Performances of a catalytic foam trap for soot abatement

A catalytic trap for soot particles was prepared by deposition of Cu–V–K–Cl catalyst on a ceramic foam. Catalytic trap performances were evaluated by treating the exhaust of a gas oil burner under different operating conditions. The results obtained showed that ceramic foam is a particularly suitable support for this application since it yields low gas pressure drop, good soot collection efficiency (“deep bed” filtration mechanism), high thermal shock resistance and good contact throughout the filter between soot particles and catalyst surface. In addition, the catalytic foam trap is able to spontaneously regenerate at operating conditions comparable to those typical of diesel engine exhaust and after more than 70 test hours it retains its activity towards soot oxidation.     

GAS MICROEMBOLI—DETECTION, QUANTITATION AND ELIMINATION

The need for removing gas microemboli (GE) from The returned blood during extracorporeal circulation is well recognized. One of the methods used to safeguard against the perfusion of GE is the employment of arterial line filters. These devices separate and eliminate solid as well as GE from the extracorporeal blood stream. The major difficulty in any determination of the number or size of GE, is that bubbles may coalesce or divide and may even dissolve or be released from the blood. Thus to study filter “efficiency” comparison of bubble “counts” upstream and downstream of the filter is not meaningful; more pertinent is the proportion of gas volume that passes the filter. This paper reviews factors involved in the design of effective arterial filters for the elimination of gas microemboli, identifies possible areas of improvement, and presents evaluation methods and laboratory data obtained with several filters currently in use.     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d_s and γ^d_l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d_s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^-2 K^-1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d_s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d_s and d(γ^d_s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

THE KINETIC MODEL OF ONE-COMPONENT GAS FLOW DURING EVAPORATION IN A POROUS LAYER

A new approach is developed for mass transfer by making use of the statistical model of a porous body based on the methods of the kinetic theory of gases. The collision integral in the one-dimensional kinetic equation is replaced by the effective “external” force, which is the result of the collective interaction of gas molecules with the motionless particles. Evaporation from a recessed boundary and gas filtration in a porous layer are considered. Simple expressions are obtained for the permeability coefficient and pressure jump (output resistance) at the gas-porous medium boundary as a function of the Kn number. Theoretical and experimental results are compared.     

Drying of Porous Material During the Constant and the Falling Rate Period: A Critical Review of Existing Hypotheses

During drying of porous material a so-called “falling rate” period is observed, where the drying rate decreases as the moisture content decreases. This behavior is usually described by the well known “shrinking core model.” This model, however, contradicts experimental findings and violates basic laws of multiphase mass transfer in porous media as well. A new model, named “wet surface model,” is suggested which eliminates those discrepancies.     

EFFECT OF SPRAY MIXING ON TRAY EFFICIENCY I. One Dimensional Mixing

The usual models for predicting the effect of liquid mixing assume a diffusion model as is reasonable for the foam and froth regimes. Here a one-dimensional spray regime model is developed with finite spray “throw,” allowing for inlet and outlet conditions and the effect of spray mixing on tray efficiency is evaluated. The extension to less restricted models is indicated.     

MODELING OF STRONGLY EXOTHERMIC REACTION ON A SUPERCOMPUTER

In this work, we review the status of numerical methods used for solution of partial differential equations, describing heat and mass transfer and a strong exothermic reaction, using vector computers. A discussion of relevant aspects of simulation such as generating adaptive meshes and integrating stiff differential equations is included. The goal of the paper is to illustrate attractive ways of modeling combustion problems on a supercomputer. Four examples, “solid-solid” combustion, “gas-gas” combustion, exothermic reaction with gas filtration and free convection with exothermic reaction, are presented.     

ADAPTIVE ACTUAL PID CONTROL WITH AN ADJUSTABLE IDENTIFICATION INTERVAL

A method of design for an adaptive PID controller in an “actual” form is developed. The controller is expressed as an ideal PID controller with a low-pass filter. The parameters of the controller are determined by using the ITAE criterion based on a first-order plus dead time model which is directly obtained from an identified second-order model. In comparison with the ideal PID controller, the actual one gives better results especially for systems with noises.     

Study of Catalytic Filters for Soot Particulate Removal from Exhaust Gases

Two ceramic supports (sintered and foam) were employed for the preparation of catalytic filters for soot removal at diesel exhausts. Laboratory tests showed that while the foam filter is appropriate for small size and low engine backpressure, the sintered filter is more suitable for achieving high filtration efficiency. Tests carried out at the exhaust of a diesel engine showed that the catalytic filter can be continuously regenerated at operating conditions typical of diesel exhaust.     

Analogies with optical bistability in ferroelectrics

Mathematical analogies are developed between the formalism used to describe regenerative pulsations accompanying optical bistability in ferroelectrics and that used to parametrize the transition from steady flow to laminar vortex generation in viscous fluids. An “effective Reynolds number” and an “effective specific viscosity” are both defined for the optical bistability model. The characteristic length in the problem is defined in a way similar to that in Abrikosov's theory of Type II superconductors.     

A CRITICAL EVALUATION OF THREE EQUATIONS OF STATE FOR DENSE GASES AGAINST OBSERVED DATA

The van der Waals, the Benedict-Webb-Rubin, and a virial equation of state predictions for dense gases are evaluated against observed “integral” properties (p, ρ, T) and “slope” properties like the speed of sound [(∂p/∂p)^1/2₃], isothermal compressibility coefficient [(∂ In ρ /∂p)_T], and few other thermodynamic properties directly derived from the observed data. The documented procedure thus constitutes a stringent test methodology to evaluate the applicability of these equations of state to dense gases which may also be followed for appraising any other equation of state. The graphical comparisons between the predictions and the observed data are presented and discussed critically     

Analysis of Moisture Content and Density of Pears During Drying

Solar dried pears of the “S. Bartolomeu” variety are a very much appreciated and preferred dried food product in Portugal. Nevertheless, the traditional solar drying is carried out at open air during the months of 07 and 08, and this nowadays is a disadvantage for larger productions. This work is to evaluate the possibility of producing dried pears from this and other varieties, maintaining the characteristics of the traditional dried pears. In this study four different types of pears were studied, including “S. Bartolomeu” as a basis for comparison and the drying method employed was the traditional one. From the results it was concluded that, although the behaviour of the four varieties do not vary significantly, one particular variety (“D. Joaquina”) is a good alternative to the “S. Bartolomeu” pear.     

Assessment of surface and depth filters by filter quality

This paper reviews the concept of filter quality (q_F) for dust filtration media composed of different structures: metal fiber beds (MFB), fabric filters (BF), and fly ash filters (FAF). Filter quality is a useful index of the filtration performance, which incorporates both pressure drop and filtration efficiency. Major parameters affecting the filter quality are filtration velocity in the range of 0.06-0.19 m/s, dust loading, porosity of the medium in the range of 75-93%, and internal structure of the medium. The experimental observation showed that filter quality decreased with increasing filtration velocity or dust concentration. A unique increase in filter quality during the initial stage of filtration appeared with the FAF as a result of the predominately surface filtration with less pore clogging. Nevertheless, the filter quality cannot be taken as an absolute indicator of filter performance, but rather it should be used just as a reference parameter depending on operating conditions. The results of this work show that fly ash filters are capable of providing more stable performance, particularly during the initial stage of filtration, and thereafter of a certain time filter quality initiates to decline as other filters.     

Automatic instrument for aerosol samples using the beta-particle attenuation

This work describes an intrument developed for the routine measurement of aerosol mass using the β-particle attenuation method. The design of the present instrument is particularly well suited for the automatic mass measurement of membrane filters used for airborne particulate collected. The instrument uses electromechanical devices for the automatic positioning of filters into the sampling and measuring holders and the coming back to their stand by locations, where the filters are stored for off-line testing purposes and documentation. The instrument is designed with very low system “dead time” and high sensitivity.     

Zur frage der Abscheidung von Aerosolteilchen durch Diffundierende Gase

A simple model for the diffusiophoresis in the lung was tested. It consists essentially of two channels, which have been divided by a membrane filter. In both channels aerosol was flowing with a different carrying gas. Gas exchange through the membrane filter occurred and caused different deposition rates on each side of the filter. For equimolar counterdiffusion the deposition on the side of the heavier gas predominated. For model experiments with a “respiratory quotient” of 0·85 (volume-ratio of exhaled CO₂ to inhaled O₂) more particles have been deposited on the side of the lighter gas, but the deposition rate was much lower than in the case of equimolar counterdiffusion. The experimental results are supported by theoretical calculations. The effect of diffusiophoresis is small compared to other deposition mechanisms in the lung.     

COMPREHENSIVE STUDY OF THE GAS HOLD UP AND BUBBLE SIZE DISTRIBUTION IN HIGHLY VISCOUS LIQUIDS I. GLYCEROL SOLUTIONS

The overall gas hold up, E_G, and bubble size distribution were separated into the particular gas hold up, E_GK, and Sauter diameter. d_SG. due to “small bubbles” as well as E_GG and d_SG, due to “intermediate to large bubbles.” Bubbles are defined to be “small” if they remain in the bubbling layer 15 seconds after the gas flow is turned off. The bubbles which leave the layer during this time are considered to be “intermediate to large bubbles.” The time dependences of E_G E_GK and E_GG, as well as of bubble size distribution after initiating the aeration of the liquid, is investigated. The steady state E_G, E_GK and E_GG, Sauter diameter and specific geometrical surface area of “small” and “intermediate to large” bubbles as well as of the entire bubble population were determined in bubble columns employing 50, 70, 90 and 95% glycerol solutions and perforated plates with different hole diameters (d_H = 0.5. 1.0 and 3.0 mm) respectively. In highly viscous media the “small” and “very large” bubble fractions are high. A comparison of the specific geometrical bubble surface areas with the corresponding volumetric mass transfer coefficients, k_La's, measured earlier indicate that the “small” bubbles do not contribute to k_La. The influence of the “small” bubbles on the fluiddynamics of the two phase system is discussed.     

Chemical composition and bond structure of aerosol particles of amorphous hydrogenated silicon forming from thermal decomposition of silane

Aerosol particles of amorphous hydrogenated silicon resulting from thermal decomposition of silane were investigated by hydrogen evolution, IR-, EPR-, NMR spectroscopy, and transmission electron microscopy.

The experimental data show that aerosol particles contain to a various extent {SiH₂}_n polymer structures and two types of monohydride groups SiH- “clustered” and “dilute” monohydride groups. The hydrogen atoms of the “clustered” monohydride groups are located close to each other. The “clustered” monohydride groups are inaccessible to the ambient because they are embedded in the amorphous network. The “dilute” monohydride groups are relatively isolated from each other. The majority of “dilute” monohydride groups are open to the ambient. They are located on the surface of preferentially interconnected microchannels and microvoids.

Interaction between the “dilute” SiH groups and atmospheric oxygen results in formation of OSiH groups in which hydrogen and oxygen are bonded to a common silicon atom. Evidently, the interaction occurs throw the oxygen reaction with weak bonds associated with “dilute” monohydride groups. There is no interaction between oxygen and both “clustered” SiH groups and {SiH₂}_n chain because the former are inaccessible to atmospheric oxygen and the latter has presumably no weak bonds in the chains.     

Predicting Thermal Efficiency in Timber Radio Frequency Vacuum Drying

In this work, the efficiency of transforming dielectric energy into evaporated water is analyzed for the case of timber radio frequency vacuum drying. Based on well-known heat and mass transfer equations, a simplified mathematical model is proposed that estimates the drying efficacy in regards to the thermo-physical properties of wood. Although not exact, the theoretical results are close to the experimental observations and elucidate some phenomena like the tendency of the timber to dry from inside to outside, and the drying rate increase with the rise of the timber gas permeability. The theoretical efficiency model also predicts a range of wood permeability values for which the drying efficiency changes from 100 to 0%, thus providing a quantitative scale for classifying the spectrum of “difficult-to-dry” all the way to “easy-to-dry” wood species when using radio frequency vacuum technology.     

Adhesion Mechanisms at Amine-Cured Epoxy/Aluminium Interfaces

Because the structure and the chemical composition of the interface can have a large effect on the adhesion properties of polymeric materials to metallic surfaces, many investigations have concentrated on the study of the interphase region. However, the complexity of the materials often leads to the use of model compounds to mimic the interfacial reaction. We have presented a critical discussion of three different approaches which have been used to understand the adhesion mechanism at amine-cured epoxy/aluminium interfaces: i) fracture of “real world” joints; ii) deposition of model (amino-alcohol) molecules on “real world” substrates; i) deposition of model (amino-alcohol) molecules on clean, oxidised and hydroxylated Al (100) surfaces. We have shown that model compounds can adequately duplicate the interface chemistry observed in “real world” joints. However, a detailed understanding of the exact nature of the interactions and of the role of the different reactive sites can only be achieved through studies performed on a model surface under controlled ultrahigh vacuum conditions.     

Synthesis, Characterization and Catalytic Applications of Organized Mesoporous Aluminas

The synthesis of organized mesoporous aluminas has opened a very interesting area for application of this type of materials, particularly as catalysts or catalyst supports. This review focuses on the individual synthesis routes to produce organized mesoporous aluminas with large surface areas and narrow pore size distributions, and on the evaluation of their textural, chemical and thermal properties and outlines examples of catalytic applications of organized mesoporous alumina-based catalysts. We tried to rationalize the synthetic approaches to prepare organized mesoporous aluminas, to relate their properties to synthetic procedures used as well as to their catalytic behavior in different reactions. Utilization of various structure-directing agents for “cationic,” “neutral,” “anionic,” “nanocasting,” and special approaches leading to scaffolding and lathlike organized mesoporous aluminas is discussed in the first part of this review, as well as textural and structural characterization and thermal stability of mesoporous aluminas synthesized by different synthetic approaches. In the second part, catalytic applications of organized mesoporous aluminas described in the open literature are evaluated from the standpoint of the importance of these reactions for technological applications.