El grupo de Mecánica Computacional los invita a su nuevo seminario sobre: Experimental and CFD evaluation of the influence of nozzle and degree of agglomeration on the dispersion phenomena inside the 20l sphere.
Conferencista: Felipe Muñoz. Profesor Asociado, Departamento de Ingeniería Química. Universidad de los Andes.
Fecha: Jueves 19 de Abril (Entrada libre – Cupo limitado)
Hora: 11:00 a 12:30PM
The 20L Sphere is one of the most common devises used for characterizing a combustible dust in terms of its explosivity parameters and severity of its potential explosion at certain conditions. This test is largely accepted as a reference normativity and standard under the ASTM E1226(2013). However, during the past years, a few concerns about the reliability of this standard test have arisen, making the revision of its methodology and procedures an imperative matter. These concerns are mainly based on the suggestion that the change on the particle size that occurs during the dispersion process due to particle agglomeration and de-agglomeration has a significant influence on the measurements that the test currently does not consider. Additionally, the test operates with the assumption that the hybrid mixture (gases and solid particles) is homogeneous in its properties throughout the entirety of the system. These considerations about the uncertainty of the test could ultimately induce inaccurate or incorrect design of process security equipment and therefore have catastrophic consequences. In this context, the purpose of this work was to evaluate the influence of seven different disperser geometries and three different initial agglomerate shapes in the degree of agglomeration/de-agglomeration reached the end of the dispersion process for micrometric carbon-black and wheat starch particles. This work considered both, computational and experimental approaches in order to validate, question and further explain the dispersion phenomena inside the 20L Sphere. The computational approach was developed in the commercial software Star-CCM+ V12.02.010 using a lagrangian-lagrangian approximation to the two-phase flow phenomena, whereas in the experimental approach, the velocity of a particle sample was analyzed through Particle Imaging Velocimetry (PIV), and the Particle Size Distribution (PSD) was measured using laser diffraction techniques. The results obtained show that the computational model established can predict the experimental results in an acceptable matter, given that the average difference in the sphere pressure profiles between these two approximations is 7%. The results also show that the initial agglomerate shape has a much higher influence on the fragmentation rate than the type of disperser used, and that this fragmentation occurs mainly during the injection step. Nevertheless, the velocity profiles clearly show that fragmentation also occurs at the stages that follow the injection and it is caused by the high levels of turbulence encountered in the system. Finally, the dust concentration profiles along the system show that the local concentration is always lower than the nominal concentration, leading to conclude that the homogeneity assumption of the test is, in fact, highly questionable.