The ejectors used for the fuel cell recirculation are more reliable and low cost in maintenance than high-temperature blowers. In this paper, an anode and cathode recirculation scheme, equipped with ejectors, was designed in a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system. The ejector model, SOFC model, and other component models and the validation were conducted to investigate the performance of the hybrid system with anode and cathode ejectors. The geometric parameters of the ejectors were designed to perform the anode and cathode recirculation loops according to the design conditions of the hybrid system with a blower-based recirculation loop. The cathode ejector geometries are much larger than the anode ejector. In addition, the sensitivity analysis of the primary fluid for the standalone anode and cathode ejectors is investigated. The results show that the ejector can recirculate more secondary fluid by reducing the ejector outlet pressure. Then, the anode and cathode ejectors were integrated into the SOFC-GT hybrid system. A blower gets involved downstream, and the compressor is necessary to avoid high expensive cost of redesigning compressor. The off-design and dynamic performance were characterized after integrating the anode and cathode ejectors into the hybrid system. The dynamic and off-design performances show that the designed ejectors are effectively integrated into the anode and cathode recirculation loops to replace the blower-based recirculation loops. The safety range of relative fuel flow rate is 0.62–1.22 in the fixed rotational speed strategy, and it is 0.53–1.1 in the variable rotational speed strategy. The variable rotational speed strategy can ensure higher system efficiency, which is more than 61% at a part-load condition.

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/Al 2 O 3 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.

Thermal management of Li-ion battery packs is a critical technological challenge that directly impacts safety and performance. Removal of heat generated in individual Li-ion cells into the ambient is a considerably complicated problem involving multiple heat transfer modes. This paper develops an iterative analytical technique to model conjugate heat transfer in coolant-based thermal management of a Li-ion battery pack. Solutions for the governing energy conservation equations for thermal conduction and convection are derived and coupled with each other in an iterative fashion to determine the final temperature distribution. The analytical model is used to investigate the dependence of the temperature field on various geometrical and material parameters. This work shows that the coolant flowrate required for effective cooling can be reduced significantly by improving the thermal conductivity of individual Li-ion cells. Further, this work helps understand key thermal–electrochemical trade-offs in the design of thermal management for Li-ion battery packs, such as the trade-off between temperature rise and energy storage density in the battery pack.

Several experiments have proved that water in liquid phase can be present at the anode of a PEM fuel cell due to vapor condensation resulting in mass transport losses. Nevertheless, it is not yet well understood where exactly water tends to cumulate and how the design of the gas channel (GC) and gas diffusion layer (GDL) could be improved to limit water cumulation. In the present work, a three-dimensional lattice Boltzmann based model is implemented in order to simulate the water cumulation at the GC–GDL interface at the anode of a PEM fuel cell. The numerical model incorporates the H2–H2O mixture equation of state and spontaneously simulates phase separation phenomena. Different simulations are carried out varying pressure gradient, pore size, and relative height of the GDL. Results reveal that, once saturation conditions are reached, water tends to cumulate in two main regions: the upper and side walls of the GC and the GC–GDL interface, resulting in a limitation of the reactant diffusion from the GC to the GDL. Interestingly, the cumulation of liquid water at the interface is found to diminish as the relative height of the GDL increases.

The objective of this research is to predict how the placement of structural light guides within a column photobioreactor (PBR) affects the fluid mechanics and heat transfer of the system. The photobioreactor studied is modeled and analyzed using computational fluid dynamics (CFD). A bubble sparger provides carbon dioxide and mixing. Five different arrays and eight carbon dioxide volumetric flow rates are tested. Based on this setup, the bubble flow patterns, velocities, and temperature distributions are analyzed and the recommended placement of light guides is determined for predicting the growing conditions suitable for microalgae and other photosynthetic organisms.

Manufacturing of catalyst layers is one of the key processing steps in making membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). The catalyst ink, which usually contains catalysts, ionomers, solvents, and additives, is generally applied to the substrate by a wet-coating technique. Established coating techniques which are used for manufacturing catalyst layers for fuel cells are knife-coating, screen-printing, and spraying. Slot-die coating is also an established coating technique, but not currently used for making fuel cell electrodes. For each coating technique the properties of the catalyst layer will depend on the properties of the coating technique and the properties of the substrate. Also each coating technique requires the catalyst ink to be adjusted to its specific rheological requirements. In this study, slot-die coating is developed as a new method for the continuous manufacture of catalyst layers for direct methanol fuel cells. The rheological demands for a homogeneous layer thickness are studied with model inks and a suitable catalyst ink is prepared. With this ink, decal electrodes are fabricated and CCM-type MEAs are made. Fuel cell tests show that the performance of the slot-die coated electrodes is comparable to electrodes made by knife-coating.

In this paper, the prototype of a circular molten carbonate fuel cell (MCFC) built in the laboratories of FN SpA Nuove Tecnologie e Servizi Avanzati is analyzed using a tridimensional computational fluid dynamic (CFD) model. The prototype is the result of FN and Politecnico di Torino activities developed for the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) within the framework of Ministry of Economic Development, MSE-ENEA. This model considers heat, mass and current transfer as well as chemical and electrochemical reactions. The results show that some inhomogeneous distributions in the reactants, causing nonoptimal use of the reactant surfaces. An effective way to improve the distribution in current density consists in tracing tree shaped channels on the surface onto the distribution porous medium. In this paper, Y shaped channels are adopted to improve the distribution of gas within the fuel cell and consequently to enhance the performance of the original design of the fuel cell. In addition, the configuration of the outlet of the anodic compartment is also investigated in order to further increase the performance of the fuel cell. The geometrical parameter identifying the topology of distribution channels are chosen accordingly to the constructal theory. The results show that significant improvements can be achieved. Power density is increased of about 6% when the tree-shaped channel is adopted. If a double anodic inlet is also considered, the enhancement in the power density is of about 11% with respect to the initial configuration.

In this paper we analyze the three-dimensional flow field in anode and cathode gas channels of polymer electrolyte membrane (PEM) fuel cells operating at high temperature (T >100 °C). Different gas flow channel designs (pin-type, parallel channels, comb-tipe and multiple serpentine), as well as different channel sections (squared, trapezoidal and rounded with different curvature radii) are evaluated in function of some relevant parameters. The analysis is performed accounting for overall pressure losses, gas distribution over the electrode area and residence time with focus on channel hydraulic diameter, active surface ratio, gas path. Differences with low temperature (LT) PEM fuel cell design are also adressed. The investigation is conducted by means of 3D-CFD softwares and the results of our simulations are compared to experimental data in literature.

This work presents direct numerical simulations of two-phase flows in fuel cell minichannels. Different two-phase flow configurations can be observed in such minichannels, which depend on gas-flow rate, liquid holdup, and wettability of each wall. These flows are known to have a significant impact on the fuel cell’s performance. The different two-phase flow configurations must be studied specially concerning the prediction of the transition among them. In the fuel cell minichannels, experimental investigations are difficult to perform because of the small size of the device and the difficult control of the wettability properties of the walls. In such systems, numerical approach can provide useful information with a perfect control of the flow characteristics, particularly for the wettability aspect. The numerical code used in this study is the JADIM code developed at IMFT, which is based on a “volume of fluid” method for interface capturing without any interface reconstruction. The numerical description of the surface tension is one of the crucial points in studying such systems where capillary effects control the phase distribution. The static and the dynamics of the triple line between the liquid, the gas, and the wall is also an essential physical mechanism to consider. The numerical implementation of this model is validated in simple situations where analytical solutions are available for the shape and the pressure jump at the interface. In this paper we present the characteristics of the JADIM code and its potential for the studies of the fuel cell internal flows. Numerical simulations on the two-phase flows on walls, in corners, and inside channels are shown.

Cost, durability, and reliability are the major issues hindering the commercialization of polymer electrolyte membrane fuel cells. Electrolyte membranes present in the fuel cell fails under chemical, thermal, and mechanical influences, which, in turn, results in the overall fuel cell failure. In the present work, 2D studies are performed to understand the effect of manufacturing processing conditions and materials on the quality of the high-temperature membranes. Multiphase computational fluid dynamics models are used for solving the flow behavior of a shear-thinning non-Newtonian fluid. The viscosity and velocities were found to have a profound effect on the membrane structure.

A three-dimensional steady-state electrochemical mathematical model is developed where the mass, fluid, and thermal transport processes are considered, as well as the electrochemical reaction phenomena. The influences of the parameters of interest, which include porosity, permeability, and the thickness of the gas diffusion layer, and the inlet gas stoichiometric ratio on the performance of fuel cells are identified. By applying the Powell algorithm, the optimum values of multiple parameters are obtained while optimizing the potential of the electrolyte phase at the membrane/cathode interface at a typical value of the cell voltage. Compared with the reference case, the optimized results, such as the oxygen mole fraction and the local current density distribution, provide useful information for a better design of fuel cells.

The use of proton exchange membrane fuel cells (PEFC) based power trains and stationary systems has been technically demonstrated but is still far from commercial application. Technical development is still required to reach cost and durability targets, and to this aim, modeling and simulation are useful tools to obtain both better understanding of the fundamental occurring processes and to shorten design-associated costs and time. In this paper, a hierarchical 3D-1D approach is proposed, to overcome the deficiencies of a full 1D approach and the characteristic computational costs of a full 3D approach. The polymeric membrane and catalyst layers are represented by a local 1D model, while channels, gas diffusion layers, and solid electrodes are modeled by a full 3D approach. The model capabilities are first investigated with respect to experimental data by means of a full fuel cell simulation; the main chemical, fluid dynamic, and thermal fields are then analyzed in a straight channel configuration. The proposed 3D/1D model is able to accurately represent PEFC specific phenomena and their physical coupling. It could be then successfully applied to both design and development.

Particle image velocimetry was used to measure 2D velocity fields in representative regions of interest within flow channels of interdigitated and single-serpentine proton exchange membrane (PEM) fuel cell models. The model dimensions, gas diffusion layer (GDL) permeability, working fluid, and flow rates were selected to be geometrically and dynamically similar to the cathode-side airflow in a typical PEM fuel cell. The model was easily reconfigurable between parallel, single-serpentine, and interdigitated flow fields, and was constructed from transparent materials to enable optical imaging. Velocity maps were obtained of both the primary and secondary flow within the channels. Measurements of the secondary flows in interdigitated and single-serpentine flow fields indicate that significant portions of the flow travel between adjacent channels through the porous medium. Such convective bypass can enhance fuel cell performance by supplying fresh reactant to the lands regions and also by driving out product water from under the lands to the flow channels.

Researchers at the National Institute of Standards and Technology have measured the performance of a residential fuel cell system when subjected to various environmental and load conditions. The system, which uses natural gas as its source fuel, is capable of generating electrical power at three nominal power levels (2.5, 4.0, and 5.0 kW ) while providing thermal energy for user-supplied loads. Testing was conducted to determine the influence of ambient temperature, relative humidity, electrical load, and thermal load on system performance. Steady-state and transient tests were conducted. The steady-state tests were performed in accordance with the American Society of Mechanical Engineering Fuel Cell Power Systems Performance Test Code (PTC-50) for fuel cell power systems. The results of the investigation are being used to develop a proposed rating procedure for residential fuel cell units.

The aim of this work is to build up a complete dynamical model of a molten carbonate fuel cell (MCFC) stack, describing both the thermo-fluid-dynamical and the electrochemical phenomena involved, i.e., both slow and (relatively) fast dynamics. Following a first-principle approach, a set of differential and algebraic equations is written, based on mass, momentum, energy, and charge balance referred to as small control volumes inside a cell. The outlined two-three-dimensional description takes into account the strong point-to-point anode and cathode reaction coupling due to gas crossflow. Simulations (carried out after suitable thermodynamical and electrochemical parameter tuning) highlight, for instance, the presence of dynamics, linked to the electrochemical behavior, with time constants on the order of a second; besides, rather fair matching to data which can be found in the literature is achieved, in terms of external potential difference and of electric power production. The obtained numerical results, therefore, support model correctness and reliability. This is useful in view of model-based cell operation analysis and control, both in stationary and in transient conditions.

Pressurized high temperature fuel cells and gas turbine integrated power systems are receiving growing attention as capable of reaching very high electrical conversion efficiency even in small size power plants. In this system the fuel and the oxidant (air) enter the cell after being compressed. The fuel oxidation reaction occurs predominantly within the fuel cell. The reaction is completed in a combustion chamber and the pressurized combustion products are exhausted through a turbine. The dynamic interdependences related to the integration of the fuel cell and the gas turbine are not completely understood and unexpected complications and dangers might arise. In fact as a consequence of both the relatively large volume of the pressurized portion of the plant and the shape of the stalled characteristic of available compressors, the plant could be affected by the inception of fluid-dynamic instabilities. In particular, surge could be detected in the transient off-design operational conditions occurring during plant regulation, start up and shut down. The paper presents a new experimental fuel cell gas turbine simulation facility that has been constructed at the Mechanical Engineering Department of the University of Trieste, Italy. The facility was designed to examine the effects of transient events on the dynamics of these systems. The theoretical analysis of the plant is completed using a dynamic model of the system purposely developed.

This paper presents the bubble transport phenomenon at the anode of a micro-direct methanol fuel cell ( μ DMFC ) from a mesoscopic viewpoint. Carbon dioxide bubbles generated at the anode may block part of the catalyst/diffusion layer and also the flow channels that cause the μ DMFC malfunction. Lattice-Boltzmann simulations were performed in this paper to simulate the two-phase flow in a microchannel with an orifice which emulates the bubble dynamics in a simplified porous diffusion layer and in the flow channel. A two-dimensional, nine-velocity model was established. The buoyancy force, the liquid-gas surface tension, and the fluid-solid wall interaction force were considered and they were treated as source terms in the momentum equation. Simulation results and parametric studies show that the pore size, the fluid stream flow rate, the bubble surface tension, and the hydrophilic effect between the fluid and the solid wall play the major roles in the bubble dynamics. Larger pore size, higher methanol stream flow rate, and greater hydrophilicity are preferred for bubble removal at the anode diffusion layer and also the flow channels of the μ DMFC .