The Abstracts of the paper carried by the Journal of JACA
As a method for removing fine particles, HEPA (High Efficiency Particulate Air) filter is generally used. However, HEPA filter is clogged easily with fine particles and it is expensive for general use. We have developed a fine particle removal method by spraying mist instead of filter method. However, fine particles are difficult to remove by spraying mist because of their size. The fine particle size (<1.0μm) is much smaller than the sprayed droplet size (50μm), so the fine particle rarely collide with the sprayed droplet. In order to solve this problem, fine particles are charged to the positive polarity by the ionizer and sprayed droplets are charged to the negative polarity by electrostatic atomization. Electrostatic attraction occurs between electrically charged fine particles and droplets, so that the collection efficiency of fine particles can be improved.
In this study, we investigated to remove not only particles of 2.5μm but also particles of 0.1μm which are equivalent to virus size by spraying electric charged mist.
Air filters collect particles by the mechanical collection mechanisms, namely, inertia, interception, gravitational settling, and Brownian diffusion. There exists the most penetrating particle size (MPPS) in submicron size range for which none of the collection mechanisms work effectively. In this study, we propose a new type of filter named as “centrifugal filter,” which collects aerosol particles by centrifugal force together with the conventional mechanical collection mechanisms. The centrifugal filter is rotated by a motor in the rotation axis parallel to the airflow. In addition to the mechanical collection mechanisms, small migration of particles due to the centrifugal force enhances the collection efficiency of submicron particles. The performance tests of centrifugal filter are conducted by changing the fiber diameter, the air flow velocity and the rotation speed. We found that the collection efficiency of filter is enhanced significantly by rotating the filter without increasing the pressure drop and that the filter efficiency is well predicted by the conventional filtration theory accounting for the centrifugal force.
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 liquid particles on the fiber. The modified electret filter has been 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 has been verified that the surface modification significantly improves durability of the electret filter for tobacco smoke. Further, the surface modification significantly improves durability of the electret filter for tobacco smoke. Further, the surface modification has become 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.
It has been known that ultrafine particles (UFPs) less than 100nm are emitted from laser printers and multifunction peripherals. Potential health risk to individuals is reported to be caused by their inlalation. The emission rate of UFPs is regulated less than 3.5×1011 particles per 10 minutes for the printing devices regardless of its volume. Several studies to characterize their emission and explore the mechanism for their formation have been reported. However, the characterization of collection performance of air filters for them has not been studied sufficiently.
In this study, we attempt to characterize their filtration performance of electret filters composed of two kinds of charged melt blown nonwoven media using different electrification methods. Their filtration performance has evaluated for UFPs emitted from a commercialized laser printer using a test chamber and evaluated with test particles for its filter media. As a result, the collection performance has been different from electret methods, and it has confirmed that the filtration performance of charged filter media is different to between charged and uncharged particles.
This article reviews the histories of air pollution in Japan since the era of rapid economic growth and its current issues with relation to particle pollution such as PM2.5 and regulation of ship. For the regulation of ship exhaust emission, the emission of sulfur oxides in the exhaust gas has been regulated by designating the sea area surrounding the Japanese islands as an area to rank next to the sulfur emission control area (SECA) in 2020. Ship owners have to choose three typical measures to deal with the regulation. The first is to employ low-sulfur heavy oil as an alternative fuel. The second is to install exhaust gas treatment facilities such as gas scrubbers onto the existing ships. The third is to construct new ships that consume LNG (liquefied natural gas) as fuel.
JIS B 9908, the JIS standard for general ventilation air filters, has been established in 2019 to replace the conventional 2011 version. Based on the international standard ISO16890 series have established in 2016, the concept of particulate matter efficiency J-ePMx has been newly introduced. This paper mainly describes the transition of JIS standards, classification according to the 2019 edition, comparison with existing overseas standards, and future issues for medium class air filters.
A plant factory is a facility that precisely controls the internal environment to allow year-round and systematic culture of plants, such as vegetables. Plant factories are now said to be in the thrd boom. Along with its increasing awareness among cunsumers, vegetables produced in plant factories are catching on in the market.
There are two types of plant factories: artificial lighting type and sunlight type. The artificial lighting type plant factory is a closed system with high cleanliness, which enables highly controlled cultivation environment, suitable to the production of high value-added plants. However, the factory requires air conditioning to cool heat generated by artificial lamps.
This article focuses on the closed plant factory with artificial lighting and introduces the outline of the control of atmospheric conditions for plants.