In the international standardization of air filters, there are two existing national standards accepted world-wide. They are similar but very much different in test dusts and measuring instruments, resulting in serious confusion among users as well as manufacturers. ISO/TC142 tries to mitigate much of the confusion caused by a multiplicity of national standards. Japanese mirror committee has proposed the usage of JIS-11 (JIS Z 8901) test dust as a substitute of currently-adopted test dusts for both initial collection efficiency measurements and loading dust since it has wide size distribution covering 0.3-5 μm. The present work studied the generation method of JIS-11 dust, the size distribution, the influence of charging state on the initial filter collection efficiency, and the relationship between light-scattering equivalent diameter and aerodynamic particle diameter. As a result, it was suggested that JIS-11 dust can be used for the measurements of initial collection efficiency covering particle diameter ranging from 0.3 to 5 μm.
Air filter efficiency testing methods have historically consisted of the volumetric, colorimetric, and particle counting methods. With the global expansion of the air filtration market, ununified test methods and definitions of filter efficiency has brought some confusion in the global market. In order to resolve this confusion, ISO / TC 142 / WG 3 was reinstalled in 2006 towards the standardization of general ventilation air filter test methods, and issued ISO / FDIS 21220. However, unfortunately it was rejected by the FDIS vote. The Japanese TC 142 mirror committee has been considering the possibilities of a particle diameter-based, fractional filter efficiency test method that employs JIS-11 test particles as an alternative to ISO / FDIS 21220. An overview of this project is introduced here.
Diesel vehicles have advantages over gasoline vehicles in fuel economy,with a big feature of less CO2 emission. However, it is well known that diesel vehicles exhaust nitrogen oxide (NOx) and the particulate matter (PM) , which causes air pollution. In order to encourage the broad use of diesel vehicles, it is necessary to develop clean diesel engines that are installed with a revolutionary high-performance after-treatment devices such as DPF, CSF. In this report, the recent trends of R & D's of the advanced after-treatment devices are introduced.
Inertial filter, which classifies nanoparticles by inertial filtration, has been developed by Otani et al. (Aerosol and Air Quality Research, 7, 343-352 (2007) ) . The present work is aimed at formulating the fundamental design rules for the inertial filters with an appropriate cutoff size at a low pressure drop. We numerically calculated the classification performance for nanoparticles and compared the results with the experimental data obtained with TEM grids which has rigid and uniform structure as a model filter. As a result, thorough the theoretical calculation and experiments, (1) the collection efficiency of inertial filter can be successfully predicted by the conventional filtration theory based on the single fiber collection efficiency. (2) A filter with a finer fiber diameter can achieve smaller cutoff size at a lower pressure drop, however, the theoretical calculation suggested (3) an inertial filter consisting of fibers smaller than 14 μm cannot suppress the diffusional collection of nanoparticles with the diameter of 20 nm even at a filtration velocity of 30 m/s.
By simulating the conditions of bed-laid patients in a biological clean room, experiments are carried out in order to study the airflows around the patients when horizontal commutation aseptic laminar flow units are operated at an airflow velocity of 0.3 or 0.5 m/s. When a patient is absent from the room, the airflows show a higher capability to transfer and remove particles at an airflow velocity of 0.5 m/s compared to that at 0.3 m/s. However, when a patient is present in the room, the airflows have a lower air exchange rate at an airflow velocity of 0.5 m/s than 0.3 m/s. This is because turbulent flow occurs downstream of the patient. The present results suggest that an increase in airflow velocity does not necessarily lead to an increase in ventilation because the wake size downstream of the patient increases with the airflow velocity.