Numerical Study of Particle Motion in Jet Milling

Jet mills are common devices used in industry for fine milling of dry particulate materials. The size reduction is caused by repeated events of impacts between particles. Although many parameters affect the performance of a jet mill, only a few of them were investigated. Particles' motions in a jet mill have great influence on the comminution process and energy consumption. Therefore, as a first step for a full simulation of the jet-mill process, it was decided to investigate the particle motion inside the jet mill by neglecting particle-particle interaction and particle breakage. In this way, the numerical simulations provide a better understanding of the classification process. In the present study, three-dimensional numerical simulations of particle motion in an industrial full-scale jet mill were conducted. The predictions of the numerical simulations were compared with experimental data and used to analyze the flow field characteristics.     

Distributed Multi-Level Recovery in Main-Memory Databases

In this paper we present recovery techniques for distributed main-memory databases, specifically for client-server and shared-disk architectures. We present a recovery scheme for client-server architectures which is based on shipping log records to the server, and two recovery schemes for shared-disk architectures—one based on page shipping, and the other based on broadcasting of the log of updates. The schemes offer different tradeoffs, based on factors such as update rates.Our techniques are extensions to a distributed-memory setting of a centralized recovery scheme for main-memory databases, which has been implemented in the Dalì main-memory database system. Our centralized as well as distributed-memory recovery schemes have several attractive features—they support an explicit multi-level recovery abstraction for high concurrency, reduce disk I/O by writing only redo log records to disk during normal processing, and use per-transaction redo and undo logs to reduce contention on the system log. Further, the techniques use a fuzzy checkpointing scheme that writes only dirty pages to disk, yet minimally interferes with normal processing—all but one of our recovery schemes do not require updaters to even acquire a latch before updating a page. Our log shipping/broadcasting schemes also support concurrent updates to the same page at different sites.     

Constructing a Complex Precast Tilt-Up-Panel Structure Utilizing an Optimization Model, 3D CAD, and Animation

This paper presents the concept used to construct a complex residential tilt-up-panel structure utilizing three-dimensional (3D) modeling and animations. The residence comprises of 108 precast concrete panels of varying rectangular shapes with “dog legs” and window and door “cutouts” that look like an assembled jigsaw puzzle. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often in 90° joints between panels. 3D animations were used to experiment with the construction process on the computer screen prior to construction in order to avoid potential costly on-site errors. In addition, the 3D animations were also used as a training tool for the contractors. This paper focuses on describing the methodology used to integrate a crane selection algorithm and optimization model with 3D modeling and animation for the selection, utilization, and location of cranes on construction sites. Analytical optimization processes were used to decrease the traveling time and distance of the selected crane, to improve the crane lifting sequence and to minimize the use of panel casting slabs.     

Queue Lengths and Waiting Times for Multiserver Queues with Abandonment and Retrials

We consider a Markovian multiserver queueing model with time dependent parameters where waiting customers may abandon and subsequently retry. We provide simple fluid and diffusion approximations to estimate the mean, variance, and density for both the queue length and virtual waiting time processes arising in this model. These approximations, which are generated by numerically integrating only 7 ordinary differential equations, are justified by limit theorems where the arrival rate and number of servers grow large. We compare our approximations to simulations, and they perform extremely well.     

The solubility parameters of aromatic polyamides

The degrees of swelling of rigid aromatic polyamide networks in various solvents, nonsolvents, and solvent mixtures were used to determine their solubility parameters. This was made possible because of the amorphous nature of the rigid networks and the low levels of intersegmental H-bonding. The solubility parameters are: δ = 23.0 (MPa)^1/2, δ_d = 18.0 (MPa)^1/2, δ_p = 11.9 (MPa)^1/2, and δ_H = 7.9 (MPa)^1/2. The determined values are believed to be good approximations of the solubility parameters of stiff linear aromatic polyamides, because of the essential identity of their structure and the stiff segments in the networks.     

Rigid backbone polymers

Summary It is shown that the inverse velocity of a fallingball in, or _m the apparent minimum viscosity of, anisotropic solutions of poly(n-hexylisocyanate) in toluene, are molecular weight dependent. The molecular weight dependence follows two linear branches. Below M_w=42600 the apparent minimum viscosity is very weakly dependent on M_w. Above M_w=42600 the apparent minimum viscosity of the anisotropic solution is strongly dependent on the molecular weight.     

INTERACTION BETWEEN ADSORPTION AND CONDENSATION PROCESSES IN A PORE AND ITS EFFECT ON HYSTERESIS

Capillary condensation is treated on the basis of its relation to the properties of the interface between the pore walls and the condensed sorbate. Effects resulting from the interaction between adsorption and condensation processes at the pore are examined. The approach allows a more accurate assessment of the sorption isotherm, and leads to a simple explanation of hysteresis.     

Mathematical Modeling of Drying of Liquid/Solid Slurries in Steady State One-Dimensional Flow

A mathematical model of simultaneous mass, heat and momentum transfer for two-phase flow of a gas and a solid/liquid slurry was developed. The model was applied to calculation of the drying process of coal-water slurry droplets in a gas medium in a steady one-dimensional flow. The model was based on the well-known two-stage drying process for slurry droplets. After the first period of drying, in which the evaporation rate is controlled by the gas phase resistance, the evaporating liquid diffuses through the porous shell (crust) and then, by convection, into the gas medium. Inside the dry external crust of the drop, a wet central core forms, which shrinks as evaporation proceeds. The temperature of the slurry droplet rises. The process ends when the temperature of the dry outer crust reaches the coal ignition temperature in the case of combustion or when the moisture of the particle reaches the final required moisture. The developed model was based on one-dimensional balance equations of mass, energy and momentum for the liquid/solid and gas phases. The system of governing equations was represented by first-order differential equations and solved simultaneously. The numerical solution of the governing equations was obtained using Gear's method. The model permitted calculation