a penalty of high pressure – loss. The predictions indicate that the local transport of the reactant gas would enhance the local current densities and the fuel cell performance in presence of baffle in the channel.

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Bipolar plates are the most important and expensive components used in fuel cells. Metallic bipolar plates are the best choice to replace graphite or machined thick metal plates due to their lightweight and low cost. Selection of suitable forming process is one of the main subjects in fuel cell technology. Nowadays, hydroforming process is commonly used for the production of metallic bipolar plates because of its capability in forming light weight and complex parts. Among the various patterns of bipolar plates, serpentine flow field pattern inevitably brings two main defects of rupture of material during forming process and uneven flow distribution in practical operations. In this research, forming of a slotted interdigitated serpentine pattern on SS304 stainless steel sheet by hydroforming process has been examined using finite element simulation and experimental approach. The effects of process parameters and die geometry on the thickness distribution and filling percent are also studied. It is concluded that by increasing the forming pressure, filling percent of the die increases and the thickness of critical region is more reduced due to the increasing of drawing ratio. Also, it was found that hydroforming process has high repeatability.

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In this paper, the efficiency of Proton membrane exchange (PEM) fuel cell system by using ejector for returning the additional fuel in the fuel supply circuit and comparison with conventional systems, with compressor in fuel supply circuit, are studied. For this purpose a semi - analytical developed model for calculating the amount of efficiency increment, as well as the amount of power saving as a result of employing ejector in the fuel cell return line is provided by extending the previous models. In this developed model the important stack design parameters and ejector design parameters are correlated by presenting a new dimensionless parameter. The results for a typical fuel cell show that the amount of efficiency increment at different values of current density is different and there is a maximum point for it. The amount of power saving as a result of employing ejector compared with fuel cell power is considerable and will increase with increasing the current density. These results indicate that the ejector for those applications that require high power (for instance the transport applications) is more efficient.

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In this paper, a single solid oxide fuel cell with internal reforming and parallel flow is modeled and optimized. The single fuel cell is a part of a stack of fuel cell system used for cogeneration of heat and work. The governing equations including the conservation equations of mass, momentum, energy and electrochemistry relations are solved by gPROMS software and validated using the data available in literatures. The effect of quantities such as the rate of fuel consumption, the amount of excess air and the percentage of pre reforming of fuel on the power and the efficiency of the fuel cell were evaluated. The results show that the percentage of the fuel pre reforming on the performance of fuel cell is more effective than other parameters and the power output and energy efficiency increase with increase of it. Optimal working point of fuel cell with three objective functions (output power, the product of output voltage in voltage efficiency and output power in energy efficiency) has been obtained. The optimal current density is less than the current density of maximum power output. the optimal power output and energy efficiency with considering minimum energy dissipation are 1.11W/cm2 and 42% respectively and with considering minimum exergy are 1.46 W/cm2 and 24%, respectively.

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In this paper, a non - isothermal and two-phase flow in the cathode gas diffusion layer (GDL) of PEM fuel cell is modeled. To achieve more accurate boundary conditions, other components of fuel cell (membrane and anode GDL) are modeled. Governing equations including energy, mass and momentum conservation and auxiliary equations are solved by numerical method and the effect of gas mixture pressure in channels, relative humidity and effect of contact and mass exchange between two phases are investigated. Results show, it is necessary that both the contact and mass exchange between the gas and liquid phase to be considered. The performance curve and temperature distribution for single and two phase flow are compared for different amount of cathode channel humidity. The relative value of performance and temperature for single and two phase flow depends on the humidity of cathode channel. With increasing the cathode pressure from 0.5 to 5atm the value of water content in membrane and gas diffusion interface will increase about 20%. With increasing the water content in the membrane therefore the ohmic loss is reduced. With the reduction in the ohmic loss the temperature distribution along the fuel cell decreases but if the anode pressure increases the temperature distribution along the fuel cell increases. Keywords

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The use of metal foam as a distributor flow field in a polymeric electrolyte membrane fuel cells reduces the weight and volume of the fuel cell, causes more uniform distribution of the reactant gases, and in some cases eliminates the machining process required to create the flow channels. In this paper five models of polymer electrolyte membrane fuel cells are simulated including: the model that the bipolar plate consists of two parallel channels (model 1); The model that is similar to model 1 except that in this case channels are filled with metal foam (model 2); The model that the rib between the channels in anode and cathode side are eliminated and in the anode, metal foam is placed (model 3); the model that is similar to model 3 except that the metal foam is placed on the cathode side (model 4); in model 5, both the anode side and the cathode side are filled with metal foam. The results show that the use of metal foam in the anode or the cathode side in addition to decreasing maximum temperature in the models also helps a more uniform temperature distribution. The uniformity index shows that the distribution of current density is much better and more uniform, when the ribs in models 3, 4 and 5 are eliminated. Comparison conducted between different models shows that the pressure drop caused by the presence of the metal foam, due to the high coefficient of permeability and porosity ‍ of the foam, is small.

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Solid oxide fuel cells competence in combination with gas turbine cycle has caused the obtained synthetic system to become as a new power production system in consideration of different researchers. One of the important applications of this type of hybrid systems is to use them in UAV propulsion systems and in airliners as an APU. The main purpose of this research is design of a hybrid APU equipped to solid oxide fuel cell that would be one of the basic requirements for electric power generation in larger aircrafts in the future. Design parameters and decision-making variables in analysis of this system are the compressor pressure ratio, gas temperatures entrance to turbine and the number of selected cells. The results show that the system’s increasing pressure causes decrease in the temperature of outlet gases from the turbine and the cell’s operating temperature; and this problem severely affects the productivity and efficiency of the electrical system. At 1000 ° C for entrance gases to the turbine, electrical efficiency of system is about 49 percent. Also, the maximum electrical efficiency of the system in fuel cell is estimated to be about 55 percent. The obtained result shows that in case of controlling the generated heat in the cell and effective usage of it, the overall system efficiency will be augmentable about 84 percent. On the other hand, increasing the number of cells will cause increasing electrical efficiency and reducing the overall efficiency of the fuel cell hybrid system.

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The present study investigates the manufacturing process of metallic bipolar plates made of SS316L with a thickness of 0.1 mm using rubber pad forming process. Two deformation types, convex or concave patterns, were used for producing channels in bipolar plates. The effect of concave and convex patterns on forming forces and slots filling will be created in this present study and then suitable condition for both patterns of deformation are achieved. For carrying out the experimental examination, two dies, convex and concave pattern within equal dimensions were designed and manufactured. In order to correct comparison of two die patterns, a rubber pad with hardness of Shore A 85 and thickness of 25 millimeters was used for forming of plates. A hydraulic press with capacity of 200 tons was used to make force on die. The concluded results signify that in an equal magnitude of force, die with convex pattern shows more depth of filling than concave die. By increasing magnitude forming force up to maximum limit, depth of filling in concave die will be constant and more increasing in magnitude of force will cause to destroy the rubber.

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Reactant gases should be humidified before entering a polymer electrolyte membrane (PEM) fuel cell stack. Humidification of the gases can be performed by a membrane humidifier. In the present study, an analytical model has been proposed to investigate the performance of a water-gas membrane humidifier which is used in the fuel cell systems. At first, a set of nonlinear equations was obtained by applying the mass and energy conservation laws on the gas side of the humidifier. The temperature and the humidity ratio of the outlet gases from the humidifier are the unknowns of these nonlinear equations. The proposed model can evaluate the performance of the humidifier based on the temperature and relative humidity of the outlet gases from the humidifier. The effects of different parameters like: gas flow rate, channel's length and depth, temperature and pressure of the inlet gases on the performance of the humidifier were studied by the developed model. The results show that the channel depth does not have an effect on the temperature and humidity of the humidified outlet gases. In addition, increasing the channel length causes an increase on the dew point of the outlet gases but the relative humidity of the dry inlet gas does not have a noticeable effect on the dew point of the outlet gases. Increasing the temperature of the inlet gases cannot improve the humidifier performance, considerably. The results of the model show that increasing the inlet pressure and using less air flow improve the humidifier performance.

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Using the renewable energy resources has attracted the attention of researchers and automobile companies, because of limited fossil fuel resources, low efficiency of internal combustion engines and their environmental pollutions. By using the fuel cell systems instead of internal combustion engines can be partially overcome these problems. In this regard, the present article examines a PEM fuel cell system for using in an urban vehicle. In the first part of this article, by using the real component of system, the fuel cell system components including stack, membrane humidity of air and hydrogen, air compressor, water pump and pump cooler stack has been modeled in MATLAB Simulink environment. The mentioned model can evaluate the power consumption of system and its peripheral component and also required water, hydrogen and air for system. At the base case and the current density of 0.7A / cm2, 14% of power productions of stack are consumed by auxiliaries units. At this current density, the overall and net system efficiencies are 48.15% and 34.3%. In the second part of this article, the system from the point of view of the first law of thermodynamics has been optimized with objective functions of maximum output power and maximum efficiency. The results indicate that first model search method is best method for optimization, second at the Optimization with the aim of maximum power, pure power and system efficiency are increased 11.9% and 4% respectively and the power consumption by auxiliary unit is reduced 42%.