Particle Deposition Phenomena Research Articles

Indoor air quality among Mumbai's resettled populations: Comparing Dharavi slum to nearby rehabilitation sites

This study presents results from an experimental investigation of the severity and sources of household air pollution across two low-income housing archetypes in Mumbai. Experimentation was carried out in Dharavi—one of the world's largest slums—and two nearby communities representing Mumbai's current slum resettlement scheme. Household surveys were conducted to understand aspects of occupant behavior that impact indoor air quality. Multi-pollutant logging sensors were installed inside units and in nearby outdoor locations to measure concentrations of particulate matter (PM2.5) and CO2. While rehabilitation architecture and gas cookstoves are often assumed to provide higher indoor air quality than in traditional slums, field monitoring and occupant behavior surveys demonstrated that indoor pollution levels were consistent across the two typologies even after infrastructure enhancements and ubiquitous gas cookstove usage. Indoor PM2.5 measurements ranged between 150 and 300 μg/m3, substantially higher than World Health Organization (WHO) guidelines. PM2.5 indoor/outdoor (I/O) ratios spiked during cooking periods but were otherwise less than 1.0 in over half of logged instances in rehabilitation units, highlighting the role of particle deposition phenomena and ambient-sourced PM2.5 in indoor environments. To minimize the impact of both indoor and outdoor pollutant sources while respecting culturally-normative occupant behavior, this study points to the need for architectural design guidelines and enhanced indoor air quality interventions.

2-4.石炭ガス化炉壁面近傍での灰粒子冷却過程の推算による灰付着現象の解析(Session(2)石炭利用)

2-4.石炭ガス化炉壁面近傍での灰粒子冷却過程の推算による灰付着現象の解析(Session(2)石炭利用)

Real-time Particle Deposition Monitoring of Operational Cleanroom Quality

Abstract Real-time particle deposition monitoring is a new way to monitor the operational quality of a cleanroom. Up to now the performance of a cleanroom is often monitored with light-scattering airborne particle counters. These give valuable information on airborne particles, but no information on the potentially threatening macroparticles in a cleanroom. In this paper, particle deposition phenomena and ways to determine particle deposition are discussed. A real-time particle deposition monitor using holographic imaging of the witness plates in a sensing device is described. Some practical experiences with real-time particle deposition measurements are demonstrated. Real-time particle deposition monitoring can be a valuable method to control the operational quality of a cleanroom where personnel are working.

Correlation between particle deposition and the size ratio of particles to patterns in nano- and micro-patterned membrane filtration systems

Abstract Recently, membrane surface patterning has attracted much attention as an innovative alternative to control membrane fouling that occurs with membrane filtration used in water and wastewater treatment. However, limited attention has been focused on patterned membranes with nano-scale features due to their difficult fabrication. As a result, there is a lack of research on membrane fouling by particle deposition occurring with a wide range of pattern sizes. In this study, we prepared patterned membranes with nano-scale hexagonally packed arrays using nanoimprint lithography as well as micro-scale patterned membranes. Filtration tests were conducted using the membranes in cross-flow ultrafiltration to demonstrate the effect of the size ratio of particles to membrane patterns on fouling by particle deposition on the membrane surface. We found that particle deposition was most efficiently mitigated by the patterned membranes when the size ratio was approximately 3. On the other hand, when the size ratio was much smaller than 3, particle deposition was significant and was nearly as much as that of non-patterned membranes. In addition, when the size ratio was larger than 3, particle deposition increased with the increase in the size ratio. We explained the correlation between particle deposition and the size ratio of particles to membrane patterns in terms of shear stress near the surface of the membrane patterns using a computational fluid dynamics simulation technique. We anticipate that this study will provide a deeper understanding of the particle deposition phenomena in nano- and micro-patterned membrane filtration.

Mechanisms of nanoparticle and bioparticle deposition – Kinetic aspects

Particle deposition phenomena were theoretically analyzed in terms of a hybrid theoretical approach where the bulk transport is described by continuity equations and the surface transport by the random sequential adsorption (RSA) models. RSA modeling furnishes maximum coverages and blocking functions for spherical and anisotropic particles. These parameters are used as boundary conditions for the bulk transport equation. This enables one to derive theoretical results describing kinetics of convection and diffusion-controlled transport of particles to interfaces, which is discussed next. The utility of this theoretical approach is confirmed by experimental data obtained for various colloid systems involving micro- and nanoparticles using optical and fluorescence microscopy AFM, SEM and TEM imaging of particle monolayers. Comparison of theoretical and experimental results shows that the electrostatic interactions play a dominant role affecting the maximum coverage of and the structure of deposited particle monolayers. Particle deposition on heterogeneous surfaces formed by a controlled deposition of nanoparticles and proteins (latex, hematite, fibrinogen) is also considered. These phenomena are properly interpreted in terms of the RSA model considering fluctuations in the particle density. The classical DLVO theory, based on the mean-field (averaged) zeta potential concept proved inadequate. It is also shown that the colloid particle deposition on protein monolayers can be used to efficiently determine the coverage and a real charge distribution under wet, in situ conditions. It is concluded that particle and protein deposition phenomena show deep analogies. This suggests that the results acquired for nanoparticles can be used as convenient reference systems for interpretation of molecular adsorption phenomena inaccessible to direct measurements.

砂が関係する熱流体現象のマルチフィジックスCFDシミュレーション(<小特集>マルチフィジックスCFD/EFDの最前線)

A single-physics CFD simulation has been established now, and it is daily used in design and analysis processes of various machines. Therefore, a multi-physics CFD simulation would be a key technology to be researched and developed in near future. We can easily find a number of multiphysics phenomena in nature and machines, but we cannot simulate most of them. That is, there still remain many difficulties in a multi-physics CFD. For example, the modeling of physics except for heat and fluid flow has not been developed yet. In the present article, I briefly explain the state of the art of a multi-physics CFD simulation, focusing on the coupling method between flow and other physics, and then describe our researches on (1) sand transfer in a desert and its suppression with a wind-breaking fence and (2) particle deposition phenomena on the turbine vane in a jet engine. In both simulations, a weak coupling method was employed, taking into account the time scales of the physics embedded in the phenomena. Using the computational results, the characteristics of each phenomenon were discussed and some useful insights for improving the multi-physics simulation were obtained.

Modeling of a coal-fired slagging combustor: Development of a slag submodel

In a slagging combustor or furnace, the high combustion temperature makes the molten slag layer cover the wall and capture the particles. If these particles contain combustible matter, they will continue to burn on the running slag. As a result, the total amount of ash deposition will be much greater than that in dry-wall combustors and the total heat flux through the deposition surface will change greatly. Considering the limitations of existing simulation methods for slagging combustion, this paper introduces a new wall burning model and slag flow model from the analysis of particle deposition phenomena. Combined with a conventional combustion simulation program, the total computational frame is introduced. From comparisons of simulation results from several kinds of methods with experimental data, the conclusion is drawn that the conventional simulation methods are not very suitable for slagging combustion and the wall burning mechanism should be considered more thoroughly.

Effect of calendering of filter cloth on transient characteristics of cake filtration

In this article, the effects of a filter fabric calendering treatment and the permeability of filaments with regards to the particle deposition phenomena onto or into filter fabrics at the initial stage of filtration are conducted quantitatively using a microscopical forces analysis. The flow pattern and the resistance to fluid flow in the calendered interstice were obtained numerically by using the fluid-flow software FLUENT™. Based upon the numerical data of continuous phase, a program is devised to simulate the transient behaviours of pore clogging and cake formation by ways of the Lagrangian approach and this estimates the change of filtrate clarity at the initial stage of filtration for various calendered fabrics porosities and various filament permeabilities. Results show that in the case of tightly woven filter cloths, the flow is predominantly through the yarns of the cloth; while flow will generally be directed around the yarns of a loosely woven cloth, especially if the yarn is twisted tightly. Therefore, filtrations with tightly woven but loosely twisted yarn can increase the unfavourable but inevitable clogging problem. The simulated results further show that although the filtration resistance of woven filter fabric increases after calendering, the permeability is rectified and the clogging of the filter pores is also improved. After the calendering finishing of the filter fabric has taken place, only the cake formation mode in accordance with the law of blocking for all types of pore is evident shown. The critical concentration proposed by previous investigators is not observed for the calendered filter fabrics.

Particle adsorption and deposition: role of electrostatic interactions

This work demonstrates how electrostatic interactions, described in terms of the classical DLVO theory, influence colloid particle deposition phenomena at solid/liquid interfaces. Electrostatic interactions governing particle adsorption in both non-polar and polar media (screened interactions) are discussed. Exact and approximate methods for calculating the interaction energy of spherical and non-spherical (anisotropic) particles are presented, including the Derjaguin method. Phenomenological transport equations governing particle deposition under the linear regime are discussed with the limiting analytical expressions for calculating initial flux. Non-linear adsorption regimes appearing for higher coverage of adsorbed particles are analysed. Various theoretical approaches are exposed, aimed at calculating blocking effects appearing due to the presence of adsorbed particles. The significant role of coupling between bulk transport and surface blocking is demonstrated. Experimental data obtained under well-defined transport conditions, such as diffusion and forced convection (impinging-jet cells), are reviewed. Various experimental techniques for detecting particles at interfaces are discussed, such as reflectometry, ellipsometry, streaming potential, atomic force microscopy, electron and optical microscopy, etc. The influence of ionic strength and flow rate on the initial particle deposition rate (limiting flux) is presented. The essential role of electrostatic interactions in particle deposition on heterogeneous surfaces is demonstrated. Experimental data pertinent to the high-coverage adsorption regime are also presented, especially the dependence of the maximum coverage of particles and proteins on the ionic strength. The influence of lateral electrostatic interactions on the structure of particle monolayers is elucidated, and the links between colloid and molecular systems are pointed out.

Interparticle hydrodynamic interactions in deposition processes

The approximate solution of the Stokes equation has been used in order to estimate the magnitude of the hydrodynamic interactions between deposited and flowing particles. The calculations show that these interactions are likely to be responsible for removing weakly-bound particles. The origin and extent of the blocking effects in particle deposition phenomena are also discussed.