Solution of adsorption problems involving steep moving profiles

The moving finite element collocation method proposed by Kill et al. (1995) Chem. Engng Sci. 51 (4), 2793-2799 for solution of problems with steep gradients is further developed to solve transient problems arising in the field of adsorption. The technique is applied to a model of adsorption in solids with bidisperse pore structures. Numerical solutions were found to match the analytical solution when it exists (i.e. when the adsorption isotherm is linear). The method is simple yet sufficiently accurate for use in adsorption problems, where global collocation methods fail. (C) 1998 Elsevier Science Ltd. All rights reserved.

A comparative study of the fluidized-bed coating of cylindrical metal surfaces with various thermoplastic polymer powders

This paper reports the results of an experimental investigation into the fluidized-bed coating of cylindrical metal specimens using two types of thermoplastic powders, Rilsan(R) PA11, a nylon-11 powder produced by Elf Atochem, France and Cotene(TM) 4612, a linear low density polyethylene powder produced by J.R Courtenay (New Zealand). The effects of dipping time, preheat temperature and particle size distribution on coating thickness and surface finish were investigated. Consistent trends in coating thickness growth with dipping time were obtained for both nylon-11 and polyethylene powders with increases in coating thickness with preheat temperature. For the same preheat temperature, the lower melting point of polyethylene results in thicker coatings compared to those of nylon-11. There is a negligible change in the coating thickness for sieved powders compared to that for unsieved powders. A pre-heat temperatures of between 240 degrees C and 300 degrees C is necessary to achieve an acceptable surface finish with both nylon-11 and polyethylene powders. To minimize errors in achieving the desired coating thickness, dipping times shorter than 2 s are not recommended. The use of graphs of coating thickness versus dipping time in combination with the coating surface roughness plots presented in this paper enable the optimal choice of pre-heat temperature and dipping time to achieve acceptable surface finish. (C) 1999 Elsevier Science S.A. All rights reserved.

Physical properties and fluidization behaviour of fresh green bean particulates during fluidized bed drying

Changes in the physical properties (such as particle density, bulk density of the bed, shrinkage and bed porosity) of fresh green bean particulates were investigated during drying. Three length:diameter ratios (1:1, 2:1 and 3:1) were considered, using drying conditions of 50 +/- 2 degrees C and 13 +/- 2% relative humidity in a heat pump dehumidifier system. The fluidization behaviour was also evaluated at 10 levels of moisture content. The fluidization experiments demonstrated that the minimum fluidization velocity decreases as the drying proceeds due to the reduced moisture content and changes in the physical properties of the bean particulates. Empirical relationships of the following nature were developed for the change in shrinkage [VR = 1 - Be-kMR], particle density [rho(p) = A + BMR + C (exp)(-D MR)], bulk density [rho(b) = a(1) + b(1)MR + c(1)MR(2)] and bed porosity [epsilon = a(2) + b(2)MR + c(2)MR(2)] with the moisture content during fluidized bed drying.

Beach water table fluctuations due to spring-neap tides: moving boundary effects

Tidal water table fluctuations in a coastal aquifer are driven by tides on a moving boundary that varies with the beach slope. One-dimensional models based on the Boussinesq equation are often used to analyse tidal signals in coastal aquifers. The moving boundary condition hinders analytical solutions to even the linearised Boussinesq equation. This paper presents a new perturbation approach to the problem that maintains the simplicity of the linearised one-dimensional Boussinesq model. Our method involves transforming the Boussinesq equation to an ADE (advection-diffusion equation) with an oscillating velocity. The perturbation method is applied to the propagation of spring-neap tides (a bichromatic tidal system with the fundamental frequencies wt and wt) in the aquifer. The results demonstrate analytically, for the first time, that the moving boundary induces interactions between the two primary tidal oscillations, generating a slowly damped water table fluctuation of frequency omega(1) - omega(2), i.e., the spring-neap tidal water table fluctuation. The analytical predictions are found to be consistent with recently published field observations. (C) 2000 Elsevier Science Ltd. All rights reserved.

Water wave-driven seepage in marine sediments

The action of water waves moving over a porous seabed drives a seepage flux into and out of the marine sediments. The volume of fluid exchange per wave cycle may affect the rate of contaminant transport in the sediments. In this paper, the dynamic response of the seabed to ocean waves is treated analytically on the basis of pore-elastic theory applied to a porous seabed. The seabed is modelled as a semi-infinite, isotropic, homogeneous material. Most previous investigations on the wave-seabed interaction problem have assumed quasi-static conditions within the seabed, although dynamic behaviour often occurs in natural environments. Furthermore, wave pressures used in the previous approaches were obtained from conventional ocean wave theories: which are based on the assumption of an impermeable rigid seabed. By introducing a complex wave number, we derive a new wave dispersion equation, which includes the seabed characteristics (such as soil permeability, shear modulus, etc.). Based on the new closed-form analytical solution, the relative differences of the wave-induced seabed response under dynamic and quasi-static conditions are examined. The effects of wave and soil parameters on the seepage flux per wave cycle are also discussed in detail. (C) 2000 Elsevier Science Ltd. All rights reserved.

A dual catalyst bed system for the elimination of hydrogen from CO2 feed gas in urea synthesis

A dual catalyst bed system (Au/Fe2O3 + Pt-Pd/Al2O3) for eliminating hydrogen from the CO2 feed gas in urea synthesis is found to be far superior to commercially available and patented catalysts in catalytic activity. At relatively low temperatures, hydrogen is eliminated and coexistent CO is also oxidized completely to useful CO2. This can avoid effectively the accidental explosion of hydrogen-oxygen-ammonia mixed gases, thus ensuring the safety of urea synthesis.

Modeling of heat transfer in fluidized-bed coating of cylinders

A numerical model of heat transfer in fluidized-bed coating of solid cylinders is presented. By defining suitable dimensionless parameters, the governing equations and its associated initial and boundary conditions are discretized using the method of orthogonal collocation and the resulting ordinary differential equations simultaneously solved for the dimensionless coating thickness and wall temperatures. Parametric Studies showed that the dimensionless coating thickness and wall temperature depend on the relative heat capacities of the polymer powder and object, the latent heat of fusion and the size of the cylinder. Model predictions for the coating thickness and wall temperature compare reasonably well with numerical predictions and experimental coating data in the literature and with our own coating experiments using copper cylinders immersed in nylon-11 and polyethylene powders. (C) 2001 Elsevier Science Ltd. All rights reserved.

On the solute coupling at the moving solid/liquid interface during equiaxed solidification

Integral mass conservation was widely accepted for the solute coupling to solve solute redistribution during equiaxed solidification so far. The present study revealed that the integral form was invalid for moving boundary problems as it could not represent the mass balance at the moving interface. Accordingly, differential mass conservation at the solid/liquid interface was used to solve solute diffusion for spherical geometry. The model was applied for hydrogen diffusion in solidification to validate that the hydrogen enrichment was significant and depended on the growth rate. (c) 2006 American Institute of Physics.

Numerical modelling of tide-induced beach water table fluctuations

Field studies have shown that the elevation of the beach groundwater table varies with the tide and such variations affect significantly beach erosion or accretion. In this paper, we present a BEM (Boundary Element Method) model for simulating the tidal fluctuation of the beach groundwater table. The model solves the two-dimensional flow equation subject to free and moving boundary conditions, including the seepage dynamics at the beach face. The simulated seepage faces were found to agree with the predictions of a simple model (Turner, 1993). The advantage of the present model is, however, that it can be used with little modification to simulate more complicated cases, e.g., surface recharge from rainfall and drainage in the aquifer may be included (the latter is related to beach dewatering technique). The model also simulated well the field data of Nielsen (1990). In particular, the model replicated three distinct features of local water table fluctuations: steep rising phase versus flat falling phase, amplitude attenuation and phase lagging.

Modeling the optical constants of solids using acceptance-probability-controlled simulated annealing with an adaptive move generation procedure

The acceptance-probability-controlled simulated annealing with an adaptive move generation procedure, an optimization technique derived from the simulated annealing algorithm, is presented. The adaptive move generation procedure was compared against the random move generation procedure on seven multiminima test functions, as well as on the synthetic data, resembling the optical constants of a metal. In all cases the algorithm proved to have faster convergence and superior escaping from local minima. This algorithm was then applied to fit the model dielectric function to data for platinum and aluminum.

Simulated-annealing-based genetic algorithm for modeling the optical constants of solids

We propose a simulated-annealing-based genetic algorithm for solving model parameter estimation problems. The algorithm incorporates advantages of both genetic algorithms and simulated annealing. Tests on computer-generated synthetic data that closely resemble optical constants of a metal were performed to compare the efficiency of plain genetic algorithms against the simulated-annealing-based genetic algorithms. These tests assess the ability of the algorithms to and the global minimum and the accuracy of values obtained for model parameters. Finally, the algorithm with the best performance is used to fit the model dielectric function to data for platinum and aluminum. (C) 1997 Optical Society of America.

Melanonychia: the importance of dermatoscopic examination and of nail matrix/bed observation

Melanonychia, from the Greek melaina, means black and is the result of an increased deposition of melanin on the nail plate, originating in the nail matrix. It may have different causes, including subungueal melanoma, making early etiologic diagnosis very important.

Moving ear syndrome: The role of botulinum toxin

We report a 30-year-old man with moving ear syndrome caused by focal myoclonic jerks of the right temporal muscle. This focal myoclonus would disappear while the patient was sleeping, swallowing, or speaking. He was treated with botulinum toxin type A with a favorable outcome. Previous reports of this condition and possible therapeutic approaches are discussed. (c) 2007 Movement Disorder Society.