Direct determination of granular pressure in liquid fluidized beds using a DEM-based simulation approach

In this paper, the fluidization of 8 mm glass particles in water has been simulated using a new methodology developed within the DEM framework. In this methodology, random liquid fluctuating velocities are used as direct input into the drag model. The specific aim of this study is to directly compute the granular pressure in a liquid fluidized bed. The granular pressure is defined using the particle-wall collision frequency and the corresponding particle momentum transport during the collision. Initially, we validated our model by comparing the relationship between superficial fluid velocity and bed expansion against the well-known Richardson-Zaki [1] equation. The results demonstrated a good agreement of our model. The granular pressure and temperature, as well as the particle-wall collision frequency, in the liquid fluidized bed were determined for superficial fluid velocities in the range between 0.08 and 0.32 m/s. The granular pressure exhibited a maximum (between 0.3-0.4 solid fraction) that matched the experimental measurements of Zenit et al. [2] for high inertia particles. The granular temperature also revealed a peak at a solid concentration of around 0.2 which is in line with the experimental measurements of Zivkovic et al. [3] and the model of Gervin et al. [4]. The set of the results presented in this study suggests that the approach used here is valid for obtaining the granular pressure and temperature for a wide range of volume fractions in liquid fluidized beds

Ibrutinib as initial therapy for patients with chronic lymphocytic leukemia

Background: chronic lymphocytic leukemia (CLL) primarily affects older persons who often have coexisting conditions in addition to disease-related immunosuppression and myelosuppression. We conducted an international, open-label, randomized phase 3 trial to compare two oral agents, ibrutinib and chlorambucil, in previously untreated older patients with CLL or small lymphocytic lymphoma. Methods: we randomly assigned 269 previously untreated patients who were 65 years of age or older and had CLL or small lymphocytic lymphoma to receive ibrutinib or chlorambucil. The primary end point was progression-free survival as assessed by an independent review committee. Results: the median age of the patients was 73 years. During a median follow-up period of 18.4 months, ibrutinib resulted in significantly longer progression-free survival than did chlorambucil (median, not reached vs. 18.9 months), with a risk of progression or death that was 84% lower with ibrutinib than that with chlorambucil (hazard ratio, 0.16; P<0.001). Ibrutinib significantly prolonged overall survival; the estimated survival rate at 24 months was 98% with ibrutinib versus 85% with chlorambucil, with a relative risk of death that was 84% lower in the ibrutinib group than in the chlorambucil group (hazard ratio, 0.16; P=0.001). The overall response rate was higher with ibrutinib than with chlorambucil (86% vs. 35%, P<0.001). The rates of sustained increases from baseline values in the hemoglobin and platelet levels were higher with ibrutinib. Adverse events of any grade that occurred in at least 20% of the patients receiving ibrutinib included diarrhea, fatigue, cough, and nausea; adverse events occurring in at least 20% of those receiving chlorambucil included nausea, fatigue, neutropenia, anemia, and vomiting. In the ibrutinib group, four patients had a grade 3 hemorrhage and one had a grade 4 hemorrhage. A total of 87% of the patients in the ibrutinib group are continuing to take ibrutinib. Conclusions: ibrutinib was superior to chlorambucil in previously untreated patients with CLL or small lymphocytic lymphoma, as assessed by progression-free survival, overall survival, response rate, and improvement in hematologic variables. (Funded by Pharmacyclics and others; RESONATE-2 ClinicalTrials.gov number, NCT01722487.)

Influence of Shell Thickness on the Colloidal Stability of Magnetic Core-Shell Particle Suspensions

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m2, could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process

High-resolution analysis of the influence of reactant concentration on nucleation time and growth of polyethyleneimine-trimethoxymethylsilane particles

High-resolution dynamic light scattering (DLS), scanning electron microscopy (SEM), time-lapse photography, and attenuated total reflectance Fourier transform infrared spectroscopy were used to analyze the growth kinetics of polyethyleneimine (PEI)-silica particles fabricated from the condensation of hydrolyzed trimethoxymethylsilane (TMOMS) and PEI/phosphate buffer (PEI/PB). Depending on the concentration of hydrolyzed TMOMS and PEI/PB, three stages were identified. We observed the existence of a nucleation time that has never been reported in the literature when TMOMS has been used. During this nucleation time, particles of less than 25 nm were detected using in situ DLS measurements taken every 15 s (high resolution), a DLS time-scale resolution not previously reported. In addition, the length of the nucleation time depended mainly on the PEI/PB concentration, but also TMOMS concentration. The growth stage was evident from the rapid increase of particle size with time. Due to the high resolution of the DLS measurements, a peak could be observed in the particle diameter during particle growth, which corresponds to a secondary population of particles required for the larger particles to further increase in size. Finally, during the equilibrium region, particles reached their maximum diameter that was independent of the concentration of PEI/PB and only changed with concentration of hydrolyzed TMOMS

Direct determination of granular pressure in liquid fluidized beds using a DEM-based simulation approach

In this paper, the fluidization of 8 mm glass particles in water has been simulated using a new methodology developed within the DEM framework. In this methodology, random liquid fluctuating velocities are used as direct input into the drag model. The specific aim of this study is to directly compute the granular pressure in a liquid fluidized bed. The granular pressure is defined using the particle-wall collision frequency and the corresponding particle momentum transport during the collision. Initially, we validated our model by comparing the relationship between superficial fluid velocity and bed expansion against the well-known Richardson-Zaki [1] equation. The results demonstrated a good agreement of our model. The granular pressure and temperature, as well as the particle-wall collision frequency, in the liquid fluidized bed were determined for superficial fluid velocities in the range between 0.08 and 0.32 m/s. The granular pressure exhibited a maximum (between 0.3-0.4 solid fraction) that matched the experimental measurements of Zenit et al. [2] for high inertia particles. The granular temperature also revealed a peak at a solid concentration of around 0.2 which is in line with the experimental measurements of Zivkovic et al. [3] and the model of Gervin et al. [4]. The set of the results presented in this study suggests that the approach used here is valid for obtaining the granular pressure and temperature for a wide range of volume fractions in liquid fluidized beds

Hugh Tracey memorial service

Philip Tobias speaking of his first encounter with Hugh Tracey's; Hugh Tracey's contribution on his works of anthropology; his pioneer study of African music termed as ethnomusicology; summary of Hugh Tracey as 'black man with a white face' whose writings were excellent, great communicator and that Hugh Tracey saw music of Africa as the voice of the soul of Afric

Fine particle beneficiation through selective agglomeration with an emulsion binder

A high internal phase (HIP) water-in-oil emulsion was used as the binder in the selective agglomeration of fine coal from an aqueous suspension of coal and mineral particles. Traditionally, this agglomeration is achieved by a pure oil, hydrophobic, binder. However, the high cost associated with using pure oil makes the process economically unfeasible. Therefore, the emulsion binder introduced in this work was motivated by the economic need to reduce the amount of organic liquid required in the process. The effect of the agitation time during the agglomeration process and the composition of the emulsion on its performance as a binder were investigated. The best result obtained was for a HIP emulsion made from 3 wt % aqueous NaCl and diesel oil with sorbitan monooleate as the emulsifier. This emulsion had a dispersed phase volume fraction of 0.94 and achieved a 7.5-fold reduction in the amount of organic liquid required to achieve agglomeration

Influence of fluid properties on bubble formation, detachment, rising and collapse; Investigation using volume of fluid method

Numerical simulations have been carried out to investigate the formation and motion of single bubble in liquids using volume-of-fluid (VOF) method using the software platform of FLUENT 6.3. Transient conservation mass and momentum equations with considering the effects of surface tension and gravitational force were solved by the pressure implicit splitting operator (PISO) algorithm to simulate the behavior of gas-liquid interface movements in the VOF method. The simulation results of bubble formation and characteristics were in reasonable agreement with experimental observations and available literature results. Effects of fluid physical properties, operation conditions such as orifice diameter on bubble behavior, detachment time, bubble formation frequency and bubble diameter were numerically studied. The simulations showed that bubble size and bubble detachment times are linear functions of surface tension and decrease exponentially with the increase in liquid density. In contrast, only a small influence of the fluid viscosity on bubble size and detachment time was observed. Bubble collapse at a free surface simulation with VOF method was also investigated

Film formations of aggregates due to lateral capillary forces

The lateral capillary force is of significant importance in liquid film coating processes [1]. This force, for particles much smaller than the capillary length, decays with the inverse of the separation distance between particles centres and is, thus, considered a longrange force [2]. In this paper, we study the role of this long-range force on the final structure of a film containing partially submerged nanoparticles. We have used computer simulations based on Discrete Element Method (DEM) to investigate film formation of mono and binary disperse particle systems. The particle radii were 80 nm, 100 nm, and 120 nm with combinations of these particle sizes for the binary disperse system. To determine the nearest neighbours for the calculation of the lateral capillary force a Delaunay Triangulation method was used. The surface coverage of the partially submerged particles was 0.05, which coincides with a parallel experimental research. The forces included in the model are the lateral and vertical capillary forces, Brownian motion, contact forces, van der Waals attraction, fluid drag and hydrodynamic resistance. The structure of the aggregates formed was compared using three parameters, the isotropic ordering factor, non-dimensional boundary length and the pair (radial) correlation function. The simulation results show that particles self-organise into isotropic aggregates due to lateral capillary forces. Particle size was shown to have little effect on final aggregate structures. Binary disperse systems were shown to have less ordered structures when compared to monodisperse systems as suggested by the decrease in peak sharpness of the pair correlation function. Increasing the particle size gap resulted in less ordering in the binary systems