Numerical Characterization of Particle Beam Collimation: Part II Integrated Aerodynamic-Lens–Nozzle System

As a sequel to our previous effort on the modeling of particle motion through a single lens or nozzle, flows of gas–particle suspensions through an integrated aerodynamic-lens–nozzle inlet have been investigated numerically. It is found that the inlet transmission efficiency (η_t) is unity for particles of intermediate diameters (D_p ～ 30–500 nm). The transmission efficiency gradually diminishes to ～40% for large particles (D_p > 2500 nm) because of impact losses on the surface of the first lens. There is a catastrophic reduction of η_t to almost zero for very small particles (D_p ≤ 15 nm) because these particles faithfully follow the final gas expansion. We found that, for very small particles, particle transmission is mainly controlled by nozzle geometry and operating conditions. A lower upstream pressure or a small inlet can be used to improve transmission of very small particles, but at the expense of sampling rate, or vice versa. Brownian motion exacerbates the catastrophic reduction in η_t for small particles; we found that the overall particle transmission efficiency can be roughly calculated as the product of the aerodynamic and the purely Brownian efficiencies. For particles of intermediate diameters, Brownian motion is irrelevant, and the modeling results show that the transmission efficiency is mainly controlled by the lenses. Results for an isolated lens or nozzle are used to provide guidance for the design of alternative inlets. Several examples are given, in which it is shown that one can configure the inlet to preferentially sample large particles (with η_t > 50% for D_p = 50–2000 nm) or ultrafine particles (with η_t > 50% for D_p = 20–1000 nm). Some of the results have been compared with experimental data, and reasonable agreement has been demonstrated.     

Analytical models of adhesively bonded joints—Part II: Comparative study

The literature survey presented in Part I describes the major analytical models for adhesively bonded joints, especially for single lap joints. By consulting the summary table given in Part I, the designer can choose from a wide range of models which is the best for a particular situation. However, the information given in the summary table is not sufficient for a proper selection. The designer also needs to know the time required for setting up an analysis and solving it. Another important factor is the accuracy of strength prediction. Therefore, models of increasing complexity were selected from the summary table and a comparative study was made in terms of time requirements and failure prediction for various cases. Three main situations were considered: elastic adherends and adhesive, elastic adherends with nonlinear adhesive, and nonlinear analyses for both adherends and adhesive. The adherends were both isotropic (metals) and anisotropic (composites). The effects of the overlap length and the adhesive thickness were also considered.     

Structural Basis for Intumescence—Part II: Synthesis and Characterization of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

Taking the spirophosphorus compound 3,9-dichloro-2,4,8,10-tetraoxo-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide as one of the reactive monomers, a family of aromatic spirophosphates was synthesized using dihydric phenols, viz., resorcinol, hydroquinone, 4,4′–dihydroxydiphenyl, bisphenol-A and fluorene dicarbinol as the other monomers. The polymers were synthesized employing melt condensation technique under vacuum and characterized using FT-IR, ¹H-, ¹³C- and ³¹P-NMR spectroscopic methods. The number average molecular weight of the polymers was determined using vapour phase osmometry. Thermal properties of the polymers were studied using differential scanning calorimetry and thermogravimetry techniques. These studies indicated that the polymers containing spirophosphato moiety undergo eruptive degradations in the temperature region 310°–380°C leading to the formation of dense carbonaceous foam. The present study confirmed the spirophosphate structure as an essential requirement to show intumescence.     

From laboratory experiments to simulation studies of methanol dehydration to produce dimethyl ether reaction—Part II: Simulation and cost estimation

The vapor phase dimethyl ether (DME) synthesis is simulated by Hysys process simulation software and relevant cost analysis is also conducted. Based on cost estimation results, it is found that capital investment of the classic DME process is greatly influenced by the distillation towers and operating costs. Accordingly, to solve these problems an innovative DME process based on a top-wall dividing-wall column (DWC) in vapor phase is proposed, in this work. It is shown that the novel proposed DWC process leads to 44.53% reduction in operating costs compared to the conventional one, while both schemes predict almost the same output specifications.     

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.     

Use of the Weibull model on sizing thickeners—Part II: Methods of thickener sizing

Among several methods employed for sizing thickeners available in the literature, the Kynch, Biscaia Jr., Talmadge and Fitch, Roberts, Coe and Clevenger, and Oltmann methods use experimental data from sedimentation curves and graphical approaches. By using the Weibull distribution, it is possible to represent sedimentation curves with algebraic equations, which does not require the use of graphical approaches and provides more accuracy and speed for sizing calculations. In the present work, the main objective is the development of a set of equations for sizing continuous thickeners, for six conventional methods found in the literature, using the Weibull model. A comparative analysis of calculated and literature diameters for each graphical method presented variations between 0.73% and 8.93%. The use of the Weibull model presented the best accuracy for the Biscaia Jr. method, with a 0.73% average absolute error.     

Clarification of suspensions: a study of particle deposition in granular media: Part II—A theory of clarification

The observations in Part I [1] on particle deposition have been incorporated into theoretical equations to describe pressure drop and concentration over the complete clarification run—i.e. from the initial transient to the final steady state. The equations differ from those of previous workers in having no arbitrary constants or empirical correlations—all parameters have a precise physical significance and the pressure drop is derived directly from the Kozeny equation. Experiments were performed on a model bed, a packed bed and a sintered disc filter. In all three cases, deviation from the theoretical curves was about 5 per cent maximum in those runs in which parameter values were measured directly, and about 15 per cent maximum when these parameters were estimated completely independently of the run.     

Chloride-induced corrosion of steel in cracked concrete—Part II: Corrosion rate prediction models

Chloride-induced corrosion rate (i_corr) prediction models for RC structures in the marine tidal zone that incorporate the influence of crack width (w_cr), cover (c) and concrete quality are proposed. Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in the tidal zone. Experimental variables were w_cr (0, incipient crack, 0.4, 0.7 mm), c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). The two proposed models (one each for accelerated and natural i_corr) can aid not only in quantifying the propagation phase, but also provide a novel way to select c, w_cr and concrete quality.     

Addition of thianthrene cation radical to non-conjugated dienes—Part I: Addition to one double bond

Reaction of thianthrene cation radical tetrafluoroborate and hexafluorophosphate with an excess of 1,4-hexadiene, 1,5-hexadiene, 1,7-octadiene, 1,8-nonadiene and 1,9-decadiene gave, in each case, a mixture of bis- and monoadduct from addition to one of the diene’s double bonds. Addition to both double bonds did not occur. The monoadduct of each diene and the bisadduct (7a) of 1,5-hexadiene were isolated. All monoadducts and 7a were characterized with ¹H and ¹³C NMR spectroscopy. By reaction on activated alumina adducts were converted into (E)- and (Z)-(5-thianthreniumyl)dienes, all of which were characterized with ¹H and ¹³C NMR spectroscopy. The monoadduct (6a) of 1,4-hexadiene and the bisadduct 7a were characterized with X-ray crystallography.     

Fouling Control in a Submerged Flat Sheet Membrane System: Part II—Two‐Phase Flow Characterization and CFD Simulations

Abstract

Gas‐liquid two‐phase flow has been shown to be very effective in reducing fouling for different membrane modules with different feeds, including submerged flat sheet membranes used in membrane bioreactors for treatment of wastewater. Although gas‐liquid two‐phase flow occurring on the lumen side of tubular or hollow‐fiber membranes has been very well characterized the two‐phase flow regime in submerged membrane processes is different to that inside external membranes. Characterization of two‐phase flow in submerged flat sheet membrane modules has not been previously reported and hence the use of two‐phase flow in these modules has not yet been optimized. This paper reports on characterization of two‐phase flow for a submerged flat sheet membrane module with the aim of identifying the most effective flow profiles for fouling minimization. In order to better understand the fouling control process by two‐phase flow, CFD simulations were also conducted. It was found experimentally that an increase in the bubble size leads to an increase in the cleaning effect, however, for bubbles larger than the channel gap between the submerged flat sheet membranes, any further increase in the bubble diameter had only a minor effect on the cleaning process. CFD simulations revealed that flux enhancement was primarily due to an increase in the overall shear stress on the membrane and to more turbulence generated by introduction of the gas phase.     

Slag-fly ash and slag-metakaolin binders: Part II—Properties of precursors and NMR study of poorly ordered phases

Sodium silicate-activated slag-fly ash binders (SFB) and slag-metakaolin binders (SMKB) are room-temperature hardening binders that have excellent mechanical properties and a significantly lower carbon footprint than ordinary Portland cement (OPC). The aim of this study was to use nuclear magnetic resonance (NMR) spectroscopy to study the nanostructure of poorly ordered phases in SFB by varying slag/fly ash ratio, curing time, and curing temperature. Fly ash was completely substituted with metakaolin and the effect of this substitution on the poorly ordered phases was studied. It was observed that the proportion of geopolymer was generally higher in SMKB when compared to SFB. Although C–N–A–S–H and geopolymer coexisted in SFB and SMKB, C–N–A–S–H was the major product phase formed. The mean chain length (MCL) and the structure of C–N–A–S–H gel were estimated as a function of time, temperature, and slag/fly ash ratio. The MCL was found to have a negative correlation with slag/fly ash ratio and Ca/(Si+Al) ratio, but positive correlation with curing temperature. The average Si/Al atom ratios for geopolymers were also estimated. Lastly, the increased proportion of five-coordinated aluminum (Al(V)) in metakaolin resulted in the decreased unreacted metakaolin in the hardened binder but did not increase the geopolymer content.     

Application of differential sensitivity analysis to nonlinear mixed boundary value problems—II. Computational results and convergence studies

The well-known consecutive reaction system A → B → C is chosen for a digital computer study of the optimization of a recycle reactor. The associated nonlinear mixed boundary value problem is solved by a weighted gradient-cum-Newton—Raphson iteration which uses differential sensitivity measures developed in Part I. The effectiveness of the method is borne out by a comparative numerical study of the quasilinearization scheme applied to the same problem. The global convergence properties of the algorithm are established by means of a convergence theorem, which also proves that the rate of approach to the optimum is superlinear.Das wohlbekannte Folgereaktionssystem A → B → C wurde gewählt für eine Digital Computer Studie der Optimisierung eines Rücklaufreaktors. Das damit verbundene Problem des nichtlinearen gemischten Grenzwertes wird mittels bewerterem Gradienten und Newton— Raphsonscher Iteration unter Verwendung der im 1. Teil entwickelten Differentialsensitivitätsanalyse gelöst. Eine vergleichende numerische Studie des Quasilinearisierungsschemas, auf das gleiche Problem angewendet, bewies die Wirksamkeit der Methode. Die globalen Konvergenziegenschaften des Algorithmus werden mit Hilfe eines Konvergenztheorems festgestellt, das ebenfalls beweist, dass die Annäherungsrate an das Optimum superlinear ist.     

Qualitative analysis of the behaviour of nonlinear parabolic equations—II: Application of the methods for the estimation of domains of multiplicity

The application of linearizatio, orthogonal collocation and difference method is discussed for various reaction engineering problems. Following cases are considered: (a) heat transfer and exothermic chemical reaction of zero order (b) mass transfer in a porous catalyst accompanied by chemical reaction with Langmuir—Hinshelwood reaction rate expression (c) heat and mass transfer in a porous catalyst for (α) slab and sphere in a non-uniform external field (β) reaction with a volume-change (d) heat and mass transfer in recycle-reactor.     

Influence of slag chemistry on the hydration of alkali-activated blast-furnace slag — Part II: Effect of Al2O3

The hydration and microstructural evolution of three alkali activated slags (AAS) with Al₂O₃ contents between 7 and 17% wt.% have been investigated. The slags were hydrated in the presence of two different alkaline activators, NaOH and Na₂SiO₃·5H₂O. The formation of C(A)–S–H and hydrotalcite was observed in all samples by X-ray diffraction, thermal analysis and scanning electron microscopy. Higher Al₂O₃ content of the slag decreased the Mg/Al ratio of hydrotalcite, increased the Al incorporation in the C(A)-S-H and led to the formation of strätlingite. Increasing Al₂O₃ content of the slag slowed down the early hydration and a lower compressive strength during the first days was observed. At 28 days and longer, no significant effects of slag Al₂O₃ content on the degree of hydration, the volume of the hydrates, the coarse porosity or on the compressive strengths were observed.     

Removal of Trace Cd2+ Using Continuous Multistage Ion Foam Fractionation: Part II—The Effects of Operational Parameters

A multistage ion foam fractionation column with bubble-cap trays was employed to study the removal of cadmium ions from simulated wastewater having low Cd concentrations (10–30 mg/L), examining the effects of foam height, air flow rate, feed flow rate, and feed Cd concentration. Sodium dodecyl sulfate (SDS) was used to generate foam in this study. An increase in foam height, which reduces liquid hold-up in the generated foam, resulted in the enhancement of the enrichment ratios of both SDS and Cd while the removal and residual factor of Cd showed insignificant change. An increase in air flow rate increased the foam generation rate, foamate volumetric ratio, and the removal efficiency of Cd but decreased the enrichment ratios of both Cd and SDS. The separation factors of both Cd and SDS decreased with increasing feed flow rate, which is mainly attributable to both the effects of the enhancement of foamate volumetric ratio and the increases in both SDS and Cd input rates. An increase in feed Cd concentration was found to increase Cd effluent concentration and SDS removal but to decrease the enrichment ratios of both Cd and SDS because of the increasing liquid entrainment in the produced foam.     

From laboratory experiments to simulation studies of methanol dehydration to produce dimethyl ether—Part I: Reaction kinetic study

Most of the reaction rate equations for methanol dehydration are derived from the experiments conducted for crude methanol as feed and laboratory prepared catalysts, which are not exactly the same as industrial reactors conditions. In the present contribution, it is attempted to find suitable rate of reactions for pure methanol with no water as feed and commercial catalysts of HZSM-5 and γ-alumina at industrial conditions in methanol dehydration process. In addition, a comparison between the performances of the catalysts is performed. It is found that HZSM-5 has superior performances compared to the γ-alumina in terms of conversion. Modeling results are also indicated that the proposed rate of reaction predicts the behavior of the process, properly.     

Simbad: a process simulator linked to a DBMS—II. the structure of memory

A network type Data Base Management System is used to support the data structure of a modular-sequential, steady state process simulator. The DBMS of a standard CODASYL type is based on the definition of records and the set relationships between an owner and a member record. The structure defined, or SCHEMA, responds to the way data is stored and used during the simultations in order to minimize access time, while maintaining flexibility. An example is developed to illustrate the way data is linked for a particular process application.     

The effect of powder characteristics on washcoat quality. Part II: Zirconia,titania washcoats — multilayered structures

Novel automotive catalyst designs based on the use of washcoat systems such as yttria-stabilized zirconia (YSZ) and titania, in combination with the traditionally used γ-alumina have been recently proposed. For the development of an integrated, robust multi-layered system, good adhesion of the inner layer on the support as well as among the various layers has to be ensured. In the present work, the adhesion of zirconia and titania washcoats on cordierite honeycombs was investigated. Irrespective of the nature of the powder used, reduction of the agglomerates’ size down to the order of few (2–5) microns is necessary in order to ensure firm adhesion of the washcoat to the support, comparable to that of commercial catalysts. In the deposition of multi-layered structures, particle size compatibility of the powders of the various washcoat layers can enhance the adhesion among them and induce better coherence of the overall washcoat.