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Polymer electrolyte membrane fuel cells (PEMFCs) exhibit encouraging potential as an enabling technology for the Hydrogen Economy. Currently an important barrier to commercialization is the cost associated with existing PEMFC materials; this project???s goal was to investigate alternative materials for PEMFC bipolar plates. Conductive thermoplastic materials offer the promise of low density, low cost processing, and inexpensive resins, and were the focus of material development for PEMFC bipolar plate applications. In order to develop a thermoplastic bipolar plate this study utilized the combination of a low cost injection moldable commodity polymer resin, and low cost carbon materials as conductive fillers. The materials selected and tested included; a polypropylene copolymer; acetylene carbon black; Vulcan carbon black; and short carbon fiber. The components were combined in a twin screw extruder and injection molded into samples for testing. The result was a spectrum of composite samples with a range of filler loadings from 0 to 60 wt% and varying filler type ratios. Synergy between the different carbon types was achieved which led to better physical properties, specifically conductivity. The novel blends produced were tested for electrical conductivity, mechanical properties, rheology, microscopy, and actual plates were made and tested in a single cell PEMFC. These trials enabled discussion around the feasibility of the materials with respect to processability, cost, and performance (both in the fuel cell and in potential applications). The most significant results were measured using a composite blend with 54 wt% filler loading and a 1:1:1 filler ratio. Mechanical results achieved 68% and 100% of the industry targets for tensile and flexural strength, respectively. Tensile strength attained 27.7 MPa and flexural strength measured 82.8 MPa. Electrical conductivity results for the same samples varied between the two methods of measurement used. Using a fuel cell industry recommended procedure 2.2 S/cm was achieved and using a four point ASTM measurement technique 12.0 S/cm was reported. These values represent 3% to 12% of the industry target. Actual 16 cm2 fuel cell plates were produced, fuel cell hardware constructed and assembled, and the power output was found to be 51% relative to graphite plates. Thermoplastic bipolar plates for PEMFCs made of composite materials is promising, but optimum filler loading that balances all properties is still required in order to achieve conductivity targets. Nevertheless this study has demonstrated that conductive thermoplastic bipolar plates can be produced via injection molding.

A theoretical treatment of the problem of unsteady turbulent free convection over a vertical flat plate is presented in this dissertation. An exhaustive review of the relevant publications revealed, that at the present time no solution of this problem has been given. The development of a method, by which the abovementioned problem could be tackled, is a substantial part of the dissertation. The equations of conservation of mass, momentum, and energy, written in a general form, were the starting point of the derivation. Various assumptions, simplifying the partial differential equations, were introduced. In the end, boundary layer equations were obtained. Turbulence was simulated by a phenomenological model, consisting of an algebraic law of the wall and a partial differential rate equation. The turbulence model is based on the concept of effective viscosity. Also, a constant turbulent Prandtl number was employed. The problem of an isothermal plate in a stagnant non-stratified fluid was treat; d, and appropriate initial and boundary conditions were formulated„ The system of equations was solved by an explicit finite- difference method. The numerical stability criteria were established. A computer programme, based on the numerical scheme, was developed and employed for calculations. The calculations were carried out for dry air, water, and mercury, representing gases, liquids, and liquid metals, respectively. In this way, a broad range of Prandtl numbers was covered. Temperature velocity, and effective viscosity profiles are presented here together with some other results of the calculations* An important observation is that the overall heat transfer coefficient goes through a temporary minimum before attaining its steady state value. The transient, which is extremely fast, can be divided into throe characteristic stages: the initial conduction regime, an intermediate stage, and the steady state. Our results were verified by comparison with data available from other independent sources. Due to the lack of data covering ■the whole transient, only the first and third stages were considered, The initial conduction regime was compared with an analytical solution and the final steady state results with experimental data of various authors, respectively. The agreement is good and no serious discrepancies were discovered. Although the present method produces reliable results, it cannot be widely employed, because the computing times are almost prohibitive with the present-day computers.

Le premier problème abordé dans cette thèse est la description de la topologie du dual unitaire des groupes de Lie à radical nilpotent co-compact, en particulier les produits semi-directs G = K x N des groupes compacts K avec les groupes de Lie nilpotents N. L’espace dual G de G a été déterminé par la théorie de Mackey et la paramétrisation géométrique donnée par R. L. Lipsmann qui ont prouvé l’existence d’une bijection entre G et l’espace des orbites coadjointes admissibles de G. Notre objectif est de comparer la topologie de Fell du dual unitaire avec la topologie quotient de l’espace des orbites coadjointes admissibles. Le premier exemple traité dans ce travail est le cas des groupes de déplacement Mn = SO(n) x Rn. Nous avons prouvé que l’espace dual de Mn est homéomorphe à son espace des orbites coadjointes admissibles. Ce résultat peut être vrai aussi pour les groupes Gn = U(n) x Hn, où Hn est le groupe de Heisenberg de dimension 2n + 1 (il est uniquement prouvé pour le groupe G1). Le deuxième problème considéré dans cette thèse est la déterminaton des représentations unitaires irréductibles p d’un groupe G, dont le noyau de p dans L1(G) est donné par les fonctions dont la transformée de Fourrier s’annule sur l’orbite Op de p. Ce problème a été résolu dans le cas de groupes de Lie nilpotents par J. Ludwig, qui a montré que ker(p) = {ƒ ? L1(G); ƒ[accent circonflexe](Op) = {O}} si et seulement si l’orbite coadjointe Op est plate. Le travail consiste à prouver qu’on a un résultat équivalent pour les groupes de Lie complètement résolubles / The first problem treated in this thesis is the description of the dual topology of Lie groups with co-compact nilpotent radical, in particular the semi direct products G = K x N of compacts groups K with nilpotent Lie groups N, The dual space G of G had been determined via Mackey’s theory and the geometric parametrization given by R. L. Lipsmann who had proved that there is a bijection between G and the admissible coadjoint orbit space of G. Our object is to compare the Fell topology of the dual space with the natural topology of the quotient space of admissible coadjoint orbits. The first example treated in this work is the case of the motion groups Mn = SO(n) x Rn. We have shown that the dual pace of Mn is homeomorphic with its admissible coadjoint orbit space. This result may be true also for the groups Gn = U(n) x Hn, where Hn is the 2n+1 dimensional Heisenberg Lie group (it is only proved for the group G1). The second issue regarded in this thesis is the determinaton of the irreducible unitary representation p of a group G, for which the kernel of p in L1(G) is given by the functions whose the Fourrier transform annihilates on the orbit O of p. This problem was solved for the case of nilpotent roups by J. Ludwig who had shown that ker(p) = {ƒ ? L1(G); ƒ[accent circonflexe](Op) = {O}} if and only if Op is a flat orbit. The work is to prove that this result remains true for completely solvable Lie groups

Digitized by Kansas Correctional Industries / Department: Civil Engineering.

Digitized by Kansas Correctional Industries

Typescript. / Digitized by Kansas Correctional Industries