Search

Rain-water and/or snow-melt water infiltrate into or through waste rock dumps at mine sites and dissolve minerals (salts) from rock surfaces. Collecting and treating the drainage is required to meet mine-water-discharge regulations. Generally speaking, less solute loadings in the collected drainage would mean lower cost (e.g., less lime consumption). Thus it is important to identify the rate-control mechanisms of mineral dissolution under different storage configurations of waste rock dumps. In this paper, the authors present an analysis of rate-control mechanisms. The main point is the rate of water-infiltration Q relative to the rate of solute production (kβλ), i.e., (kβλ)/Q. Here k represents the effective kinetic constant of a mineral species’ dissolution from a rock surface, β represents rock dump depth, and λ represents the sum of rock surface areas that are flushed by infiltrated water within a unit volume of rocks. One significance of the quotient (kβλ)/Q is its quantitative indication of the rate-control mechanisms. When (kβλ)/Q becomes smaller, say (kβλ)/Q 2.5, infiltration rate Q is in control, that is, the solute concentration would become close to the saturation concentration of the mineral species and the solute loading would become proportional to infiltration rate Q; when 0.5 < (kβλ)/Q < 2.5, both water-infiltration rate Q and the rate of solute production (kβλ) are in control, a mixed control mechanism.

This paper presents an improvement to the truncated modal summation representation of eigenvector derivatives for free-free structures. In this method, the eigenvector derivative is assumed to be spanned by the available lower modes and the unavailable higher modes. The contribution due to the available modes to the eigenvector derivative is computed from the governing equation for the eigenvector derivative, while the contribution due to the unavailable modes is explicitly and accurately expressed using the available modes and the system matrices. An approach to the singularity of the stiffness matrix is presented, in which a shift in eigenvalues is introduced to avoid the singularity and accelerate the convergence speed. A numerical example is given to illustrate the effectiveness of the present method.

When the parameters of the structures are uncertain, the structural natural frequencies become uncertain. In this paper, we deal with the vibration problem of the structure with interval parameters, the eigenvalue problem of the structures with interval parameters is transferrd into two different eigenvalue problems to be solved. The perturbation method is applied to the vibration problem of the structures with interval parameters, the numerical results show that the proposed method is sufficiently accurate and needs little computational efforts.

Optimal water levels in polymer electrolyte membrane (PEM) fuel cells are the key to prevent liquid water flooding and to reduce membrane dry out. A good understanding of liquid water transport is therefore essential to maintain an optimum water balance. In this study, a two-dimensional, two-phase, volume-averaged numerical model is developed and used to simulate the effect of catalyst layer structure and its surface wettability on liquid water transport in the cathode catalyst layer (CCL) of PEM fuel cells. The model is capable of handling liquid water transport across both the catalyst and gas diffusion layers. The simulation results are compared with literature, and a good agreement is found. The highest liquid water saturation in the CCL is observed under the rib, and the lowest value is observed under the flow channel. It is also observed that the wetting and geometric characteristics of CCL have significant influence on the liquid water transport, and the mobile liquid water saturation in a hydrophilic catalyst layer decreases with CCL surface wettability, that is, lower CCL contact angle yields lower liquid water saturation. © 2011 John Wiley & Sons, Ltd.

A probabilistic method to evaluate the effect of uncertainties in geometrical and material properties of structures on the vibration response of random excitation is presented. Comparison between the random response caused by random structural properties and that caused by random excitation is performed through numerical examples. The results of this study indicate that the uncertainties in structural parameters have significant effects on the structural response.

The microstructure of catalyst layers (CLs) is a naturally random medium and changes in it greatly affect the performance of polymer electrolyte membrane fuel cells. In this paper, the mechanical analysis method, developed in Part I for understanding the mechanism of microstructure changes, is further extended to describe CLs as random three-phase microstructures. Microstructure reconstruction is accomplished using statistical information from experimental images of practical CLs. In the microscopically complex reconstructed microstructure, mechanical analysis is performed in order to understand the mechanism of changes caused by the cycling of start-up and shutdown during operation. Numerical simulation shows that, although different reconstructed microstructures have different changes, there have in common the competition between crack initiations in phases and delamination between different phases in the CLs. This competition plays an important role in microstructure change and results in performance degradation, indicated by the decrease in connection length among different solid components in the CLs after certain duty cycles.