RESUMO
RESUMO Neste estudo, foram obtidas as cinéticas e isotermas de adsorção do fenol presentes em efluentes sintéticos em reator batelada e coluna de leito fixo, utilizando como adsorvente carvão ativado de casca de coco. O objetivo foi a obtenção dos parâmetros cinéticos e de equilíbrio do processo para simular diferentes condições operacionais em uma coluna de adsorção em leito fixo. Foram avaliadas a influência do pH, a massa de adsorvente, a concentração inicial de fenol e três diferentes temperaturas para os testes em reator batelada. Foi possível trabalhar no pH natural da solução e o aumento da temperatura indicou adsorção exotérmica, favorável e espontânea. Os dois modelos de isoterma (Langmuir e Freundlich) representaram bem os dados experimentais (R2 ≈ 0,9). Valores aproximados de capacidade máxima de adsorção foram encontrados para o reator batelada e para a coluna de leito fixo (qmáx = 41,69 mg.g-1 para o reator batelada e qmáx = 41,98 mg.g-1 para a coluna de leito fixo). O método de Volumes Finitos foi utilizado na discretização das equações matemáticas e um algoritmo computacional foi implementado em linguagem FORTRAN. O código computacional foi validado com dados experimentais deste trabalho (erro médio de 13%), podendo-se assim simular diferentes condições operacionais do sistema de adsorção em coluna de leito fixo com vista a futuras aplicações industriais.
ABSTRACT In this study, the kinetics and adsorption isotherms of phenol present in synthetic effluents were obtained in a batch reactor and fixed bed column, using adsorbent coconut shell activated carbon. The objective was to obtain the kinetic and equilibrium parameters of the process to simulate different operating conditions in a fixed bed adsorption column. The influence of the pH, adsorbent mass, initial phenol concentration, and three different temperatures for the batch reactor tests were evaluated. It was possible to work on the natural pH of the solution and the temperature increase indicated exothermic, favorable, and spontaneous adsorption. Both isotherm models (Langmuir and Freundlich) represented the experimental data (R2 ≈ 0.9). Approximate values of maximum adsorption capacity were found for the batch reactor and for the fixed bed column (qmax = 41.69 mg g-1 for the batch reactor and qmax = 41.98 mg g-1 for the fixed bed column). The Finite Volume method was used in the discretization of the mathematical equations and a computational algorithm was implemented in FORTRAN programming language. The computational code was validated with experimental data of this work (mean error of 13%) and it was possible to simulate different operational conditions of the fixed bed column adsorption system for future industrial applications.
RESUMO
Objective To analyze the distribution characteristics of blood flow and wall shear stress with the consideration of elasticity of the artery wall and to investigate the biomechanical factors inducing aneurismal rupture. Methods The three-dimensional patient-specific internal carotid artery aneurysm model was constructed based on two-dimensional medical scan images. The artery wall model was created based on the statistical data of human body. According to the condition of the pulsatile blood flow in human body, hemodynamics in internal carotid aneurysm with fluid structure interaction was simulated using finite volume method and finite element method. Results An obvious vortex flow in aneurismal cavity was found with the direction unchanged during a cardiac cycle. There was a region at the aneurismal neck and aneurismal dome where the value of wall shear stress was relatively high. It also found two regions in the aneurismal neck and the aneurismal dome where the value of Von Mises Stress reached the maximum locally. In view of the material strength, it should be easy to have aneurismal rupture in these areas. Conclusions The distribution characteristics of vascular wall stress can be obtained by the calculation of fluid structure interaction to further predict the possible position of aneurismal rupture.
RESUMO
Objective To investigate effects of endovascular stents with different structures and wire cross section shapes on the treatment of internal carotid aneurysm and its influence on hemodynamics and flexibility. Method Based on the same model of internal carotid aneurysm, five models with different stent intervention treatment were constructed, which had different stent structions or wire cross section shapes while their porosity rates were approximately the same. Numerical simulations were performed using finite volume method to get quantitative information of biomechanics. Results Among the five models, the mean flow rate in aneurismal cavity decreased maximally in the model with stent of rectangular cross section. Wall shear stress in aneurismal dome and aneurismal neck were found to decrease much more in models with circular cross section and rectangular spiral stent. The flexibility of mesh stent was far better than that of the spiral stent. Conclusions Mesh stent with rectangular cross section has better biomechanical influence on the treatment of internal carotid aneurysm. These findings may help clinicians to select a proper stent when treating arterial aneurysm.