vol.60-6 (2023/3/31)

Application of light scattering particle counter to high concentration aerosols

Optical Particle Counters (OPCs) have been commonly used to determine the number concentration and particle size distribution of aerosols based on a single particle light scattering under low concentration conditions, such as in a cleanroom. In recent years, OPCs have been increasingly applied to measure relatively high concentration aerosols in indoor and ambient environment due to the great concern to environmental and health impact of hazardous airborne particulate matters, i.e. PM_2.5, PM₁₀, and droplets containing coronaviruses. However, there would be a large coincidence error when the concentration exceeds the maximum measurable concentration of OPCs. Thus, the use of OPC without the awareness on coincidence loss might lead to wrong interpretations of measured data. The present work is focused on examining the effect of particle coincidence on response of OPC under relatively high concentration conditions. OPC studied in the present work is a newly developed OPC (PP 8306, Particles Plus, Inc.) with a detectable size range of 0.3–10 μm at the sampling flowrate of 2.83 LPM.

Derivation of 3D flow field using PIV data in multiple cross sections
-Proposal and application of an advanced three-dimensional flow analysis technique-

Recently, image processing and visualization techniques such as PIV (Particle Image Velocimetry) have been applied in various fields as experimental analysis methods for fluid dynamics. However, the flow field which can be analyzed by general PIV systems is in two-dimensional cross-sections and velocity components obtained are also limited in two directions (2D2C). An advanced method was developed to derive a three-dimensional (3D3C) flow field from 2D2C data in multiple cross-sections obtained by PIV analysis. In this paper, the transition of PIV technology and the outline of the newly developed advanced three-dimensional fluid analysis method are explained.

Experimental removal performance evaluation of airborne molecular contaminant by air washer using conductivity control method

The supply water method for air washers often uses a conductivity control method that can significantly reduce the amount of water being supplied. However, there is almost no data on AMC removal performance, such as SO₂ and NH₃ for drip type air washers using the conductivity control method.
In this study, a drip type air washer with an actual air processing volume of 12,500 m³/h was built, and SO₂ and NH₃ removal performance with the conductivity control method was investigated. As a result, we found that there is a correlation between the pH of the absorbing liquid and the removal rate of SO₄^2- and NH₄⁺. Moreover, it was also found that the higher the conductivity of the absorbing liquid was, the lower the NH₄⁺ removal rate became. Therefore, in order to maintain the NH₃ removal performance of the air washer, it is necessary to lower the set value of conductivity while controlling the pH of the absorbing liquid.

Comparison of aerial fungi (outdoor, indoor) measurement method and characteristics of annual transition

Airborne fungal measurement is diverse, but there is no unified evaluation method. The measurements are taken indoor and outdoors using the actual on-site method.
The purpose of this research is to compare the airborne fungal collection method with the air sampler and the natural dropping method. The amount collected by the air sampler is 100L in each time. The natural dropping method is to expose the medium for 10 and 30 minutes. From the results, the two methods are quantitatively correlated on the CFU . There is a specifical difference in the number of fungi between indoors and outdoors, and also a difference in the dominant species such as Cladosporium and Penicillium. Therefore, useful information is obtained on the airborne fungal survey method, environment of measurement location and microbiological distribution of dominant airborne fungi.

Study on airflow control technology for indoor spaces using artificial droplet generator

Airflow control technology such as ventilation is important as a countermeasure against droplet nuclei infection in COVID-19. In this study, we aimed to quantitatively evaluate droplet nuclei infection using a simulated droplet generator in order to develop airflow control technology useful for preventing droplet nuclei infection. In this paper, we focused on the composition of the artificial mucus of the simulated cough generator and investigated the behavior of droplets using a solution similar to the composition of actual human saliva. When the new artificial mucus containing mucin was diluted 500 times, the particle size distribution of droplets similar to that of conventional artificial mucus was obtained. As a result of comparison by varying the residence time in the aging duct, the concentration decay was slower for the conventional artificial mucus. This difference in droplet behavior may be due to the physical properties of the components of the artificial mucilage in the submicron range.

Possibility of ultraviolet sterilization for infectious disease

Before Coronavirus disease (COVID-19) epidemic, the MHLW (Ministry of Health, Labour and Welfare) had pointed out the importance of drug resistance measures (AMR) and infection control based on One Health. Ultraviolet (UV) had been touted as a disinfection method for a variety of locations. On the other hand, due to mercury-free and LED applications, it was necessary to evaluate the sterilizing effect and energy efficiency of alternative wavelengths to the mercury lamp wavelength (254m). The authors therefore experimentally have determined the amount of UV radiation required to kill bacteria and molds for six lamps and three LEDs of different wavelengths. The energy efficiency and the mechanism of sterilization have been also investigated. The results have showed that for the same power consumption, mercury lamps have showed the highest sterilizing effect. In addition, UV lamps 222nm and 280nm and LED 285nm have been characterized by their sterilizing properties and miniaturization, suggesting the possibility of energy saving for different applications.

Types and functions of air cleaning devices in industrial cleanrooms

Industrial cleanrooms are used for the manufacture of semiconductor chips, liquid crystal panels and the like. The cleanroom requires a clean environment free of airborne fine particles and of molecular contaminants. In the cleanroom, a non-unidirectional flow cleanroom, a unidirectional flow cleanroom and a combined system are used. Fan filter units for removing fine particles are installed on the ceiling of the cleanroom. In order to prevent contaminants from entering the cleanroom, outdoor air handling units are used to remove fine particles and molecular contaminants in outdoor air. Air showers are used to prevent operators from bringing in contaminants. As air cleaning devices that make up the industrial cleanroom, outdoor air handling units, fan filter units, air showers and floor-mounted chemical filter units are introduced. In addition, improved fan filter units for energy saving, resource saving and cost reduction are introduced.