The present review gives an introduction of recent studies on application of direct numerical simulation of colloidal suspension to microfiltration. First, we presented the numerical method for a coupled scheme combining the immersed boundary method and the discrete element method (DEM) to simulate colloidal particle dispersion flow in microfiltration membrane. The simulation results can reveal the relationship between the permeation dynamics of colloidal suspension, and the behaviors of water permeation flux and rejection. In addition, we presented a numerical method for coordinating the microporous structure calculated by the phase-field model with direct numerical simulation of colloidal particle dispersion flow to describe the permeation dynamics of colloidal suspension through the realistic structure of microfiltration membrane. To coordinate fluid computation and particle computation with the microporous structure calculated by the phase-field model, the immersed boundary method and the level set method were applied, respectively. Two types of microporous structure were prepared by varying initial polymer concentration using the phase-field model to demonstrate the present method. The direct numerical simulation of the permeation of colloidal suspension flow was then performed. The permeation behaviors between the two types of microporous structures were markedly different.

Dust collection technology is used not only for countermeasure of air pollution but also for the removing technology of nano-particles, simultaneous removal of gas and dust, equipment for extreme conditions such as high and low pressures and temperatures. Furthermore, particle concentration in the atmosphere, especially PM2.5 does not decrease despite that discharged dust concentration from stationary source decreases. And it is said to be caused by the exhaustion of condensable and/or reactive gaseous materials are discharged and it forms secondary particles. These facts suggest the necessity of improvement of dust collection technology.

In this article, recent development in dust collection technology, especially bag filtration and electrostatic precipitator are described. International standards relating bag filtration are also explained.

Smaller grinding media beads in bead mills are well known for determining high grinding performances. However, the post-grinding separation between beads and slurry might be a difficult task, especially in bead mills with centrifugal bead separation, where the separating performances are strongly affected by the shape of the rotors in the mill. Aiming to study and design grinding operations, the discrete element method (DEM) is a powerful tool which allows for predicting the grinding and separating performances in the mill. In this study, by using DEM simulations, we examined the slurry-beads separation in a bead mill and we investigated the influence of the rotor shape on the separating performances. We compared the performances of two kinds of rotors, one with conventional shape and one with outside projections for the activation of the media beads. Results of DEM simulation were in good agreement with experimental results.

The submerged pleated filter with bubble jet function was developed and the constant rate filtration experiment of cornstarch suspensions was carried out at different filtrate flow rates and particle concentrations. In contrast to dead-end filtration without bubble jet in which the pressure rises remarkably, the pressure rise is suppressed by removal of the filter cake in filtration with bubble jet, leading to an equilibrium value. Thus, the proposed filtration system is useful as one of the dynamic filtration modes. Moreover, the partial dynamic filtration model was established and as a result the experimental data could be well described by this model. The model analysis clearly demonstrated that the filtration performance was determined by a product of the filtrate flow rate and the particle concentration, i.e., the feed rate of particles. Also, it was revealed that the maximum ratio of cake-exfoliated area of the pleated filter used in this study was 0.65.

We have developed and evaluated a cyclone type classifier with improved collection boxes for classifying particles swilling down near the wall surface in order to separate coarse particles. These studies were performed under low solids loading condition to clarify the classification mechanism. However, the further examination under high solids loading condition is indispensable to the practical application.

In this study, the particles feed rate was increased from 2 g/min up to 100 g/min. The remarkably high concentration of particle provably aggregates particles near the wall at the inlet, causing the saltation flow, targeted for the classification in our study, to transfer into sliding bed flow where the classification is impossible. Therefore, we introduced the secondary flow injected in the upper section of the cyclone. The secondary flow could disperse the particles and minimize the decrease in the classification performance. This result showed that the device is sufficient for practical use.

Electrostatic precipitator (ESP) is a major dust collection equipment in pulverized coal combustion boiler in Japan. As the environmental influence of fine particle such as PM2.5 in the atmosphere is focused recently, the improvement of the collection efficiency of fine particle on ESP is desired. An advanced low temperature ESP operated under 363 K has been used recently because of its availability for high electric resistivity coal ash. In this study, the separation characteristics of fine coal ash particle by the control of operation condition on advanced low temperature ESP in a pulverized coal combustion boiler is investigated. It is estimated that the fractional collection efficiency of advanced low temperature ESP shows a minimum value at the particle size in the range 0.5 to 1.0 μm. The collection efficiency of fine particle under 2.5 μm is improved by the increase of current density of ESP and the control of gas flow pattern in ESP is one of the effective method for the improvement of the collection efficiency of ESP.

In order to characterize the emission behavior of PM2.5/PM10 mass concentration from stationary sources, such as power plants, factories and waste incinerator plants, two-stage virtual impactors were developed for in-stack separation and collection of PM2.5/PM10 in flue gas. This method was adopted as international standard, ISO 13271 (2012) to determine the actual emission behavior of PM2.5/PM10 from stationary sources. PM2.5 separation performance of a virtual impactor was compared with that of a real impactor, which was also international standard method as ISO 23210 (2009). With the conventional cascade real impactor method PM2.5 mass concentration was overestimated by the particle bounce and re-entrainment of coarse particles from the collection plates.

Electret filters severely lose electrostatically enhanced particle collection efficiency when they are exposed to tobacco smoke. Tobacco smoke particles consist mainly of liquid substances at room temperature. Thus, captured tobacco smoke particles spread over an electret fiber and seriously weaken an electrical field around it. We have developed a novel surface modification treatment to avoid the spreads of tobacco smoke particles on the fiber. The modified electret filter was examined in comparison with the unmodified one. The surface modification treatment caused no adverse effect on initial collection efficiency and electrostatic charge stability of the electret filter. It was verified that the surface modification significantly improves durability of the electret filter for tobacco smoke. Further, the surface modification was effective also for many kinds of liquid particles such as oil mist. The electret filters modified by the developed treatment are useful for application to air purifier filters, respirators and so on.

This paper presents microcapsule powder production of d-limonene using emulsifier and spray dryer. The size of emulsion samples were affected by the number of pass times and feed pressure of raw materials into emulsifier. The emulsifier used in this work led to sharp droplet distribution at low feed pressure, and the emulsion size became smaller as increasing the number of pass times. In case of the smaller droplet size in emulsion, the more oil component microcapsule particles produced from emulsion of d-limonene by spray dry were contained. The weight loss on drying as an indicator of the oil content in particles using a raw material of five times passed into emulsifier was 4.8 mass%.