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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.

To improve proton exchange membrane (PEM) electrolyzes’ performance the voltage loss through them should be avoided. In this work, it is intended to analyze losses including of diffusion loss, ohmic loss due to electrode, bipolar plate (BP), and membrane resistances, and gas crossover associated with the water transferring mechanisms. All of the losses are associated with water transferring mechanisms, which is created due to electro-osmoic drag, pressure differential between the anode and cathode sides, and diffusion. Furthermore, the effect of membrane thickness, cathode pressure, and operating temperature on the hydrogen crossover is examined. In addition, the contribution of ohmic loss due to electrode bipolar plate (BP), and membrane resistances is studied and, the contribution of different losses on the cell performance is discussed. Results show that raising cathode pressure from 1 to 40 bar lead to the increment of anodic hydrogen content from 1.038% to 21% at the specific current density of 10,000 A/m2. Enhancing the thickness of membrane has considerable impact on decrementing anodic hydrogen content, but the mass transfer loss rises from 0.022 to 0.027 V with enhancing membrane thickness from 50 to 300 μm, respectively. Furthermore, the contribution of voltage losses, assigned to each of losses are equal to 85%, 3%, and 12% for activation, diffusion and ohmic losses, respectively. It is found that, from the reported contribution for ohmic loss, the contribution of electrode BP, and membrane resistances are 31% and 69%, respectively.

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.

In this paper, a finite volume numerical method is developed to investigate a high temperature polymer exchange membrane (PEM) electrolyzer cell using a three-dimensional and non-isothermal model. The results that are obtained for the single cell are generalized to a full stack of electrolyzer and an exergoeconomic analysis is performed based on the numerical data. The effects of operating temperature, the pressure of cathode, gas diffusion layer (GDL) thickness, and membrane thickness on the energy and exergy efficiencies and exergy cost of the electrolyzer are examined. This study reveals that by increasing the working temperature from 363 K to 393 K, the exergy cost of hydrogen decreases from 23.16 $/GJ to 22.39 $/GJ, and the exergy efficiency of PEM electrolyzer stack at current density of 10,000 A/m2 increases from 0.56 to 0.59. The results indicate that increase of pressure deteriorates the system performance at voltages below 1.4 V. It is concluded that operation of the electrolyzer at higher pressures results in decrease of the exergy cost of hydrogen. Increase of membrane thickness from 50 μm to 183 μm leads to increase of the exergy cost of hydrogen from 23.24 $/GJ to 35.99 $/GJ.

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.

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.

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.

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 m...

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.

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.

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.

In the present study, a three dimensional numerical simulation is performed to investigate the heat and water transfer enhancement in a polymer membrane humidifier with partially blocked channel. The experimental tests are also conducted for validation purposes. The thermal-hydraulic performance factor (JF) is introduced as the main parameter to evaluate the humidifier performance with considering pressure drop. The higher value of JF indicates the higher heat transfer with the lower pressure drop. When there are equal mass flow rates at both wet and dry sides, three ranges of flow rates are identified. At low flow rates (less than 4.4 mg/s), with and without considering pressure drop, the blocked humidifier shows weaker performance than the simple humidifier, so blocking is not recommended under any circumstances. At moderate flow rates (between 4.4 mg/s and 6.65 mg/s), regardless of pressure drop, the performance of the blocked humidifier is better than that of the simple humidifier, and with considering the pressure drop, the blocked humidifier performs weaker. At high flow rates (greater than 6.65 mg/s), with and without considering pressure drop, the blocked humidifier performs better than the simple humidifier. The same trend holds for the case of constant dry side flow rate with the variable wet side flow rate.

A three-dimensional numerical model is developed to investigate and compare the performance of humidifiers with counter-flow and parallel-flow configurations. This model has a set of coupled equations including conservations of mass, momentum, species and energy. The results indicate that in counter-flow humidifier, water and heat transfer is more than that of the parallel-flow that leads to a higher dew point at dry side outlet, consequently, a better humidifier performance. An increase in temperature and a decrease in mass flow rate at dry side inlet lead to a better humidifier performance. However at the low flow rates the humidifier performance does not change a lot by preheating the inlet dry gas. An increase in relative humidity at dry side inlet does not offer any advantage.

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.

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.

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.

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.

Phosphorescence spectra of natural singlet oxygen 16O2(1Δg) and its heavier isotope 18O2(1Δg) have been recorded in several O2(1Δg) weakly deactivating solvents. Lifetimes of singlet oxygen were determined for both isotopes in 21 solvents. From these data rate constants kXY of deactivation of singlet oxygen by terminal oscillators X—Y of the solvent molecules are calculated revealing a graduated isotope effect of 1.0 ≤ 16kXY/18kXY ≤ 1.9. The unexpectedly low isotope effect points to the important role of overtone excitations of X—Y during O2(1Δg) deactivation. A modified collisional deactivation model including overtone excitation of the energy accepting oscillator reproduces the experimental findings: the tremendeous graduation of kXY of almost 5 orders of magnitude, the heavy atom effect, the O2 isotope effect and the very weak temperature effect on kXY.

The deactivation of O 2 ( 1 Δ g ) by ground-state O 2 was investigated by the direct time-resolved phosphorescence technique in four perhalogenated solvents at 295 K. A very strong isotope effect of k 16 Q / k 18 Q =70 was observed on the quenching rate constant, which is reproduced by the model developed by Maier, Wild, Klingshirn and Plotz for O 2 ( 1 Δ g ) deactivation in pure O 2 . Thus, solvent molecules do not support quenching by O 2 . k 16 Q ranges from 2600 M −1 s −1 in perfluorohexane to 4100 M −1 s −1 in perflourodecalin and is about three times larger than in gaseous 16 O 2 . The variation of k 16 Q correlates with changes in the packing fraction of the solvents.

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