W. Vicente

An Eulerian model for the simulation of an entrained flow coal gasifier

Abstract A numerical model is used to simulate the gasification of coal inside an entrained flow gasifier. The model is based on the Eulerian–Eulerian concept. Both gas and particulate phases conservation Eulerian equations are solved. The model used includes the coal particle processes, such as drying, volatilization, heterogeneous reactions of combustion and gasification, particle drag and turbulent dispersion, as well as heat-up. The model is applied to the investigation of the gasification of coal in a commercial entrained flow gasifier, from which experimental data is available. The results obtained show good agreement for both the main and minor species, and temperature.

PDF MODELING OF CO AND NO FORMATION IN LEAN PREMIXED METHANE FLAMES

In this paper, CO and NO formation in a premixed turbulent methane flame is simulated with a stochastic model of combustion. The model proposed is a combination of both the computational fluid dynamics and the Monte Carlo methods for the solution of the joint probability density function. Finite chemical kinetics is represented by a GRI-derived reduced-chemistry model. This resultant model is used to simulate a lean, premixed, bluff-body, stabilized flame for which experimental data are available. Under this condition, the prediction of NO formation is a challenge because of its low concentrations (typically a few parts per million) and because every NO-formation route is relevant. The model used for the molecular mixing includes a variable mixing time, covering the range from the Kolmogorov scale to the integral scale. A lookup table is used to estimate the thermochemical properties and is found to be more adequate than direct integration. The results are compared with an experimental database.

Numerical Analysis of Turbulent Flow in a Small Helically Segmented Finned Tube Bank

Abstract A full finned tube bank is represented as a small finned tube bank in order to analyze numerically mean properties behavior in the streamwise direction. The main goal is to obtain criteria for implementing periodic boundary conditions in a single isolated finned tube module. The simulation is carried out with the Reynolds Averaged Navier–Stokes method and the turbulence effect is modeled with the Renormalization Group k-ϵ model. The complex geometry of finned tube is represented by means of a cut-cell method. Numerical results are compared with experimental data, experimental visualizations, and semi-empirical correlations. Predictions show an adequate hydrodynamics and heat transfer representation. Additionally, mean properties in the streamwise direction show quasi-sinusoidal behavior, and the heat transfer presents approximately identical values in every finned tube in the fully developed flow zone. Therefore, periodic boundary conditions for turbulent kinetic energy and its dissipation rate and a constant wall heat flux condition in the fully developed flow are proposed in numerical simulations on a single isolated finned tube module.

Simulación de un Sistema de Gasificación Integrado a un Ciclo Combinado

Se presenta la aplicacion de un modelo numerico para simular un sistema de gasificacion integrado a un ciclo combinado. El modelo considera un enfoque global para cada uno de los equipos del sistema y una condicion de equilibrio quimico para la composicion del gas de sintesis. El combustible que se utiliza es coque de petroleo y se caracteriza de la forma CmHnNsSr. Los balances de materia y energia aplicados al sistema se resuelven mediante el metodo de Gauss-Jordan. Los resultados se comparan con datos de plantas en operacion. El analisis comparativo muestra que la metodologia para la evaluacion tecnica de sistemas de gasificacion integrados a ciclos combinados es aceptable.

Building a three-dimensional model of the upper gastrointestinal tract for computer simulations of swallowing

We aimed to provide realistic three-dimensional (3D) models to be used in numerical simulations of peristaltic flow in patients exhibiting difficulty in swallowing, also known as dysphagia. To this end, a 3D model of the upper gastrointestinal tract was built from the color cryosection images of the Visible Human Project dataset. Regional color heterogeneities were corrected by centering local histograms of the image difference between slices. A voxel-based model was generated by stacking contours from the color images. A triangle mesh was built, smoothed and simplified. Visualization tools were developed for browsing the model at different stages and for virtual endoscopy navigation. As result, a computer model of the esophagus and the stomach was obtained, mainly for modeling swallowing disorders. A central-axis curve was also obtained for virtual navigation and to replicate conditions relevant to swallowing disorders modeling. We show renderings of the model and discuss its use for simulating swallowing as a function of bolus rheological properties. The information obtained from simulation studies with our model could be useful for physicians in selecting the correct nutritional emulsions for patients with dysphagia.

Statistical analysis of clothing drying in a venting type dryer

Abstract An experimental study of the drying process using the prototype of a venting type dryer is presented. The machine has two motors: one for moving the drum and another for moving the turbine; electrical resistance is used as the heat source. The prototype operates under controlled test conditions in accordance with the Department of Energy (DOE) Standard 10 CFR 430. The aim of this study is to statistically determine the impact of the main factors and their interactions involved in the drying of clothing from a complete design of experiments. Statistical analyses for drying time and the energy consumption are determined from the studied factors. The factors studied are turbine motor frequency (to admit and expel air from the dryer); power supplied to the electric coil, amount and moisture of clothing and restriction of exhaust duct the gases. The results show that all of the studied factors and four of the interactions are statistically significant in the drying of clothes. The shortest drying time and the lowest energy consumption were obtained with the higher level of restriction and the lower initial moisture of clothing.