Sample Dispersion Due to Buffer Disturbances and Zeta Potential Variability in Electroosmotic Microchannel Flows

This paper presents detailed simulations to study analyte dispersion in electroosmotic microchannel flow. We focus on electrokinetic and hydrodynamic dispersion caused by buffer disturbances and random zeta potential variability. A two-dimensional microchannel model is used that considers the coupled momentum, species transport, and electrostatic field equations, including a model for the dependence of the zeta potential on pH and buffer molarity. The chemistry model accounts for pH-dependent protein labeling reactions as well as detailed buffer electrochemistry in a mixed finite-rate/equilibrium formulation. The model also has the unique capability to account for uncertainty in input parameters, such as species mobilities, as well as for stochastic processes, such as random zeta potential variability. These uncertainties and variabilities are handled using polynomial chaos representations for model inputs and field quantities. The results show a strong increase of analyte dispersion for increasing species charge number and for increasing zeta potential variability.

An Application of Digital Human Modeling and Ergonomics Analysis in Workplace Design

In today’s challenging environment, companies gain a competitive advantage by reducing time-to-market of their products. This effort requires an integration of various technologies and effective utilization of simulation tools. As an integral part of any manufacturing environment, operator health and safety is a primary focus of the companies. Digital human modeling and virtual reality tools provide an excellent solution to factor human element early in the design phase and to make proactive choices in workplace and equipment design decisions. In this paper, the process of ergonomics analysis within digital environment is discussed, and an application is summarized. The case study gives details of the integration of digital human modeling, motion capturing, and ergonomics analysis in an automobile part sub-assembly process.

Nano Science and Engineering in Mechanics and Materials

The transcendent technologies include nanotechnology, microelectronics, information technology and biotechnology as well as the enabling and supporting civil infrastructure systems and materials. These technologies are the primary drivers of the twenty first century and the new economy. Mechanics and materials are essential elements in all of the transcendent technologies. Research opportunities, education and challenges in mechanics and materials, including nanomechanics, carbon nano-tubes, bio-inspired materials, coatings, fire-resistant materials as well as improved engineering and design of materials are presented and discussed in this paper.

Assessing the Use of Tensor Closure Methods With Orientation Distribution Reconstruction Functions

Orientation tensors are widely used to describe fiber distri-butions in short fiber reinforced composite systems. Although these tensors capture the stochastic nature of concentrated fiber suspensions in a compact form, the evolution equation for each lower order tensor is a function of the next higher order tensor. Flow calculations typically employ a closure that approximates the fourth-order orientation tensor as a function of the second order orientation tensor. Recent work has been done with eigen-value based and invariant based closure approximations of the fourth-order tensor. The effect of using lower order tensors tensors in process simulations by reconstructing the distribution function from successively higher order orientation tensors in a Fourier series representation is considered. This analysis uses the property that orientation tensors are related to the series expansion coefficients of the distribution function. Errors for several closures are investigated and compared with errors developed when using a reconstruction from the exact 2nd, 4th, and 6th order orientation tensors over a range of interaction coefficients from 10−4 to 10−1 for several flow fields.

Functionally Graded Polymeric Composites Having Micro-Tailored Structure Formed by Electric Field

A solid composite having locally micro-tailored structure can be produced by curing liquid polymeric suspensions in an electric field. The redistribution effect of the field-induced forces exceeds the effect of centrifugation, presently employed to manufacture functionally graded materials. Moreover, unlike centrifugational sedimentation, one can electrically rearrange the inclusions in desired targeted areas. The applied electric field can be employed to produce a composite having uniformly oriented structure or only modify the material in selected regions. This technology enables polymeric composites to be locally micro-tailored for given design objectives. We discuss electrical and rheological inteactions in liquid suspensions. Relationships between microstructure and mechanical properties of the obtained functionally graded composites are presented.

A Development of Virtual Manufacturing System for Magnesium High Pressure Die Casting Processes

In recent years, high-pressure die-casting magnesium components have been gaining currency worldwide because of the excellent properties that magnesium alloys can offer to meet new product requirements. With the increasing application of magnesium parts worldwide, many research and development projects have been carried out to advance HPDC technology. However, truly optimized mold design and production of defect free castings remains a challenge for die casters. For many HPDC magnesium products, especially those specified for porosity-free and high cosmetic requirement, the challenge not only comes form a lack of a deeper understanding of how molten magnesium alloys fill the mold cavity and form defects, but also from improper preliminary part design. This study proposes a virtual prototyping system that integrates several effective soft and hardware tools for both the part and mold-design engineer to evaluate part manufacturability. Also, investigated in this study are the major causes of those defects that are the predominant cause of rejection of thin walled, leak-free magnesium parts requiring highly cosmetic finishes.

CFD Simulation of Fluid Flow Through Porous Media: Application to Decomposed Gases Flow Through Foam Pattern in Lost Foam Casting

Numerical simulation of decomposed gases through foam pattern was conducted using finite element analysis. A new kinetic model is proposed for gaseos phase flow between molten metal and foam material. The computations were performed for a wide range of Reynolds numbers. The results of the simulations are compared with the experiemental data obtained in this study.

Peclet Number Behaviour on the 1-D Heat Conduction-Convection Problem With a Control Volume Capacitance Method

Modelling of solidification with transport of mass is of paramount importance for the heat transfer community. Phase change problems have received considerable research attention over the last two decades. Numerical methods for fixed and moving grids have been developed with increasing accuracy and performance, although fundamental aspects still elude modeling such as numerical oscillations. The discovery of Control Volume Capacitance Methods (CVCM) is an attempt to eliminate the need to use classical Petrov-Galerkin and Bubnov-Galerkin formulations. The theory underpinning CVCM methods is presented. A novel modified CVCM is presented which is transformable into a FEM that is similar to that used to model heat-conduction. The method is applied to the 1-D semi-infinite problem, where mesh is spatially fixed whilst mass is transported, in order to investigate the Peclet number behavior. Numerical tests are compared against analytical solutions; the approach is shown to be accurate, stable and computationally competitive.

A Bistable Electromagnetic Actuated Microvalve With Integrated Switching Mechanism

This paper presents a new design and fabrication method for a bistable electromagnetic actuated microvalve. The complete magnetically close structure has been designed by ANSYS 5.7 [1] and was fabricated in 7 masks steps. The fabrication processes were entirely done by surface micromachining and electroplating on a single wafer with the maximum fabrication temperature of 300 °C, providing potentially a CMOS compatible process. The microvalve has additional feature called integrated switching mechanism used to detect the position of the membrane under fully open or closed position. The fabrication steps for the microvalve are different from previous work; the hole is etched through the back of wafer after the whole valve structure been built on the top of wafer. This provides the flexibility to fabricate an actuator first before finally producing a microvalve.

Two-Color Micro PIV Measurements of Particle and Fluid Motion in AC Electrokinetics

Two-Color μ-PIV is developed and used to uniquely determine the fluid velocity based on the micron-resolution Particle Image Velocimetry (μ-PIV) technique [1–3]. The fluid velocity field was obtained by measuring the motion of two different sizes particles, 0.7 and 1.0 μm. The different sizes of particles contain different fluorescent dyes, allowing them to be distinguished using fluorescent filter cubes. By comparing the velocity fields from the two different size particles, the underlying fluid motion can be uniquely determined, without a priori knowledge of the electrical properties of the particles, or the electrical field. The test section is formed by two wedge-shaped electrodes sandwiched between two glass wafers. In the presence of nonuniform ac electric fields, the particles experience dielectrophoretic (DEP) forces due to polarization and drag forces due to viscous interaction with the suspending medium, and the fluid motion is induced by the electrothermal effect and/or ac electroosmosis. The micro-PIV measurements are used to determine quantitatively the physical characteristics of the AC electrokinetic effects.