Separation characteristics of various solutes from the aqueous solutions with ultrasonic atomization were experimentally investigated. Monohydric alcohols and ketone were concentrated in the atomized droplets from the aqueous solution, while alcohol and amides were diluted in the droplets. These results suggest that the hydrophilic and hydrophobic properties of solute molecules may determine the separation characteristics of ultrasonic atomization. In order to develop a concentrator with ultrasonic atomization, ultrasonic atomization of ethanol aqueous solution was conducted. The atomization rate of water was the highest at the beginning of atomization, and the initial depth of solution which gave the maximum atomization rate of water was decreased with increasing the ultrasonic frequency. The atomization rate of ethanol was increased with the net electric power applied to the ultrasonic transducer, but it remained almost constant at different ultrasonic frequencies. At a relatively high net electric power, the atomization rate of water increased with the diameter of reservoir, while alcohol content in the atomized droplets were unaffected by the reservoir diameter.
It has been claimed in the literature that selective ethanol separation from ethanol-water solution can be made through ultrasonic atomization. The causes of separation were explained in terms of parametric decay instability of capillary waves, accumulating acoustic energy in a highly localized surface of the capillary wave and effecting ultrasonic atomization. In this study, the atomization process is examined visually with some mechanistic view, and the dynamics of interfacial oscillations occurring along the perturbed protrusion or conical “liquid column/fountain jet” over the ultrasonic transducer are analyzed by high-speed imaging. It is found that the atomization process could be initiated by a sudden increase in surface roughness of microscale, which would be viewed as localized surface patches of two-dimensional capillary waves, often associated with contraction expansion sequence of surface to-pology. Such surface patches could bring further instability in generating a swarm of liquid droplets of microscale around the expanded phase of liquid column.
Ultrasonic atomization, in general, generates mist of liquid droplets with the diameter of micrometer order. Recently, our measurements with small-angle X-ray scattering (SAXS) at SPring-8 have revealed that the droplets of 1 nm dominate the whole population of atomized mist of ethanol. This article describes the details of SAXS measurements and discusess the mechanisms of the nano-sized droplet generation.
When mist particles are generated from ethanol-water mixtures by ultrasonic atomization at a low temperature, ethanol is concentrated in the atomized mist particles. This paper explains the mechanisms of ethanol thickning in atomized droplets based on the cluster-level structures analysed by the mass spectrometry. When ultrasonic atomization of equimolar ethanol-water mixture is carried out at a lower temperature, e.g. 10°C, small clusters composed of only ethanol molecules can transfer from the liquid phase to the gas phase, while the large clusters consisting of both ethanol and water molecules cannot move across the interface. This leads to the thickning of ethanol in the atomized mist particles. The cluster-level structures of ethanol-water mixture, which varies with the ethanol concentration and the liquid temperature, directly determines the characteristics of ultrasonic atomization of ethanol aqueous solution.
Separation through ultrasonic atomization has advantages in industrial application over distillation, i.e., low energy consumption, unheated process and quick start of opertion. The first application of ultrasonic atomization was sake refining by utilizing the advantage of no heating, its application is now growing in various industrial processes, for example, ethanol purification, waste water treatment, micro-nanometer ice formation, sugar concentration etc. In addition, carbon dioxide emission by ultrasonic atomization separation is extremely low compared to distillation. The ultrasonic atomization separation will replace many conventional separation processes because of the superior characteristics.
In this review, we describe in detail the methods to produce various nanoparticles using ultrasonic spray pyrolysis. In general, droplets generated by an ultrasonic nebulizer have a size of approximately 5 micrometers so that submicrometer particles are typically produced by the conventional spray pyrolysis (CSP). In order to produce nanoparticles, modifications in technique such as adding salts or polymers to precursor solutions are necessary. However, salt assisted-SP requires an additional treatment of washing to dissolve and remove residual material from the produced nanoparticles. The addition of polymers does not require washing process because they are decomposed and volatilized during the pyrolysis. Both methods produce isolated nanocrystals. In flame spray pyrolysis, the formation of nanoparticles is dominated by the evaporation-condensation route, and therefore the flame temperature controls the formation of nanoparticles. This review concludes that ultrasonic nebulization with subsequent pyrolysis is one of the effective methods to produce nanoparticles.
Ammonia (NH3) in ambient air was measured at Cape Hedo, Okinawa, in spring 2008 using a photo-acoustic spectroscopy method (TGA310, Omnisens). Average concentration and standard deviation (1σ) of NH3 was 0.56±0.50 ppbv. It is considered that the variation in NH3 concentration does not come from the long range transport. The concentration and standard deviation (1σ) of ammonium ion (NH4+) measured using an aerosol mass spectrometer (Q-AMS, Aerodyne) was 2.2±1.4 µgm-3 and NH4+ was more than 80% for NH3+NH4+ when NH4+ was transported over long-range associated with sulfate (SO42-). NH4+ was deficient when SO42-/(SO2+SO42-) was large in air masses.
The purpose of this study is to characterize airflow fluctuation, which occurs by the motion of large transport vehicles, and to improve airflow environment in the cleanroom. 1/10-scale model was used for this study. This model has a rack area and a vehicle’s running area. The rack area is equipped with FFUs (Fan Filter Units) on sidewall and ceiling, and they provide airflow distribution from the rack area toward the vehicle’s area. The pressure at the boundary between these areas shows a steep change while the vehicle was moving across the measuring point, and it causes a counter flow which may bring contamination in the rack area. The airflow around the measuring point was visualized using laser light sheet and water mist, and flow at different FFU operation conditions were compared. Through these comparison the most desirable airflow condition was obtained.