Chemical and Biological Engineering Conference Presentations and Proceedings
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A Study of the Testing Effect in an Engineering Classroom
<p>This research paper describes a study that examines a testing effect intervention deployed in an engineering classroom setting. The testing effect is based on the premise that learning is improved when students engage with newly acquired information by challenging themselves to answer questions about the content instead of using other means of interacting with the content, such as rereading a text. The testing effect has been established in laboratory research studies [1]. To translate this finding into educational practice, classroom research studies [2]-[6] aim to define the conditions for which the testing effect remains robust in authentic classroom settings. In the classroom domain, a testing effect intervention often consists of low- or no-stakes quizzing with feedback during the learning period, followed by a summative assessment at the end of the unit. Previous investigations have studied the impact of conditions, such as the question type (identical or related; definitional or application), the quiz participation incentives, and the quiz delivery patterns on the testing effect outcome for all participants in the study. Nguyen & McDaniel [7] review several classroom studies aimed at improving student learning through the use of quizzing.</p>

https://lib.dr.iastate.edu/cbe_conf/20
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Development of high-order realizable finite-volume schemes for quadrature-based moment method
<p>Kinetic equations containing terms for spatial transport, gravity, fluid drag and particle-particle collisions can be used to model dilute gas-particle flows. However, the enormity of independent variables makes direct numerical simulation of these equations almost impossible for practical problems. A viable alternative is to reformulate the problem in terms of moments of velocity distribution. Recently, a quadrature-based moment method was derived by Fox for approximating solutions to kinetic equation for arbitrary Knudsen number. Fox also described 1st- and 2nd-order finite-volume schemes for solving the equations. The success of the new method is based on a moment-inversion algorithm that is used to calculate non-negative weights and abscissas from moments. The moment-inversion algorithm does not work if the moments are non-realizable, meaning they do not correspond to a distribution function. Not all the finite-volume schemes lead to realizable moments. Desjardins et al. showed that realizability is guaranteed with the 1 st-order finite-volume scheme, but at the expense of excess numerical diffusion. In the present work, the nonrealizability of the standard 2 nd-order finite-volume scheme is demonstrated and a generalized idea for the development of high-order realizable finite-volume schemes for quadrature-based moment methods is presented. This marks a significant improvement in the accuracy of solutions using the quadrature-based moment method as the use of 1st-order scheme to guarantee realizability is no longer a limitation.</p>

https://lib.dr.iastate.edu/cbe_conf/10
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A fully coupled fluid-particle flow solver using quadrature-based moment method with high-order realizable schemes on unstructured grids
<p>Kinetic Equations containing terms for spatial transport, gravity, fluid drag and particle-particle collisions can be used to model dilute gas-particle flows. However, the enormity of independent variables makes direct numerical simulation of these equations almost impossible for practical problems. A viable alternative is to reformulate the problem in terms of moments of the velocity distribution function. A quadrature method of moments (QMOM) was derived by Desjardins et al. [1] for approximating solutions to the kinetic equation for arbitrary Knudsen number. Fox [2, 13] derived a third-order QMOMfor dilute particle flows, including the effect of the fluid drag on the particles. Passalacqua et al. [4] and Garg et al. [3] coupled an incompressible finite-volume solver for the fluid-phase and a third order QMOM solver for particle-phase on Cartesian grids. In the current work a compressible finite-volume fluid solver is coupled with a particle-phase solver based on third-order QMOM on unstructured grids. The fluid and particle-phase are fully coupled by accounting for the volume displacement effects induced by the presence of the particles and the momentum exchange between the phases. The success of QMOM is based on the moment inversion algorithm that allows quadrature weights and abscissas to be computed from the moments of the distribution function. The moment-inversion algorithm does not work if the moments are non-realizable, which might lead to negative weights. Desjardins et al. [1] showed that realizability is guaranteed only with the 1st-order finite-volume scheme that has excessive numerical diffusion. The authors [5, 6] have derived high-order finite-volume schemes that guarantee realizability for QMOM. These high-order realizable schemes are used in this work for the particle-phase solver. Results are presented for a dilute gas-particle flow in a lid-driven cavity with both Stokes and Knudsen numbers equal to 1. For this choice of Knudsen and Stokes numbers, particle trajectory crossing occurs which is captured by QMOM particle-phase solver.</p>

https://lib.dr.iastate.edu/cbe_conf/9
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Modeling fluidization in biomass gasification processes
<p>Extensive validation of computational fluid dynamics (CFD) models is required when modeling biomass fluidization, because several required model inputs are not know or not easily measured experimentally for biomass. In the present work, CFD fluidization modeling of a biomass bed is validated by comparison with X-ray computed tomography experimental data. A parametric study was carried out by employing ground walnut shell or ground corncob as model biomass bed materials, and fluidization was performed at a gas velocity twice the minimum fluidization velocity. An important result is the use of an "effective density" for biomass in the CFD model, the use of which is necessary because the biomass particles can be characterized by an irregular shape and some degree of porosity, whereas CFD models assume the biomass particles to be solid spheres. If the mid-value of the density range provided by the manufacturer is employed, the bulk density of the solid phase in the bed is overestimated. The results also suggest that the value of COR has a negligible effect on the predictions for biomass systems.</p>

https://lib.dr.iastate.edu/cbe_conf/8
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Instantaneous particle acceleration model for gas-solid suspensions at moderate Reynolds numbers
<p>Gas-solid flows are encountered in many industrial applications such as fluidized beds and coal gasification. The design and scale-up of such industrial devices required a better understanding of the characteristics of gas-solid suspensions. Device-scale computational fluid dynamics (CFD) simulations that solve for average quantities such as solid volume fraction and phasic mean velocity fields are being extensively used in the industrial design process. The capability of the simulations to accurately predict the characteristics of gas-solid flow depends upon the accuracy of the models for unclosed terms that appear in the equations for mass, momentum and energy conservation. Hrenya and Sinclair (1997) show that the particle granular temperature (particle velocity variance) plays an important role in the prediction of the core annular structure in riser flows. In statistically homogeneous suspensions undergoing elastic collisions, the particle acceleration-velocity covariance alone governs the evolution of granular temperature.</p>

https://lib.dr.iastate.edu/cbe_conf/7
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Numerical simulation of turbulent gas-particle flow in a riser using a quadrature-based moment method
<p>Gas-particle flows are used in many industrial applications in the energy, oil and gas fields, such as coal gasification, production of light hydrocarbons by fluid catalytic cracking, catalytic combustion and different treatments aiming to reduce or eliminate pollutants. The particle phase of a gas-particle flow is described by analogy to a granular gas, by finding an approximate solution of the kinetic equation in the velocity-based number density function. In the recent past, many studies have been published on the mathematical modeling of gas-particle flows using hydrodynamic models (e.g. Enwald et al. 1996), where Navier-Stokes-type equations are solved to describe the particle phase as a continuum, computing its stress tensor using moment closures from kinetic theory (Gidaspow 1994). These closures, however, are obtained assuming that the flow is dominated by collisions and near equilibrium, which corresponds to considering a very small particle-phase Knudsen number. This assumption leads to inconsistencies and erroneous predictions of physical phenomena when these models are applied to dilute fluid-particle flows, where rarefaction effects are not negligible. In these flows, the wall Knudsen layers extend inside the bulk of the fluid, and cannot be accounted for with the simple addition of partial-slip boundary conditions. Recently Desjardin et al. (2008) showed that two-fluid models are unable to correctly capture particle trajectory crossing, seriously compromising their ability to correctly describe any velocity moment for finite Stokes numbers. These authors clarified that the particle segregation captured by two-fluid models for finite Knudsen numbers is artificially high due to their mathematical formulation, which leads to the formation of delta-shocks. In order to overcome these shortcomings, Fox (2008) developed a third-order quadrature-based moment method for dilute gas-particle flows, which has been successfully coupled to a fluid solver to compute dilute and moderately dilute gas-particle flows by Passalacqua et al. (2010) in two dimensions. These authors validated their model against Euler-Lagrange and two-fluid simulations. In this work, the fully coupled quadrature-based fluid-particle code described in Passalacqua et al. (2010) is applied to simulate turbulent gas-particle flow in the riser described by He et al. (2009), using a three-dimensional configuration. This application shows the predictive capabilities and the robustness of the quadrature-based moment method to predict the behavior of gas-particle flows in accordance with experiments (He et al. 2009).</p>

https://lib.dr.iastate.edu/cbe_conf/6
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Numerical Description of Dilute Particle-Laden FLows by a Quadrature-Based Moment Method
<p>The numerical simulation of gas-particle flows is divided into two families of methods. In Euler-Lagrange methods individual particle trajectories are computed, whereas in Euler-Euler methods particles are characterized by statistical descriptors. Lagrangian methods are very precise but their computational cost increases with instationarity and particle volume fraction. In Eulerian methods (also called moment methods) the particle-phase computational cost is comparable to that of the fluid phase but requires strong simplificaions. Existing Eulerian models consider unimodal or close-to-equilibrium particle velocity distributions and then fail when the actual distribution is far from equilibrium. Quadrature-based Eulerian methods introduce a new reconstruction of the velocity distribution, written as a sum of delta functions in phase space constrained to give the right values for selected low-order moments. Two of the quadrature-based Eulerian methods, differing by the reconstruction algorithm, are the focus of this work. Computational results for two academic cases (crossing jets, Taylor-Green flow) are compared to those of a Lagrangian method (considered as the reference solution) and of an existing second-order moment method. With the quadrature-based Eulerian methods, significant qualitative improvement is noticed compared to the second-order moment method in the two test cases.</p>

https://lib.dr.iastate.edu/cbe_conf/3
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Turbulent Combustion of Polydisperse Evaporating Sprays with Droplet Crossing: Eulerian Modeling and Validation in the Infinite Knudsen Limit
<p>The accurate simulation of the dynamics of polydisperse evaporating sprays in unsteady gaseous flows with large-scale vortical structures is both a crucial issue for industrial applications and a challenge for modeling and scientific computing. The difficulties encountered by the usual Lagrangian approaches make the use of Eulerian models attractive, aiming at a lower cost and an easier coupling with the carrier gaseous phase. Among these models, the multi-fluid model allows for a detailed description of the polydispersity and size-velocity correlations for droplets of various sizes. The purpose of the present study is twofold. First, we extend the multi-fluid model in order to cope with crossing droplet trajectories by using the quadrature method of moments in velocity phase space conditioned by size. We identify the numerical difficulties and provide dedicated numerical schemes in order to preserve the velocity moment space. Second, we conduct a comparison study and demonstrate the capability of such an approach to capture the dynamics of an evaporating polydisperse spray in a 2-D free jet configuration. We evaluate the accuracy and computational cost of Eulerian models and related discretization schemes vs. Lagrangian solvers and show that, even for finite Stokes number, the standard Eulerian multi-fluid model can be accurate at reasonable cost.</p>

https://lib.dr.iastate.edu/cbe_conf/2
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Electron Microscopic Observations of Interfacial Voids in Aluminum Created by Alkaline Dissolution
<p>We report evidence from electron microscopy and positron annihilation spectroscopy (PAS) for the formation by alkaline dissolution of nm-scale voids in aluminum near the metal-oxide interface. Imaging was carried out using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and field emission scanning electron microscopy (FESEM). EM images supported the PAS finding that voids were found within tens of nm of the interface, and revealed that the void number density increased by at least 10 times due to dissolution. From TEM, void number densities were on the order of 108 cm-2. From TEM and SEM, voids appeared circular in cross-section and were ~ 20 nm in diameter.</p>

https://lib.dr.iastate.edu/cbe_conf/11
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-77.03687070000001,38.9071923,4
A Quadrature-based Moment Closure for the Williams Spray Equation
<p>Sprays and other dispersed-phase systems can be described by a kinetic equation containing terms for spatial transport, acceleration, and particle processes (such as evaporation or collisions). In principle, the kinetic description is valid from the dilute (non-collisional) to the dense limit. However, its numerical solution in multi-dimensional systems is intractable due to the large number of independent variables. As an alternative, Lagrangian methods "discretize" the density function into "parcels" that are simulated using Monte-Carlo methods. While quite accurate, as in any statistical approach, Lagrangian methods require a relatively large number of parcels to control statistical noise, and thus are computationally expensive. A less costly alternative is to solve Eulerian transport equations for selected moments of the kinetic equation. However, it is well known that in the dilute limit, Eulerian methods have great difficulty describing correctly the moments as predicted by a Lagrangian method. A two-point quadrature-based Eulerian moment closure is developed and tested here for the Williams spray equation. It is shown that the method can successfully handle highly non-equilibrium flows (e.g., impinging particle jets, jet crossing, and particle rebound off walls) that heretofore could not be treated with the Eulerian approach.</p>

https://lib.dr.iastate.edu/cbe_conf/5
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Conditional-moment Closure with Differential Diffusion for Soot Evolution in Fire
<p>The conditional-moment closure (CMC) equation for the evolution of a large Lewis number scalar, soot, is derived starting from the joint probability density function (pdf) equation for the gas-phase mixture fraction, ξ g , and the soot mass fraction, Y s . Unlike previous approaches starting with the joint pdf, the residual terms that result from the typical closure models were retained. A new formulation of the one-dimensional turbulence (ODT) model suitable for spatially evolving flows with buoyant acceleration and radiative transport in participating media was employed to carry out simulations of a prototypical ethene fire. The resulting ODT evolution of ξ g and Y s was used to assess the significance of various terms in the CMC equation including the residual correlations. The terms involving differential diffusion are found to be important along with the soot source terms and the large-scale evolution of both ξ g and Y s . Of particular importance in the regions in mixture-fraction space around the soot production and consumption is a residual term, not previously identified, related to the correlation between the differential diffusion and Y s . This term results in a diffusion-like behavior of Y s in the mixture fraction coordinate that has an apparent Lewis number near unity. In scenarios where the large Lewis number component is a non-negligible component of the mixture fraction (i.e., large soot loading), it is found easier to employ a mixture fraction neglecting this component. Such a mixture-fraction variable has a chemical source term, but this appears easier to model than the differential diffusion and dissipation terms that result when the large Lewis number component is retained in the mixture-fraction definition.</p>

https://lib.dr.iastate.edu/cbe_conf/4
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Surface processes accompanying corrosion-induced hydrogen absorption into aluminum
<p>The role of hydrogen-containing species in the alkaline dissolution of aluminum was studied by secondary ion mass spectrometry (SLMS). Large number densities of submicron particles nucleated and then disappeared during dissolution, at intervals of approximately 3 min. The particles were composed of aluminum hydride, with an aluminum hydroxide surface layer. When particles first appeared, the aluminate ion concentration near the surface was at the solubility of Al(OH)3, and the potential was close to the Nernst potential for oxidation of AlH3 to Al(OH)3. The observed formation of AlH3 indicates that the dissolving Al surface was poised near this equilibrium potential, i. e. that a hydride species serves as an intermediate in the dissolution process.</p>

https://lib.dr.iastate.edu/cbe_conf/13
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-86.85152790000001,21.161908,4
Model for the steady-state growth of porous anodic alumina films
<p>Simulations were developed for the distributions of electrical potential and incorporated anions in porous anodic alumina (PAA) films during steady-state growth. Predictions of a model for the potential distribution based on Laplace's equation were compared to those of the current continuity equation in conjunction with high-field conduction. It was found that Laplace's equation, which has been used previously in PAA models, resulted in strong violations of charge conservation, when the current density was evaluated using the high field conduction equation. Interface motion predicted by the current continuity equation was nearly uniform except near convex ridges on the metal-film interface. This model was extended to predict the distribution of anions in the film, since incorporated anions may provide suppression of conduction near the ridge. The spatial distribution of acid anions predicted by the model agreed with experimental observations.</p>

https://lib.dr.iastate.edu/cbe_conf/12
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Injection of hydrogen and vacancy-type defects during dissolution of aluminum
<p>Formation of interfacial nanoscale voids in Al during room-temperature caustic corrosion was characterized by positron annihilation spectroscopy (PAS) and compared with measurements of deuterium absorption using secondary ion mass spectrometry (SIMS). The hypothesis was investigated that voids are created from vacancy-hydrogen (Vac-H) defects introduced during corrosion. Evidence for both mobile and immobile forms of absorbed hydrogen was obtained, the latter present within distances of 50 nm from the metal-oxide interface, where voids were also found. During corrosion, the immobile hydrogen was found only during discrete 1-2 min intervals of time separated by periods of 1-2 min when it was not present. Model calculations suggested that this transient behavior is consistent with repeated nucleation and dissolution of clusters of Vac-H defects. Only some aspects of the time-dependence of the void concentration from PAS corresponded with that of absorbed hydrogen; the former is believed to be influenced by metallic impurities.</p>

https://lib.dr.iastate.edu/cbe_conf/14
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-118.2436849,34.0522342,4
Numerical Simulations of Turbulent Bluff-body Flames using Multi-environment Presumed PDF Method with Realistic Chemistry
<p>A Computational Fluid Dynamics (CFD) tool for performing turbulent combustion simulations that require finite rate chemistry is developed and tested by modeling a series of bluff-body stabilized flames that exhibit different levels of finite-rate chemistry effects ranging from near equilibrium to near global extinction. The new modeling tool is based on the multi-environment probability density function (MEPDF) methodology and combines the following: the direct quadrature method of moments (DQMOM); the interaction-by-exchange-with-the-mean (IEM) mixing model; and realistic combustion chemistry. A pseudo time splitting scheme is adopted to solve the MEPDF equations; the reaction source terms are computed with a highly efficient and accurate in-situ adaptive tabulation (ISAT) algorithm. The modeling results agree very well with the experimental data, including mixing, temperature, major species and important minor species such as CO. More importantly, compared to the Montel-Carlo joint PDF method, the new method provides comparable accuracy and reduces the computational cost by at least one order of magnitude.</p>

https://lib.dr.iastate.edu/cbe_conf/16
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Continuous-Time Block-Oriented Adaptive on-Line Modeling for Time Varying Systems
<p>The development and maintenance of accurate predictive models for dynamic systems are highly challenged by system complexity, limited information (i.e., data), changing cross and time correlation structures and changing model parameters. Thus, for a model or modeling method to achieve long term success in implementation into a real system, it must be phenomenologically sound and adaptive, as well as being capable of immediate update from recently obtained process data (i.e., plant data). A model is phenomenologically sound when its structure accurately captures physical input and output relationships, and the stochastic behavior of process and measurement noise. On-line adaptive methods are critical to success because process variations that cause changes to noise correlation structures and model coefficients are frequent in real systems. A common occurrence in non-adaptive, off-line, model identification is the requirement of a new model by the time the model is ready for implementation due to significant process variations. For a method to have on-line adaptive abilities, it must be capable of using process data (which have a low signal to noise ratio, and limited range over the operating space) to update its fitting performance.</p>

https://lib.dr.iastate.edu/cbe_conf/17
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-84.51201960000003,39.1031182,4
Treatment of fast chemistry in FDF/LES: In situ adaptive tabulation
<p>The feasibility to implement fast-chemistry reactions in a three-dimensional large eddy simulation (LES) of a turbulent reacting flow using a filtered density function (PDF) technique is studied. Low-density polyethylene (LDPE) is used as an representative reaction due to the stiff nature of the ordinary differential equation (ODE's) describing the kinetics. In FDF/LES, the chemistry needs to be evaluated many times for a large number of fictitious particles that are tracked in the flow, and therefore a constraint is put to the CPU time needed to solve the kinetics. Pope (1997) developed an in situ adaptive tabulation (ISAT) to treat complex chemistry computationally very efficiently when many evaluations of the chemistry are needed. Kolhapure and Fox (1999) successfully applied IS AT to LDPE using a quasi steady state assumption (QSSA). In the present paper, the aim is to optimize the latest version (ISAT Version 4.0, Pope, 2003) for the full LDPE reaction (i.e. without QSSA), in terms of accuracy and speed up by varying the error tolerance and the number of trees used by ISAT. For this purpose, a pairwise mixing stirred reactor (PMSR) is employed, since it forms a stringent test for the chemistry solver due to the large accessed region of composition space that can be established. For a number of trees of Ntree = 8 and an error tolerance of Îµtol = 10-5 the best overall performance of ISAT was obtained: compared with direct integration, a speed up factor of more than ten combined with an relative error in temperature of about 1% was found.</p>

https://lib.dr.iastate.edu/cbe_conf/1
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-117.16108380000003,32.715738,4
A Reusable Calcium-Based Sorbent for Desulfurizing Hot Coal Gas
<p>There is a continuing need for an inexpensive, regenerable sorbent for desulfurizing hot coal gas. Such a material is needed especially for advanced power generating systems including integrated gasification combined-cycle (IGCC) systems and other systems which employ various topping cycles. Maximum power generation efficiency can be achieved by cleaning the gas at nearly gasifier outlet temperatures which can range up to 1200 K or more.</p>

https://lib.dr.iastate.edu/cbe_conf/18
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-79.9558968,39.629526,4
Effect of Impurities on Interfacial Void Formation in Aluminum
<p>The effect of impurities on formation of interfacial metallic voids, during uniform dissolution of aluminum in 1 M NaOH, was investigated. These voids are thought to act as initiation sites for pitting. Foils of three different bulk purities were used: 99.98% (3N), 99.997% (4N), and 99.9995% (5N). Positron Annihilation Spectroscopy (PAS) and Atomic Force Microscopy (AFM) revealed that nm-scale voids were formed by dissolution in each foil. The void volume fraction increased to a maximum during dissolution, at a time which increased with foil purity. The concurrent accumulation of near-surface Cu and Fe impurities during caustic etching was characterized using Rutherford backscattering spectrometry (RBS). For the three foils, a correlation of void volume fraction with Cu surface concentration was suggested. Processes involving Cu impurities may then at least partly control the formation of voids.</p>

https://lib.dr.iastate.edu/cbe_conf/15
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-111.89104739999999,40.7607793,4
Resource Recovery from Wastewater Treatment Sludge Containing Gypsum
<p>The disposal of wastewater treatment sludge generated at the Radford Army Ammunition Plant (RAAP) is a serious problem. The sludge is produced by neutralizing spent acid contained in the wastewater with lime, and consists principally of very finely divided wet gypsum (calcium sulfate dihydrate). Although the sludge is presently being disposed of in a landfill, the sludge is difficult to handle and convert into a load-bearing material. Therefore an alternative method of disposal is being developed and evaluated.</p>
<p>The alternative method involves drying and granulating the sludge, followed by high temperature calcination in a fluidized bed reactor to recover usable sulfur dioxide and lime. If the method is adopted, these products would be used within the plant with considerable cost savings. The sulfur dioxide would be added to the feed stream of an oleum manufacturing facility and the lime would be reused in wastewater treatment.</p>

https://lib.dr.iastate.edu/cbe_conf/19
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