Pore network simulation of fluid imbibition into paper during coating—III: modelling of the two-phase flow

Extensive computer simulations have been carried out to model imbibition of a coating fluid into a paper. The microstructure of the paper's pore space is represented by a network of interconnected channels or pore throats that are formed between the paper's fibers. The geometrical characteristics of the channels, such as their effective radius and length, as well as their connectivity, are selected from the experimental data presented in Part II of this series. The imbibition process that we simulate is the result of forcing the coating fluid into the pore space by applying a time-dependent flow-driven pressure distribution to the external surface of the paper, or is driven only by capillary forces. The dynamic pressure distribution is representative of a high-speed coating process. The simulations indicate that the connectivity of the pore throats, the anisotropic structure of the paper's pore space, and the dynamic pressure distribution all have a strong influence on imbibition of a coating fluid into a paper's pore space and, hence, on the quality of the coating.     

A simulation model to approximate penetration of a non-Newtonian fluid into a porous media during slot die coating

A computational fluid dynamics (CFD) model has been developed to predict the penetration depth of a non-Newtonian fluid as it is directly coated onto porous media by a slot die coating process. The model couples 1-D modified Blake–Kozeny equations and Navier–Stokes equations. Experiments of coating a non-Newtonian solution (black strap molasses) onto carbon paper (Toray 090) are conducted and the penetration depths are measured to validate the model. Preliminary results show that predicted and measured penetration depths follow the same trend; that is, as the coating speed increases the penetration depth decreases. However, the simulated penetration depths are found to be one to two times higher than measured values at low coating speeds. Even so, the results are considered reasonable, due to imposed simplifications and approximations of the CFD model and errors associated with the experiments and measurements.     

Interaction of droplets with porous structures: Pore network simulation of wetting and drying

In fluidized bed spray agglomeration, the time evolution of a liquid droplet deposited on a porous particle is of paramount importance for the success of the process. The combination of droplet penetration into the pores and evaporation, either directly from the droplet surface or from the surrounding wet pores, determines how long free liquid remains on the particle surface so that other particles can bind via liquid bridges. In this work, a two-dimensional pore network model that combines the algorithms of liquid migration and drying is developed to track the full droplet evolution, from its deposition on network surface to complete evaporation of the liquid. The influence of the pore structure for mono-modal and bi-modal networks with different spatial correlation of the pore size on the evolution of the liquid droplet is investigated. The effect of the liquid viscosity on the evolution of the droplet in the pore network is studied. Moreover, pore network simulations with multiple depositions of liquid droplets on the same network are presented as a rough approximation of spray agglomeration process.     

Investigating liquid-fronts during spontaneous imbibition of liquids in industrial wicks. Part II: Validation by DNS

To validate the experimental results of Part-1, we conducted a two-phase flow simulation of imbibition of a wetting liquid through 2D microstructures made of ellipses of varying aspect ratios. The flow simulation in the particulate microstructures, characterized by low (ellipse) aspect ratio, produced somewhat even micro-fronts, thus replicating the sharp fronts at the visual (macroscopic) scale observed in Part-1. Whereas simulations in the fibrous microstructures produced highly uneven micro-fronts, suggesting the formation of semi-sharp or diffuse visual fronts. Increasing the porosity from 50% to 70% resulted in solid-phase clustering and led to further increase in the unevenness of micro-fronts, pointing to purely diffuse visual fronts. The evolution of the saturation plots along the flow direction, obtained from area-averaging of fluid-distribution plots, pointed to diffusing of sharp fronts with time. The predictions matched our previous experimental and numerical observations, that is, the particulate media create sharp fronts while the fibrous media create semi-sharp/diffuse fronts.     

Pore network model of deactivation of immobilized glucose isomerase in packed-bed reactors II: three-dimensional simulation at the particle level

Immobilized glucose isomerase is widely used for converting glucose to fructose by enzymatic isomerization. The process takes place in a packed-bed reactor consisting of mesoporous particles with distributed pore sizes and interconnectivities. Its efficiency is, however, significantly affected by deactivation of the mesoporous particles. In this paper, we study deactivation of the mesoporous particles using a three-dimensional pore network model of the pore space with distributed pore sizes and interconnectivities, and investigate several plausible mechanisms of deactivation of the porous particles. The results of the present study, which will be used as the input for simulation of the phenomenon at the reactor level, demonstrates the strong effect of the particles’ morphology on the deactivation process.     

Characterization of the permeability of a high performance composite coating to cathodic protection and its implications on pipeline integrity

In this work, the permeability of a high performance composite coating (HPCC) and its component layers, fusion bonded epoxy (FBE) and medium-density polyethylene (MDPE), to cathodic protection (CP) was investigated by various electrochemical measurements. Results demonstrate that the permeability of the coatings to water is ranked as FBE > MDPE > HPCC. Compared to FBE, MDPE, as a highly non-polar coating, plays a key role in protecting the HPCC from the water permeation. HPCC is impermeable to CP, and shows a pure capacitive behavior, with ultra-high low-frequency impedance at the order of 10¹⁰ Ω cm² during the test period. Both FBE and MDPE coatings are permeable to CP, which will make up the degradation of the coatings due to the water-uptaking. Therefore, under an appropriate CP application, the two coatings are capable of maintaining the pipeline integrity. HPCC provides an excellent alternative to maintain the pipeline integrity in the soil environment.     

Iron oxide-impregnated filter paper (Pi test): II. A review of its application

The iron oxide impregnated filter paper test (P_i test) is a recently developed soil test for phosphorus (P) in which the FeO paper acts as an infinite sink for P mobilized in a soil solution. Several papers have been published evaluating the effectiveness of the test for predicting plant availability of P under different soil conditions. The use of FeO paper to predict algal availability of P in water bodies and runoffs has also been studied.The purpose of this paper is to review studies on the use of the P_i test to evaluate plant availability of P in soils, and predict availability of P to algae in an aquatic environment. Phosphorus extracted by the FeO paper is primarily physically bound extractable (resin P) and correlates significantly with Bray I and Mehlich P in acid soils and Olsen P in calcareous soils. Dry-matter yield and P uptake by maize (Zea mays L), kidney beans (Phaseolus vulgaris L), and upland rice (Oryza sativa L) grown in acidic soils correlated well with P_i-P. Likewise, in calcareous soils, P_i-P was as good as Olsen-P in predicting crop response. Field trials have shown that the P_i test is a good predictor of plant yield in soils with wide ranging properties. Compared to the standard method to measure bioavailable P to algae in waters and agricultural runoffs involving lengthy algal essays culturing selenastrum capricornutum with sediment samples, the P_i method is a faster and easier method to estimate P that may be potentially available for uptake by algae.     

Development of polymer blend morphology during compounding in a twin-screw extruder. Part II: Theoretical derivations

In Part II of the work, the intermeshing twin-screw extruder is briefly described and the theoretical procedures used to model its operation are summarized. Based on the microrheological considerations discussed in Part I, a predictive procedure of the morphology evolution during compounding of two immiscible polymers is proposed. In this first generation model, only the shear flow effects are considered. Furthermore, to avoid complications due to coalescence a low concentration of the dispersed phase was assumed. In the procedure, two drop breakup mechanisms are discussed. The first assumes that the drops do not break under flow while the second postulates that breakup occurs under flow. Two dispersion mechanisms are considered, the first postulating continuously increasing polydispersity of drop size and the second postulating that drop polydispersity is inversely proportional to deformation strain. The influence of the screw configuration and operating conditions on blend morphology evolution is studied. It is expected that the computed drop size distribution provides limiting values for the experimental data. Dependency of predicted morphology on operating conditions is also investigated. Increasing screw rotating speed (resulting in increasing energy consumption) and decreasing throughput (resulting in decreasing productivity) lead to prediction of finer drop size. In practice, therefore, a compromise would be required. The proposed procedure is limited to melt flow (excluding the die region) within the region of large capillary parameter values, k > 4k_crit.     

Raney nickel activated H2-cathodes Part II: Correlation of morphology and effective catalytic activity of Raney-nickel coated cathodes

Raney nickel activated hydrogen-cathodes obtained by caustic leaching of cathodically deposited Ni/Zn precursor alloy coatings on nickel substrates were investigated with respect to their effective catalytic activity. Important factors influencing this activity are the surface specific amount of the inner surface of the Raney nickel coatings and, in particular, the tertiary structure of the catalyst coating. Coarse pores and cracks are developed during leaching of the Ni/Zn precursor which, due to unsteady deposition conditions, show a layered structure. These cracks are essential for a high catalytic activity, since micropores of Raney nickel coatings are utilized to pore depths of no more than 10 m. The generation of layered structures of the coatings with changing zinc content, which is experienced by Ni/Zn codeposition from acidic solutions, is influenced by a number of process parameters. The most important parameter is the cathode potential which may fluctuate strongly during cathodic deposition of the Ni/Zn precursor coatings due to minute temperature and/or pH changes.     

Self-ignition and combustion of a water-fuel emulsion during its injection into heated air. II. Ignition delay time of M-40 fuel oil

We studied experimentally the influence of the degree of water emulsification ofM-40 mazut heated to the water boiling point on the self-ignition time with its pulsed high-pressure injection into heated air. It is shown that water addition does not change the chemistry of the reaction and heating the water-fuel emulsion leads to the disappearance of differences in the ignition character of the emulsion and the moisture-free fuel. It is confirmed that the features of selfignition are determined mostly by conditions of mixture formation. Indirect evidence is obtained that the dynamic tensile strength of the fluid strongly influences the primary dispersion of the jet during its outflow from the sprayer nozzle.Institute of Theoretical and Applied Mechanics, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 20–25, July–August, 1995.     

Reaction injection molding of polyureas. II: Rheo-kinetic changes and model simulation

An experimental and theoretical study of reaction injection molding (RIM) of polyurea was conducted in this work. A lab-scale RIM machine was used to carry out the polyurea bulk polymerizations. A “free-table” viscometer was designed to measure the fast rheological changes and liquid-solid transition. A mathematical model was proposed to simulate the fast reaction and rheological changes in the polyurea RIM process. The parameters of this model were determined based on the solution polymerization data from FTIR and Haake rheometer measurements. Combined with an appropriate heat transfer equation, this model predicts fairly well the adiabatic temperature and viscosity rises of bulk polyurea reactions in RIM.     

Characterization of fluoroelastomer networks: II. SEC,FTIR, and ODR analysis

The role of an accelerator in the nucleophilic cure of fluorocarbon compounds was further examined by preparing materials without a crosslinker. Under the previously used curing conditions, ODR reveals the formation of a secondary, accelerator-induced network that is unstable at slightly higher temperature, i.e., ≥190°C. Increased crosslink density and color are observed with the cure time, indicating slow curing reactions and likely formation of conjugated unsaturation. SEC of selective solvent-soluble fractions derived from specimens obtained from the key cure stages shows initially a falling refractive-index response. However, this change is followed by a shift in MWDs toward lower average molecular weights. On the other hand, infrared examination shows a continuous increase in the 1718 cm⁻¹ absorption, but no major presence for the 1680 cm⁻¹ absorption seen in the previous study in the presence of a crosslinker. The concurrent increase in the 3114 cm⁻¹ peak confirms the presence of a  CFCH double bond. The solvent-soluble portions and bulk specimens have very similar infrared features. © 1996 John Wiley & Sons, Inc.     

Characterization of the nonvolatile compounds formed during the thermal oxidation of 1-linoleyl-2,3-distearin: II. The acidic fraction

Four compounds were isolated from the acidic fraction of 1-linoleyl-2,3-distearin which was heated at 200 C for 24 hr with aeration. Following saponification of the oxidation mixture, the fatty acids were partitioned between ethanol and pentane-hexane (Skellysolve F). The ethanol soluble acids were subsequently esterified with methanol and subjected to further separation by preparative thin layer and gas liquid chromatography. A combination of chemical and instrumental analyses as well as a comparison with standard compounds was used to determine the structures. Substances characterized were isomeric C₁₈ aromatic esters, isomeric methyl keto-octadecanoates, isomeric methyl keto-octadecenoates and dimethyl undecane-1,11-dioate. This work represents a portion of a thesis presented by L. R. Wantland as partial fulfillment of the requirements for the Ph.D. degree at the University of Illinois.     

Continuous emulsion polymerization of vinyl acetate. Part: II Parameter estimation and simulation studies

Conversion data obtained over a wide range of operation of a continuous latex reactor for vinyl acetate polymerization were used to estimate the unknown kinetic parameters of a transient CSTR reactor model. Conversion-time histories were adequately fitted by models of two levels of sophistication: a comprehensive model which solves for the age distribution function of polymer particles, and a simplified model that neglects the effect of particle size distribution for the case of continuous particle nucleation. These models were then used for simulation and control studies in an attempt to devise a practical control strategy⁽¹¹⁾. The existence of sustained oscillations was investigated by examining the behavior of the state variables in the phase-plane.     

Microthrowing power of electrolytes for the deposition of nickel-iron alloys. II. Levelling effect of iron in nickel-iron electrolytes and its microdistribution in the alloy coating

Investigations were aimed at demonstrating and clarifying the levelling effect of the iron component in a saccharin-containing nickel-iron alloy plating electrolyte. The results provide evidence that levelling probably follows the adsorbtion-diffusion mechanism proposed by Kardos and Foulke, as well as by Edwards and Watson. Microprobe analysis shows that the microdistribution of iron in the alloy deposit is not uniform, its content being higher in the alloy plated on the micropeaks of the cathode profile. A quantitative evaluation of the non-uniform distribution of iron is proposed and a linear empirical relationship has been established between this calculated value and levelling determined by profilometric measurements.     

Isomerization during hydrogenation of soap: II. Potassium elaidate and potassium linoleate

Potassium elaidate in slightly alkaline solution was hydrogenated for up to 7 hr with 1.5% of Rufert nickel catalyst at 150 C and 20 kg/sq cm pressure. Potassium linoleate was similarly hydrogenated with 1.0% catalyst for 7 hr, and the hydrogenation continued for another 7 hr after addition of 0.5% fresh catalyst. Periodic samples from each were analyzed for component acids. The positional isomers in thecis andtrans monoenes, isolated by preparative argentation thin layer (TLC) or column chromatography, were estimated after oxidation to dicarboxylic acids. Some diene fractions were isolated for further examination. In potassium elaidate hydrogenation,cis monoenes were initially produced in considerable amounts, but to a lesser extent thereafter. Positional isomers were similarly distributed in bothcis andtrans monoenes after prolonged hydrogenation. In the hydrogenation of potassium linoleate, a drop in iodine value (IV) of 60 units occurred in the first hour, and 38% oftrans monoenes (in which the 10- and 11-monoenes constitute 32% each) were formed. The IV then fell only slowly, and up to 38% ofcis monoene (mostly 9- and 12-isomers) was formed. Addition of fresh catalyst caused a major shift ofcis monoenes totrans forms. The diene fraction was mostly nonconjugated material with the first double bond at the 9, 8 and 10-positions. Minor amounts of conjugated dienes were present as well as a dimeric product.     

PtSiO2: II. Characterization of the gel and the platinum particles by X-Ray diffraction

Modern techniques for analysis of X-ray diffraction profiles have been applied to several of the platinum-silica gel catalysts described in Part I to determine average platinum crystallite size, percentage exposed, crystallite shape, size distribution, lattice parameter, residual stresses and strains, presence or absence of faulting, and mean-square amplitude of vibration. In addition the surface area of the gel was determined with small-angle scattering (SAS). There is good agreement between the percentage exposed of platinum measured by gas adsorption in Part I and the results reported here, calculated from crystallite sizes, indicating the crystallite size is the true platinum particle size. Crystallites to sizes as small as ≈25 Å have been examined. Furthermore, the crystallites are equiaxed in shape (and definitely not cuboidal) and are strain and defect free, except in the case where the average size is near the pore size of the gel. Size distributions are sharper when the catalyst preparation is by impregnation rather than by ion exchange. The size distributions indicate that there is coalescence of some surface species during preparation rather than coarsening (Ostwald ripening). The meansquare amplitude of vibration of platinum increases by ≈30% as the particles decrease in size from ≈100 to ≈25 Å. There is no change in the lattice parameter greater than ≈0.1%. The gel surface areas determined by SAS are in agreement with those determined in Part I by physisorbtion of nitrogen.     

Influence of thickness and processing history on fatigue fracture of nylon 66. Part II: Crack tip morphology

Fatigue crack propagation rates in injection molded nylon 66 were previously shown to be strongly affected by prior processing history. To provide a physical basis for the observed acceleration in crack growth rates, microtomed sections were cut through the tips of stable fatigue cracks and examined by optical microscopy. A reduction in spherulite size occurs with reprocessing along with an accompanying decrease in the amount of deformation at the crack tip. For the initially processed nylon 66 this deformation consists of a vast array of independently initiated craze-like zones. Patchy type regions observed on the fatigue fracture surface are similar in size to the initially formed crazed zones. Crack advance occurs by the breakdown and coalescence of the crazed regions via matrix shearing. The extensive damage zone is believed to result in a reduction in stress intensity at the crack tip thereby reducing the crack propagation rates. For the reprocessed nylon 66, one observes fewer crazes and a sharper fatigue crack tip with a consequent acceleration in crack propagation rates and a smoother fracture surface.     

管道等离子喷涂Cr_2O_3复合涂层及其耐蚀性能

采用等离子喷涂技术在X70管线钢表面喷涂Cr_2O_3复合涂层,利用X射线衍射仪、扫描电镜、维氏硬度计、划痕仪、电化学工作站等方法表征了涂层相关特征与性能。结果表明,相成分主要是Cr_2O_3和TiO_2,硬度可达4.928GPa,结合力可达46.15N,粘结层+陶瓷层试样腐蚀速率显著降低,对基体有很好的耐蚀保护作用。