Simulation of a cross-flow airclassifier at high solid feed rates

El clasificador de polvo de flujo cruzado es un equipo de clasificación que trabaja por vía seca. El uso de este tipo de dispositivos se evalúa actualmente para reemplazar a los métodos húmedos de clasificación en la producción de arena de trituración. La influencia del contenido de polvo es de importancia crítica para el diseño del proceso. Una manera de estimar esta influencia es a través de simulación numérica. En éste trabajo se simula el proceso de clasificación de polvo mediante fluidodinámica computacional (CFD). La interacción entre partículas se modela mediante un método de elementos discretos (DEM). Las simulaciones se optimizan para minimizar el error a través de la elección entre dos modelos de turbulencia y entre dos modelos para la inyección de sólidos. Se simula la clasificación de polvo con tres distintos contenidos de polvo. Se establece que el contenido de sólidos alimentados al clasificador tiene una gran influencia en el proceso de clasificación, por lo que es un parámetro crítico para el correcto diseño del clasificador.The cross-flow air classifier is a dry process device. The use of such separators is being evaluated to replace the wet classification methods in the production of manufactured sand. The influence of the solid feed rate is critical for the correct design of the process. One method to analize the influence of the feed is by using numerical simulation. In this work, the powder classification process is simulated by computational fluid dynamics (CFD). The particle-particle interaction is modeled with a discrete element method (DEM). Simulations are optimized to better represent the experimental data by choosing between two turbulence models and two models for the injection of solids. Dust classification at three different solid rates is simulated. It is established that the amount of solids has a great influence in the classification process. This fact indicates that the solids content is a critical parameter for a proper design of the device.Peer Reviewe

Statistical Analysis of Composite Spectra

We consider nearest neighbor spacing distributions of composite ensembles of levels. These are obtained by combining independently unfolded sequences of levels containing only few levels each. Two problems arise in the spectral analysis of such data. One problem lies in fitting the nearest neighbor spacing distribution to the histogram of level spacings obtained from the data. We show that the method of Bayesian inference is superior to this procedure. The second problem occurs when one unfolds such short sequences. We show that the unfolding procedure generically leads to an overestimate of the chaoticity parameter. This trend is absent in the presence of long-range level correlations. Thus, composite ensembles of levels from a system with long-range spectral stiffness yield reliable information about the chaotic behavior of the system.Comment: 26 pages, 3 figures; v3: changed conclusions, appendix adde

Thick brane in 7D and 8D spacetimes

We consider a thick brane model supported by two interacting scalar fields in 7D and 8D general relativity. Using the special type of a potential energy, we obtain numerically the regular asymptotically flat vacuum solutions. A possibility of obtaining the similar solutions for an arbitrary number of the extra spatial dimensions is estimated.Comment: 3 Ref's are adde

Water requirements and single and dual crop coefficients of sugarcane grown in a tropical region, Brazil

A field experiment was conducted throughout 2009/2010 in a sugarcane field of a commercial distillery located on the coastal area of Paraiba state, Brazil. The objectives were to determine sugarcane water requirements and to test the single and dual crop coefficients by comparing the calculated values of ET with measured ones. Crop evapotranspiration was determined by field water balance, reference evapotranspiration (ETo) by the Penman-Monteith approach, while single and dual crop coefficients were computed through the standard FAO-56 methodology. The experi- mental area was cultivated with irrigation ap-plied weekly by a centre pivot system in addition to rainfall and the irrigation scheduling was based on 100% ETo. Three statistical tests, mean bias difference (MBD), normalized root mean square difference (NRMSD) and regression analysis, were used to evaluate the performance of single and dual crop coefficients. Results showed that there was a notable symmetry between ET meas- ured and ET calculated by Kc dual. The ET val- ues, calculated from Kc single, underestimated those obtained from soil water balance meas- urements by 36%