Yushi Hirata

Acidification of Growing Cloud Droplet by Rainout of SO2(g)

Growing cloud droplets absorb such atmospheric gaseous pollutant as SO2(g), condensing atmospheric water vapor into themselves. Then, the cloud droplets are acidified by absorption of SO2(g) during condensational growth on cloud condensation nuclei (CCN). Characteristics of this process, which is a part of rainout, have not been made clear yet. In order to estimate the contribution of rainout to acid rain formation, the acidification of growing cloud droplets is investigated numerically, using a mathematical model. The numerical simulations show that: (1) the time to attain the equilibrium state for mass transfer (acidity and growth) and heat transfer (temperature) is much longer than the time for disappearance of CCN; (2) time variation of acidity and temperature of cloud droplets are greatly dependent on the existence of undissolved CCN; and (3) there seems to be a close correlation between the time variation of the acidity and that of the temperature.

Characteristics of Raindrop Acidification by Co-Washout of SO2(G)-H2O2(G)-HNO3(G)

In order to investigate the acid rain formation under the coexistence of SO2(g), H2O2(g), and HNO3(g) in the air, a mathematical model has been built and some numerical simulations have been carried out with use of the model. The simulation reveals that SO2(g) absorbed into a raindrop is released and then re-absorbed as the fall distance increases. The desorption and re-absorption processes of SO2(g) are caused by: (1) the fact that the equilibrium concentration of H2O2(aq) and HNO3(aq) in raindrops are much higher than that of SO2(aq), and (2) the fact that the oxidation reaction rate of HSO3− with H2O2(aq) increases with H+ concentration in raindrops. The degree of acidification of the rainwater has been estimated by introducing a raindrop size distribution. The acidification is mainly caused by the adsorption of SO2(g) in the usual case where the atmospheric concentration of SO2(g) is much higher than that of HNO3(g). With the increase in the atmospheric concentration of HNO3(g), the concentration of H+ generated from SO2(g) decreases and the contribution of HNO3(g) to the generation of H+ becomes dominant.

Freeze Concentration with Ice-Lining in a Crystallizer of Agitated Vessel

A new method of freeze concentration with ice-lining has been developed, in which concentration of the solution can be performed only through the growth of an ice layer pre-coated on the inner wall of a crystallizer of agitated vessel with cooling jacket. From the measurements of concentration and volume of the residual solution during freezing process of cphalosporin C sodium solution, it was revealed that this method has an excellent superiority in recovery of high concentrate to the simple method without ice-lining.

In-situ Electrokinetic Remediation of Soil and Water in Aquifer Contaminated by Heavy Metal

The electrokinetic method for the remediation of contaminated aquifers is realized by applying a fixed low voltage direct current between an anode and a cathode placed into the contaminated zone. The purge water is injected into the anode well and drawn out from the cathode well with the pollutants. Therefore the application of this method to in-situ remediation of aquifers is relatively simple. This method can be applied effectively to remove heavy metals. These cannot be decomposed by other methods such as bioremediation, although this method can be used also for decontamination of organic chemicals in aquifers. However, the variations of the operational variables of this method have not been made clear, because this method is relatively new and is an inovative technique. In order to investigate the operational variables of electrokinetic remediation, a mathematical model has been constructed based on the physico-chemical transport process of heavy metals in the pore water of a contaminated aquifer. The transport of heavy metals is driven not only by the hydraulic flow due to the purge water, but also by electromigration caused by the electric potential gradient. The electric potential between the anode and the cathode is the important operational variable for electrokinetic remediation. From the numerical simulations using this model it is confirmed that remediation starts from the upstream anode and the heavy metal is gradually transported downstream towards the cathode and is drawn out through the purge water.

Ground Improvement. Modelling of Remediation of Polluted Soil by In-Situ Electrokinetic Treatment.

In order to investigate the efficiency of the in-situ electrokinetic method for the remediation of the soil contaminated with heavy metals, a mathematical model based on the physico-chemical transport phenomena has been constructed and the remediation process is simulated numerically with use of the model. The elecrokinetic remediation is realized by applying a fixed low voltage direct current between the anode and the cathode which are set into the contaminated zone and saturating the zone with purge water. The numerical simulations show that the electrokinetic method is effective for the remediation of the polluted soil especially with heavy metals. The electric current and the electric potential between the anode and the cathode are the important operational variables for the elecrokinetic remediation. It has been proved that the removal process can be divided into the two stages, i.e., the first stage and the second stage, according to the manner of the time variation of the electric current (i.e., the time variation of the spatial characteristics of the removal). The remediation process progresses from the anode to the cathode.

Condensational Growth Of Cloud Droplet On Atmospheric (NH4)2 SO4, Particle

In order to investigate the acidification process of cloud drops (i.e., acid rain formation) due to rainout (in cloud scavenging) of gaseous pollutants as 882 (g) and NOx(g)> the non-steady characteristics of the growth of single cloud droplet by condensation of the atmospheric water vapor is simulated numerically with use of a mathematical model. The mathematical model is constituted by the conservation laws of water mass and heat energy and the state equation of ideal gas. The time variation of droplet heat Qw is very fast compared with that of droplet mass m^. Therefore, usually droplet temperature Ta can be treated as in quasi-steady state. The equilibrium droplet size â is approximately dependent on the 3/2 power of the initial radius OgQ of cloud condensation nucleus (NĤ SĈ . Because for large condensation nuclei it takes considerably long time compared with the lifetime of cloud to grow up to its equilibrium radius, the conventional Kohler equation may bring about not a little error in the estimation of cloud drop size.

Effect Of Electric Field Induced Within Rain Drops OnAcid Rain Formation

In order to take account of the effect of the electric potential induced by charged chemical species in rain drops on acid rain formation, a new mathematical model, which contains the electro-migration term in addition to the conventional terms, has been constructed. The electric field in rain drops is brought about by the movement of ions which is produced by the absorption of acidic atmospheric pollutant. The ions undergo the electric force caused by the electic field in rain drops and they move toward the certain direction depending on their charge. The numerical simulations by the new model developed here discloses that: (1) the electro-migration of ions makes H+ concentration higher than that estimated neglecting the electro-migration; (2) the distibution of H+ concentration tends to uniform under the elecric potential field; and (3) the electric potential is higher at the drop center than at the drop surface.

Computation Transport Phenomena in Chemical Engineering. Analysis on Benard Convection Pattern with Pattern Evolution Equation.

ベナール対流場でみられる水平面内のパターンの時間変化を, パターン変数による一般化Ginzburg-Landau型の発展方程式を用いて数値シミュレーションし, 既往の実験や理論解析の結果と比較した.現象論的に導出されたパターン発展方程式は, 一個の非線形微分方程式であるにも拘わらず, 超臨界レイリー数域でみられるロールセル, 六角セル, ジグザグロール, クロスロールなどの様々な対流パターンや波数の変化を表現することができる.このような解析法は, パターン形式を伴う現象の解析を大幅に簡略化することができる.

Separation of rare-earth ions by electrophoretic focusing.

錯体を利用した希土類金属イオンの等電点電気泳動分離原理をイオンの輸送方程式に基づいて記述し, 泳動分離帯の濃度分布を解析的に表現した.通常の印加電圧では, 濃度分布はガウス分布で良好に近似できる.これに基づき, 希土類イオン高純度化の達成に必要な電位勾配, 錯化剤濃度勾配ならびに分取出口幅に関する解析的関係式を導出した.EDTAの錯安定度定数を用いて本等電点電気泳動法が希土類元素の高度分離法として有望であることを明らかにした、得られた諸関係式は, 電気泳動分離装置の設計・操作指針として工学的に重要である.

Visualization of turbulent pipe flow.

The hydrogen-bubble method was applied to visualizing turbulent pipe flow in the range of Re from 5×103 to 1.5×104. Platinum wires were set in a pipe cross-section so as to form a regular polygon periphery, from which hydrogen bubbles were generated continuously. The hydrogen bubbles were visualized by lightening cross-section to observe them from downstream by TV camera and their fluctuating bahavior recorded on video tapes was analized using personal computer image processing system.Mean value of circumferential intervals between adjacent bursts decreases as the radial position of the platinum wires for generation of hydrogen bubbles approaches wall and has a limiting value of ?? 100 in the vicinity of the wall. Difference between flow structures in the buffer region and the turbulent region has been clearly indicated by drawing quasi-3D space-time profiles and contours of fluctuation of hydrogen bubbles.