Electrochemical treatment of water containing chlorides under non-ideal flow conditions with BDD anodes

In this work a undivided parallel plate cell equipped with boron doped diamond (BDD) anode was tested as electrochemical reactor for disinfection of water. Two configurations were adopted: a single pass configuration (SPC) and a recirculated configuration (RC) in which also a reservoir was inserted in the hydraulic circuit. In both the experimental configurations the system worked in continuous mode with a flow rate ranging from 0.05 to 0.42 dm³ min⁻¹; in the RC the recirculating flow rate ranged from 0.45 to 6 dm³ min⁻¹. Thermostated (25 °C) galvanostatic electrolyses were carried out with aqueous solutions containing 100 mg dm⁻³ of chloride ions: values of current density from 2.5 to 5.0 mA cm⁻² were used. Steady state data revealed that active chlorine and chlorate ions were the main oxidation products. Particular attention was paid to the hydrodynamics both for SPC and RC: pulse-response curves were experimentally obtained with an inert tracer, and the behaviour of the system was interpreted by models based on a combination of ideal flow reactors, bypass flow elements, and dead zones. The hydrodynamic models were utilized to predict the outlet concentration of the electrolysis products. A good agreement between model predicted and experimental data was obtained for a wide range of experimental conditions. Preliminary disinfection tests were then performed using Escherichia coli as model microorganism. Results were discussed in terms of both disinfection efficiency and by-products formation.     

Atomic force microscopy analysis of nanoparticles in non-ideal conditions

Nanoparticles are often measured using atomic force microscopy or other scanning probe microscopy methods. For isolated nanoparticles on flat substrates, this is a relatively easy task. However, in real situations, we often need to analyze nanoparticles on rough substrates or nanoparticles that are not isolated. In this article, we present a simple model for realistic simulations of nanoparticle deposition and we employ this model for modeling nanoparticles on rough substrates. Different modeling conditions (coverage, relaxation after deposition) and convolution with different tip shapes are used to obtain a wide spectrum of virtual AFM nanoparticle images similar to those known from practice. Statistical parameters of nanoparticles are then analyzed using different data processing algorithms in order to show their systematic errors and to estimate uncertainties for atomic force microscopy analysis of nanoparticles under non-ideal conditions. It is shown that the elimination of user influence on the data processing algorithm is a key step for obtaining accurate results while analyzing nanoparticles measured in non-ideal conditions.     

Convective diffusion of particles deposition under electrostatics from turbulently-mixed conditions

A theoretical model is presented to describe inertialess particle deposition onto smooth surfaces under the influence of electrostatic force. Both Boltzmann and combined diffusion and field charging mechanisms are investigated. A modified Fick's law equation accounting for Brownian and turbulent diffusion, spatially-independent external force, i.e. gravitational and Coulombic force, is presented based on the simplified three-layer model. The results show that the concentration boundary layer thickness is very thin and the previous three-layer model can be further simplified. The Coulombic force influences the particle deposition significantly and for considerably high charge and electric field, deposition is independent on turbulent intensity. The model predictions agree very well with the literature DNS results.     

Study of ash deposition during coal combustion under oxyfuel conditions

This paper presents a comparative study on ash deposition of two selected coals, Russian coal and lignite, under oxyfuel (O₂/CO₂) and air combustion conditions. The comparison is based on experimental results and subsequent evaluation of the data and observed trends. Deposited as well as remaining filter ash (fine ash) samples were subjected to XRD and ICP analyses in order to study the chemical composition and mineral transformations undergone in the ash under the combustion conditions. The experimental results show higher deposition propensities under oxyfuel conditions; the possible reasons for this are investigated by analyzing the parameters affecting the ash deposition phenomena. Particle size seems to be larger for the Russian coal oxy-fired ash, leading to increased impaction on the deposition surfaces. The chemical and mineralogical compositions do not seem to differ significantly between air and oxyfuel conditions.The differences in the physical properties of the flue gas between air combustion and oxyfuel combustion, e.g. density, viscosity, molar heat capacity, lead to changes in the flow field (velocities, particle trajectory and temperature) that together with the ash particle size shift seem to play a role in the observed ash deposition phenomena.     

Particle monolayers formed under irreversible conditions: jamming coverages and structure

The random sequential adsorption (RSA) approach was used for modelling irreversible adsorption phenomena of polyatomic particles at homogeneous interfaces. Particles of spherical and spheroidal shape, characterised by various axis ratio parameter A, were considered. In the latter case, the flat (side-on) and unoriented adsorption was discussed. The sticking probability (available surface function) was determined for various particle shapes together with “jamming” coverages for clean and precovered surfaces. The structure of adsorbed particle monolayers (under transient and jammed states) was analysed quantitatively in terms of the pair correlation functions. Methods of extrapolation of these results to interacting (soft) particle systems were also discussed. The theoretical predictions were confronted with existing experimental results derived for monodisperse spherical particles. A good agreement with theory was found both in respect of jamming coverages and the monolayer structure. These theoretical and experimental studies demonstrated that minor amounts of small particles (nanometer size range) exert decisive influence on adsorption of larger particles. This phenomenon can be treated as analogous to the surface poisoning effect occurring in heterogeneous catalytic systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fundamental ash deposition characteristics in pulverized coal reaction under high temperature conditions

Three types of coal with the different melting temperature and ash content were burned under the condition of high-temperature air pulverized coal reaction. A water-cooled tube was inserted into the furnace to make the ash adhere. Particle size and composition distributions of ash particles in both reacting coal particles and depositing layer were analyzed, using a Computer Controlled Scanning Electron Microscope, to study the deposition behaviors of ash particles. As a result, quantity of the ash deposition on the tube surface increases with a decrease of the melting temperature of coal ash. Index of fraction of the ash deposition depended on the coal type. For structure of the deposit layer, fine particles of size less than 3 μm mainly consisted of the initial layer for three types of coal, and the thickness was about 30 μm. Deposition of fine particulates of about 3 μm became a trigger of initial deposition at the stagnation point of tube even if irrespective of coal type is burned. The chemical compositions of ash particles in the reacting particles differed from those in the initial deposition layer. The deposition phenomenon relates to the particle size distribution of ash formed, the flow dynamics surrounding the probe, the chemical compositions in each ash particle and so forth.     

A study of electrochemical kinetics of copper deposition under pulsed current conditions

The investigation is concerned with the drop of current efficiency (CE) of copper deposition under pulsed current conditions. A mathematical model which is based on different charge transfer rates between the following two reactions, (1) $$Cu^{2 + } + e \to Cu^ + $$ and (2) $$Cu^ + + e \to Cu$$ has been formulated to describe the behaviour of a Cu/CuSO₄ system under pulsed current conditions on a rotating disc electrode. The results indicate that the CE drops continuously as the difference between the exchange current densities of the two reactions increases. The exchange current densities of Reactions 1 and 2 were estimated to be 0.034 mA cm^?2 and 0.024 mA cm^?2, respectively. Prediction of CE using the mathematical model agreed to within 3.5% with experimental data over a range 80.4–93.7%.     

Particle size separation by alternating electrophoretic deposition

This paper describes a study of the size distribution of the particles deposited under different frequencies by alternating electrophoretic deposition. A low concentration suspension of SnO₂ particles was prepared in acetone and particles of SnO₂ were deposited on electrodes by the low frequency alternating electrophoretic deposition method. Scanning electron microscopy (SEM) showed that increasing the frequency from 0 to 1000 Hz reduces the average size of the SnO₂ particles deposited. Particle size distributions obtained from the SEM images show the sizing capability of the alternating electrophoretic deposition method.     

Particle slip velocities in air jets under atmospheric pressure and soft vacuum conditions

Laser Doppler anemometry (LDA) is used for the measurement of gas and particle velocities in an air jet under atmospheric pressure and soft vacuum conditions. The slip velocity between the particles and the carrier gas at the exit of a particle injection probe is shown to depend on the geometry of the probe tip. With a standard probe tip, the particle velocity lagged behind the gas velocity at the exit of the probe. The addition of a section with a sudden expansion at the downstream end of the probe, results in the rapid drop of the gas velocity at the exit of the probe without a corresponding drop of the particle velocity. The results show that the proposed probe tip configuration can be effectively used to achieve a positive particle slip condition at the exit of the probe, with the particle velocity equal to or higher than that of the carrier gas.     

Influence of voltammetric parameters on Zn–Ni alloy deposition under potentiodynamic conditions

The phase composition of Zn–Ni alloys electrodeposited from acetate-chloride plating solutions containing Zn⁺² and Ni⁺² ions at ratio of 1–12.8 at 50 °C was investigated by the potentiodynamic stripping method. Two anodic current density (i _a) peaks emerged in potentiodynamic stripping curves (PDC) at E < 0.0 V and E > 0.0 V (vs. Ag/AgCl/KCl_sat), that were attributed to oxidation of certain phases of the Zn–Ni alloy. The ratio of these phases in deposited Zn–Ni alloys under potentiodynamic conditions was affected by the potential sweep rate (ν) and maximum cathodic current density (i _c) The ratio of Zn and Ni in certain phases of Zn–Ni alloy was determined by the partial potentiodynamic stripping technique. Experimental data show that Zn–Ni alloy, containing 6.5 at.% Zn and 93.5 at.% Ni and dissolved in i _a peak H (E > 0.0 V), provides the black coloration of the Zn–Ni alloy.     

Particle deposition in the guinea pig respiratory tract

Equations relating particle size of aerosols to deposition by impaction, diffusion and sedimentation are applied to a previously established model of the guinea pig lung using a tidal volume of 4.44 cm³ and a respiratory rate of 60 breath min⁻¹. These calculated deposition values are combined with measured values of nasal deposition to give an estimate of the particle deposition characteristics of the guinea pig respiratory tract. The nasopharyngeal-tracheobronchial (NP-TB) region removes 99% of unit density spherical particle 10 μm or more in diameter. Deposition in this region reaches a minimum of 10% at a particle diameter of 0.8 μm. For particles less than 0.8 μm, deposition increases because of diffusion. Deposition in the pulmonary region is about 17% for particle diameters from 0.08 to 4 μm. For typical polydisperse aerosols with mass median diameters above 1 μm, a greater fraction of the mass than of the count is deposited in the NP-TB region, while a smaller fraction of the mass than of the count is deposited in the pulmonary region. Aerosol clouds with mass median diameters less than 0.1 μm deposit a greater fraction of the count than of the mass in the NP-TB region and a smaller fraction of the count than of the mass in the pulmonary region.     

Particle deposition in the wake of charged spheres

Earlier work in this laboratory, wherein aerosols were collected from gas streams moving around charged water droplets, indicated the likelihood of high rates of deposition on the aft side of the droplet where flow conditions are not adequately represented by potential flow theory. Further tests were made with metal spheres and the aerosol deposition pattern observed with scanning electron microscopy. Results from these test confirm that the developed wake has a definite influence on the collection pattern as well as the overall collection efficiency. Generally, minima were observed aft of the separation point at an angle at which the vortices flow tangentially to the sphere. Maxima appeared forward of the separation and advanced toward the forward stagnation point as the Reynolds number increased and overall collection efficiency declined. At higher levels of field intensity the deposition profile appeared flat as one scanned around the sphere, with a peak at the rear stagnation point. Very little information is available concerning deposition in the wake of moving droplets. This seems particularly important for scrubbers and spray towers where particles are collected by droplets moving at high Reynolds numbers where wakes and eddies are quite common.     

Effect of polyethylene pipe on wax deposition under different temperature and flow rate conditions

Wax deposition is an important but troublesome boulder in petroleum industry that has always plagued pipeline engineering operators. In this study, wax deposition in the polyethylene pipes has different behaviors comparing wax deposition in stainless steel pipes such as smaller weight of wax deposits and lower wax content. After wax deposition experiments, some important parameters, including diffusivity and temperature gradient, were measured and calculated to explore the differences between two material pipes. Moreover, those factors can make a significant impact on radial mass flux. A series of results in polyethylene pipes suggests that higher diffusivity enhances diffusion flux of wax in the radial direction. But it was found that radial concentration gradient accounted for a larger proportion. These factors are the relationship of competition and cooperation and the combination of them results in different performances of wax deposition between polyethylene and stainless steel pipes.     

Particle emission from gasoline powered vehicles: Emission, deposition and re-emission under different traffic density situations

Particle emission, re-emission and deposition from a gasoline fueled car were investigated during driving conditions in streets. The measurement facility was carried on a trailer behind the testcar. Filter collection and sedimentation samplers were used for particle collection. Measurements were performed in different environmental and meteorological situations.

Particle emission was also measured in laboratory conditions at temperatures of + 20 and − 20°C using gasoline and diesel engines.

The elemental composition of the particle samples was analyzed by the PIXE-method and the composition data by a statistical cluster-method. The results for re-emission and condensation growth of aerosols were compared with theoretical calculations.

The re-emission fraction in summer conditions was obtained to be over 70% in high traffic densities and about 50% in low densities. The condensation growth was about four times higher in the cold air than in the warm weather.     

Particle formation and growth in ab initio emulsifier-free emulsion polymerisation under monomer-starved conditions

Particle formation and growth in the monomer-starved emulsifier-free emulsion polymerisation of monomers with different water solubility including methyl acrylate (MA), methyl methacrylate (MMA), and vinyl acetate (VA) were studied. The rate of formation of precursor particles, via homogenous nucleation, is proportional to the monomer concentration in the water phase. One may think that the maximum number of particles will be obtained when the water phase is saturated with the monomer. The number of PMA particles showed a maximum when the water phase was starved with the monomer. The number of PVA particles did not show any sensitivity to the monomer concentration in the water phase. More unexpectedly the final number of PMMA particles showed a minimum when the water phase was just saturated with the monomer. The minimum in the final number of PMMA particles was correlated with the enhanced rate of particle growth due to the gel effect. Under monomer-starved conditions, the number of particles produced was in the order of water solubility of the monomers; MA > VA > MMA. A reverse order was produced under monomer-saturated conditions as particle coagulation became progressively more important for some of the monomers.     

析湿工况下翅片管式换热器表面粉尘沉积过程的数值模型

空调器采用翅片管式换热器作为蒸发器,在制冷工况下换热器表面发生析湿及粉尘沉积,导致性能衰减。建立湿翅片表面粉尘颗粒物沉积过程的数学模型,模拟冷凝水捕集颗粒物以及湿积灰层黏附颗粒物的过程。被冷凝水捕集的颗粒物数量等于运动轨迹与水表面轮廓会出现相交的入射颗粒物的数量;后续的入射颗粒物与湿积灰层碰撞时,部分入射颗粒物会发生沉积且部分被碰撞的已沉积湿颗粒物会发生移除,这两部分的颗粒物数量相减即为被湿积灰层黏附的颗粒物数量。模拟与实验结果的对比表明,预测的湿积灰层形状与实验照片的吻合度较好,预测的单位面积颗粒物沉积质量与91%的实验数据之间的误差在±20%之间,平均误差为11.8%。