Stack Concept Research Articles

Development and performance of a 10kW PEMFC stack

PEM fuel cells are viewed as one of the most environmentally friendly propulsion systems for automotive travel in the future. However, the PEM fuel cell is still too expensive for wide-spread commercialization. Besides the membrane electrode assembly, manufacturing of bipolar plates by milling from graphite or graphite composites is a very expensive process. In order to achieve cost reduction and at the same time meeting several technical requirements for mass production, a stack concept using graphite composite bipolar plates was developed. The tests reported in this paper show that the design goal of 10 kW could be significantly exceeded.

Interoperability between UMTS and cdma2000 networks

In overlaying an existing cdma2000 network with a UMTS network, service transparency and number portability are important requirements for end users and hence the network operator. To support both requirements, one could introduce a protocol conversion node between the two networks; however, such a solution does not fully meet the requirements due to inherent technical constraints imposed by the differing standards. This article describes a network architecture based on the dual stack concept that satisfies the service transparency and number portability requirements across UMTS and cdma2000 networks, and also defines the functionality of the network nodes and the call processing procedures.

Modeling of Cross-Flow Stack: Sensitivity to Thermal Properties of the Materials

LENI activities in SOFC are focused on development of a new planar stack concept based on anode supported cells in collaboration with the company HTceramix SA. Modeling of repeat element, stack and systems is starting in parallel. This work presents a model of a SOFC stack in cross flow configuration. Concentrations, temperature and current density fields are computed, with a focus on sensitivity study for thermal parameters, while operating parameters are kept constant for the different cases. The main parameter considered was the thickness of the metallic interconnect and the related thermal conductivity. Stack height and cell size effects are presented as well. Importance of the temperature field on the design point and degradation behavior is briefly discussed.

Demonstration and Stack Concept of Quick Startup/shutdown SOFC (qSOFC)

The quick startup/shutdown operation of solid oxide fuel cells (SOFC) was demonstrated. It took only 15 seconds to startup with butane as fuel. The demonstration confirmed that a small tubular cell could endure thermal stress caused by rapid heating up to operating temperature. A new stack concept of small tubular cells was also proposed for quick startup application. A three-cell prototype stack equipped with a rapid heating burner was examined.

Base-Stacking-Induced Intermolecular NOE Cross Peaks for Nucleotides

The concept of base stacking of nucleotides in solutions has been well accepted. However, direct evidence has not been found. Here we report for the first time the intermolecular NOE cross peaks between ATP (adenosine 5'-triphosphate) and GTP (guanosine 5'-triphosphate), which unambiguously indicates the base stacking of nucleotides in solutions. In 400 mmol.L-1 ATP-GTP solutions, the base protons of ATP, AH2 and AH8, show NOE cross peaks with the sugar protons of GTP, GH1', GH2' and GH3', Also there are NOE cross peaks between the base proton of GTP (GH8) and the sugar protons of ATP. Possible conformations of base stacking in solutions have been discussed, and the distance between the stacked bases is estimated.

Electrically Driven Microseparation Methods for Pesticides and Metabolites: I. Micellar Electrokinetic Capillary Chromatography of Carbamate Insecticides with MEGA-Borate and SDS Surfactants

Abstract The migration behavior of some representative carbamate insecticides in micellar electrokinetic capillary chromatography (MECC) was investigated over a wide range of elution conditions, including the nature and concentration of the surfactant and the concentration of added urea in the running electrolyte. Decanoyl-N-methylglucamide (MEGA 10) surfactant was compared with the traditionally used sodium dodecyl sulfate (SDS) surfactant for separation of the carbamate insecticides under investigation. The MEGA 10 micellar system is based on the complexation of MEGA 10 with borate, yielding an in situ charged micelle (i.e., MEGA 10-borate micelle), whose surface charge density can be readily manipulated by varying the pH and the concentrations of borate and MEGA 10 in the running electrolyte. This flexibility, in turn, allowed the modulation of the migration time window and, consequently, the analysis time. Because of its relatively weaker hydrophobic character, the MEGA 10-borate micellar system permitted the resolution of 9 different carbamate insecticides in about 12 min. Conversely, with the SDS micellar system, whose hydrophobicity is higher, the separation of all 9 solutes necessitated the addition of 4.0M urea, a condition that brought about a doubling of the analysis time. In addition, the MEGA 10-borate micellar system produced twice as many plates per min as did the SDS micellar system. Because MEGA 10-borate yielded results superior to those of the SDS micellar system, on-column preconcentration of the carbamate insecticides was attempted in MEGA 10-borate by using the concept of field-amplified sample stacking (FASS). Thus far, only a few attempts have been made toward the application of FASS in MECC of neutral compounds such as carbamate insecticides.

Solid oxide fuel cell stacks using extruded honeycomb type elements

Abstract A solid oxide fuel cell (SOFC) stack concept is described which comprises “condensed-tubes” like extruded honeycomb sections of ceramic electrolyte (ZrO2-based) and interconnectors of nickel sheet as key elements. According to this concept, well known and extensively tested construction principles can be realised in a low-cost production. The cells are self-supported with in-plane conduction. A demonstrator model stack of five honeycomb elements and six nickel sheet seals/interconnectors was built and operated for 860 h at 1000°C. Volumetric power densities of 160 kW/m3 were obtained with H2 vs. air, of close to 200 kW/m3 with H2 vs. O2.

A novel configuration for direct internal reforming stacks

This paper presents a stack concept that can be applied to both molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC) internal reforming stacks. It employs anode recycle and allows the design of very simple system configurations, while giving enhanced efficiencies and high specific power densities. The recycle of anode exit gas to the anode inlet has previously been proposed as a means of preventing carbon deposition in direct internal reforming (DIR) stacks. When applied to a normal stack this reduces the Nernst voltages because the recycle stream is relatively depleted in hydrogen. In the concept proposed here, known as the `Smarter' stack, there are two anode exit streams, one of which is depleted, while the other is relatively undepleted. The depleted stream passes directly to the burner, and the undepleted stream is recycled to the stack inlet. By this means high Nernst voltages are achieved in the stack. The concept has been simulated and assessed for parallel-flow and cross-flow MCFC and SOFC stacks and graphs are presented showing temperature distributions. The `Smarter' stacks employ a high recycle rate resulting in a reduced natural gas concentration at the stack inlet, and this reduces or eliminates the unfavourable temperature dip. Catalyst grading can further improve the temperature distribution. The concept allows simple system configurations in which the need for fuel pre-heat is eliminated. Efficiencies are up to 10 percentage points higher than for conventional stacks with the same cell area and maximum stack temperature. The concept presented here was devised in a project part-funded by the EU, and has been adopted by the European Advanced DIR–MCFC development programme led by BCN.

Capillary electrophoresis of herbicides: IV. Evaluation of octylmaltopyranoside chiral surfactant in the enantiomeric separation of fluorescently labeled phenoxy acid herbicides and their laser-induced fluorescence detection.

A novel chiral nonionic surfactant, namely octyl-b-D-maltopyranoside (OM), was evaluated in chiral capillary electrophoresis of fluorescently labeled phenoxy acid herbicides. The labeling of the analytes with 7-aminonaphthalene-1,3-disulfonic acid (ANDSA) permitted a concentration detection limit of 5 x 10-10 M using laser-induced fluorescence detection. This limit of detection allowed the determination of ultradiluted solutions of the ANDSA-derivatized phenoxy acid herbicides whose concentration was a low as 10-11 M (i.e. 2.2 ppt) by applying the concept of field-amplified sample stacking (FASS). The sample injection by FASS did not adversely affect separation efficiencies, resolution and reproducibility of the electrophoretic system. The tagging of the phenoxy acid herbicides with ANDSA increased the hydrophobicity of the analytes, thus favoring an enhanced solubilization of the derivatized herbicides in the OM micellar phase. The net results of this effect were a much shorter analysis time and an improved enantiomeric resolution of the derivatives when compared to underivatized phenoxy acid herbicides. The optimum surfactant concentration required for maximum resolution decreased with increasing hydrophobicity of the analyte, with the least hydrophobic analyte requiring higher surfactant concentration. Because of the two permanently charged sulfonic acid groups of the ANDSA tag, the pH of the running electrolyte had little effect on the enantiomeric resolution of the derivatized herbicides. Due to its salting-out effect and increasing the micellized surfactant concentration, increasing the ionic strength of the running electrolyte increased the enantiomeric resolution of the least hydrophobic analytes. Conversely, increasing the percent methanol in the running electrolyte decreased the enantiomeric resolution of the least hydrophobic analytes due to a decrease strength of solute-micelle association. For hydrophobic analytes, existed an optimum percent of methanol existed for maximum enantiomeric resolution.

Effective medium theory applied to photonic crystals composed of cubic or square cylinders

Using the effective medium theory, I interpret the band-gap opening in photonic crystals with simple geometries as an interference effect between alternating layers of high and low optical indices and introduce the interesting concept of multidimensional quarter-wave stacks. The interpretation provides a simple insight into band-gap opening processes. For several simple crystal geometries, I analyze the variations of the gap width and depth with respect to the light polarization, the incident angle, and contrast inversion. For two- and three-dimensional structures composed of cubic and square cylinders, I show that the effective medium theory can be used to predict accurately the gap width, the central wavelength, and the attenuation at the central wavelength. The validity domain of the effective medium theory predictions is checked with results from rigorous computations.

Three-dimensional micro flow manifolds for miniaturized chemical analysis systems

A three-dimensional (3D) stack concept for the assembly of photolithographically fabricated microfluidic components is presented and discussed. The system uses silicon-based micropumps and simple planar structures which mimic standard elements of conventional flow systems. Detection is provided either by solid state electrochemical sensors or small volume optical detection. The general advantages of using micromachined flow manifolds for microchemical analysis are addressed. The particular benefits to be derived from this an approach compared with other assembly methods are also examined.

An approach to optimum slant stack; its application as a seismic noise attenuator

The concept of stacking, data together to form a trace with a signal to noise ratio (S/N) which is better than that of the individual contributors to the stack is not new, and now forms a key step in most seismic processing sequences, namely CDP stack. While not specifically for geophysical applications, Brennan (1955) showed that there is a universal method for computation of stack S/N and indicated how the S/N of the stacked trace could be maximized (the optimum stack). Brennan's method involved sealing of the input data, by application of weights, and he showed how the contributing traces should be weighted in order to achieve optimum stack.

Pre-Stack and Post-Stack Noise Attenuation using the Diversity τ-p Transform

A new method for attenuating seismic noise, the diversity t-p transform (DTPT), is presented and illustrated with synthetic and field data examples. This method can be used either with pre-stack or post-stack data. Furthermore, the method can also be used for trace interpolation. In the pre-stack case, the DTPT is implemented exploiting the benefits provided by the classical t-p transform using hyperbolic velocity filtering during the transform procedure and diversity scaling applied to the data prior to the t-p transformation. This approach permits attenuation of complex noise ? for example, aliased noise, non-linear noise trends, noise bursts, spikes, etc. Conventional f-k and f-x modelling techniques do not cope well with these types of noise. Most importantly, with the use of the DTPT technique, the useful signal does not suffer distortion in any part of the frequency spectrum at any offset. In the post-stack case, the DTPT method is performed using the local slant stack concept. A discrete t-p representation of the data can be determined which minimises the presence of random noise and compresses the t-p response of linear events so that aliasing effects are much reduced. The DTPT technique used as a post-stack noise attenuator has significant benefits when compared with conventional approaches to noise attenuation. It attenuates noisy isolated traces (spikes, noise bursts, etc.) and does not demand uniform spatial sampling (as required by f-k and f-x prediction techniques). In addition, by exploiting the DTPT characteristics mentioned above, the DTPT technique may be utilised for trace interpolation purposes ? thus improving the lateral resolution of the seismic data prior to the migration process. Trace interpolation is achieved during the inverse t-p transform by outputting traces at a finer spatial sampling than the original input data. In addition, the output spatial sample interval may be uniform even though the input interval may not be.

M-C Power commercialization program for MCFC power plants

M-C Power Corporation was established by the Institute of Gas Technology (IGT) to develop, manufacture, market, sell and service commercial MCFC power plants using IGT's IMHEX® fuel cell stack concept. M-C Power has created an integrated commercialization program to develop a market-responsive, natural gas-fueled MCFC power plant. M-C Power's market entry offering will range from 500 kW to 3 MW and will be designed for on-site and distributed power applications. Future products will include a wider range of sizes for distributed power and power plants for dispersed (30–50 MW) and base load ( > 100 MW) power generation, the latter fueled by coal-derived gases. M-C Power Corporation has established the world's most advanced MCFC components and stack manufacturing facilities at its plant in Burr Ridge, IL, capable of producing 3 MW/year of stacks based on one shift per day, five days per week operation. This capacity can be increased to 12 MW/year by adding one tape casting machine and operating three shifts per day for 330 days/year. An industry group has been formed to guide, support, and stimulate the IMHEX® Commercialization Program. This group is called the Alliance to Commercialize Carbonate Technology (ACCT). ACCT members include electric, gas and combination utilities as well as pipeline companies and potential industrial users. In addition, the program enjoys wide support from government, industry and research institutions.

A New CMP Stack Concept Based on the Born Approximation

Abstract The standard common-midpoint (CMP) stack procedure becomes questionable as soon as varying reflector dips at about the same two-way time (TWT) are involved. There are several ways to handle that problem ranging from pre stack migration to dip moveout (DMO). This paper presents a new alternative which employs the same physical model of the medium that is in common use for migration: scatterers embedded in a known reference velocity field. Provided that backscattering can be described by the (first) Born approximation, it is possible to derive a zero-offset trace from a CMP gather by a procedure that relies entirely on known processing steps like normal moveout (NMO) and stacking.

Discussion of the stack‐array concept continues

I have been very interestedly following the discussions on the stack‐array criterion of Nigel Anstey. I am very grateful to him on behalf of my colleagues for bringing the old concept of CDP stacking on the agenda again. However, I want to make some comments on his December 1986 reply.

Stack method in program semantics

In this paper, we describe firstly a formal concept of stack and introduce some operational rules on it. Then we extend the denotational semanties to “the denotational semanties with stacks”, by which we make a formal semantics for a real PASCAL (subset) which can run on a computer. By an example of program with procedures it will be seen that our method can be used to describe the basic principles of compiling. Finally, we have succeeded in building a formal semanties model of a PROLOG (subset).

Introduction of the concept of stream stack and structured flowsheeting to a chemical process system simulator.

A compact but powerful chemical process system simulator called SCHEMER (Structured CHEMosynthesizER) is developed by focusing attention on the analogy between chemical processing and data processing. Introduction of the concept of the stream stack has released the SCHEMER compiler from management of the stream numbers, affording high performance per unit byte of memory. Since SCHEMER is an adaptable computer language in which special commands concerning chemical processing are added to the regular commands for data processing, the user may use both. Moreover, he may compose new commands by combining some of those commands and even newly composed ones. Such structured flowsheeting dramatically increases the productivity of the simulator.

Semantic errors reconsidered in the procedural light of stack concepts

The purpose of this paper is to demonstrate the relevance of the stack concept in neuropsycholinguistics, a stack being a file with serially ordered elements. Number names (one, two, three, …) and the names of the days in the week may be viewed in this way. In a stack structure, any element is identified by two pieces of information: the particular stack to which it belongs and its position within that stack. Two experiments are reported that demonstrate a double dissociation. A deep dyslexic patient with agrammatism was found to sort stack elements on the basis of identity of position-within-stacks, while a fluent aphasic with semantic verbal paraphasias used another criterion, grouping together the items of the same stack. First revealed when handling number names, the two psycholinguistic procedures are also shown to be differentially operative with other linguistic material. Introducing the stack concept thus permits a procedural reinterpretation of some “semantic confusions,” particularly but not exclusively those dealing with quantities.

Plume rise from multiple sources: A new model

In 1974 and 1975, Briggs presented two semiempirical models for computing plume rise from multiple sources for stacks with the same height and emission. Since in our country there are many power plants with more than one stack and generally of different heights and emissions, we developed a new model based on “virtual” stack concept, able to provide estimates of maximum plume height for this problem. Firstly we compared a simplified expression, derived from our model for the case of chimneys of equal heights and emissions, with the above mentioned Briggs' models and with a series of data quoted by Briggs in his 1974 paper. Then we tested our model with a few experimental data relative to stacks of different heights and obtained during the La Spezia field experiments. All the comparisons made showed a satisfactory agreement. Finally a comparison among an empirical expression due to Montgomery et al. giving the correction factor for ground level concentrations in the multiple sources case and the analogue ones derived from our and Briggs' models is presented.