Outline of the removal of discrete solid particles adhered to a solid surface using a high-speed impinging air jet is introduced with particular attention to the effect of operating conditions on removal efficiency. The operating conditions described in detail here are the air pressure in the jet nozzle and the distance between the nozzle tip and the surface. It was shown that the effect of the air pressure and the distance could be evaluated from the dynamic pressure of air jet which can be estimated from analytical equations based on fluid dynamics and thermodynamics. This means that the removal performance of a nozzle can be expressed by an index reflecting time averaged flow characteristics. In addition, the improvement in removal performance of the pulsed air jet method is also introduced. These results imply that flow fluctuation characteristics dominate the removal efficiency.
We introduce a surface cleaning technique called two-fluid jet method, which employs gas and liquid mixture. With this technique, droplets are accelerated by high-speed gas flow, and sprayed on a target surface. The detail of droplet impacts and the mechanisms of cleaning are discussed. Especially splash formations after droplet impact are focused. In addition, the effects of surrounding gas species on the splash formation are discussed.
In cleanrooms where micro devices such as LSIs and FPDs are manufactured, the energy saving has been demanded to reduce the operation cost and the environmental burden. The air conditioning system for cleanrooms is normally divided into an indoor system and outdoor air system. In winter, the indoor system is operated in the cooling mode while the outdoor air system is operated in the heating mode, and thus both heat and cold sources run simultaneously causing heat loss and uneconomical running of the facilities. In order to resolve this problem, we proposed a humidification system with one-fluid type spray nozzles. This humidification system can reduce CO2 emissions by over 15% for the cleanroom where an exhaust heat recovery equipment has been already introduced.
Spot air-conditioning system has been frequency adapted as a countermeasure for protecting workers from severe operations in a machinery factory during hot summer. However, the conventional system is not effective because it supplies the cold air surrounded by the hot air induced by the discharge of cooled air through a supply air opening. In this article, we proposed a new spot air-conditioning system with a nozzle, which supplies fine fog to obtain the sufficient cooling performance. The effectiveness in lowering the room temperature and the degree of comfort for workers by the introduction of new system were evaluated through the experiments with a model room. It was found that the system was effective in protecting workers from operations in the severe hot environments. In addition, CFD simulation results of spatial distribution of air flow velocity, temperature and humidity in the model room were qualitatively in good agreement with the experimental data, implying that CFD is an effective tool for predicting the cooling performance of a new spot air-conditioning system and obtaining various parameters necessary for designing the system.
The carbon nanoparticle-added ultrasonic spray pyrolysis (CNA-USP) method has been developed by the authors to produce porous submicron Gd0.1Ce0.9O1.95 (GDC) particles which are an electrolyte material for a solid oxide fuel cell. In the method, a uniform dispersion of carbon nanoparticles (CN) in the precursor solution is important technique to form droplets in which much amount of CN are included. In this study, effects of pH on the dispersion of CN were investigated experimentally. The pH was controled by adding NH3 aqueous solution. The amount of carbon nanoparticles in submicron GDC particles synthesized at pH = 10.6 (with NH3) and the reaction temperature of Tr = 600ºC was about 3.7 times larger than that at pH = 3.3 (without NH3). When the porous submicron particles synthesized at Tr = 1000ºC were suspended in pure water and broken by ultrasonification for 30 minutes, all particles synthesized at pH = 10.6 were broken down to nanoparticles with 20-40 nm in diameter, but only few particles synthesized at pH = 3.3.
This paper focuses on the long-term trend and current status of air pollution in China. In particular, fine particulate matter (PM2.5) in Beijing city was introduced. The annual number of scientific journal publications regarding PM2.5 in China has been increased from zero before 2000 to more than 100 in the past two years. The concentrations of PM10 in Beijing have been decreased from 169±94 µg/m3 in 2001 to 109±73 µg/m3 in 2012. Researchers should note that Beijing is not a representative city of China because it was uniquely developed due to the hosting of the 2008 Summer Olympic Games. The concentrations of PM2.5 in Beijing have almost been constant at a level of 100 µg/m3 from April 2010 to October 2013 except in January 2013, showing remarkably high monthly average PM2.5 concentrations (200 µg/m3). This highly polluted situation was probably due to a tentative meteorological condition in that period, and this did not cause any elevation of PM2.5 concentration in Japan. The chemical composition of PM2.5 in 2010 was similar to that in 2000, however, the content of carbonaceous species in PM2.5 was likely to have decreased from 2000 to 2010 when compared to water-soluble ionic species. The concentrations of air pollutants decreased by up to 50% in the summer of 2008 due to Olympic Game related environmental control measures, but they increased again in 2009. It seems difficult for many Chinese cities to satisfy the ambient air quality standard for PM2.5 even though the standard is not strict when compared to other countries. Since the status of atmospheric environment in China changes abruptly, the continuous monitoring is mandatory.
We describe the improvement in the sensitivity of an aerosol spectrometer that simultaneously measures the size-dependent concentration and chemical composition of particulate organic matter.The spectrometer studied in the present work consists of a differential mobility analyzer (DMA) for the size classification and a gas chromatography mass spectrometer (GC-MS) for the composition analysis.Size-classified particles of hydrocarbons were directly introduced into a thermal desorption (TD) tube packed with absorbent. Hydrocarbon molecules thermally desorbed from the TD tube were then introduced into the GC-MS. We improved the vacuum level in the ion source section of the GC-MS by changing the GC-MS carrier gas, and increased the velocity of carrier gas that expelled the hydrocarbon vapor from the TD tube into the GC-MS by reducing the size of the pipe. For a particle size of 330 nm, the detection sensitivity of the spectrometer for nonylbenzene particles was approximately 30 times as high as that of the spectrometer developed in our previous work (Okada et al., 2012). From the results of our investigation of the adsorption and desorption efficiency of the TD tube and the lower detection limit of the GC-MS using nonylbenzene vapor as a sample, we found that nonylbenzene weighing more than 6.6×10-2 ng could be measured with our spectrometer, i.e., the lower detection limit.