Optimized Cooling System for PEM Fuel Cell Stack Based on Entropy Generation Minimization

Cell temperature in fuel cells is an important parameter which highly affects fuel cell stack efficiency. A suitable cooling system should satisfy an acceptable temperature range. In this research a relevant cooling system for a specified PEM fuel cell stack has been proposed complying with the criteria and cooling requirements of the fuel cell. The effect of various parameters on the entropy generation and temperature distribution in the cooling plates are surveyed. The number of cooling plates, the number of channels in each cooling plate and the channel width is determined. Two flow regimes namely laminar and turbulent flows of the cooling fluid in channels are analyzed and a design methodology is proposed for each regime of flow. The proposed design methodology in turbulent flow will be optimized while the work destruction is minimized. However, the proposed design in laminar flow is not the optimum one but the most efficient between different configurations. The comparison between these two proposed designs show that the turbulent flow has a lower entropy generation. In addition to entropy generation minimization, to have a desirable optimum cooling system, other parameters such as the size of the cooling plates and temperature uniformity inside cooling system have been investigated in this analysis.

Numerical Prediction of Erosion of Mild Steel Surfaces by Boiler Fly Ash Particles

Fly ash particles entrained in the flue gas from boiler furnaces in coal-fired power stations can cause serious erosive wear on steel surfaces along the downstream flow path. This paper describes research into fly ash impingement erosion on such surfaces, with particular reference to the heat transfer plates in rotary regenerative air heaters. The effect of the ash particle impact velocity and impact angle on the erosive wear of mild steel surfaces was determined through experimental investigations, using three different power station ash types. The experimental data were used to calibrate a fundamentally-derived model for the prediction of erosion rates. This erosion model was incorporated into a particle-tracking CFD flow simulation of the ash-laden flue gas flow through the complex channels between corrugated air heater plates. The predicted erosion rates were compared with measured erosion rates obtained using a large accelerated-erosion test facility located at a power station. Good agreement was obtained, the predictions generally being within 20 percent of the measured values.

Development of Advanced Alloying Process Using Micro-EDM Deposition Process

The development of an advanced alloying process using Micro-Electrical Discharge Machining Deposition is described in the present paper. The new process uses a micro-sized bimetal tool electrode, which is composed of two halves; each part made of a different metal. The alloying process of the two metals occurs during the deposition process previously proposed by the authors, which can create 3-dimensional micro-sized objects. The quality of alloyed metal was verified using X-ray analysis. In the present experiment the two metals used are YNi-1 (nickel alloy used in TIG welding) and S45C (medium carbon steel). EPMA results of the obtained deposit show that the nickel and iron distribution in the deposit is uniform when the tool electrode spins during the deposition process. Also, it was found that the chemical composition of the main metal in the deposited object is proportional to the cross sectional area in the bi-metal electrode section. Therefore, not only the deposition process takes place but also the chemical composition of the deposit can be simultaneously controlled using this process.

Influence of Mechanical Properties of Adhesives on Stress Distributions in Lap Joints

This paper deals with stress analysis of a single lap-jointed cantilevered beam using the three dimensional linear elastic finite element analysis (FEA) technique. Numerical examples are provided to show the influence on the stresses of the single lap-jointed cantilevered beams using adhesives of different characteristics which encompass the entire spectrum of viscoelastic behaviour. The results indicate that the stress distributions of a single-lap jointed cantilevered beam are strongly affected by both Young’s modulus and Poisson’s ratios. The maximum stress ratio was used to determine maximum values of Young’s Modulus required in order that the static stresses of an adhesively bonded cantilevered beam will not be more than given value of that of the equivalent homogeneous structure, that is a geometrically similar beam but without a joint. The analysis results also show that by choosing suitable adhesives, the maximum stresses can be reduced and the strength can be improved.

Visualisation of Two-Phase Gas-Liquid Pipe Flows Using Electrical Capacitance Tomography

Electrical Capacitance Tomography (ECT) has been used over a number of years to measure concentration distribution, and more recently velocity distribution, in two-phase flows. ECT is non-intrusive, and the reconstruction of the concentration and velocity distribution can be undertaken in real time and over an arbitrary number of zones in the flow cross-section. In this paper the concept of a ‘virtual instrument’ is introduced where zones of the image can be structured for comparison with other measurements. Numerical agreement with gamma-ray density measurements is shown to be excellent in slug and stratified flows. We present a series of measurements undertaken in complex oil/gas slug flows in a large flow loop. We present a variety of 2-D cross-sectional images, time series velocity and concentration graphs and 3-D contour plots. The good temporal and spatial resolution of ECT throws an extensive new light on these otherwise difficult to measure dynamic flow structures. In particular with bubbly-slug structures known as ‘ghosts’ ECT shows clearly that they are in fact bubbly waves which have extended ‘wings’ up and around the pipe.

Processing and Characterization of Particulate SiC Reinforced Copper Matrix Composites

Copper Matrix Composites reinforced with particulate Silicon Carbide were consolidated by Vacuum Hot Pressing and Press-Sinter routes. The reinforcement content was varied from 10% to 30% by volume. The composites were then characterized for their microstructure, density, X-ray diffraction (XRD), Coefficient of Thermal Expansion (CTE), hardness, tensile strength, electrical conductivity and elastic modulus. The properties were compared with those of Copper Tungsten alloys. Cu/SiC composites are found to be potential materials for electrical contact and welding applications. An attempt has also been made to evaluate the suitability of copper matrix composites as a replacement to copper tungsten alloys.

A Corotational Elastoplastic Formulation With Subloading Surface Model for Hardening Materials

In this paper a corotational constitutive model for the large elastoplastic deformation of hardening materials using subloading surface model is formulated. This formulation is obtained by refining the large deformation theory of Naghdabadi and Saidi (2002) adopting the corotational logarithmic (Hencky) strain rate tensor and incorporating it into the subloading surface model of Hashiguchi (1980, 2003) falling within the framework of the unconventional plasticity. As an application of the proposed constitutive model, the large Elastoplastic deformation of simple shear example has been solved and the results have been compared with classical elasto-plastic model using the Hencky strain tensor. Also the effect of the choice of corotational rates on stress components has been studied.

A Means of Generating Polyethylene Wear Particles With Desired Size and Shape for Biological Studies of Osteolysis

Metallic and ceramic counterfaces with artificial surface textures were rubbed against ultra high molecular weight polyethylene (UHMWPE) pins in water-lubricated wear tests and the characteristics of wear debris were studied. Two types of surface textures were utilized. In the first type, an array of wedge shaped features was created on silicon wafers by microfabrication. It was found that the mean size of UHMWPE wear particles strongly depended on the length of the cutting edge of the wedge. For instance, for wedges with a cutting edge length of 55 μm, 15 μm, and 7 μm, it was found that more than 75% of wear particles had a mean length of 30–60 μm, 6–15 μm, and 4–10 μm, respectively. In the second type of textured surfaces, unidirectional patterns were created on the stainless steel discs. These unidirectional patterns consisted of long, parallel edges and grooves and were created by abrading the discs by different grits of sand papers. The length of the majority of unidirectional edges was found to be approximately equal to the dominant size of elongated wear debris. The narrowly distributed wear debris produced in this investigation can be used in the biological study of the effects of size and shape of UHMWPE wear particles in total joint replacements on osteolysis.

Centrifugal Water Pump Driven With a DC Motor Powered by an Emulator of MK5-E Proton Exchange Membrane Fuel Cell Stacks

Direct Current (DC) motors can be directly powered by Proton Exchange Membrane Fuel Cell (PEMFC) Stacks, to obtain plants with little maintenance and good reliability. To obtain a suitable efficiency working plant, it’s necessary to correctly match the load in order to operate in proximity to the best power line of the FC stacks generator. Otherwise by a proper field current regulation of a separately excited DC motor directly powered by a FC stacks generator, it is possible to extract from the generator itself the correct power for every temperature level. The present interest for this problem has advised the Authors to perform an experimental investigation, whose results are reported in this paper, about a centrifugal water pump powered as above c/o the machines laboratory of the Mechanical Department of the University of Palermo.

Research on Nonlinear Damping Characteristics of Damping Alloy With Uniform Stress Field

For the high damping metal material like damping alloy, the damping capacity usually changes with the strain amplitude and frequency nonlinearly. First, to extract the pattern of the internal damping versus strain, two time-domain calculation methods are presented in this paper. One is the moving exponent method (MEM for short) based on FFT (MEM+FFT) and the other is the moving autoregressive model method (MARM). The computing accuracy of the two methods has been compared through numerical simulations. The nonlinear relation curve of loss factor versus strain is achieved by the impulse excitation experiment employing uniform stress field. Then, to extract the pattern of the internal damping versus vibrating frequency, the sine sweep-frequency excitation experiment based on the half-power bandwidth method is carried out. The resulting curve indicates that the internal damping is also a nonlinear function of frequency.