Method to Characterize the Air Flow and Water Removal Characteristics During Vacuum Dewatering. Part II—Analysis and Characterization

This is part II of a study reported earlier on a method to characterize the air flow and water removal characteristics during vacuum dewatering. This article presents experimental data and analysis of results from the use of a cyclically actuated vacuum dewatering device for removing moisture from wetted porous materials such as paper with the intermittent application of vacuum and accompanying air flow though the material. Results presented include sheet moisture content as a function of residence time and hence water removal rate under a variety of process conditions. Also, experimental results on air flow through the wet porous structure and hence the role and importance of air flow during vacuum dewatering are presented. Vacuum dewatering process conditions include exit solids content between 11 and 20% solid under applied vacuum conditions of 13.5 to 67.7 kPa (4 to 20 in. Hg). Regression analysis indicated that the exit sheet moisture content exhibited a nonlinear relationship with residence time with exit solids reaching a plateau after a certain residence time. Final moisture content correlated linearly with the average overall flow rate of air through the paper sample and the basis weight of the material.     

Sillimanite,Kyanite and Andalusite in China and Their Applications Part I .Their Reserve,Distribution and Characteristics

Sillimanite,kyanite and andalusite are advantageous natural refractory raw materials for aluminosilicate refactories to attain improved key properties.This paper are divided into parts to introduce their resource and technical characteristic in the first part,and their applications in refractories in the second aprt to be succeeded.In this part,based on authors‘ knowledge and sources,information on their reserve,distribution,composition and characteristic is provided,to bring it to light that China is rich in the reserve of them,in particular andalusite.The sillimanite group minerals are characterized by their phase transformation to form primary mullite and secondary mullite when added in high alumina system,accompanied by volume expansion,which can be taken use to improve creep resistances and thermal shock resistance of the related refractories.     

The mechanism of mass transfer during formation,release and coalescence of drops. Part I—Mass transfer to drops formed at a moderate speed

A study of the rate of mass transfer to drops growing at a moderate speed has been made. The system used was that of isobutanol drops in a continuous water phase.A model for the behaviour of the different parts of a drop during formation and release has been proposed. On this basis a comparison has been made between the growing of a drop by stretching of the surface or by addition of fresh surface elements. The influence of a restdrop, remaining at the capillary after drop release has been taken into account. The surface and volume of the drops during formation have been determined photographically.The drops could be formed so that the time of formation was independent of the frequency of the drop formation. In the experiments the final drop volume has been kept constant.The experimental results showed that during drop formation fresh surface elements are formed. The equation for the case investigated appeared to be

     

Applicability of Vacuum Impregnation to Modify Physico-Chemical,Sensory and Nutritive Characteristics of Plant Origin Products—A Review

Vacuum impregnation is a non-destructive method of introducing a solution with a specific composition to the porous matrices of fruit and vegetables. Mass transfer in this process is a result of mechanically induced differences in pressure. Vacuum impregnation makes it possible to fill large volumes of intercellular spaces in tissues of fruit and vegetables, thus modifying physico-chemical properties and sensory attributes of products. This method may be used, e.g., to reduce pH and water activity of the product, change its thermal properties, improve texture, color, taste and aroma. Additionally, bioactive compounds may be introduced together with impregnating solutions, thus improving health-promoting properties of the product or facilitating production of functional food.     

Reconstruction of Grenfell Tower fire. Part 3—Numerical simulation of the Grenfell Tower disaster: Contribution to the understanding of the fire propagation and behaviour during the vertical fire spread

The dramatic event of the Grenfell Tower (June 2017), involving a combustible façade system, has raised concerns regarding the fire risk that these systems address. Indeed, as façades are complex systems, it is not straightforward to assess which part of the system is involved in the global fire behaviour. Understanding such façade fires is thus very complex as it depends on a combination of various products and system characteristics, including window frames or air gap or cavity barriers. Fire development inside the initial apartment was investigated using an appropriate CFD model with different scenarios for the fire source and ventilation conditions in a previous study. Fire propagation through the window to the external façade and to higher apartments was modelled and validated against visual observations. This paper describes CFD modelling of the complete Grenfell tower facade, and investigates vertical fire spread behaviour over the full height façade from the initial apartment. Contributions from the combustion of all the apartments' furniture, depending on window failure, and architectural details of the refurbished façade are considered in the numerical model. The modelling results are validated by comparison with photographic and video observations of the real fire.     

Passivation of zinc in concentrated alkaline solution—I. Characteristics of active dissolution prior to passivation

As a preliminary stage in the study of the active—passive transition on zinc in concentrated (6.8 mol dm⁻³ solutions of KOH the reported mechanisms have been reviewed and the characteristics of active dissolution prior to passivation have been investigated. The theory of Armstrong and Bulman has been extended in order to relate all the experimentally important parameters. These include electrode potential, current, angular electrode rotation speed and surface concentrations of Zn(OH)²⁻₄ and OH⁻ ions. In common with other observations, it is demonstrated that zinc dissolves quasi-reversibly over a considerable range of potentials. The relationship of this behaviour to other metal/metal-ion systems is discussed. At high current densities (> 100 mA cm⁻²) depletion of hydroxide ions occurs at the zinc surface causing a severe deviation in the exponential dependence of the active dissolution current on potential.     

Stability of rare earth oxides in a moist environment at high temperatures—Experimental and thermodynamic studies. Part I: The way to assess thermodynamic parameters from volatilisation rates

A methodology based on a weight loss measurement was used to quantify the volatility of yttria in high temperature water vapor. This method was first assessed on silica. Sintered materials with a shape of pellets were exposed at temperatures between 1000 and 1400 °C in air with 50 kPa of water at atmospheric pressure, under a flowing gas velocity of 5 cm s^?1. Besides the volatilisation rate, the nature of the volatile gaseous species was determined using a kinetic study. Knowing the nature of flows in the furnace, partial pressures of yttrium (oxy-)hydroxide in equilibrium over Y₂O₃ were calculated, and used to assess the enthalpies of formation of YO(OH) and Y(OH)₃.     

Absolute Mass and Size Measurement of Monodisperse Particles Using a Modified Millikan's Method: Part I—Theoretical Framework of the Electro-Gravitational Aerosol Balance

A new method for accurate mass and size measurement of monodisperse particles is proposed. In this method, charged aerosol particles are introduced into parallel plate electrodes similar to the Millikan cell, and the number of particles left suspended after a certainty holding time has elapsed is measured. The particle survival rate as a function of the voltage applied to the electrodes is used to determine the particle mass. The particle size is deduced by using the particle density which is determined in a separate experiment. The expression of the particle survival function, which is defined as the survival rate as a function of the mass, for particles with and without Brownian diffusion is derived. The sensitivity of this method to the number average diameter, as well as other size distribution parameters, is analyzed on the basis of the survival function.     

Dynamic responses to perturbations in the non-isothermal CSTR: Times to ignition and times for temperature decay—I. Adiabatic operation

When a simple exothermic reaction is carried out in an open system, discontinuous jumps between stationary states (ignitions and extinctions) may occur in response to continuous variation of control parameters such as inflow-temperature or average residence-time. This paper examines the dynamics of such jumps for reaction in a CSTR operating adiabatically. Two problems are analysed: (a) the dependence of time-to-ignition on the degree of supercriticality and (b) the decay of small perturbations to the steady state for marginally sub-critical conditions (“critical slowing down”).It is shown that both the time-to-ignition (and time-to-extinction) and the decay to a stationary state obey universal formulae characteristic of the category of instability, increasing rapidly as criticality is approached: time-to-ignition ∝ (degree of supercriticality) ^-1/2We illustrate our results chiefly by reference to a single, first-order, deceleratory reaction. We at first exploit the exponential approximation to the Arrhenius temperature law but the treatment is quite general and can cope with any temperature-dependence of reaction-rate.     

Liquid phase formation in the system AlN–Al2O3–Y2O3. Part I: Experimental investigations

The liquid phase formation in the system AlN–Al₂O₃–Y₂O₃ was investigated via differential thermal analysis (DTA) combined with thermogravimetry (TG). For this purpose 17 samples covering a broad composition area of the quasi-ternary system were densified and heat-treated to achieve the equilibrium state. Melting temperatures were determined by DTA. SEM, EDX and XRD were used to study the phase assemblages and microstructures formed. The results were compared with thermodynamic calculations.     

Fully Automated Three-Dimensional Column-Switching SPE–FIA–HPLC System for the Characterization of Lipids by a Single Injection: Part I. Instrumental Design and Chemometric Approach to Assess the Effect of Experimental Settings on the Response of ELSD

This article presents the first application of fully automated three‐dimensional (3D) column‐switching SPE–FIA–HPLC system for the characterization of lipids by a single injection. The whole system was designed and set up by modifying Agilent 1200 Series HPLC system in our laboratory. By using this system, a complete separation profile of the oil samples was achieved in a very short time period by using single injections. This approach was applied on vegetable oils which contains a large number of relatively high‐class lipid components, such as TG, FFA, sterols, tocopherols, DG, ester and MG. In this part of the study, we focused on the optimization of evaporative light scattering detector (ELSD) by using an experimental design and RSM. Three experimental parameters were chosen as an independent variables which are the flow rate of mobile phase, nebulization temperature and evaporation temperature. A multivariate five level experimental design was used to establish a quadratic model as a functional relationship between the response values and independent variables. The optimal values of parameters were found to be a flow rate of 1.25 mL min^?1, nebulization temperature of 80 °C, and evaporation temperature of 40 °C. Regression analysis with an R² values indicated as a satisfactory correlation between the experimental and predicted values. ANOVA test results were also illustrate that the models can be successfully used to predict the optimum parameters of ELSD. Thus, the proposed system is suitable for a large number of applications including research and development of new quality control and characterization methods for vegetable oils.     

The cobalt hydroxide electrode—I. Structure and phase transitions of the hydroxides

X-ray powder photography, electron microscopy and powder conductivity measurements have been employed to characterize cathodically deposited cobaltous hydroxide, and the compounds formed from it by anodic and chemical oxidation in alkaline solution.     

Reconstruction of the Grenfell Tower fire – Part 4: Contribution to the understanding of fire propagation and behaviour during horizontal fire spread

The tragic events at Grenfell Tower in 2017, involving a combustible façade system, have raised concerns regarding the fire risk that these systems pose. In this series of articles, so far published, fire development inside the initial apartment has been investigated using an appropriate computational fluid dynamics (CFD) model. Several scenarios including different fire sources and ventilation conditions were addressed. Fire propagation through the window to the external façade and to higher apartments was modelled. This model was validated by comparing the numerical results with the visual observations reported in the Grenfell Inquiry. A CFD model of the complete east face of the Grenfell Tower was then created. This paper details CFD modelling of the complete Grenfell Tower façade during the late horizontal phase of fire spread. As the physics of lateral flame spread is different from that for upward flame spread, it is important to assess the validity of the model, thus far developed, for this configuration. Fire propagation over the whole façade is modelled and compared with observations from the real disaster. This provides a better understanding of its fire behaviour and of the contribution of architectural details and their impact on fire spread.     

Mechanism of anodic dissolution of iron-chromium alloys investigated by electrode impedances—I. Experimental results and reaction model

Stainless steels are characterized by their ability to passivate spontaneously in a corrosive medium. This ability is dependent on many factors, among them the kinetics of the anodic process has a particular importance. In fact, the addition of chromium to iron decreases drastically the critical current density, that is the current maximum during the alloy dissolution, making the passivation process easier to set up.Steady-state polarization curves and electrode impedances measured on FeCr alloys of various chromium contents show how the chromium addition modifies the kinetics of iron dissolution.On the basis of experimental results a reaction model for the dissolution-passivation process of iron—chromium alloy in acidified sulfate media is proposed. The reaction mechanism of alloy is depicted as that of iron perturbed by the chromium addition.     

Unipolar Field and Diffusion Charging in the Transition Regime—Part I: A 2-D Limiting-Sphere Model

This work examines the unipolar charging of aerosol particles smaller than 100 nm by ions (at STP) both theoretically (Part I) and experimentally (Part II).

Among numerous well-known models for particle charging by ions a gap has been identified for the case of diffusion charging with superimposed external electric field in the transition regime. A two dimensional extension of the classical Fuchs-model Fuchs, 1963 Fuchs, N. A. 1963. On the Stationary Charge Distribution on Aerosol Particles in a Bipolar Ionic Atmosphere. Geofisica Pura e Applicata, 56: 185–193. [Crossref] , [Google Scholar]) has been developed in order to bridge this gap in the knowledge. For the first time the complete expression for the electrostatic potential between a particle and an ion has been included.

By using FEM-simulations, the quantitative influence of an external electric field on the charging process has been predicted. It is shown that an external electric field increases the average particle charge linearly. Compared to pure diffusion charging, an electric field of 10 kV/cm increases the charge on metallic particles up to 28% (30 nm particles), 55% (60 nm), and 95% (100 nm), respectively.

When compared to the Fuchs-model, the assumptions of the new model introduce additional uncertainty of less than 3%. Comparison with the simpler, but physically less reasonable continuum model by Lawless (1996) Lawless, P. A. 1996. Particle Charging Bounds, Symmetry Relations and an Analytic Rate Model for the Continuum Regime. J. Aerosol Sci., 27: 191–215. [Crossref] , [Google Scholar] shows similar charge predictions (deviations < 20% for n·t-products 10¹³ s/m³), even for 30 nm particles. So, that continuum charging model can serve as simple approximation of the more accurate charging model for the transition regime.