bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of a Concentrating Solar Power Plant With Molten-Salt Thermocline Storage for Optimized Annual Performance
Authors: Flueckiger Scott M. , Iverson Brian D. , Garimella Suresh V.
Published: December 2013

A finite-volume-based model of a molten-salt thermocline tank is developed to achieve simulation at a sufficient level of detail but at low computational cost. Combination of this storage model with a system-level power tower plant model enables yearlong thermocline tank simulation in response to historical weather data and corresponding plant control. The current study simulates a 100 MWe molten-salt power tower plant to optimize annual plant performance as a function of the thermocline tank size and the plant solar multiple.

Thermocline storage performance is characterized by the effectiveness of the tank in storing and delivering utilizable heat for steam generation and power production. Additional system-level metrics include thermal energy discard due to saturation of storage capacity and annual plant capacity factor. Economic assessment of the power output is characterized with a simple levelized cost of electricity. Minimum cost is observed with a solar multiple of 3 and a thermocline tank storage capacity of 16 hours.
Application of New Timber Structure Building Envelope in China’s Solar Buildings
Authors: Luo Zhixing , Sun Yunlin , Liu Peng , Lu Junfan
Published: December 2013

Sustainable development could be seen as indispensable condition for survival of civilization. The development of timber products is a new paradigm in material and building science research in China, requiring the accounting for carbon emissions, carbon sequestration, material embodied energy, and material thermal properties for this renewable resource. This paper studies the application of the timber lattice wall in Chinese solar buildings. Firstly, it is analyzed timber structural form and mechanical property of the multi-ribbed composite wall, proving its high anti-seismic property and firmness by finite element modeling. Secondly, the timber structure filled with wheat straw brick contributes to low U-value of the wall, which is only 0.3 Watts per square meter per degree Celsius and far better than the code of Chinese building, greatly promoting building energy efficiency. Besides, the timber structure and straw brick are both “Cradle to Cradle” materials and reduce carbon emission compared to common building envelope. In the end, the paper is analyzed the promising market of the multi-ribbed composite wall for its competitive price and outstanding environmental performance.
Phase Change Material Thermal Energy Storage System Design and Optimization
Authors: Qiu Songgang , Galbraith Ross , White Maurice
Published: December 2013

Thermal energy storage (TES) system integrated with concentrated solar power provides the benefits of extending power production, eliminating intermittency issues, and reducing system LOCE. Infinia Corporation is under the contract with DOE in developing TES systems. The goal for one of the DOE sponsored TES projects is to design and build a TES system and integrate it with a 3 KWe free-piston Stirling power generator. The Phase Change Material (PCM) employed for the designed TES system is a eutectic blend of NaF and NaCl which has a melt temperature of 680° C and energy storage capacity of 12 KWh. This PCM was selected due to its low cost and desired melting temperature. This melt temperature ensures the Stirling being operated at designed operating hot end temperature. The latent heat of this eutectic PCM offers 5 to 10 times the energy density of a typical molten salt. The technical challenges associated with low cost molten salt TES systems are the low thermal conductivity of the salt and large thermal expansion. To address these challenges, an array of sodium filled Heat Pipes (HP) is embedded in the PCM to enhance the heat transfer from solar receiver to PCM and from PCM to Stirling engine. The oversized dish provides sufficient thermal energy to operate a 3KWe Stirling engine at full power and to charge up the TES. The HP arrays are optimally distributed so that the solar energy is transferred directly from receiver to Stirling engine heat receiver. During the charge phase, the Stirling engine absorbs and converts the transferred solar energy to electricity and the excess thermal energy is re-directed and stored to PCM. The stored energy is transferred via distributed HP from PCM to Stirling engine heat receiver during discharge phase.

The HP based PCM thermal energy storage system was designed, built, and performance tested in laboratory. The TES/engine assembly was tested in two different orientations representing the extremes of system operation when mounted on sun-tracking dish, horizontal and vertical. Horizontal represents the zero elevation at sun rise and the vertical represents the extreme of solar noon. The testing allows the examination of orientation effect on the heat pipe performance and the maximum charge and discharge rates. The total energy stored and extracted was also examined. The areas for further system refinements were identified and discussed.
Analysis of the Manifold Area Change in a Flat Solar Collector
Authors: Uzarraga-Rodriguez N. C. , Gallegos-Muñoz A. , Payan-Rodriguez Luis A. , Belman-Flores Juan M.
Published: December 2013

A numerical analysis of the characterization of the water flow through a flat solar collector is presented. The manifold area change for minimizing the water flow variation in the solar collector is analyzed. The area ratio in the inlet and outlet of the manifolds were modified in a range of Am/Ao = 1 to 4, where Am and Ao are the cross-sectional area modified and original of the manifolds, respectively. The solar collector investigated is equipped with six riser tubes, which are attached to the manifolds pipe. The numerical study was developed in a commercial Computational Fluid Dynamics (CFD) using FLUENT®. This code allows to solve the Reynolds averaged Navier-Stokes equations and the transport equations of the turbulence quantities. The results shown that increasing the inlet and outlet area of the manifolds allow a more uniform flow distribution compared to the original configuration of the solar collector. It also shows that the overall pressure drop in the solar collector is reduced.
Fabrication of Low Cost Metal-Based Micro-Capillary Channels for Thermal Scavenging and Heat Transfer
Authors: Ogbonnaya E. , Weiss L.
Published: December 2013

In this work, we present a low cost method for the fabrication of a heat exchanger utilizing metal-based microchannels using the LiGA technique. Lithography is used to pattern dry film negative photoresist (Ordyl P-50100) on the substrate. The resist is laminated over the substrate and exposed with a UV source. The use of dry film resist allows for simple and inexpensive microchannel patterns without requiring advanced cleanroom equipment. Following the lithography process, electrodepostion of metals is used to fill the recesses patterned in the resist. In this work, nickel has been electroplated into the bounding resist structure. After electroplating, the remaining resist is dissolved leaving free standing metal structures. The fabricated exchanger is then evaluated based on thermal absorption of simulated waste heat sources and capillary action of the metal channels themselves.

Channels are fabricated to heights of 60, 70 and 90 μm respectively using these methods. Working fluid mass transfer rate from the heated MHE is utilized as a basic metric of operation. The mass transfer rate recorded from the nickel-based MHE is 3.35, 3.37 and 3.41 mg/s respectively for the different channel heights. This implies an effective thermal power consumption rate of 2.54, 2.56 and 2.59 kW/m2 respectively.
Development of Self-Cleaning Solar Collectors for Minimizing Energy Yield Loss Caused by Dust Deposition
Authors: Mazumder Malay , Horenstein Mark , Stark Jeremy , Erickson Daniel , Sayyah Arash , Jung Steven , Hao Fang
Published: December 2013

Concentrated Solar Power (CSP) systems used for photothermal conversion of solar energy to electricity are capable of meeting a large fraction of the global energy requirements. CSP plants are inherently robust with respect to the availability of materials, technology, and energy storage. However, dust depositions on solar collectors cause energy yield loss annually, ranging from 10 to 50% depending upon their location in the semi-arid and desert lands. Mitigation of energy loss requires manual cleaning of solar mirrors with water. A brief review of the soiling related losses in energy yield of the CSP plants is presented, which shows that cleaning of the CSP mirrors and receivers using water and detergent is an expensive and time-consuming process at best and is often impractical for large-scale installations where water is scarce. We report here our research effort in developing an electrodynamic dust removal technology that can be used for keeping the solar collectors clean continuously without requiring water and manual labor. Transparent electrodynamic screens (EDS), consisting of rows of transparent parallel electrodes embedded within a transparent dielectric film can be integrated on the front surface of the mirrors and on the receivers for dust removal for their application as self-cleaning solar collectors. When the electrodes are activated, over 90% of the deposited dust is removed. A summary of the current state of prototype development and evaluation of EDS integrated solar mirrors and experimental data on the removal of desert dust samples are presented. A brief analysis of cost-to-benefit ratio of EDS implementation for automated dust removal from large-scale solar collectors is included.
Using Integration of Thermal-Balance Based and Data-Driven Models to Determine Single Duct Variable Air Volume System Cooling Baseline
Authors: Shim Gyujin , Song Li , Wang Gang
Published: December 2013

In order to use real-time energy measurements to identify system operation faults and inefficiencies, a cooling coil energy baseline is studied in an air-handling unit (AHU) through an integration of physical models and a data driven approach in this paper. A physical model for an AHU cooling coil energy consumption is first built to understand equipment mechanism and to determine the variables impacting cooling coil energy performance, and then the physical model is simplified into a lumped model by reducing the number of independent variables needed. Regression coefficients in the lumped model are determined statistically through searching optimal fit using the least square method with short periods of measured data. Experimental results on an operational AHU (8 ton) are presented to validate the effectiveness of this approach with statistical analysis. As a result of this experiment, the proposed cooling energy baselines at the cooling coil have ±20% errors at 99.7% confidence. Six-day data for obtaining baseline is preferred since it shows similar results as 12-day.
Model Based Analysis of an Integrated System of Vapor-Compression Chiller and Absorption Heat Pump
Authors: Kung Yi-Shu , Qu Ming , Peng Steve
Published: December 2013

Subcooling of the refrigerant at the exit of the condenser in a vapor compression refrigeration system could be an effective method to improve the coefficient of performance (COP). This method allows the refrigerant entering the evaporator with a lower mass fraction of vapor and absorbs more heat in the evaporator. The effort in this paper investigates a solar based integrated system of an electricity-driven vapor-compression chiller (VC) and an absorption heat pump (ABS) to provide both heating and cooling to space. Thermodynamic and heat transfer models of the integrated system were developed to estimate the system performance. The modeling results showed the integrated system can achieve 40% of the reduction on electricity consumption and 66% of the improvement in cooling COP. Furthermore, the hot water supply temperature can reach 50.25°C.

The models have also been used to conduct parametric sensitivity analysis. The key parameters which affect the performance of the system were the heat source temperature, the hot water return temperature, and the outdoor air flow rate. Hot water flow rate only has significant influence on the hot water supply temperature. Increasing the temperature and flow rate of the heat source can have benefits on both heating and cooling performance. However, increasing the outdoor air flow rate can only benefit on energy saving and cooling performance.
Investigating the Correlation Between Wind and Solar Power Forecast Errors in the Western Interconnection
Authors: Zhang Jie , Hodge Bri-Mathias , Florita Anthony
Published: December 2013

Wind and solar power generation differ from conventional energy generation because of the variable and uncertain nature of their power output. This variability and uncertainty can have significant impacts on grid operations. Thus, short-term forecasting of wind and solar power generation is uniquely helpful for balancing supply and demand in an electric power system. This paper investigates the correlation between wind and solar power forecast errors. The forecast and the actual data were obtained from the Western Wind and Solar Integration Study. Both the day-ahead and 4-hour-ahead forecast errors for the Western Interconnection of the United States were analyzed. A joint distribution of wind and solar power forecast errors was estimated using a kernel density estimation method; the Pearson’s correlation coefficient between wind and solar forecast errors was also evaluated. The results showed that wind and solar power forecast errors were weakly correlated. The absolute Pearson’s correlation coefficient between wind and solar power forecast errors increased with the size of the analyzed region. The study is also useful for assessing the ability of balancing areas to integrate wind and solar power generation.
A Development of the Fuel Cell System That the Jet-Pump is Applied
Authors: Jung Se Kwon , Noh Yong Gyu , Jeon Ui Sik
Published: December 2013

A fuel cell system is developed by applying a jet-pump system that performs hydrogen supplying and anode recirculation functions. The jet-pump system made up of an ejector and a proportional valve is designed to substitute conventional ejector-blower hydrogen recirculation system. The impulsive fuel feeding applied to overcome the ejector performance limits in low-power conditions. The fuel supply valve moves like injector to operate ejector at a design point in short time and does not works in remain time of each period. Therefore, average performance of ejector is better than continuous fuel feeding condition. The jet-pump compares aerodynamic performances with the blower and installed in the 100kW fuel cell system also. As a result, 25Hz and duty 75% conditions show above 80% of ejector-blower performance under 10kW emulation condition and three conditions demonstrates better performance over 10kW condition. Applicability of Jet-pump is verified at fuel cell system also. The system integrated jet-pump maintains stable state and shows equal level of ejector-blower applied case in Min. cell ratio and voltage decrease test results.
Water Management in PEMFC With Ultra-Thin Catalyst-Layers
Authors: Das Prodip K. , Weber Adam Z.
Published: December 2013

A two-dimensional non-isothermal multi-physics proton-exchange-membrane fuel-cell (PEMFC) modeling has been undertaken to investigate the interplay between the platinum (Pt) loading, water-capacity, water transport and cell performance at low operating temperatures (< 40 °C). Two ultra-thin catalyst layers (CLs), traditional Pt/C with extremely low Pt loading and nano-structured thin-film (NSTF), have been the main focus in the present model. Modeling data are compared with experimental polarization curves for both NSTF and traditional Pt/C CLs. Using the model, the interplay between the inherent CL water-capacity versus its removal rate through either the anode or cathode side of the PEMFC is explored. The controlling parameters for the water removal and accumulation (e.g., thickness of catalyst layer, existence of microporous layer, etc.) are also analyzed and the tradeoff between these parameters elucidated with a path towards efficient water management for ultra-thin CLs.
Exergogravimetric Design for Increased SOFC System Power Density
Authors: Haynes Comas , Miller Ryan
Published: December 2013

Compact subsystems are pivotal to aeronautical applications, inclusive of advanced energy concepts. Regarding size minimization, an “exergogravimetric” approach has recently begun that attempts an exergy-aided weight reduction of advanced energy systems (inclusive of fuel); and this is based upon the added design insights afforded by Second Law considerations. The chief rationale and objective are to leverage the advancements that exergoeconomics affords in the realm of cost-effective thermal system design to aid size-effective thermal system design. A conceptual solid oxide fuel cell (SOFC) system for long-duration unmanned aerial vehicle (UAV) applications has been initially modeled and simulated, inclusive of exergy analysis, and preliminary findings are discussed. Additionally, the concepts and methodologies can be extended to other advanced energy system technologies.

There are project-specific and general milestones and conclusions drawn from the initial investigation. Specific to the project, a conceptual SOFC system simulation was completed via physics-based and literature-verified models along with structured language (i.e., MATLAB) numerical implementation. Specific component-level contributions to lost power potential and added mass were preliminarily resolved. Thermal exergy destruction and loss are predominant sources of unutilized specific power potential. Operational and physical degrees-of-freedom were explored, with the aid of exergy analysis, to resolve better design pathways. This included a counterintuitive preliminary finding that larger cell interconnects may facilitate smaller and more efficient system operation.

Generally, exergy analyses allow a system design opportunity to gain higher resolution insights (i.e., to component- and spatial-extents) regarding inefficiencies throughout a thermal system, and this is afforded by the comprising blend of 1st Law and 2nd Law considerations. There is also an added means of accounting for 2nd Law effects. The traditional 2nd Law verification point of entropy generation being non-negative does not provide the same level of process analysis closure as does the related constraint that all processes have to account for exergy being stored, converted, destroyed or rejected through any defined control volume. This alternative 2nd Law perspective facilitates verification and validation of simulations.
Effect of PTFE on Thermal Conductivity of Gas Diffusion Layers of PEM Fuel Cells
Authors: Sadeghifar Hamidreza , Djilali Ned , Bahrami Majid
Published: December 2013

Through-plane thermal conductivity of 14 SIGRACET gas diffusion layers (GDLs), including series 24 & 34, as well as 25 & 35, are measured under different compressive pressures, ranging from 2 to 14 bar, at the temperature of around 60 °C. The effect of compression, PTFE loadings, and micro porous layer (MPL) on thermal conductivity of the GDLs and their contact resistance with an iron clamping surface is experimentally investigated. The contact resistance of MPL coated on GDL with the substrate of that GDL is measured for the first time in this paper. A new robust mechanistic model is presented for predicting the through-plane thermal conductivity of GDLs treated with PTFE and is successfully verified with the present experimental data. The model can predict the experimentally-observed reduction in thermal conductivity as a result of PTFE treatment and provides detailed insights on performance modeling of PEMFCs.
Design and Balance-of-Plant of a Demonstration Plant With a Solid Oxide Fuel Cell Fed by Biogas From Waste-Water and Exhaust Carbon Recycling for Algae Growth
Authors: Gandiglio M. , Lanzini A. , Leone P. , Santarelli M.
Published: December 2013

The design and balance-of-plant of an integrated anaerobic digestion (AD) biogas solid oxide fuel cell (SOFC) demonstration plant is presented. A notable feature of the plant is the CO2 capture from the SOFC anode exhaust via an oxy-combustion reactor. The captured CO2 is fed to a photobioreactor installation downstream of the SOFC where C is fixed in an algae bio-fuel.

The main plant sections are described in detail including the gas cleaning unit, fuel processing, SOFC ‘hot-box’, oxy-combustor, CO2/H2O condensation unit and finally algae bioreactor.

The demonstration plant is fed with biogas from AD of the by-product sludge of the greatest waste-water treatment plant in Italy, serving over 2 million population equivalents in the Torino metropolitan area.

In this work, the main BoP components and engineering issues concerning the design of the SOFC plant are detailed. The as-produced biogas is firstly treated to remove moisture and then filtered to remove sulfur, halogens and siloxanes. Dry clean biogas (roughly 60–65% CH4, 35–40% CO2) is sent to a steam-reformer. The reformate gas is thus used to feed a 2 kWe SOFC module (operated at ∼ 800 °C). The cathode off-gas is kept separated from the anode and is used to pre-heat inlet fresh air; the anode outlet stream is sent first to an oxy-combustor to yield an almost pure H2O-CO2 mixture that is eventually cooled down to 300–400 °C. Steam is condensed and separated in a dedicated condenser unit. The resulting pure CO2 is thus pressurized (8 bar) and available for sequestration or other uses. Due to the limited size of the demo plant, the choice was to feed it to bioreactors with algae, where the latter are grown with sunlight and CO2 indeed. A tubular photo-bioreactor has been chosen with a productivity of 20 g/day/m2 of dry algae. The outlet stream will be an algae purge that, due to its low mass flow, could be re-sent to the biogas digesters.

A system analysis of a scaled-up version of the biogas fed SOFC power plant, with heat integration included, is also carried out with a calculated overall electrical efficiency exceeding 55% (LHV basis).
Crack Generation in Catalyst Layer and Micro Porous Layer by Wet-Dry Cycles and its Impact on PEMFC Performance
Authors: Matsui Y. , Suzuki T. , Deevanhxay P. , Tsushima S. , Hirai S.
Published: December 2013

In this study, we focused on nano- and micro-scale cracks in the catalyst layer and the micro porous layer of polymer electrolyte membrane fuel cells (PEMFCs) and its impact on cell performance. We applied wet-dry cycles to a conventional test cell to investigate crack generation in the catalyst layer and the micro porous layer. Wet-dry cycles, in which cell temperature was kept at 353K with high- and low-humidified gas alternately applied to the cell, potentially induced mechanical stress to a membrane electrode assembly (MEA) due to membrane hydration and dehydration. As a result, significant degradation of performance was found after the wet-dry cycles. We performed cross-sectional analysis of MEA by using a cross-sectional polisher (CP) and scanning electron microscopy (SEM) to investigate nano- and micro-scale crack generated by the wet-dry cycles in the MEA. The SEM images showed that nano- and micro-scale cracks were significantly generated in the catalyst layer as well as in the micro porous layer after the cycles. We identified cracks in the MEA with different morphologies according to the SEM images, hence, through-plane cracks and in-plane cracks. Through-plane cracks have a deep-valley structure in the MEA while in-plane cracks are formed in an interfacial region between the catalyst layer and the micro porous layer. In-plane cracks could be generated by detachment of the catalyst layer from the micro porous layer due to the wet-dry cycles and potentially decrease in cell performance due to deterioration of electron transport in the MEA. In addition, in case liquid water is accumulated in in-plane cracks, these cracks potentially disturb gas diffusion from the micro porous layer to the catalyst layer. These results clearly showed that mechanical stress induced crack generation in the MEA, resulting in intensive effects on cell performance in PEMFC.
Effect of Gravity on Droplet Growth and Detachment Inside a Simulated PEM Fuel Cell Air Flow Channel With Hydrophobic Walls
Authors: Munoz Andres , Mukherjee Abhijit
Published: December 2013

Water management still remains a challenge for proton exchange membrane fuel cells. Byproduct water formed in the cathode side of the membrane is wicked to the air supply channel through the gas diffusion layer. Water emerges into the air supply channel as droplets, which are then removed by the air stream. When the rate of water production is higher than the rate of water removal, droplets start to accumulate and coalesce with each other forming slugs consequently clogging the channels and causing poor fuel cell performance. It has been shown in previous experiments that rendering the channels hydrophobic or super-hydrophobic cause water droplets to be removed faster, not allowing time to coalesce, and therefore making channels less prone to flooding. In this numerical study we analyze water droplet growth and detachment from a simulated hydrophobic air supply channel inside a proton exchange membrane (PEM) fuel cell. In these numerical simulations the Navier-Stokes equations are solved using the SIMPLER method coupled with the level set technique in order to track the liquid-vapor interface. The effect of the gravity field acting in the −y, −x, and +x directions was examined for an array of water flow rates and air flow rates. Detachment times and diameters were computed. The results showed no significant effect of the gravity field acting in the three different directions as expected since the Bond and Capillary numbers are relatively small. The maximum variations in detachment time and diameter were found to be 8.8 and 4.2 percent, respectively, between the horizontal channel and the vertical channel with gravity acting in the negative x direction, against the air flow. Droplet detachment was more significantly affected by the air and water flow rates.
Non-Isothermal Hydrodynamic Modelling of the Flowing Electrolyte Channel in a Flowing Electrolyte-Direct Methanol Fuel Cell
Authors: Duivesteyn Eric , Cruickshank Cynthia A. , Matida Edgar
Published: December 2013

The performance of a direct methanol fuel cell (DMFC) can be significantly reduced by methanol crossover. One method to reduce methanol crossover is to utilize a flowing electrolyte channel. This is known as a flowing electrolyte-direct methanol fuel cell (FE-DMFC).

In this study, recommendations for the improvement of the flowing electrolyte channel design and operating conditions are made using previous modelling studies on the fluid dynamics in the porous domain of the flowing electrolyte channel, and on the performance of a 1D isothermal FE-DMFC incorporating multiphase flow, in addition to modelling of the non-isothermal effects on the fluid dynamics of the FE-DMFC flowing electrolyte channel.

The results of this study indicate that temperature difference between flowing electrolyte inflow and the fuel cell have negligible hydrodynamic implications, except that higher fuel cell temperatures reduce pressure drop. Reducing porosity and increasing permeability is recommended, with a porosity of around 0.4 and a porous material microstructure typical dimension around 60–70 μm being potentially suitable values for achieving these goals.
In-Plane Microstructure of Gas Diffusion Layers With Different Properties for PEFC
Authors: Mortazavi Mehdi , Tajiri Kazuya
Published: December 2013

Gas diffusion layer (GDL) is undoubtedly one of the most complicated components used in a polymer electrolyte fuel cell (PEFC) in terms of liquid and gas transport phenomena. An appropriate fuel cell design seeks a fundamental study of this tortuous porous component. Currently, porosity and gas permeability have been known as some of the key parameters affecting liquid and gas transport through GDL. Although these are dominant parameters defining mass transport through porous layers, there are still many other factors affecting transport phenomena as well as overall cell performance. In this work, microstructural properties of Toray carbon papers with different thicknesses and for polytetrafluoroethylene (PTFE) treated and untreated cases have been studied based on scanning electron microscopy (SEM) image analysis. Water droplet contact angle as a dominant macroscale property as well as mean pore diameter, pore diameter distribution, and pore roundness distribution as important microscale properties have been studied. It was observed that the mean pore diameter of Toray carbon paper does not change with its thickness and PTFE content. Mean pore diameter for Toray carbon papers was calculated to be around 26μm regardless of their thicknesses and PTFE content. It was also observed that droplet contact angle on GDL surface does not vary with GDL thickness. The average contact angle for 10 wt.% PTFE treated GDLs of different thicknesses was measured about 150°. Finally, the heterogeneous in-plane PTFE distribution on the GDL surface was observed to have no effect on mean pore diameter of GDLs.
Comparison of Solid Oxide Fuel Cell Stack Performance Using Detailed and Simplified Models
Authors: Nishida R. T. , Beale S. B. , Pharoah J. G.
Published: December 2013

Two computational fluid dynamics models have been developed to predict the performance of a solid oxide fuel cell stack, a detailed and a simplified model. In the detailed model, the three dimensional momentum, heat, and species transport equations are coupled with electrochemistry. In the simplified model, the diffusion terms in the transport equations are selectively replaced by rate terms within the core region of the stack. This allows much coarser meshes to be employed at a fraction of the computational cost. Following the mathematical description of the problem, results for a single cell and multi-cell stack are presented. Comparisons of local current density, temperature, and cell voltage indicate that good agreement is obtained between the detailed and simplified models, confirming the validity of the latter as a practical option in stack design.
On-Line In-Situ Diagnostics of Processes Within HT-PEM Fuel Cells Membrane by Raman Microscopy
Authors: Bettermann Hans , Labus Martin , Majerus Anne , Korte Carsten , Lehnert Werner
Published: December 2013

This contribution describes how Raman spectroscopy can be applied to investigate the distribution of molecular species inside an ABPBI membrane of a running PEM fuel cell. For the in-situ measurements an experimental setup was first developed and then used to identify phosphoric acid species and to record how they change their concentrations when the current consumption of the fuel cell was changed. The observation port to look inside the membrane was placed next to the cathode. At that location among orthophosphoric acid, H3PO4·H2O, a lot of oligophosphoric acid species are present where pyrophosphoric acid could unambiguously be identified. In comparison to all identified species pyrophoshoric acid and polyphosphoric acid undergo largest concentration changes when the current was changed.
Effect of Porosity and Thermal Conductivity of a Porous Transport Layer on Saturation and Thermal Transport in a Low-Temperature Fuel Cell
Authors: Konduru Vinaykumar , Medici Ezequiel , Allen Jeffrey S.
Published: December 2013

Water transport in the Porous Transport Layer (PTL) plays an important role in the efficient operation of polymer electrolyte membrane fuel cells (PEMFC). Excessive water content as well as dry operating conditions are unfavorable for efficient and reliable operation of the fuel cell. The effect of thermal conductivity and porosity on water management are investigated by simulating two-phase flow in the PTL of the fuel cell using a network model. In the model, the PTL consists of a pore-phase and a solid-phase. Different models of the PTLs are generated using independent Weibull distributions for the pore-phase and the solid-phase. The specific arrangement of the pores and solid elements is varied to obtain different PTL realizations for the same Weibull parameters. The properties of PTL are varied by changing the porosity and thermal conductivity. The parameters affecting operating conditions include the temperature, relative humidity in the flow channel and voltage and current density. A parametric study of different solid-phase distributions of the PTL and its effect on thermal, vapor and liquid transport in the PTL under different operating conditions are discussed.
Experimental Studies of a Formic Acid Electrolyte: Direct Methanol Fuel Cell
Authors: Ouellette David , Cruickshank Cynthia Ann , Matida Edgar
Published: December 2013

A new methanol fuel cell that utilizes a liquid formic acid electrolyte, named the formic acid electrolyte-direct methanol fuel cell (FAE-DMFC) is experimentally tested. Three fuel cell configurations were examined; a flowing electrolyte and two circulating electrolyte configurations. From these three configurations, the flowing electrolyte and the circulating electrolyte, with the electrolyte outlet routed to the anode inlet, provided the most stable power output; where minimal decay in performance and less than 3 and 5.6 % variation in power output were observed in the respective configurations. The flowing electrolyte configuration also yielded the greatest power output by as much as 34 %. Furthermore, for the flowing electrolyte configuration, several key operating conditions were experimentally tested to determine the optimal operating points. It was found that an inlet concentration of 2.2 M methanol and 6.5 M formic acid, as well as a cell temperature of 52.8 °C provided the best performance.
Transient Response of Polymer Electrolyte Membrane Fuel Cell to Variations in Operating Parameters
Authors: Verma A. , Pitchumani R.
Published: December 2013

Due to rapid change in loads during automotive applications, study of dynamic behavior of proton exchange membrane (PEM) fuel cells is of paramount importance for their successful deployment in mobile applications. Toward understanding the effects of changes in operating parameters on the transient behavior, this paper presents numerical simulations for a single channel PEM fuel cell undergoing cyclic changes in operating parameters. The objective is to elucidate the complex interaction between power response and complex species (water, hydrogen and oxygen) transport dynamics for applied cyclic changes. This study focuses on studying the transient response of fuel cell for specified changes in operating parameters — voltage, pressure and stoichiometry at the cathode and the anode. Numerical studies are carried out on single-channel PEMFC’s to illustrate the response of power as the operating parameters are subjected to specified changes. The operating parameters are further optimized using a one dimensional physics based model with an objective to match the power requirements of a drive cycle over a defined period of time.
Reconstruction of Anode Nanostructures for Solid Oxide Fuel Cells
Authors: Wang Yan-feng , Yuan Jinliang , Sundén Bengt , Hu Yu-li
Published: December 2013

Previous research works on solid oxide fuel cells (SOFCs) have mainly focused on the large length scale phenomena, such as physical and chemical transport phenomena at macroscale. A new approach is proposed in this work, which combines concepts from all-atom (AA) modeling with coarse-graining (CG) molecular dynamics (MD) method to reveal the replacement mechanism of Yttria-Stabilized Zirconia (YSZ) and establish the nanostructures of a NiO-based anode and an YSZ-based electrolyte. Lattice constants of NiO and YSZ are obtained by special measurements. Nanocrystalline structures of anode and electrolyte material structures under disparate conditions are generated via Atomistic Simulation Environment (ASE). By combining this technique with the local lattice constants, the effect of temperature on crystal formation and the influence of sintering conditions on the volume shrinkage are predicted. The combined AA-CG-MD method is validated and subsequently applied to an equilibrated anode and electrolyte nanostructures with a box length of 50 nm. The resulting nanostructures of the materials show good agreement with the distributions from experiments based on Transmission/Scanning Electron Microscopy (TEM/SEM) techniques, and provide insight into atom/pore distribution and the volume shrinkage at a length scale which is expanded into atomistic/molecular dynamics simulation to capture the best materials’ performance and the balance of oxygen-ion conductivity and material stability.
A Parameter Identification Approach of a PEM Fuel Cell Stack Using Particle Swarm Optimization
Authors: Salim Reem I. , Noura Hassan , Fardoun Abbas
Published: December 2013

The fear of fossil fuels depletion as well as the constantly increasing pollution rates motivated most of today’s engineers and researchers towards focusing on renewable energies and their applications. Fuel Cells are one of the green technologies that are being explored extensively around the world. The work of this paper was done on the 3kW ElectraGen™ fuel cell system under study for domestic use in the United Arab Emirates (UAE). Several experiments were conducted at different operating points and relatively high ambient temperatures. The experimental I/V characteristics of the system are matched by identifying 13 different modeling parameters using basic fitting. The obtained model is then further optimized using Particle Swarm Optimization (PSO). The resulting model is validated experimentally and was found to highly resemble the system’s I/V characteristics yielding less than 1.5 V H∞ norm of the error.
Controlling Spatial Temperature Variation in a Rapid Load Following SOFC
Authors: Fardadi Mahshid , McLarty Dustin F. , Jabbari Faryar
Published: December 2013

Power tracking and temperature control of solid oxide fuel cell (SOFC) for co-flow and counter-flow configurations have been studied. Partial internal reformation has been used to address many of the difficulties associated with delays in balance of plant (BOP). High performance controllers are used to reduce thermal stresses that can result from rapid and significant power tracking. Both co-flow and counter-flow designs are considered and advantages and disadvantage of each are then reviewed.
In Vitro
Photodynamic Inactivation of Plant-Pathogenic Fungi Colletotrichum acutatum and Colletotrichum gloeosporioides with Novel Phenothiazinium Photosensitizers
Authors: de Menezes Henrique D. , Rodrigues Gabriela B. , Teixeira Simone de Pádua , Massola Nelson S. , Bachmann Luciano , Wainwright Mark , Braga Gilberto U. L.
Published: December 2013

The increasing tolerance to currently used fungicides in both clinical and agricultural areas is of great concern. The nonconventional light-based approach of antimicrobial photodynamic treatment (APDT) is a promising alternative to conventional fungicides. We evaluated the effects of APDT with four phenothiazinium derivatives (methylene blue [MB], new methylene blue N [NMBN], toluidine blue O [TBO], and the novel pentacyclic phenothiazinium photosensitizer [PS] S137) on conidia of three fungal species (
Colletotrichum acutatum
,
Colletotrichum gloeosporioides
, and
Aspergillus nidulans
). The efficacy of APDT with each PS was determined, initially, based on photosensitizer MICs. Additionally, the effects of APDT with two selected PSs (NMBN and S137) on survival of conidia were evaluated. The subcellular localization of the PS in
C. acutatum
conidia was determined. The effects of photodynamic treatments on leaves of the plant host
Citrus sinensis
were also investigated. APDT with S137 showed the lowest MIC. MICs for S137 were 5 μM for the three fungal species when a fluence of 25 J cm
−2
was used. APDT with NMBN (50 μM) and S137 (10 μM) resulted in a reduction in the survival of the conidia of all species of approximately 5 logs with fluences of ≥15 J cm
−2
. Washing of the conidia before light exposure did not prevent photodynamic inactivation. Both NMBN and S137 accumulated in cytoplasmic structures, such as lipid bodies, of
C. acutatum
conidia. No damage to orange tree leaves was observed after APDT.
Potentially Pathogenic Escherichia coli Can Form a Biofilm under Conditions Relevant to the Food Production Chain
Authors: Nesse Live L. , Sekse Camilla , Berg Kristin , Johannesen Karianne C. S. , Solheim Heidi , Vestby Lene K. , Urdahl Anne Margrete
Published: December 2013

The biofilm-producing abilities of potentially human-pathogenic serotypes of
Escherichia coli
from the ovine reservoir were studied at different temperatures and on different surfaces. A possible influence of the hydrophobicity of the bacterial cells, as well as the presence of two virulence factors, the Shiga toxin-encoding (Stx) bacteriophage and the
eae
gene, was also studied. A total of 99
E. coli
isolates of serotypes O26:H11, O103:H2, and O103:H25 isolated from sheep feces were included. The results show that isolates of all three
E. coli
serotypes investigated can produce biofilm on stainless steel, glass, and polystyrene at 12, 20, and 37°C. There was a good general correlation between the results obtained on the different surfaces.
E. coli
O103:H2 isolates produced much more biofilm than those of the other two serotypes at all three temperatures. In addition, isolates of serotype O26:H11 produced more biofilm than those of O103:H25 at 37°C. The hydrophobicity of the isolates varied between serotypes and was also influenced by temperature. The results strongly indicated that hydrophobicity influenced the attachment of the bacteria rather than their ability to form biofilm once attached. Isolates with the
eae
gene produced less biofilm at 37°C than isolates without this gene. The presence of a Stx bacteriophage did not influence biofilm production. In conclusion, our results show that potentially human-pathogenic
E. coli
from the ovine reservoir can form biofilm on various surfaces and at several temperatures relevant for food production and handling.
Amplification and Purification of T4-Like Escherichia coli Phages for Phage Therapy: from Laboratory to Pilot Scale
Authors: Bourdin Gilles , Schmitt Bertrand , Marvin Guy Laure , Germond Jacques-Edouard , Zuber Sophie , Michot Lise , Reuteler Gloria , Brüssow Harald
Published: December 2013

We investigated the amplification and purification of phage preparations with respect to titer, contamination level, stability, and technical affordability. Using various production systems (wave bags, stirred-tank reactors, and Erlenmeyer flasks), we obtained peak titers of 10
9
to 10
10
PFU/ml for T4-like coliphages. Phage lysates could be sterilized through 0.22-μm membrane filters without titer loss. Phages concentrated by differential centrifugation were not contaminated with cellular debris or bacterial proteins, as assessed by electron microscopy and mass spectrometry, respectively. Titer losses occurred by high-speed pelleting of phages but could be decreased by sedimentation through a sucrose cushion. Alternative phage concentration methods are prolonged medium-speed centrifugation, strong anion-exchange chromatography, and ultrafiltration, but the latter still allowed elevated lipopolysaccharide contamination. T4-like phages could not be pasteurized but maintained their infectivity titer in the cold chain. In the presence of 10 mM magnesium ions, phages showed no loss of titer over 1 month at 30°C.
Enumeration of Salmonellae in Table Eggs, Pasteurized Egg Products, and Egg-Containing Dishes by Using Quantitative Real-Time PCR
Authors: Jakočiūnė Džiuginta , Pasquali Frédérique , da Silva Cristiana Soares , Löfström Charlotta , Hoorfar Jeffrey , Klein Günter , Manfreda Gerardo , Olsen John Elmerdahl
Published: December 2013

Salmonellae are a major cause of food-borne outbreaks in Europe, with eggs and egg products being identified as major sources. Due to the low levels of salmonellae in eggs and egg products, direct quantification is difficult. In the present study, enrichment quantitative real-time PCR (qPCR) was employed for enumeration of salmonellae in different matrices: table eggs, pasteurized egg products, and egg-containing dishes.
Salmonella enterica
serovar Enteritidis and
S. enterica
serovar Tennessee were used to artificially contaminate these matrices. The results showed a linear regression between the numbers of salmonellae and the quantification cycle (

C
q

) values for all matrices used, with the exception of pasteurized egg white. Standard curves were constructed by using both stationary-phase cells and heat-stressed cells, with similar results. Finally, this method was used to evaluate the fate of salmonellae in two egg-containing dishes, long egg and tiramisu, at abused refrigeration temperatures, and results indicated the growth of bacteria over a 1-week period. In conclusion, enrichment qPCR was shown to be reliable for enumeration of salmonellae in different egg products.
Protein Engineering by Random Mutagenesis and Structure-Guided Consensus of Geobacillus stearothermophilus Lipase T6 for Enhanced Stability in Methanol
Authors: Dror Adi , Shemesh Einav , Dayan Natali , Fishman Ayelet
Published: December 2013

The abilities of enzymes to catalyze reactions in nonnatural environments of organic solvents have opened new opportunities for enzyme-based industrial processes. However, the main drawback of such processes is that most enzymes have a limited stability in polar organic solvents. In this study, we employed protein engineering methods to generate a lipase for enhanced stability in methanol, which is important for biodiesel production. Two protein engineering approaches, random mutagenesis (error-prone PCR) and structure-guided consensus, were applied in parallel on an unexplored lipase gene from
Geobacillus stearothermophilus
T6. A high-throughput colorimetric screening assay was used to evaluate lipase activity after an incubation period in high methanol concentrations. Both protein engineering approaches were successful in producing variants with elevated half-life values in 70% methanol. The best variant of the random mutagenesis library, Q185L, exhibited 23-fold-improved stability, yet its methanolysis activity was decreased by one-half compared to the wild type. The best variant from the consensus library, H86Y/A269T, exhibited 66-fold-improved stability in methanol along with elevated thermostability (+4.3°C) and a 2-fold-higher fatty acid methyl ester yield from soybean oil. Based on
in silico
modeling, we suggest that the Q185L substitution facilitates a closed lid conformation that limits access for both the methanol and substrate excess into the active site. The enhanced stability of H86Y/A269T was a result of formation of new hydrogen bonds. These improved characteristics make this variant a potential biocatalyst for biodiesel production.
Biochemical Characterization of a Novel
l
-Asparaginase with Low Glutaminase Activity from Rhizomucor miehei and Its Application in Food Safety and Leukemia Treatment
Authors: Huang Linhua , Liu Yu , Sun Yan , Yan Qiaojuan , Jiang Zhengqiang
Published: December 2013

A novel fungal gene encoding the
Rhizomucor miehei
l
-asparaginase (RmAsnase) was cloned and expressed in
Escherichia coli
. Its deduced amino acid sequence shared only 57% identity with the amino acid sequences of other reported
l
-asparaginases. The purified
l
-asparaginase homodimer had a molecular mass of 133.7 kDa, a high specific activity of 1,985 U/mg, and very low glutaminase activity. RmAsnase was optimally active at pH 7.0 and 45°C and was stable at this temperature for 30 min. The final level of acrylamide in biscuits and bread was decreased by about 81.6% and 94.2%, respectively, upon treatment with 10 U RmAsnase per mg flour. Moreover, this
l
-asparaginase was found to potentiate a lectin's induction of leukemic K562 cell apoptosis, allowing lowering of the drug dosage and shortening of the incubation time. Overall, our findings suggest that RmAsnase possesses a remarkable potential for the food industry and in chemotherapeutics for leukemia.