http://www.mtdna.or.kr/neowiz/board/up_files/files_17/Chitin_Chitosan_polymers_chemistrySolubilityFiberFormation.pdf

Chitin and chitosan polymers: Chemistry, solubility and fiber formation

Electrospinning is a fabrication technique, which can be used to create nanofibrous non‐wovens from a variety of starting materials. The structure, chemical and mechanical stability, functionality, and other properties of the mats can be modified to match end applications. In this review, an introduction to biopolymers and the electrospinning process, as well as an overview of applications of nanofibrous biopolymer mats created by the electrospinning process will be discussed. Biopolymers will include polysaccharides (cellulose, chitin, chitosan, dextrose), proteins (collagen, gelatin, silk, etc.), DNA, as well as some biopolymer derivatives and composites.

A Review: Electrospinning of Biopolymer Nanofibers and their Applications

In this review, we have examined the different models for polymer-electrolyte fuel cells operating with hydrogen. The major focus has been on transport of the various species within the fuel cell. The different regions of the fuel cell were examined, and their modeling methodologies and equations were elucidated. In particular, the 1-D fuel-cell sandwich was discussed thoroughly because it is the most important part of the fuel-cell assembly. Models that included other effects such as temperature gradients and transport in other directions besides through the fuel-cell sandwich were also discussed. Models were not directly compared to each other; instead they were broken down into their constitutive parts. The reason for this is that validation of the models is usually accomplished by comparison of simulation to experimental polarization data (e.g., Figure 3). However, other data can also be used such as the net flux of water through the membrane. In fitting these data, the models vary not only in their complexity and treatments but also in their number and kind of fitting parameters. This is one reason it is hard to justify one approach over another by just looking at the modeling results. In general, it seems reasonable that the more complex models, which are based on physical arguments and do not contain many fitting parameters, are perhaps closest to reality. Of course, this assumes that they fit the experimental data and observations. This last point has been overlooked in the validation of many models. For example, a model may fit the data very well for certain operating conditions, but if it does not at least predict the correct trend when one of those conditions is changed, then the model is shown to be valid only within a certain operating range. This review has highlighted the important effects that should be modeled. These include two-phase flow of liquid water and gas in the fuel-cell sandwich, a robust membrane model that accounts for the different membrane transport modes, nonisothermal effects, especially in the directions perpendicular to the sandwich, and multidimensional effects such as changing gas composition along the channel, among others. For any model, a balance must be struck between the complexity required to describe the physical reality and the additional costs of such complexity. In other words, while more complex models more accurately describe the physics of the transport processes, they are more computationally costly and may have so many unknown parameters that their results are not as meaningful. Hopefully, this review has shown and broken down for the reader the vast complexities of transport within polymer-electrolyte fuel cells and the various ways they have been and can be modeled.

Modeling transport in polymer-electrolyte fuel cells.

This paper presents a dynamic electrochemical model for representation, simulation, and evaluation of performance of small size generation systems emphasizing particularly proton exchange membrane fuel-cell (PEMFC) stacks. The results of the model are used to predict the output voltage, efficiency, and power of FCs as a function of the actual load current and of the constructive and operational parameters of the cells. Partial and total load insertion and rejection tests were accomplished to evaluate the dynamic response of the studied models. The results guarantee a better analytical performance of these models with respect to former ones with a consequent reduction in time and costs of projects using FCs as the primary source of energy. Additionally, this electrochemical model was tested for the SR-12 Modular PEM Generator, a stack rated at 500 W, manufactured by Avista Laboratories, for the Ballard Mark V FC and for the BCS 500-W stack.

An electrochemical-based fuel-cell model suitable for electrical engineering automation approach

Fuel Cells are electrochemical devices that convert the chemical energy of a gaseous fuel directly into electricity. They are widely regarded as a potential future stationary and mobile power source. The response of a fuel cell system depends on the air and hydrogen feed, flow and pressure regulation, and heat and water management. In this paper, we develop a dynamic model suitable for the control study of fuel cell systems. The transient phenomena captured in the model include the flow and inertia dynamics of the compressor, the manifold filling dynamics (both anode and cathode), reactant partial pressures, and membrane humidity. It is important to note, however, that the fuel cell stack temperature is treated as a parameter rather than a state variable of this model because of its long time constant. Limitations and several possible applications of this model are presented.

/pdf/control-oriented-modeling-and-analysis-for-automotive-fuel-4h9bv9dad2.pdf

Control-Oriented Modeling and Analysis for Automotive Fuel Cell Systems

Development and application of a generalised steady-state electrochemical model for a PEM fuel cell

Chitosan fibers were wet spun from a 6% by weight chitosan in 3% by volume acetic acid solution. The fibers were collected as a 20 filament yarn intended for use as a chaff substrate. The yarn had to be sufficiently dry following spinning to allow for winding and subsequent separation of the filaments. Drying of the yarn was attempted using various techniques including direct and radiant heat, forced air, and chemical drying agents. Product yarns were analyzed for ease of separation of the filaments, as well as comparison of mechanical properties. Individual fibers were evaluated on the basis of moisture content, surface morphology and fiber diameter. Results indicate that the particular drying method or agent used has a considerable impact upon all of the characteristics listed above. A methanol dry bath was found to provide optimum drying of the chitosan yarn, producing filaments with low moisture content that separated easily from one another. Methanol drying yielded chitosan fibers with smaller diameter, superior surface smoothness and superior mechanical properties to fibers dried using forced air, heat, or other tested drying agents such as acetone and isopropanol. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1435–1444, 1998

Improvements in the drying process for wet‐spun chitosan fibers

The transition to a hydrogen economy will require an intermediate energy carrier until a sufficient hydrogen infrastructure can be implemented. A likely near-term candidate is the on-board or on-site production of hydrogen from steam-methanol reforming. The low tolerance of PEM fuel cell anode electrocatalyst, to the carbon monoxide produced during reforming, necessitates a hydrogen purification or carbon monoxide clean-up sub-system. Considerable advantages can be gained from the use of a steam-methanol reformer with a palladium-silver alloy membrane, hydrogen purification unit. In the present work we have examined such a system. A simulation comprised of a Polymer Electrolyte Membrane Fuel Cell electrochemical model, a membrane permeation model and a commercially available thermodynamics calculation package was constructed. The case investigated in this work is of a 25 kW nominal DC power generating system. A maximum efficiency of 40% was achieved at reformer and membrane unit conditions of 200°C and 300 psia with 97% conversion of the inlet methanol. The effects of variation in temperature and pressure where also investigated. It was found that the reformer and membrane unit pressure had the most significant effect on overall system efficiency. The system efficiency increases with pressure reaching a maximum at the upper limit of the operating region, 300 psia.Copyright © 2003 by ASME

Michael A.I. Hooper

Papers

Development and application of a generalised steady-state electrochemical model for a PEM fuel cell

Improvements in the drying process for wet‐spun chitosan fibers

Simulation of a 25 kW Steam-Methanol Fuel Processor/PEM Fuel Cell System