RETRIEVAL OF AEROSOL OPTICAL THICKNESS BY MEANS OF THE LEAST-MEDIAN-SQUARES ROBUST ALGORITHM

Atmospheric aerosols play an active role in the atmospheric radiative energy transfer by interacting with the solar energy through light scattering and/or absorption. Such an interaction has the potential to counter balance or enhance the warming caused by the greenhouse gases (e.g. carbon dioxide, water vapor, and methane). The interactions would depend on a variety of factors such as the microphysics and chemistry of aerosol particles, and the environmental conditions. To model the energy transfer processes accurately, several aerosol parameters such as aerosol optical thickness (AOT), single scattering albedo, scattering phase function, refractive index, and chemical composition of aerosols have to be known. In this report, a robust method for aerosol optical thickness is presented. The method is based on the least median squares (LMS) regression technique. The LMS-based technique is fundamentally different from the traditional least-squares (LS) technique commonly used today to retrieve AOT. The LMS technique was found to resist influential outliers and sustain the impacts of outliers much better than the LS in our application. The outlier-resistance property is an important design consideration for an automatic AOT retrieval algorithm. We demonstrated the strength of the new technique by using the shortwave irradiance measurements taken by one of the Multi-filter Rotating Shadow-band Radiometers installed at the Southern Great Plains in Oklahoma, U.S.A., one of the three sites operated by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program. The data cover a time period from September 1995 to May 1997. The LMS-retrieved mean top-of-atmosphere solar irradiance values (i.e. I₀) were stable based on the one-tailed Student’s t tests. It was also found that the difference between the 75th and 25th percentiles (a non-parametric robust estimate of variation) of I₀ over the 2-year period was 0.2 for the 499-nm channel, and 0.05 for the 860-nm channel. The monthly averaged AOT values over the 2-year period were from 0.05 to 0.30 for the 499-nm channel and from 0.03 to 0.15 for the 860-nm channels. AOT values peaked between May and September and reached minima in between November and January. The synoptic flow from the North might have contributed to the low level of AOT values during the wintertime, while the southerly flow, traversing through more industrial areas before reaching the site, could have contributed to the influx of particles during the summertime.     

浓度对传质系数的影响及多元物系传质

在筛板塔中对甲醇-乙醇-水三元物系进行精馏传质过程实验,考虑浓度对传质系数的影响建立了一个数学模型,对各组分在塔中的浓度分布进行模拟计算,计算结果能正确反映各组分在塔中浓度分布的变化规律.实验与计算结果都表明在某些浓度范围内乙醇呈现出比较复杂的变化规律.     

THE ON-LINE CHEMICAL ANALYSIS OF SINGLE PARTICLES USING AEROSOL BEAMS AND TIME OF FLIGHT MASS SPECTROMETRY

This paper describes an on-line instrument, capable of measuring the size and chemical composition of single, aerosol particles. Possible applications include monitoring aerosol reactors and studying atmospheric chemistry. The main conclusion is that a working prototype has been built and tested. It uses a three stage vacuum system to generate an aerosol beam with a low divergence angle and a high transmittance. The pressure is reduced sufficiently to allow the application of a time-of-flight mass analyzer. The aerosol beam is probed in the analysis section by the focused beam of a low-power helium-neon laser. Every particle crossing the laser beam scatters light, which is detected by two photomultiplier tubes, mounted at angles of 45 and 90°. The signal is stored when both detectors produce a pulse simultaneously, and this event triggers the chemical analysis cycle. A pulsed Nd: YAG laser vaporizes the particle and generates ions, which are next analyzed by a time-of-flight mass spectrometer. In this way combined information on the size and the composition of the particle is obtained.     

THE EFFECT OF VORTICES INDUCED BY BAFFLES ON CONCENTRATION POLARIZATION

A numerical analysis was performed to investigate the effect of recirculations formed by rectangular or triangular baffles on depolarization of concentration in a flat sheet membrane module. The k- ? turbulent model was used to predict the flow field in the flat channel. Control-volume-based finite difference methods were employed to solve for the two-dimensional fluid velocity and solute concentration distributions. We examined rigorously the effect of various parameters including the velocity, diffusivity, permeate flux, baffle size, baffle shape, and interbaffle spacing in an effort to find optimum operating conditions which may provide enhanced mass transfer. The vortices induced by the baffles on the membrane are found to be extremely effective in depolarizing the retained solutes at the membrane surface. The predictions show that baffle configurations and flow conditions have a great influence on depolarization of concentration. To achieve effective concentration depolarization, the baffle height should be greater than 0·5 (h = half the channel height) and the interbaffle spacing around 2h to 3h for the Reynolds number from 1,250 to 25,000. The simulated results indicate that the optimal Reynolds number is around 5,000 to 8,000 in view of both concentration polarization and energy consumption.     

运动气泡近界面浓度场的激光测量及其传质特性的研究

<正>1引言迄今为止,有关两相流气泡的传质研究已有大量报道[1-4]。这些研究均是一种黑箱式的研究方法,着眼于宏观现象的观测、分析及回归,无法从机理上展示各种宏观传递现象的差异及其内在本质,固而其研究结果均带有很大的经验性和局限性。 随着化学工程基础理论研究的深入发展,需要进一步了解运动气泡逼近界面处浓度场的变化与分布。特别是由于运动气泡的特殊性,气泡在上升过程中要发生变形[5],形成泡前区及尾涡区,在这两个区域内,界面阳近动力学特性及浓度场特性有很大差异,这就需要在更深的层次上研究这种微观差异。     

COMPOSITION AND SOURCES OF URBAN AND RURAL ATMOSPHERIC AEROSOL IN EASTERN HUNGARY

In an eastern Hungarian region urban and rural aerosol samples have been collected regularly over several years. Concentrations have been determined for 19 elements by the protoninduced X-ray emission method. The examined concentrations have been compared with other data representative for source areas influencing Hungarian atmosphere as well as for typical conditions in Western Europe. Seasonal variations, correlations with the amount of precipitation and wind sector distributions were observed for separate elements. Absolute principal component analysis revealed four typical factors contributing to the aerosol burden. Trajectory sector analysis has been used for studying the influence of long-range transport from the heavily industrialized “Black triangle” area in Central/Eastern Europe on the one hand and Saharan area on the other. Our data offer further basis to investigate the existence and nature of differences between air qualities in Western and Eastern Europe caused by structural and technological differences in the energy sector and industry of the regions mentioned.     

THE EFFECT OF FREE STREAM CONCENTRATION ON HEAT AND BINARY MASS TRANSFER WITH THERMODYNAMIC COUPLING IN CONVECTION ON A ROTATING DISC†

Simultaneous heat and mass transfer, which arises from injecting a gas (helium or hydrogen) from or through the solid surface into a flowing external stream, has been studied for a rotating disc geometry. The effects of concentration levels of the injected gas in the external stream on the thermodynamic coupling in the presence of centrifugal force have been investigated over a wide range of T_w/T_e.

Boundary layer equations for heat and mass transfer were solved numerically. Exact and linearized approximate solutions were obtained. The results have shown that the thermal diffusion effect on mass transfer becomes increasingly important as the free stream concentration increases and as T_w/T_e departs from unity. The diffusion thermo effect on heat transfer was found to be the most important when the free stream concentration is zero and as T_w/T_e approaches unity.     

EFFECTS OF MASS TRANSFER ON THE THINNING AND RUPTURE OF A PLANE PARALLEL LIQUID FILM

The effects of mass transfer and physical properties upon the thinning and rupture of adraining plane parallel film are investigated.An equation is derived in which the thinning rate is afunction of bulk properties.surface properties(surface tension,surface viscosities,and the variationof surface tension with surface concentration),intermolecular forces(London-van der Waals forcesand electrostatic double layer forces),adsorption and surface diffusion coefficients,bubble size andfilm thickness.An estimation for the critical thickness at which a film rupture is carried out and thecoalescence time is obtained by integration to the critical thickness,The coalescence time is predictedas a function of bulk and surface properties,London-van der forces,adsorption and surfacediffusion coefficients,and bubble size.     

反渗透过程的浓度极化及其传质系数测定

The relationship between osmotic pressure difference across the membrane and mass transfer coefficient is developed in this paper. On the basis of this relationship, a method for measuring mass transfer coefficient by using experimental data on reverse osmosis is established. Pitzer's equations are used to calculate osmotic pressure differences in order to assure accuracy of results. Under the conditions of constant operating pressure and bulk flow, mass transfer coefficient is scarcely affected by membrane structure, but decreases slightly with increasing feed concentration. The solute concentration in the polarization layer is calculated by using the measured values of mass transfer coefficient. Polarization layer concentration increases with augmentation in bulk concentration. However, their difference increases with increasing bulk concentration until a maximum difference is reached, and then decreases. Mass transfer coefficient increases with higher velocity of bulk flow. If mass transfer coefficient is so large that the ratio(PwΔπσ/k)becomes very small, polarization could be neglected.     

ON THE ROLE OF CONCENTRATION LEVEL OF NONDIFFUSING SPECIES IN GAS PHASE MASS TRANSFER AT HIGH TRANSFER RATES

Re-evaluation of high mass flux literature data from evaporation and absorption experiments suggest the validity of y_BM as a good correlation variable for predicting gas phase mass transfer at high transfer rates. This was done by testing Greiner and Winter's engineering model where y_BM explicitly emerges after manipulating their model equations. The manipulated model agrees well with the literature data within the range of 0.961 ≥y_BM ≥ a 0.549 and 7.3333 ≥ B ≥ -0.4757 which covers the mostly commonly chemical engineering conditions and geometries. Thus, the y_BM serves not only as a good correlation variable as has been commonly used under low to moderate mass transfer rales, but also applies to the controversial case of high mass transfer rates.     

电渗析浓缩回收硫酸钠溶液的实验研究

本文介绍了采用离子交换膜电渗析法对硫酸钠溶液进行浓缩回收的试验研究,结果表明,采用该法浓缩回收硫酸钠溶液是理想的新型处理方法。     

THE EFFECT OF THERMAL RADIATION ON THE HEAT AND MASS TRANSFER FLOW OF A VARIABLE VISCOSITY FLUID PAST A VERTICAL POROUS PLATE PERMEATED BY A TRANSVERSE MAGNETIC FIELD

The effect of temperature-dependent viscosity on free convective flow past a vertical porous plate is studied in the presence of a magnetic field, thermal radiation, and a first-order homogeneous chemical reaction. Boundary layer equations are derived and the resulting approximate nonlinear ordinary differential equations are solved numerically by the shooting method. A parametric study of all parameters involved is conducted, and a representative set of numerical results for the velocity and temperature profiles as well as the skin-friction parameter and the Nusselt and Sherwood numbers is illustrated graphically to show typical trends of the solutions. The dynamic viscosity in this study is taken as a function of the temperature although the Prandtl number is considered constant.     

超滤法浓缩纯化透明质酸钠

本文报道了采用丙烯腈三元共聚物中空纤维超滤膜浓缩纯化透明质酸钠。结果表明，经超滤浓缩纯化制得的透明质酸钠产品外观及理化指标均好，回收率高。丙烯腈三元共聚物中空纤维膜对透明质酸钠溶液有良好的抗污染性能，料液的透明速率稳定在３０Ｌ／ｍ＾２．ｈ左右，采用生理盐水正反冲洗结合方法可以使膜的性能基本恢复。     

加碱曝气-A／O组合工艺处理高浓度医药中间体废水

医药中间体三甲氧基笨甲醛(TMBA)废水色度大,有机物含量高达20 000mg·L-1以上,可生化性差.针对上述特点,采用了加碱曝气法有效地增加了废水的可生化性,BOD/COD由原来的0.24增加到0.35,采用了厌氧-好氧组合工艺处理,最终出水COD小于100mg·L-1,出水基本无色,达到工业水污染排放一级标准.     

INFLUENCE OF SOLUTE TEMPERATURE AND CONCENTRATION ON THE COMBINED OSMOTIC AND AIR DRYING

The effect of solute concentration (15-45 % sugars) and temperature (10-40 °C) on the osmotic dehydration of apple was investigated. Cylindrical samples of apple were immersed in glucose or sucrose solutions and the water loss, the volume of solids and the porosity were measured as a function of time. Water loss was proportional to the square root of time, while the volume of solids decreased and the porosity increased with time. Sugar gain and water loss decreased the compression stress of the apple samples. Osmotic pre-treatment reduced the shrinkage and the porosity of apple solids during air-drying, compared to the no-treated samples. The results of this investigation are useful in the design of efficient osmotic dehydration processes, and in the evaluation of texture of dehydration of products.     

INFLUENCE OF SOLUTE TEMPERATURE AND CONCENTRATION ON THE COMBINED OSMOTIC AND AIR DRYING

ABSTRACT

The effect of solute concentration (15–45 % sugars) and temperature (10–40 °C) on the osmotic dehydration of apple was investigated. Cylindrical samples of apple were immersed in glucose or sucrose solutions and the water loss, the volume of solids and the porosity were measured as a function of time. Water loss was proportional to the square root of time, while the volume of solids decreased and the porosity increased with time. Sugar gain and water loss decreased the compression stress of the apple samples. Osmotic pre-treatment reduced the shrinkage and the porosity of apple solids during air-drying, compared to the no-treated samples. The results of this investigation are useful in the design of efficient osmotic dehydration processes, and in the evaluation of texture of dehydration of products.     

QUALITATIVE OBSERVATIONS OF HEAT AND MASS TRANSFER EFFECTS ON THE BEHAVIOUR OF A TRICKLE BED REACTOR

This paper examines the effect of simultaneous heat and mass transfer on the hydrogenation of cyclohexene in a trickle bed reactor with particular attention given to the problem of liquid phase evaporation and transition to the gas-phase regime of operation. The reaction rates are obtained as a function of temperature and hydrogen flow rate; the concentration of the substrate in the feed displays considerable hysteresis due to an abrupt increase of the reaction rate arising from temperature gradients within the bed and in the gas film surrounding the catalyst pellet, during the transition from the liquid to the gas-phase regime. The transition is accompanied by the change of apparent kinetics of the model reaction as well as by a change of regime and operation of the pellet. In the liquid phase a pellet originally showing inter-phase and intra-particle diffusion resistances changes into the gas-phase regime with a large resistance due to inter-phase diffusion.     

表流-潜流人工湿地处理北方城市景观水体研究

根据北方地区城市景观水体的特点以西安某景观湖为例,进行了表流-潜流组合的人工湿地水处理试验。结果表明,表流区对COD、藻类和SS有很好的去除效果,减少了潜流区基质堵塞的几率,再经过潜流区COD、藻类、SS去除率分别达到80%以上;TN、TP、NH3-N主要在潜流区去除,平均去除率分别为63.7%、65.8%、79.7%。表流-潜流组合的人工湿地适合于北方地区城市景观水体的处理,为该地区构建人工湿地提供了理论依据和设计参照。