Numerical simulation of a 3-D gas-solid fluidized bed: Comparison of TFM and CPFD numerical approaches and experimental validation

This paper presents the results of a 3-D numerical simulation of a freely bubbling fluidized bed, based on the Eulerian–Lagrangian approach, using the software Barracuda (CPFD-Barracuda). The main results obtained were assessed in terms of frequency analysis, bubble pierced length, bubble size, bubble passage frequency and bubble velocity. The results obtained were also compared with experimental data obtained in a 3-D fluidized bed using pressure and optical probes, and with the numerical results using the more common Eulerian-Eulerian approach, implemented in the commercial software Fluent (TFM-Fluent).The results show that CPFD-Barracuda satisfactorily predicts the global behaviour of bubbling beds with a low computational cost, although it computes smaller bubble sizes and lower bubble velocities than TFM-Fluent and experiments. Additionally, the spectra of pressure and particle volume fraction obtained with CPFD-Barracuda resemble those from the experiments and the TFM-Fluent simulations, but with a larger contribution of lower frequencies. The peaks of the pressure spectra from CPFD-Barracuda are close to those from the experiments and the TFM-Fluent simulations, whereas those in the solid volume spectra seem to be underestimated by CPFD-Barracuda. The results also indicate that the particle fraction threshold value chosen to distinguish bubbles contours notably influences the results of the bubble characteristics, especially for TFM-Fluent, whereas CPFD-Barracuda is less sensitive to this threshold value.     

Experimental and numerical determination of the lubrication force between a spherical particle and a micro-structured surface

In many particulate processes suspensions need to be handled. Hydrodynamic forces in presence of a liquid as a surrounding continuum medium can significantly affect the particle collision behaviour. When particles approach a wall, lubrication force can become dominant with decreasing distance. This force was described analytically by different authors for a smooth flat wall. Roughness was found to be an important factor in this context, but the mechanisms are still not fully understood. In this work, the effects of topology on the lubrication force were studied using a regular prismatic micro-structured titanium surface produced by micro-milling. A nanoindentation setup was modified for the direct measurement of this force during the particle approach to polished and micro-structured surfaces in liquid. For a more detailed insight on the behaviour of the fluid in the decreasing gap between particle and surface microstructure, resolved computational fluid dynamics (CFD) simulations were performed using an overset mesh method. The comparison of simulation results with nanoindentation tests and analytical solution showed a good agreement. The effects of structure size and particle contact location at various approaching velocities on the lubrication force were investigated.     

Microdosimetric assessment of the radiation quality of a therapeutic proton beam: comparison between numerical simulation and experimental measurements

Using protons for the treatment of ocular melanoma (especially of posterior pole tumours), the radiation quality of the beam must be precisely assessed to preserve the vision and to minimise the damage to healthy tissue. The radiation quality of a therapeutic proton beam at the Centre Antoine Lacassagne in Nice (France) was measured using microdosimetric techniques, i.e. a miniaturised version of a tissue-equivalent proportional counter. Measurements were performed in a 1-μm site at different depths in a Lucite phantom. Experimental data showed a significant increase in the beam quality at the distal edge of the spread-out Bragg peak (SOBP). In this paper, the numerical simulation of the experimental setup is done with the FLUKA Monte Carlo radiation transport code. The calculated microdosimetric spectra are compared with the measured ones at different depths in tissue for a monoenergetic proton beam (E=62 MeV) and for a modulated SOBP. Numerically and experimentally predicted relative biological effectiveness values are in good agreement. The calculated frequency-averaged and dose-averaged lineal energy mean values are consistent with measured data.     

Determination of the representativity between two multidimensional data sets by a comparison of their structure

An approach for the investigation and comparison of the data structure in the multidimensional space is proposed. It is based on three properties, namely, the direction of the data sets, the variance–covariance of the data points, and the location of the data sets' centroids. A number of tests have been studied and are presented. It is shown that the combined use of these parameters allows a satisfactory estimation of the representativity between two data sets. Simulated data, as well as real case studies are presented.     

Mechanical and electrical behaviors of polymer particles. Experimental study of the contact area between two particles. Experimental validation of a numerical model

The present paper is devoted to the analysis of mechanical and electrical behaviors observed on particulate polymer granular materials. The constituting particles obtained these physical properties by coating the polymer spherical substrate with a conducting polymer: polypyrrole (PPy) which confers electrical conducting properties to the particle, while preserving its mechanical properties. Particle contacts dominate the behavior of the granular media and, consequently, size, morphology, roughness and plasticity of the particles play a crucial role in this behavior. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to study the surface state and the contact area between neighbors. An experimental set up, based on the measurement of the displacement of contacting particles subjected to a normal force and of the variation of the electrical resistance of the packing, allowed the study of both the mechanical and electrical behaviors of the particle system. The experimental results took into account the plastic deformation under varying loading and unloading conditions; they were consistent with theories of contact mechanics, thus validating the existing models.