Process intensification in particle technology: Characteristics of powder coatings produced by nonisothermal flow‐induced phase inversion

The characteristics of powder coatings manufactured through a novel processing technique based on nonisothermal Nlow‐induced phase inversion granulation enhanced by fluid injection to promote phase inversion and particle formation from melt state is summarized. Experiments were carried out in a purpose‐built granulator, which operates in a parallel disk rotor‐stator arrangement, so that the mechanism of granulation could be studied. The product of this intensive granulation was compared with that of the conventional powder coating manufacturing process. Understanding the mechanism of intensive granulation helped to redesign the equipment that resulted in smaller particles. Pigment dispersion characteristics were improved by intensive granulation. Also, the particle size span can be significantly reduced by dry granulation and gas‐phase granulation, and the flowability can be improved by wet granulation. Chemical analysis of particles by Fourier transform infrared spectroscopic analysis showed that the injection of coolant fluid had no effect on the chemical composition. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Experimental and numerical investigation of the precipitation of barium sulfate in a rotating liquid film reactor

Precipitation of nanosized barium sulfate in a rotating liquid film reactor (RLFR) has been investigated experimentally and through simulations based on the computational fluid dynamics technique including the population balance equation coupled with the Navier–Stokes equations, renormalization group k–ε model equations, and species transport equations. A comparative experiment was carried out involving conventional precipitation in a flask. The structure of the precipitate was identified by powder X‐ray diffraction (PXRD), which showed that the crystals obtained using the RLFR were smaller in size than those obtained in the flask. Transmission electron microscopy (TEM) images demonstrated that the crystals produced by the two different processes had different morphologies. Further detailed experiments involving varying the operating parameters of the RLFR were performed to investigate the effects on crystal size distribution (CSD). Increasing the speed of the rotor in the RLFR in the range 1000–5000 rpm or increasing the rotor‐stator gap in the range 0.1–0.5 mm resulted in a decrease in particle size and narrower particle size distributions. The simulation results suggested that turbulent effects and reaction processes in the effective reactor space were directly related to rotor speed and rotor‐stator gap. The simulated volume weighted mean diameter and CSD of particles of barium sulfate were almost identical to the corresponding experimental results obtained using TEM and laser particle size analyzer. The effects of other parameters such as the Kolmogorov scale and competition between induction time and mixing time are also discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Residence time distribution in a single‐phase rotor–stator spinning disk reactor

A reactor model for the single‐phase rotor–stator spinning disk reactor based on residence time distribution measurements is described. For the experimental validation of the model, the axial clearance between the rotor and both stators is varied from 1.0 × 10^?3 to 3.0 × 10^?3 m, the rotational disk speed is varied from 50 to 2000 RPM, and the volumetric flow rate is varied from 7.5 × 10^?6 to 22.5 × 10^?6 m³ s^?1. Tracer injection experiments show that the residence time distribution can be described by a plug flow model in combination with 2–3 ideally stirred tanks‐in‐series. The resulting reactor model is explained with the effect of turbulence, the formation of Von Kármán and Bödewadt boundary layers, and the effect of the volumetric flow rate. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2686–2693, 2013     

Particle capture by a rotating disk in a kitchen exhaust hood

Abstract

Chinese cooking produces large numbers of particles that can cause both indoor and outdoor air quality problems. To reduce the extraction of particles to the outdoor air, this investigation studied capture efficiency of a rotating disk in an exhaust hood. The studies were performed experimentally in a wind tunnel and numerically by computational fluid dynamics (CFD) models with the Lagrangian method for tracking particle trajectories. The experimental data were used to identify the best turbulence model among the three tested in the CFD simulations. The results show that the capture efficiency increased with disk rotation speed and particle size but decreased with exhaust airflow rate. The CFD simulations provided detailed information about the mechanisms by which particles of different sizes were captured by the rotating disk. CFD was then used to explore two methods for improving the capture efficiency: adding more wires to the middle and outer zones of the disk, and using two layers of disks. Both methods can increase the capture efficiency of the rotating disk at an acceptable pressure loss.

Copyright © 2020 American Association for Aerosol Research     

Flow‐assisted corrosion of API X‐52 steel in 3.5% NaCl solution

Corrosion behaviour of API X‐52 grade High Strength Low Alloy (HSLA) steel in 3.5% NaCl solution under flow conditions was studied. Rotating cylinder‐, rotating disk‐ and flat plate‐type rotors were used to observe the effect of rotor geometry. The empirically obtained mass transfer correlations are in agreement with those for standard geometry. An empirical relation between Reynolds number (Re) and weight loss has also been developed for the parallel disk rotor. Scanning electron microscopy of the corroded surface revealed that corrosion proceeds through an initiation of pit‐like regions and their subsequent growth.     

Particle nucleation for dewetting initiation of thin polymer films

A quantitative comparison between spontaneous dewetting and particle nucleation for thin (thickness = 17nm) polystyrene (PS) films on nonwettable silicon (Si) surfaces is presented both experimentally and theoretically. Performing experiments in a class 100 clean room, we found that ～ 23% of the observed dry patches formed because of dust particles, while the majority of the holes formed via the well known spontaneous dewetting process. The result was verified qualitatively by diffusion theory, which, however, predicted a diminished role for the airborne particles, leading to the conclusion that pre‐existing particles on the Si surfaces and/or the polymer solutions contribute substantially to the dewetting process. The driving force of particle motion into the polymer film is examined by placing aluminum oxide (Al₂O₃) particles on PS films. Finally, the effect of particle geometry is studied by placing gold (Au) disks on the free surface of PS films. An optically continuous PS film is found to be present around the periphery of the disk particles, even after the completion of the dewetting process in the rest of the sample. An attempt to explain dewetting inhibition at the vicinity of the micro‐disks, on the basis of molecular interactions developed in the system Au/PS/Si, is finally presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 138–145, 2005     

Modeling of the motion of particles in a rotary crusher

The dynamics of the gas flow in the interdisk space of a real crusher is studied. It is shown that the centrifugal force displaces the gas from the space between the rotating disks. This decreases the probability of collision between particles coming from different disks. The gas displacement near the disk surface is illustrated using the example of a system of two counterrotating flat disks. An exact self-similar solution is obtained. The flow between the two disks is demonstrated to be qualitatively rearranged in comparison with the flow over a single rotating disk. Using a two-parameter turbulence model, the gas dynamics are calculated both in the set of two disks and within a real crusher. The results of calculating the trajectories of particles are presented. The causes that limit the minimal particle size that can be reached in a rotary crusher are analyzed.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 229–235.Original Russian Text Copyright © 2005 by Derevich.     

Performance characteristics of mechanical foam‐breakers fitted to a stirred‐tank reactor

In a stirred‐tank reactor (STR), a comparison of the performance of mechanical foam‐breakers: a six‐blade turbine (F‐B), a six‐blade vaned disk (V‐D), a two‐blade paddle (T‐P), a conical rotor (C‐R), a fluid‐impact dispersion apparatus (FIDA) and a rotating disk mechanical foam‐breaker (MFRD) was carried out using defined foaming media. The foam‐breaking ranges (relative to the gas superficial velocity, U_g) of the T‐P, C‐R and FIDA were inferior to that of the F‐B, V‐D and MFRD. The power consumption, P_kc, for foam‐breaking in the MFRD was the lowest among the F‐B, V‐D and MFRD. Operation of the F‐B and V‐D in the STR caused a considerable amount of liquid droplets from the collapsed foam to be entrained with the exhaust air. © 2002 Society of Chemical Industry     

The grinding of organic dyestuffs

A mechanism for grinding disperse dyes in a sand mill is discussed which is supported by experimental data. Experimental data with disk, cylinder and vibrator agitators are examined from the point of view of dimensional analysis. All rotors exhibited fluid slip and decreased efficiencies at high rotor speeds. Cylinder rotors provided higher rates of energy input to the milling paste, and shorter grinding times, relative to disk and vibrator agitators.     

Intensification of convective heat transfer in a stator–rotor–stator spinning disc reactor

A stator–rotor–stator spinning disc reactor is presented, which aims at intensification of convective heat‐transfer rates for chemical conversion processes. Single phase fluid‐rotor heat‐transfer coefficients h_r are presented for rotor angular velocities rad s^?1 and volumetric throughflow rates m³s^?1. The values of h_r are independent of and increase from 0.95 kWm^?2K^?1 at ω = 0 rad s^?1 to 34 kWm^?2K^?1 at ω = 157 rad s^?1. This is a factor 2–3 higher than values achievable in passively enhanced reactor‐heat exchangers, due to the 1–2 orders of magnitude larger specific energy input achievable in the stator–rotor–stator spinning disc reactor. Moreover, as h_r is independent of , the heat‐transfer rates are independent of residence time. Together with the high mass‐transfer rates reported for rotor–stator spinning disc reactors, this makes the stator–rotor–stator spinning disc reactor a promising tool to intensify heat‐transfer rates for highly exothermal chemical reactions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2307–2318, 2015     

Evaluation of the mixing performance for one novel twin screw kneader with particle tracking

In this article, a novel continuous twin‐screw kneader was proposed. The end‐cross section of the screw rotor consists of convex arcs and cycloidal curves and the rotors profiles were presented. The mixing performance of the novel twin screw kneader was simulated using finite element method (FEM) combined with mesh superimposition technique (MST). Statistical analysis was carried out for flow field using particle tracking technique to research the effect of geometry parameters and working parameters on the mixing performance. To study the dispersive mixing performance, specifically the maximum shear rate, maximum shear stress, maximum mixing index, residence time distribution (RTD) and RTD density function of tracer particles, and dispersive mixing is evaluated using the mixing index in combination with the shear stress. The results show that the changes of centre distance between female and male rotor have little influence on dispersive mixing performance, the lead of rotor has little effect on maximum shear stress and maximum shear rate, while it has an obvious effect on mixing index, cumulative RTD, and RTD density function. The rotor speed has obvious influence on mixing performance, and average residence time of material decreases greatly and the mixing ability is weakened, while the self‐cleaning performance of rotor improved obviously with the increasing of rotor speed. POLYM. ENG. SCI., 54:2407–2419, 2014. © 2013 Society of Plastics Engineers     

Containment capability of 2D triaxial braided tape wound composite casing for aero‐engine

Two‐dimensional (2D) triaxial braided composites have been successfully used in aero‐engine fan containment system for weight reduction. In the current study, blade containment tests were conducted on high‐speed rotor spin tester to investigate the containment process and failure mechanisms of the composite casing. The composite casing was fabricated by winding 2D carbon fiber triaxial braided tape on a capstan into predetermined thickness and then infused with epoxy resin. Test results indicate that the damages to the containment casing increase significantly with the increase in blade released speed. In contained case, two damaged areas can be observed on the inner wall of the casing due to continued impacts of the released blade. However in uncontained case, a perforated hole was found in the casing. Finite element method was used to study this high‐speed impact process using LS‐DYNA. The influence of blade release speed and case thickness was also analyzed and found that the failure modes turns from tension to shear as the blade speed increases and casing is able to absorb more energy with increase in casing areal density. An empirical equation was derived for the triaxial braided composite casing, which can help in the design of the composite fan casing for aero‐engine. POLYM. COMPOS., 37:2227–2242, 2016. © 2015 Society of Plastics Engineers     

双转子连续混炼机混沌型转子混合性能的研究

在提出一种新型混沌型转子结构的基础上,运用Polyflow软件对其混炼过程进行三维非牛顿等温模拟,并借助于粒子示踪法对物料所经历的流场特性进行统计学分析;分析了转子结构和工艺参数对转子混合性能的影响,同时通过共混改性实验,对转子的混合效果进行了评估和表征。结果表明,高混沌型转子的分布混合能力有较大的提高,同时保持着良好的分散混合能力;混沌型转子制备的复合材料力学性能优于经典转子;转子转速的提高可以增强混沌转子的分散及分布混合能力,适当的加料速率是保证取得较好混合效果的关键因素。     

Multistage rotor‐stator spinning disc reactor

The scale up of a rotor‐stator spinning disc reactor by stacking single stage rotor‐stator units in series is demonstrated. The gas‐liquid mass transfer per stage is equal to the mass transfer in a single stage spinning disc reactor. The pressure drop per stage increases with increasing rotational disc speed and liquid flow rate. The pressure drop is more than a factor 2 higher for gas‐liquid flow than for liquid flow only, and is up to 0.64 bar at 459 rad s^?1. The high mass and heat transfer coefficients in the (multistage) rotor‐stator spinning disc reactor make it especially suitable for reactions with dangerous reactants, highly exothermic reactions and reactions where selectivity issues can be solved by high mass transfer rates. Additionally, the multistage rotor‐stator spinning disc reactor mimics plug flow behavior, which is beneficial for most processes. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

2‐Hydroxyethylmethacrylate carrying uniform porous particles: preparation and electron microscopy

Uniform macroporous particles carrying hydroxyl groups have been obtained in the size range 3–11.5 µm by seeded polymerization. For this purpose, uniform polystyrene particles in the size range 1.9–6.2 µm were used as seeds. The seed particles were successively swollen by dibutyl phthalate (DBP) and a monomer mixture comprising styrene, 2‐hydroxyethylmethacrylate (HEMA) and a crosslinker. Two different crosslinkers, divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA), were tested. Size distribution properties together with bulk and surface structures of the particles have been characterized by both scanning and transmission electron microscopy. While EGDMA provides uniform particles with a non‐porous surface, DVB produces uniform particles having a highly porous surface and interior. The comparison of FTIR and FTIR‐DRS spectra shows that the HEMA concentration is higher on the particle surface than within the particle interior. Seed latex size and monomer/seed latex ratios are identified as the most important variables affecting the final particles. Different seed latexes have been tried; the result is that highly macroporous particles with a sponge‐like pore structure both on the surface and in the particle interior have been obtained by use of the seed latex with the largest particles and the lowest molecular weight. An increase in the HEMA feed concentration leads to final particles with a non‐porous surface and a crater‐like porosity in the particle interior. The average pore size significantly decreases with increasing DBP/seed latex and monomer/seed latex ratios. © 2001 Society of Chemical Industry     

Particle dynamics in sheared particulate suspensions

Measurements of particle dynamics of neutrally buoyant suspensions of non-Brownian glass beads in a Couette cell using dynamic sound scattering are reported. The dynamics were studied under steady shear flow across the entire gap between the stator and rotor for shear rates from 0.26 to 6.59 s ⁻¹ and particle concentrations from 20% to 50%, thereby enabling a comprehensive investigation of the dynamics to be carried out. The average particle velocity profile varies linearly with depth inside the cell for all shear rates and concentrations. The fluctuations in the particle velocities are large, indicating that the particles are not confined to streamlines but continue to fluctuate substantially during steady flow. Our data indicate that the fluctuations are anisotropic. The components of the velocity fluctuations (granular temperature) parallel to the flow and in the vertical direction are much larger than in the radial direction. The fluctuation anisotropy decreases as the concentration increases. © 2018 American Institute of Chemical Engineers AIChE J, 65: 840–849, 2019     

Investigating the dynamics of cylindrical particles in a rotating drum using multiple radioactive particle tracking

The behavior of granular flows inside rotating drums is an ongoing area of research. Only a few studies have investigated non‐spherical particles despite the fact that particle shape is known to have a significant impact on flow behavior. In addition, the experimental techniques limit the interpretation of the results of these studies. In this work, we compared the flow behavior of cylindrical and spherical particles using the multiple radioactive particle tracking technique to capture the positions and orientations of cylindrical particles simultaneously. We analyzed two important components of the transverse flow dynamics, that is, the boundary between the active and passive layers, and the velocity profile on the free surface. For the cylindrical particles, two general models are proposed to calculate the velocity profiles on the free surface and the effective particle sizes in the active and passive layers. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2622–2634, 2016     

大孔二氧化硅膜上纳米碳纤维层结构化催化剂载体的制备

1 INTRODUCTION Fast gas-liquid phase reactions over solid cata- lysts easily cause concentration gradient in reactors and catalysts because of relatively slow diffusion as well as the frequent occurrence of low concentration when gasses are dissolved. Such concentration gradi- ent caused by the limitation of mass transfer influ- ences the reaction rate as well as selectivity. Conven- tional strategies for gas-liquid-solid phase catalytic reactions comprise slurry reactors and trickle bed r…     

Fabrication of Si3N4 preforms from Si3N4 produced via CRN technique

Ceramic preforms with randomly distributed particles as reticulated porous structure which are generally used for metal infiltration as reinforcement, membranes, catalyst supports etc. Preforms are characterized by open porosity making possible their infiltration by liquid metal alloys. In this work, quartz powders using carbon black as a reducing agent were used for alpha Si₃N₄ powders synthesis through a carbothermal reduction and nitridation (CRN) process. The CRN process was carried out under nitrogen flow at 1,450 °C for 4 h. At high temperatures, carbon as reducing agent reacts with the oxygen of SiO₂, and the resulting metallic silicon compounds with nitrogen gas to obtain silicon nitride powder. The reacted powders were used to obtain reticulated ceramic by replica method. The powders containing various bentonite ratios were mixed in water to prepare slurry. The slurry was infiltrated into a polyurethane sponge. A high porous ceramic foam (preform) structure was achieved after burn out of the sponge. All ceramic preforms were sintered to increase stiffness (in the temperature range 900–1,350 °C). The sintered ceramic foams were subjected to compressive tests. The scanning electron microscopy was used to examine the reticulated ceramic foam structure, and X-ray diffraction analysis was performed to determine phases.     

Effect of the surface roughness and construction material on wall slip in the flow of concentrated suspensions

Recent studies on polyethylene, elastomers, and thermoplastics have revealed that the construction material and surface roughness are two important factors affecting wall slip. In this study, to determine the true rheological behavior of model concentrated suspensions, a multiple‐gap separation method was used in a parallel disk rheometer. The model suspensions studied were poly (methyl methacrylate) particles with an average particle size of 121.2 μm in hydroxyl‐terminated polybutadiene. The aim of this study was to investigate the effect of disk R_a in the range of 0.49–1.51 μm and disk construction material on the wall slip and the true viscosity of the model concentrated suspensions. The wall slip velocity and the viscosity were found to be independent of R_a for particle size‐to‐disk R_a ratios of 80–247. Also, the true viscosity was found not to be affected by the rheometer surface construction material. Glass surfaces resulted in the highest slip velocity, whereas aluminum surfaces resulted in the lowest slip velocity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3341–3347, 2007