Reduced power consumption in stirred vessels by means of fractal impellers AlChE J. (IF 2.836) Pub Date : 2018-01-18 S. Başbuğ, G. Papadakis, J. C. Vassilicos
Abstract Earlier studies1,2 have shown that the power consumption of an unbaffled stirred vessel decreases significantly when the regular blades are replaced by fractal ones. In this paper, the physical explanation for this reduction is investigated using Direct Numerical Simulations at Re = 1600. The gaps around the fractal blade perimeter create jets that penetrate inside the recirculation zone in the wake and break up the trailing vortices into smaller ones. This affects the time-average recirculation pattern on the suction side. The volume of the separation region is 7% smaller in the wake of the fractal blades. The lower torque of the fractal impeller is equivalent to a decreased transport of angular momentum; this difference stems from the reduced turbulent transport induced by the smaller trailing vortices. The major difference in the turbulent dissipation is seen in the vicinity of trailing vortices, due to fluctuations of velocity gradients at relatively low frequencies. This article is protected by copyright. All rights reserved.
Stochastic Back-off Algorithm for Simultaneous Design, Control and Scheduling of Multi-product Systems under Uncertainty AlChE J. (IF 2.836) Pub Date : 2018-01-17 Robert W. Koller, Luis A. Ricardez-Sandoval, Lorenz T. Biegler
Abstract An algorithm that employs the back-off method to provide optimal solutions for integration of design, control, and scheduling for multi-product systems is presented, featuring a flexibility and feasibility analysis. The algorithm employs Monte Carlo (MC) sampling to generate a large number of random realizations, and simulate the system to determine feasibility. Back-off terms are determined and incorporated into a new flexibility analysis to approximate the effect of stochastic uncertainty and disturbances. Through successive iterations, the algorithm converges, terminating on a solution that is robust to a specified level of process variability due to stochastic realizations in the disturbances and uncertain parameters. The proposed algorithm has been successfully applied to a multi-product continuous stirred tank reactor for which optimal design, control, and scheduling decisions are identified, subject to stochastic uncertainty and disturbance. The present approach has been compared to a critical-set (multi-scenario) method showing the benefits and limitations of both approaches. This article is protected by copyright. All rights reserved.
Ecosystems as Unit Operations for Local Techno-Ecological Synergy: Integrated Process Design with Treatment Wetlands AlChE J. (IF 2.836) Pub Date : 2018-01-17 Varsha Gopalakrishnan, Bhavik R. Bakshi
Abstract Despite the critical importance of ecological systems for sustaining all chemical and manufacturing processes, process design has kept nature outside its system boundary. Recent efforts for sustainable process design aim to reduce environmental impact, but no design method considers the capacity of ecosystems to supply the goods and services that are needed to sustain a process. Overcoming this deficiency of conventional process design is essential to transform the chemical industry into an activity that respects ecological constraints and results in a net positive societal impact. As an important step toward meeting this goal, this work expands the boundary of process design to include ecosystems as unit operations in traditional design. Similar to tasks performed by conventional unit operations, ecological processes perform ecosystem functions resulting in goods and services required by the technological system. The goal behind designing integrated techno-ecological process flowsheets is to balance the ecosystem service demand of technological systems with the ecosystem service supply of ecological systems. Systems are optimized to balance the demand and supply subject to unit operation level constraints of technological and ecological systems, and interactions between detailed process level variables and ecological variables are explored. The Techno-Ecological Synergy (TES) Design method is developed and applied to a biofuel production system, considering ecosystem services like water provisioning and water quality regulation provided by wetland ecosystems. Comparing the integrated TES design with conventional techno-centric design shows that TES design can result in net positive impact manufacturing: a case where the ecosystem service supply is equal to or exceeds the demand, with little or no compromises in process profitability. These results should encourage close integration between technological and ecological systems while designing sustainable processes, and identify many challenges for developing TES of individual processes and across the life cycle. This article is protected by copyright. All rights reserved.
Highly Efficient Methane Reforming over a Low-loading Ru/γ-Al2O3 Catalyst in a Pd-Ag Membrane Reactor AlChE J. (IF 2.836) Pub Date : 2018-01-17 David S. A. Simakov, Yuriy Román-Leshkov
Abstract Natural gas can be reformed to syngas (CH4 + H2O = CO + 3H2), at temperatures above 850 °C. Membrane catalytic reformers can provide high CH4 conversions at temperatures below 650 °C, by separating H2 from the reactive mixture. Traditional Ni-based catalysts suffer from low activity at low temperatures and deactivate rapidly by coking, particularly at low steam/carbon ratios. In this study, an ultra-low loading (0.15 wt%) Ru/γ-Al2O3 catalyst was implemented in a lab-scale membrane reformer, using a supported 5μm Pd-Ag film membrane. Methane conversions above 90% were achieved at 650 °C, 8 bar, and H2O/CH4 = 2, 3 with contact times of ca. 10 s. The system generated up to 3.5 mol of ultra-pure H2 per mol of CH4 fed, with a maximum power density of 0.9 kW/L. No significant deactivation was observed after 200 h time on stream, even when using low H2O:CH4 ratios. This article is protected by copyright. All rights reserved.
Continuous-Time Formulations for the Optimal Planning of Multiple Refracture Treatments in a Shale Gas Well AlChE J. (IF 2.836) Pub Date : 2018-01-17 Diego C. Cafaro, Markus G. Drouven, Ignacio E. Grossmann
Abstract This work presents a continuous-time optimization model for planning multiple refracture treatments over the lifespan of a shale gas well. We demonstrate that continuous-time models can handle multiple restimulations very efficiently, increasing the net present value of the well development and refracturing plan. Well productivity is represented by a piecewise hyperbolic function, which accounts for when and how often the well has been refractured. We illustrate the application and effectiveness of the proposed approach for both the maximization of the total gas recovered and the maximization of the net present value. This article is protected by copyright. All rights reserved.
Impact of Diversity of Morphological Characteristics and Reynolds number on Local Hemodynamics in Basilar Aneurysms AlChE J. (IF 2.836) Pub Date : 2018-01-12 Marjan Rafat, Mahsa Dabagh, Martin Heller, James D. Rabinov, Howard A. Stone, Amanda Randles, Debra T. Auguste
Abstract Morphological and hemodynamic parameters have been suggested to affect the rupture of cerebral aneurysms, but detailed mechanisms of rupture are poorly understood. The purpose of our study is to determine criteria for predicting the risk of aneurysm rupture, which is critical for improved patient management. Existing aneurysm hemodynamics studies generally evaluate limited geometries or Reynolds numbers (Re), which are difficult to apply to a wide range of patient-specific cases. We focused on the association between hemodynamic characteristics and morphology. We assessed several two-dimensional (2D) and three-dimensional (3D) idealized and physiological geometries to characterize the hemodynamic landscape between flow patterns. The impact of morphology on velocity and wall shear stress (WSS) profiles were evaluated. We found that slight changes in aneurysm geometry or Re result in significant changes in the hemodynamic and WSS profiles. Our systematic mapping and non-dimensional analysis qualitatively identify hemodynamic conditions that may predispose aneurysms to rupture. This article is protected by copyright. All rights reserved.
A Square-Force Cohesion Model and its Extraction from Bulk Measurements AlChE J. (IF 2.836) Pub Date : 2018-01-11 Peiyuan Liu, Casey Q. LaMarche, Kevin M. Kellogg, Christine M. Hrenya
AbstractAccurate modeling of interparticle forces in DEM is critical to predicting the rheology of cohesive particles. Rigorous cohesion models usually include parameters associated with particle surface roughness. However, both roughness measurement and its distillation into appropriate model parameters remain challenging. We propose a square-force cohesion model, where cohesive force remains constant until a cut-off separation, above which cohesion vanishes. We demonstrate the square-force model is a valid surrogate of more rigorous models. Specifically, when two parameters of square-force model are chosen to match the two key quantities governing dense and dilute flows, namely maximum cohesive force and critical cohesive energy31, respectively, DEM results using square-force and more rigorous models show good agreement. For practical application of the square-force model to lightly cohesive systems, a method is established to extract its parameters via defluidization, enabling determination of particle-particle cohesion from simpler bulk measurements than complicated and expensive scans on individual grains. This article is protected by copyright. All rights reserved.
Globally Optimal Linear Approach to the Design of Heat Exchangers Using Threshold Fouling Modeling AlChE J. (IF 2.836) Pub Date : 2018-01-11 Julia C. Lemos, André L. H. Costa, Miguel J. Bagajewicz
AbstractThis article presents a method for the mathematical optimization of the design of heat exchangers including fouling rate modeling for the tube-side. The description of the fouling rate in crude preheat trains of petroleum distillation units is commonly based on threshold models (Ebert-Panchal model and its variants). Our formulation of the design problem employs a mixed integer linear programing approach; therefore the solution is the global optimum and common nonconvergence drawbacks of mixed-integer nonlinear programming models are totally avoided. Three different examples are employed to compare the proposed approach with an optimization procedure using fixed fouling resistances. The results indicate that in two problems was possible to obtain design solutions associated to smaller heat exchangers. Additionally, three case studies are also explored to discuss how fouling is related to crude types, pressure drop manipulation, and energy integration. This article is protected by copyright. All rights reserved.
Experimental Investigation of Particle Migration in Suspension Flow through Bifurcating Microchannels AlChE J. (IF 2.836) Pub Date : 2018-01-11 Bhaskar Jyoti Medhi, Vipin Agrawal, Anugrah Singh
AbstractExperimental measurements of velocity and concentration profiles were carried out to study transport of non-colloidal suspension in bifurcating micro channels for both diverging and converging flow conditions using a combination of Mirco Particle Image Velocimetry (PIV) and Particle Tracking Velicimetry (PTV) techniques. Migration of particles across the streamline was observed and symmetric velocity and concentration profile in the inlet branch becomes asymmetric in the daughter branches. Further migration of particles towards the center of the channel in the outlet branch make the profiles again symmetric. The evolution of velocity and concentration profiles was observed to be different in the symmetric and asymmetric bifurcation channels. The comparison of the streamlines for the fluid and the particles showed significant deviation near the bifurcation region. This may explain why there is unequal flow and particle partitioning during flow of suspension in asymmetric bifurcating channels as reported in many previous studies. This article is protected by copyright. All rights reserved.
3D Simulation of the Time-dependent Fluid Flow and Fouling Behavior in an Industrial Hollow Fiber Membrane Module AlChE J. (IF 2.836) Pub Date : 2018-01-11 Liwei Zhuang, Gance Dai, Zhen-liang Xu
AbstractA novel three-dimensional CFD model has been developed on the basis of fluid flow in the shell and lumen sides, and permeation and fouling behavior in the porous membrane zone. The simulated 25-minute dead-end outside-in filtration process showed that the energy consumed by the inlet manifold decreases during the constant pressure filtration. The velocity and pressure distributions in the module change with time. Flux distribution both in the axial and radial directions becomes increasingly more uniform, so does the cake distribution. Flux distribution and cake distribution inter-adjust each other in different modes. A correlation equation has been developed to describe the relationship between the volumetric flow rate and accumulated water production. The correlation equation with simple experiment enables the dynamic evolution of energy consumed by shell inlet manifold to be presented, which can be the criterion of how well the shell inlet manifold or module has been designed. This article is protected by copyright. All rights reserved.
A Study of Film Thickness and Hydrodynamic Entrance Length in Liquid Laminar Film Flow along a Vertical Tube AlChE J. (IF 2.836) Pub Date : 2018-01-11 Hongxia Gao, Xiao Luo, Ding Cui, Xiayi Hu, Ardi Hartono, Hallvard F. Svendsen, Zhiwu Liang
AbstractThe liquid film thickness and hydrodynamic entrance length in a vertical tube was studied experimentally and numerically. Measurements using distilled water, 30 wt% MEA and 40 wt% sugar solutions were carried out to investigate the effects of liquid flow rate on the formation of the liquid film. The experimental results validate the new Navier-Stokes based equation in cylindrical coordinates (Eq.16) and the volume of fluid (VOF) model giving a competitively high prediction of the liquid film thickness especially in the low Reynolds number region. In addition, a new empirical model and an improved minimal surface model have been firstly proposed for calculation of the hydrodynamic entrance length, with a relatively reasonable average absolute relative deviation (AARD) of 3.03% and 6.83%, respectively. Furthermore, the effects of the hydrodynamic entry length on the gas-liquid interfacial area calculated by the improved minimal surface model were comprehensively studied, and can be ignored if the ratio of the liquid film length (y) and the hydrodynamic entrance length (λE) is lower than 10. However, it should be noted that the hydrodynamic entrance length cannot be ignored in packed columns in which the liquid flow is very complex due to the packings with different structures and materials. This article is protected by copyright. All rights reserved.
Influence of Normal Contact Force Model on Simulations of Sphero-cylindrical Particles AlChE J. (IF 2.836) Pub Date : 2018-01-11 Rohit Kumar, Avik Sarkar, William Ketterhagen, Bruno Hancock, Jennifer Curtis, Carl Wassgren
AbstractThis paper investigates how the choice of elastic normal contact force model affects predictions from DEM simulations of sphero-cylindrical particles. Three force models were investigated: (1) a Hertzian force model (HFM) which assumes a circular contact area; (2) a linear force model (LFM) with a constant stiffness; and (3) a modified Hertzian force model (MFM) that accounts for various contact areas and contact transitions. With the MFM, transitions between contact area types must be accounted for otherwise discontinuities in the contact force can occur. It is found that simple force models (HFM, LFM) can be substituted for more accurate force models if only force data and bulk properties are of interest. However, if more detailed contact information, such as contact area, contact overlap, contact duration, or collision frequency are needed, for example in population balance models and transient liquid bridge modeling, then a more accurate force model should be used. This article is protected by copyright. All rights reserved.
Liquid-Liquid-Solid Mass Transfer and Phase Behavior of Heterogeneous Etherification of Glycerol with Isobutene AlChE J. (IF 2.836) Pub Date : 2018-01-11 Jingjun Liu, Bolun Yang
AbstractPrevious experiments observed auto-acceleration in the etherification of glycerol with isobutene. This paper engaged to uncover the reason for this phenomenon via investigating the heterogenicity, including liquid-liquid phase equilibrium and liquid-liquid-solid mass transfer, of the reaction system. Phase behavior analysis showed that the reaction mixture separates into two liquid phases during the whole course of the reaction. The produced mono ethers of glycerol thermodynamically promote the homogenization of the two liquid phases. The modeling results of liquid-liquid-solid mass transfer indicated that the resistance of mass transfer is insignificant during the reaction. The bulk compositions of the two liquid phases are very close to their corresponding equilibrium compositions. An increase of isobutene concentration in the reaction phase is believed to lead all reactions speeding up. This article is protected by copyright. All rights reserved.
On the Mechanisms of Secondary Flows in a Gas Vortex Unit AlChE J. (IF 2.836) Pub Date : 2018-01-11 Kaustav Niyogi, Maria M. Torregrosa, Vladimir N. Shtern, Guy B. Marin, Geraldine J. Heynderickx
AbstractThe hydrodynamics of secondary flow phenomena in a disc-shaped gas vortex unit (GVU) is investigated using experimentally validated numerical simulations. The simulation using ANSYS FLUENT® v.14a reveals the development of a backflow region along the core of the central gas exhaust, and of a counterflow multi-vortex region in the bulk of the disc part of the unit. Under the tested conditions, the GVU flow is found to be highly spiraling in nature. Secondary flow phenomena develop as swirl becomes stronger. The backflow region develops first via the swirl-decay mechanism in the exhaust line. Near-wall jet formation in the boundary layers near the GVU end-walls eventually results in flow reversal in the bulk of the unit. When the jets grow stronger the counterflow becomes multi-vortex. The simulation results are validated with experimental data obtained from Stereoscopic Particle Image Velocimetry and surface oil visualization measurements. This article is protected by copyright. All rights reserved.
Lattice Boltzmann Simulation of Asymptotic Longitudinal Mass Dispersion in Reconstructed Random Porous Media AlChE J. (IF 2.836) Pub Date : 2018-01-11 Chen Yang, Yixiong Lin, Gérald Debenest, Akira Nakayama, Ting Qiu
AbstractIn order to research macroscopic mass transport characteristics of porous media, a lattice Boltzmann method (LBM) approach was utilized to calculate asymptotic longitudinal mass dispersion. In this study, a D2Q9 model with multi-relaxation-time (MRT) collision operator, which is appropriate for incompressible flow with a high Péclet number without refining the lattice, was chosen. With respect to the microstructure of porous media, random placement (RP) method was applied to obtain randomly positioned particles. Based on the exhausted numerical results presented in the study, a new correlation of longitudinal mass dispersion was established. By comparing with available experimental data in the literature, reasonable agreements are observed in a wide porosity range from 0.3 to 0.7, indicating the validity of the proposed correlation. This article is protected by copyright. All rights reserved.
Experimental investigation of the morphology of salt deposits from drying sessile droplets by white-light interferometry AlChE J. (IF 2.836) Pub Date : 2018-01-11 F. Sondej, M. Peglow, A. Bück, E. Tsotsas
ABSTRACTThis study presents a new approach to investigate the drying behavior and the structure of deposit resulting from drying of solid containing micro droplets. It is shown that deposit structure (porosity and “footprint”) depends on drying conditions. This dependency may contribute to better understanding of particle-forming processes, such as fluidized bed coating. In the framework of this study, sessile droplets containing sodium benzoate dissolved in water were dried on thin glass plates in a small drying chamber. The drying conditions (temperature, moisture content and flow rate of drying gas) and material parameters (solid content of solution) were systematically varied. The drying rate of droplets was determined from the moisture balance of the drying gas. The final 3D shape of dried sessile droplets was measured using white-light interferometry and transformed into a 2D profile using a Monte Carlo method. Moreover the mean porosity of dried droplets was calculated. By comparison of structural information and process conditions it is shown that the drying process may have a large influence on deposit structure. This article is protected by copyright. All rights reserved.
Flow Distribution of Hydrocarbon Fuel in Parallel Mini-Channels Heat Exchanger AlChE J. (IF 2.836) Pub Date : 2018-01-11 Yu Chen, Zhiliang Lei, Tianhao Zhang, Quan Zhu, Zewei Bao, Qiyi Zhang, Xiang-Yuan Li
AbstractIn this paper, the flow distribution of the Chinese No. 3 jet fuel in parallel mini-channels heat exchanger under high temperature condition was investigated. The models of PFR and choked flow were established based on the real fluid model. The formation mechanism of flow maldistribution of the fuel in the freely-distributed channels was studied. It was found that: under low heat flux, the slight flow rate deviation will be spontaneously eliminated; under high heat flux, the slight deviation of flow rate and heat flux will be enlarged and result in the channel with smaller flow rate entering the coking region. The feasibility and influence factors of the control method of flow distribution based on choked flow were discussed. The experimental results indicated that the mini-channels fuel-cooled plate with choked flow could maintain uniform flow distribution when the total fuel outlet temperature reached 1035 K. This article is protected by copyright. All rights reserved.
Non-homogeneous flow of micellar solutions: A kinetic - network theory approach AlChE J. (IF 2.836) Pub Date : 2018-01-06 J. Paulo García-Sandoval, A. Martín del Campo, F. Bautista, O. Manero, Jorge E. Puig
Abstract The rheological behavior of micellar solutions is analyzed under non-homogeneous velocity and stress flow conditions. The framework is based on the extended irreversible thermodynamics and the transient network formulation coupled to the underlying kinetics embodying two relevant processes: formation of wormlike chains from a free micellar solution through a thermally activated process and their flow induced degradation. The second kinetic process consists in the formation of entanglements from the free wormlike chains and their flow-induced breakage. These processes are modeled in a coupled kinetic scheme constituted by a set of reversible kinetic equations describing the evolution in average of the three microstates (free short rod-like micelles, free wormlike chains and entangled wormlike chains) that reflect the complexity of macromolecular interactions. The predictions of the shear stress and first normal stress difference as a function of shear-rate under banded flow are in good agreement with experimental data. This article is protected by copyright. All rights reserved.
Non-spherical particles in a pseudo-2D fluidized bed: Experimental study AlChE J. (IF 2.836) Pub Date : 2018-01-05 Vinay V. Mahajan, Tim M.J. Nijssen, Kay A. Buist, J. A. M. Kuipers, Johan T. Padding
AbstractFluidization is widely used in industries and has been extensively studied, both experimentally and theoretically, in the past. However, most of these studies focus on spherical particles while in practice granules are rarely spherical. Particle shape can have a significant effect on fluidization characteristics. It is therefore important to study the effect of particle shape on fluidization behaviour in detail. In this study, experiments in pseudo-2D fluidized beds are used to characterize the fluidization of spherocylindrical (rod-like) Geldart D particles of aspect ratio 4. Pressure drop and optical measurement methods (DIA, PIV, PTV) are employed to measure bed height, particle orientation, particle circulation, stacking and coordination number. The commonly used correlations to determine the pressure drop across a bed of non-spherical particles are compared to experiments. Experimental observations and measurements have shown that rod-like particles are prone to interlocking and channelling behaviour. Well above the minimum fluidization velocity, vigorous bubbling fluidization is observed, with groups of interlocked particles moving upwards, breaking up, being thrown high in the freeboard region and slowly raining down as dispersed phase. At high flowrates, a circulation pattern develops with particles moving up through the center and down at the walls. Particles tend to orient themselves along the flow direction. This article is protected by copyright. All rights reserved.
The pH, Temperature and Protein Structure Effect on β-Lactoglobulin A and B Separation in Anion-Exchange Chromatography AlChE J. (IF 2.836) Pub Date : 2018-01-05 Gorgi Pavlova, James T. Hsua
AbstractThe effect of pH and temperature on separating a mixture of similar proteins, namely β-lactoglobulin A (LGA) and β-lactoglobulin B (LGB) in anion-exchange chromatography is explored. The proteins carry a slight difference in negative charge at basic pH, providing a separation basis on an Q Sepharose Fast Flow anion-exchange resin. They were separated at different temperatures and pH values, and the separation factor was evaluated. The experimental results were matched to a theoretical model to compute the equilibrium constant KA. The data shows that an increase in temperature and pH leads to an increase in the retention time of the proteins. The results were correlated with the net charge of the molecule for the separation so that the elution can be simulated for any condition that was studied. The tertiary structures of LGA and LGB are analyzed to illustrate the structure effect on the separation. This article is protected by copyright. All rights reserved.
A Regime Map for the Normal Surface Impact of Wet and Dry Agglomerates AlChE J. (IF 2.836) Pub Date : 2018-01-03 Mohammad Khalilitehrani, Joakim Olsson, Farin Daryosh, Anders Rasmuson
AbstractThe normal surface impacts of wet and dry agglomerates are simulated in a DEM framework. While the impact behavior of dry agglomerates has been addressed previously, similar studies on wet agglomerate impact are missing. We show that by adding a small amount of liquid the impact behavior changes significantly.The impact behavior of the agglomerates at different moisture contents and impact energies are analyzed through post-impact parameters and coupled to their microscopic and macroscopic properties. While increasing the impact energy breaks more inter-particle bonds and intensifies damage and fragmentation, increasing the moisture content is found to provide the agglomerates with higher deformability and resistance against breakage. It is shown that the interplay of the two latter parameters together with the agglomerate structural strength creates various impact scenarios, which are classified into different regimes and addressed with a regime map. This article is protected by copyright. All rights reserved.
Revealing Low Temperature Microwave-assisted Pyrolysis Kinetic Behaviors and Dielectric Properties of Biomass Components AlChE J. (IF 2.836) Pub Date : 2018-01-03 Hu Luo, Li-Wei Bao, Ling-Zhao Kong, Yu-Han Sun
AbstractThe kinetic characteristics of microwave-assisted pyrolysis of biomass components were investigated in a self-designed microwave TGA using the KAS model and the master plot method. Compared with conventional pyrolysis, the initial decomposition temperatures of biomass components were reduced by 50-100°C and the fastest weight loss regions were shifted to lower temperatures. The average apparent activation energies of cellulose, hemicellulose and lignin were 47.82, 44.81 and 51.54 kJ/mol, respectively. Analysis with master plot method suggested the MAP of cellulose followed the 2-D diffusion reaction model, while hemicellulose and lignin could be interpreted by 3rd order-based and 3-D diffusion model. The change of dielectric properties was consistent with the weight loss behaviors of biomass components during the pyrolysis process. The increase of dielectric properties with temperature can lead to a thermal gradient and “hot spots” within biomass, which accelerated the pyrolysis process at low temperatures and reduced the apparent activation energy. This article is protected by copyright. All rights reserved.
Heat Transfer Intensification for Retrofitting Heat Exchanger Networks with Considering Exchanger Detailed Performances AlChE J. (IF 2.836) Pub Date : 2018-01-03 Ming Pan, Igor Bulatov, Robin Smith
AbstractThe challenging of this work is to present a thorough study of implementing heat transfer intensification in heat exchanger network (HEN) retrofitting, including all details of exchanger geometry, stream bypassing and splitting, temperature-variation of properties, LMTD and its correction, and pressure drops. This leads to very complex mixed integer nonlinear programming (MINLP) problems rarely reported before. By adopting the MILP-based iterative approach proposed in the earlier work (Pan et al. in 2013), temperature-variation of properties, LMTD and its correction are initialised to parameters at first, and the rest nonlinear terms are then linearized and expressed as first order Taylor series expansions. Finally, two iteration loops are executed to find optimal solutions. A small-scale motivating problem and an industrial scale problem are presented to demonstrate the validity and efficiency of the proposed methods. This article is protected by copyright. All rights reserved.
On the construction of binary mixture p-x and T-x diagrams from isochoric thermodynamics∗ AlChE J. (IF 2.836) Pub Date : 2018-01-03 Ian H. Bell, Ulrich K. Deiters
AbstractIn this work we describe how to efficiently and reliably calculate p-x and T-x diagrams for binary mixtures of fluids. The method is based on the use of the Helmholtz energy density as the fundamental thermodynamic potential. Through the use of temperature and molar concentrations of the components as the independent variables, differential relationships can be constructed along the phase envelope surface, and this system of differential equations is then integrated to construct isotherms and isobars cutting through the phase envelope.The use of the Helmholtz energy density as the fundamental potential allows several models to be considered in this formalism, including cubic equations of state (Peng-Robinson, GC-VTPR, etc.) as well as high-accuracy multifluid equations of state (the so-called GERG mixture model). Examples of each class are presented, demonstrating the flexibility of this method. Source code, examples, and comprehensive analytic derivatives are provided in the supplemental material. This article is protected by copyright. All rights reserved.
Enhanced Water Flux through Graphitic Carbon Nitride Nanosheets Membrane by Incorporating Polyacrylic Acid AlChE J. (IF 2.836) Pub Date : 2018-01-03 Yanjie Wang, Lingfei Liu, Jian Xue, Jiamin Hou, Li Ding, Haihui Wang
AbstractMembranes assembled from two-dimensional (2D) layered materials have shown potential use in water purification. Recently, a 2D graphitic carbon nitride (g-C3N4) nanosheets membrane exhibit considerable separation performance in water purification. In this study, to further improve this water separation performance, polyacrylic acid (PAA) was introduced to tune the nanochannels formed between the g-C3N4 nanosheets. The fabricated g-C3N4-PAA hybrid membranes possessed higher water flux without sacrificing much rejection rate compared with that of the g-C3N4 membrane; however noticeable fouling was observed upon addition of the PAA into the membrane composite structure. In addition, the effect of PAA on the morphology, surface hydrophilicity, separation performance, and antifouling properties of the g-C3N4 membrane were examined in detail. Overall, incorporating PAA into the g-C3N4 nanosheets membrane was an effective and convenient method to improve the water separation performance, which could promote the application of the 2D g-C3N4 nanosheets membrane in practical ultrafiltration processes. This article is protected by copyright. All rights reserved.
CO2 Capture by Methanol, Ionic Liquid, and Their Binary Mixtures: Experiments, Modeling, and Process Simulation AlChE J. (IF 2.836) Pub Date : 2018-01-02 Mohsen Taheri, Chengna Dai, Lei Zhigang
ABSTRACTThe CO2 solubility data in the ionic liquid (IL) 1-allyl-3-methylimidazolium bis(triﬂuoromethyl sulfonyl)imide, methanol (MeOH), and their mixture with different combinations at temperatures of (313.2, 333.2, and 353.2 K) and pressures up to 6.50 MPa were measured experimentally. New group binary interaction parameters of the predictive UNIFAC-Lei model, which has been continually advanced by our group, were introduced by correlating the experimental data of this work and the literature. The consistency between experimental data and predicted results proves the reliability of UNIFAC-Lei model for CO2-IL-organic solvent systems. The newly obtained parameters were incorporated into the UNIFAC property model of Aspen Plus software to optimize a conceptual process developed for the purification of a CO2-containing gas stream. The simulation results indicate that the use of IL either mixed with MeOH or purely considerably lowers the process power consumption, and improves the process performance in terms of CO2 capture rate and solvent loss. This article is protected by copyright. All rights reserved.
Solubilities of Solid n-Alkanes in Methane: Data Analysis and Models Assessment AlChE J. (IF 2.836) Pub Date : 2018-01-02 Marco Campestrini, Paolo Stringari
AbstractThis paper reviews the results of experiments underway since 1950 studying the solid solubility of n-alkanes (from ethane up to n-triacontane) in methane and the factors influencing the global phase equilibrium behavior of the related binary mixtures.The methodology used consists of a series of comparisons of data in the composition-temperature and pressure-temperature diagrams. The kind of global phase diagram of the binary mixtures of methane referred to in the present article is found to be dependent of the ratio between the triple-point temperature of the generic n-alkane and the critical-point temperature of methane.The Peng-Robinson (1976), Predictive Soave-Redlich-Kwong, and Predictive Peng-Robinson (1978) equations of state have been applied and compared with respect to the calculation of bivariant, univariant, and invariant equilibrium data involving solid n-alkanes in binary mixture with methane. The fugacities of the solid n-alkanes have been calculated by means of the so-called classic approach. This article is protected by copyright. All rights reserved.
Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl2 or NaCl-KCl Present AlChE J. (IF 2.836) Pub Date : 2017-12-28 S. Ho-Van, B. Bouillot, J. Douzet, S. Maghsoodloo, J.M. Herri
Abstract Consistent phase equilibrium data for cyclopentane hydrates in presence of salts are vitally important to many industries, with particular interest to the field of hydrate-based water separation via cyclopentane hydrate crystallization such as desalination. However, there are very little experimental equilibrium data, and no thermodynamic prediction tools. Hence, we set up a method to generate a great deal of much needed equilibrium data for cyclopentane hydrates in diverse saline solutions with a wide range of salt concentrations. Our method does furnish verified, reliable and accurate equilibrium data. Plus, three thermodynamic approaches are developed to predict equilibrium, and provide tools for simulations, by considering the kind of salt and concentrations. All three models are in very good accordance with experimental data. One method, using a new correlation between occupancy factor and water activity, might be the best way to obtain consistent, quick and accurate dissociation temperatures of cyclopentane hydrate in brine. This article is protected by copyright. All rights reserved.
On reduced modeling of mass transport in wavy falling films AlChE J. (IF 2.836) Pub Date : 2017-12-28 P. Bandi, S. Groß, Y. Heng, W. Marquardt, A. Mhamdi, M. Modigell, A. Reusken, L. Zhang
Abstract In many industrial units such as packing columns, falling film reactors, etc., the liquid phase is designed as a falling film. It is well known that the mass and heat transfer in laminar wavy film flows is significantly enhanced compared to flat films. The kinetic phenomena underlying the increase in mass and heat transfer are, however, still not fully understood. For an efficient design of falling film units, computational models that account for these enhanced transport mechanisms are of key importance. In this paper, we present a reduced modeling approach based on a long-wave approximation to the fluid dynamics of the film. Furthermore, we introduce a new 2D high-resolution laser-induced luminescence measurement technique. Both in the numerical simulation results and in the high-resolution 2D-concentration measurements obtained in the experiments we observe similar patterns of high concentrations locally, especially in the areas close to the wave hump. This article is protected by copyright. All rights reserved.
Nanospace-Confined Synthesis of Coconut-like SnS/C Nanospheres for High-Rate and Stable Lithium-Ion Batteries AlChE J. (IF 2.836) Pub Date : 2017-12-28 Zongnan Deng, Hao Jiang, Yanjie Hu, Chunzhong Li, Yu Liu, Honglai Liu
Abstract Coconut-like monocrystalline SnS/C nanospheres are developed as anode materials for lithium-ion batteries (LIBs) by a micro-evaporation-plating strategy in confined nanospaces, achieving reversible capacities as high as 936 mAh g−1 at 0.1 A g−1 after 50 cycles and 830 mAh g−1 at 0.5 A g−1 for another 250 cycles. The remarkably improved electrochemical performances can be mainly attributed to their unique structural features, which can perfectly combine the advantages of the face-to-face contact of core/shell nanostructure and enough internal void space of yolk/shell nanostructure, and therefore well-addressing the pivotal issues related to SnS low conductivity, sluggish reaction kinetics and serious structure pulverization during the lithiation/delithiation process. The evolutionary process of the nanospheres is clearly elucidated based on experimental results and a multiscale kinetic simulation combining the microscopic reaction-diffusion equation and the mesoscopic theory of crystal growth. Furthermore, a LiMn2O4//SnS/C full cell is assembled, likewise exhibiting excellent electrochemical performance. This article is protected by copyright. All rights reserved.
Determination of Crystalline Thermodynamics and behavior of Anthracene in different Solvents AlChE J. (IF 2.836) Pub Date : 2017-12-28 Cui-ping Ye, Xiao-xiao Ding, Wen-ying Li, Hai Mu, Wei Wang, Jie Feng
Abstract To screen suitable solvents for anthracene crystallization, the solubilities of anthracene and metastable zone width were determined in four different solvents, N,N-dimethyl formamide (DMF), xylene, tetrachloroethylene, and diethylene glycol dimethyl ether from 30 to 80°C at atmospheric pressure using a self-made crystallizer. The cooling modes, solvents, and the effects of carbazole on the solvent crystallization process of anthracene were also investigated. The composition of mother liquors and solid products were measured by gas chromatography, the solids were analyzed by scanning electron microscope, X-ray diffractometer, differential scanning calorimetry, granulometer, and fluorescence spectrometer. The results showed that a uniform anthracene crystal was obtained when using DMF under the forced circulation cooling mode. Solid solution of anthracene and carbazole was initially detected in solvent crystallization. The existence of carbazole in solution has an obvious effect on the crystal morphology of anthracene, to some extent, is beneficial to the crystal growth of anthracene. This article is protected by copyright. All rights reserved.
Solvent-free polymer emulsification inside a twin screw extruder AlChE J. (IF 2.836) Pub Date : 2017-12-22 A. Goger, M.R. Thompson, J.L. Pawlak, M.A. Arnould, D.J.W. Lawton
ABSTRACT Solvent-free extrusion emulsification (SFEE) is new technique for a twin screw extruder to prepare sub-micron sized particles (100-500 nm) without using hazardous solvents. The particle size is reliant upon the thickness of striated lamellae, which can be monitored rheologically based on the viscosity change occurring at the SFEE process. The lamellae coarsening rate is predominantly affected by the interfacial energy of the system when a surfactant is added but shows stronger dependency on viscosity change when interfacial growth between the polymer and water phases is solely determined by the end-groups conversion into carboxylate species. For this latter case, the dissolution of the sodium hydroxide species and the kinetics of end-groups conversion prove to be rate-limiting phenomena to generating thinner striated lamellae. Additionally, the ionic strength of the system is notably important to the viscosity response and particle size produced, particularly when surfactant is not added. This article is protected by copyright. All rights reserved.
Convex Relaxations for Global Optimization Under Uncertainty Described by Continuous Random Variables AlChE J. (IF 2.836) Pub Date : 2017-12-21 Yuanxun Shao, Joseph K. Scott
Abstract This article considers nonconvex global optimization problems subject to uncertainties described by continuous random variables. Such problems arise in chemical process design, renewable energy systems, stochastic model predictive control, etc. Here, we restrict our attention to problems with expected-value objectives and no recourse decisions. In principle, such problems can be solved globally using spatial branch-and-bound. However, branch-and-bound requires the ability to bound the optimal objective value on subintervals of the search space, and existing techniques are not generally applicable because expected-value objectives often cannot be written in closed-form. To address this, this article presents a new method for computing convex and concave relaxations of nonconvex expected-value functions, which can be used to obtain rigorous bounds for use in branch-and-bound. Furthermore, these relaxations obey a second-order pointwise convergence property, which is sufficient for finite termination of branch-and-bound under standard assumptions. Empirical results are shown for three simple examples. This article is protected by copyright. All rights reserved.
Dynamics and Scaling of Explosion Cratering in Granular Media AlChE J. (IF 2.836) Pub Date : 2017-12-19 Ming Gao, Xiao Liu, Luana Pasetti Vanin, Ting-Pi Sun, Leonardo Gordillo, Xiang Cheng
Granular cratering is a ubiquitous phenomenon occurring in various natural and industrial contexts. Although impact-induced granular cratering has been extensively studied, fewer experiments have been conducted on granular cratering via low-energy explosions. Here, we study the dynamics and scaling of explosion granular cratering by injecting short pulses of pressurized air in quasi-two-dimensional granular media. Through an analysis of the dynamics of explosion processes at different explosion pressures, explosion durations and burial depths, we identify two regimes, the bubbling and the eruption regimes, in explosion granular cratering. Our experiments explore the distinctive dynamics and crater morphologies of these regimes and show the energy scaling of the size of explosion craters. We compare high-energy and low-energy explosion cratering as well as explosion and impact cratering in terms of their energy scalings. Our work illustrates complex granular flows in explosion cratering and provides new insights into the general scaling of granular cratering processes. This article is protected by copyright. All rights reserved.
Rheological properties and structure of step- and chain-growth gels concentrated above the overlap concentration AlChE J. (IF 2.836) Pub Date : 2017-12-18 Matthew D. Wehrman, Andrew Leduc, Holly E. Callahan, Michelle S. Mazzeo, Mark Schumm, Kelly M. Schultz
Cross-linked polymeric gels are widely used in applications ranging from biomaterial scaffolds to additives in enhanced oil recovery. Despite this, fundamental understanding of the effect of polymer concentration and reaction mechanism on the scaffold structure is lacking. We measure scaffold properties and structure during gelation using multiple particle tracking microrheology. To determine the effect of concentration, we measure gelation as polymer interactions are increased in the backbone precursor solution: below, at and above the overlap concentration, c*. To determine structural changes due to the gelation mechanism, we measure gelation between the same polymers undergoing both step- and chain-growth reactions using self-assembling maleimide:thiol and photo-initiated acrylate:thiol chemistries, respectively. We determine the critical relaxation exponent, n, a measure of structure. n decreases with increasing concentration, indicating a change from a percolated (c < c*) to a tightly cross-linked network (c* < c). The gelation mechanism does not have a measurable effect on the scaffold structure. This article is protected by copyright. All rights reserved.
Eulerian-Lagrangian Simulations of Settling and Agitated Dense Solid-Liquid Suspensions – Achieving Grid Convergence AlChE J. (IF 2.836) Pub Date : 2017-12-15 J.J. Derksen
Eulerian-Lagrangian simulations of solid-liquid flow have been performed. The volume-averaged Navier-Stokes equations have been solved by a variant of the lattice-Boltzmann method; the solids dynamics by integrating Newton's second law for each individual particle. Solids and liquid are coupled via mapping functions. The application is solids suspension in a mixing tank operating in the transitional regime (the impeller-based Reynolds number is 4,000), an overall solids volume fraction of 10% and a particle-liquid combination with an Archimedes number of 30. In this application, the required grid resolution is dictated by the liquid flow and we thus need freedom to choose the particle size independent of the grid spacing. Preliminary hindered settling simulations show that the proposed Eulerian-Lagrangian mapping strategy indeed offers this independence. The subsequent mixing tank simulations generate grid-independent results. This article is protected by copyright. All rights reserved.
Simulation of Shale Gas Transport and Production with Complex Fractures using Embedded Discrete Fracture Model AlChE J. (IF 2.836) Pub Date : 2017-12-15 Wei Yu, Yifei Xu, Malin Liu, Kan Wu, Kamy Sepehrnoori
The goal of this study is to develop a new model to simulate gas and water transport in shale nanopores and complex fractures. We first derive a new gas diffusivity equation to consider multiple important physical mechanisms such as gas desorption, gas slippage and diffusion, and non-Darcy flow. For complex fractures, we implement a state-of-the-art embedded discrete fracture model (EDFM). We verify this numerical model against a commercial reservoir simulator for shale gas simulation with multiple planar fractures. After that, we perform a series of simulation studies to investigate the impacts of complex gas transport mechanisms and various fracture geometries on well performance. The critical parameters controlling well performance are identified. The simulation results reveal that modeling of gas production from complex fractures as well as modeling important gas transport mechanisms in shale gas reservoirs is extremely significant. This article is protected by copyright. All rights reserved.
Monetizing Shale Gas to Polymers under Mixed Uncertainty: Stochastic Modeling and Likelihood Analysis AlChE J. (IF 2.836) Pub Date : 2017-12-15 Chang He, Ming Pan, Bingjian Zhang, Qinglin Chen, Fengqi You, Jingzheng Ren
This paper presents a novel framework based on stochastic modeling methods and likelihood analysis to address large-scale monetization processes of converting shale gas to polymers under the mixed uncertainties of feedstock compositions, estimated ultimate recovery, and economic parameters. A new stochastic data processing strategy is developed to quantify the feedstock variability through generating the appropriate number of scenarios. This strategy includes the Kriging-based surrogate model, sample average approximation and the integrated decline-stimulate analysis curve. The feedstock variability is then propagated through performing a detailed techno-economic modeling method on distributed-centralized conversion network systems. Uncertain economic parameters are incorporated into the stochastic model to estimate the maximum likelihood of performance objectives. The proposed strategy and models are illustrated in four case studies with different plant locations and pathway designs. The results highlight the benefits of the hybrid pathway as it is more amenable to reducing the economic risk of the projects. This article is protected by copyright. All rights reserved.
Extracting Dynamic Features with Switching Models for Process Data Analytics and Application in Soft Sensing AlChE J. (IF 2.836) Pub Date : 2017-12-15 Yanjun Ma, Biao Huang
In recent decades, soft sensors have been profoundly studied and successfully applied to predict critical process variables in real-time. While dealing with various application scenarios, data-driven methods with representation learning possess great potentials. Latent features are formulated in these approaches to predict outputs from correlated input variables. In this study, a probabilistic framework of feature extraction is proposed in the context of process data analysis. To address switching behaviours in industrial processes, multiple emission models are utilized to construct latent space. To address temporal correlations from continuously operating processes, a dynamic model is implemented in latent space. Bayesian learning strategy is then developed for parameters estimation, where modelling preferences and uncertainties from multiple models are considered. The effectiveness and practicability of the proposed feature extraction algorithm are illustrated through numerical simulations, as well as an industrial case study. This article is protected by copyright. All rights reserved.
Dynamic Catalytic Adsorptive Desulfurization of Real Diesel over Ultra-Stable and Low-Cost Silica Gel supported TiO2 AlChE J. (IF 2.836) Pub Date : 2017-12-14 Xiaoling Ren, Zewei Liu, Lei Dong, Guang Miao, Neng Liao, Zhong Li, Jing Xiao
The work aims to develop dynamic ultra-deep catalytic adsorptive desulfurization of real diesel using ultra-stable and low-cost silica gel supported TiO2. A two-stage dynamic breakthrough model was built to describe the CADS process, varied with H/R ratio and O/S ratio. The desulfurization capacity reached 1.3 mg-S/g-A at the breakthrough concentration of 5 ppm-S. Various types of silica gel were screened as the substrate for TiO2, and the textural/acidic properties and CADS capacity were correlated in high relevancy. The effectiveness of diverse oxidants on CADS and the oxidation path were elucidated via combined experiment/simulation. Adsorption enthalpy derived from fitted isotherm data was calculated as 33.4 kJ/mol. The TiO2/silica gel-based sorbent demonstrated remarkable recyclability/stability in 10 cycles. This work provides an effective and economic route to eliminate the trace amount of stubborn sulfur compounds in low-sulfur diesel, which can be potentially implemented as the final polishing step for ultra-clean diesel production. This article is protected by copyright. All rights reserved.
Towards a continuous synthesis of porous carbon xerogel beads AlChE J. (IF 2.836) Pub Date : 2017-12-14 David Eskenazi, Patrick Kreit, Jean-Paul Pirard, Philippe Compère, Nathalie Job
A continuous process for producing porous carbon xerogel beads has been developed. It consists in injecting a pre-cured aqueous solution of resorcinol and formaldehyde on top of a column filled with hot oleic acid. The latter is pumped on the top of the column and fed at the bottom, generating an upward flow that can be adjusted to match the terminal velocity of the settling beads. Thus, the bead residence time in the column can be adjusted to match the gelation time, allowing the beads to solidify before reaching the bottom of the vessel. The obtained beads are subsequently dried and pyrolyzed. The developed experimental setup proved the continuous synthesis of porous carbon beads is possible. Nevertheless, the shaping process caused various texture changes of the porous carbon, which mainly yields macropores instead of micro and mesopores. This process also leads to the build-up of a denser skin around the beads. This article is protected by copyright. All rights reserved.
Surface Nonuniformities in Latex Paints due to Evaporative Mechanisms AlChE J. (IF 2.836) Pub Date : 2017-12-14 K.B. Sutton, C.B. Clemons, K.L. Kreider, J.P. Wilber, G.W. Young
A model is developed for predicting long-wavelength nonuniformities in the thickness of drying latex paint films. The model includes the effects of temperature, latex particle volume fraction, surface surfactant density, bulk surfactant density, and several material and environmental factors. After the model is simplified by applying the lubrication approximation, equations for spatially independent base state solutions are derived. The base state solutions describe a drying latex paint film of uniform thickness. The equations for the base states are solved numerically and a linear stability analysis is conducted. This analysis indicates that evaporation, slow surfactant kinetics, low initial surface tension, substrate permeability, and high initial latex particle volume fractions destabilize the uniform film, while fast surfactant kinetics, high initial surface tension, and high viscosity are stabilizing. This article is protected by copyright. All rights reserved.
Multi-Dimensional Modeling of a Microfibrous Entrapped Cobalt Catalyst Fischer-Tropsch Reactor Bed AlChE J. (IF 2.836) Pub Date : 2017-12-12 M. S. Challiwala, B. A. Wilhite, M. M. Ghouri, N. O. Elbashir
Thermal management of highly-exothermic Fischer-Tropsch-Synthesis has been a challenging bottleneck limiting the radial dimension of the Packed-Bed (PB) reactor tube to 1.5”-ID. In this work, a computational demonstration of a novel Microfibrous-Entrapped-Cobalt-Catalyst (MFECC) in mitigating hotspot formation has been evaluated. Specifically, a 2-D model was developed in COMSOL®, validated with experimental data and subsequently employed to demonstrate scale-up of the FTS bed from 0.59” – 4”ID. Significant hot-spot of 102.39 K in PB was reduced to 9.4 K in MFECC bed under gas-phase at 528.15 K and 2 MPa. Improvement in heat-transfer within the MFECC bed facilitates higher productivities at low space velocities (≥1000 1/h) corresponding to high CO-conversion (≥90%). Additionally, the MFECC reactor provides an 8-fold increase in the reactor ID at hotspots≤30 K with CO% conversions≥90%. This model was developed for a typical FTS cobalt-based catalyst where CO2 production is negligible. This article is protected by copyright. All rights reserved.
Synthesis of Ni Nanoparticles with Controllable Magnetic Properties by Atmospheric Pressure Microplasma Assisted Process AlChE J. (IF 2.836) Pub Date : 2017-12-12 Liangliang Lin, Sergey A. Starostin, R. Lavrijsen, Wei Zhang, Sirui Li, Volker Hessel
An atmospheric pressure microplasma technique is demonstrated for the gas phase synthesis of Ni nanoparticles by plasma-assisted nickelocene dissociation at different conditions. The dissociation process and the products are characterized by complementary analytical methods to establish the relationship between operational conditions and product properties. The innovation is to show proof-of-principle of a new synthesis route which offers access to less costly and less poisonous reactant, a higher quality product, and a simple, continuous and pre/post treatment-free manner with chance for fine-tuning “in-flight”. Results show that Ni nanoparticles with controllable magnetic properties are obtained, in which flexible adjustment of product properties can be achieved by tuning operational parameters. At the optimized condition only fcc Ni nanoparticles are formed, with saturation magnetization value of 44.4 mAm2/g. The upper limit of production rate for Ni nanoparticles is calculated as 4.65 × 10−3 g/h using a single plasma jet, but the process can be scaled-up through a microplasma array design. In addition, possible mechanisms for plasma-assisted nickelocene dissociation process are discussed. This article is protected by copyright. All rights reserved.
Mass Transfer Coefficient of Tubular Ultrafiltration Membranes under High-Flux Conditions AlChE J. (IF 2.836) Pub Date : 2017-12-08 Kazuki Akamatsu, Keita Ishizaki, Shotaro Yoshinaga, Shin-ichi Nakao
The effect of suction flow on the mass transfer coefficient of tubular ultrafiltration membranes, in particular that under a high flux condition, was studied. We pointed out that Nsh is proportional to NRe 0.875 NSc 0.25 under turbulent conditions, and that the proportional constant, b, exceeds 0.023 when the effect of suction flow is not negligible. We conducted the velocity variation method using ultrafiltration membranes with MWCOs of 20k and 100k and dextrans having molecular weights of 40,000 and 70,000 at the conditions where NRe exceeded 3.6 × 103. We demonstrated that the effect of suction flow includes not only flux but also the diffusion coefficient of solute, and that the ratio of the flux to the diffusion coefficient, expressed as , is an important index. Finally, we concluded that b = 0.023 when is smaller than 2.23 × 103, giving the Deissler equation itself, and that when exceeds 2.23 × 103. This article is protected by copyright. All rights reserved.
Heat Transfer Characteristics of Polymer Hollow Fiber Heat Exchanger for Vaporization Application AlChE J. (IF 2.836) Pub Date : 2017-12-08 Jun Liu, Hong Guo, Xingxing Zhi, Lei Han, Kai Xu, Hailei Li, Baoan Li
The heat transfer characteristics of polymer hollow fiber heat exchanger were investigated by analysing the heat transfer coefficient (HTC) and the heat transfer resistance (HTR) distributions of both the lumen side and the shell side. The influences of the fiber wall thickness and the polymer thermal conductivity on the heat transfer performance were studied numerically based on the experimental validated simulation model. It is found that the original overall HTC value is below 1032 W/m2·K and the HTR is focus on the fiber wall. However, if enhancing the polymer thermal conductivity to be higher than 1.0 W/m·K and/or lowering the fiber wall thickness to be less than 0.1 mm, the overall HTC could be improved to over 2000 W/m2·K, which indicates that the fiber wall HTR is no longer the limiting factor of the polymer hollow fiber heat exchanger applications. This article is protected by copyright. All rights reserved.
Model fitting of sorption kinetics data: Rectification of misapplications overlooked AlChE J. (IF 2.836) Pub Date : 2017-12-08 Yifeng Huang, Muhammad U. Farooq, Shuixiu Lai, Panida Sampranpiboon, Xiaodong Wang, Wei Huang, Xianshe Feng
When the model fitting of sorption kinetics data was carried out using linearized pseudo second order rate equations based on constant Qe corresponding to equilibrium sorption, the instantaneous driving force for sorption was underestimated, resulting in an erroneous overestimation of the rate constant. To resolve the issue, a rectification of the model fitting was proposed by accounting for the concentration dependence of Qe in the model equation based on the fact that Qe in the equation represents the sorption capacity at that instant as sorption proceeded with time. The rectified approach was validated with experimental data for various sorption systems reported in the literature. It was shown that the rectification yielded true sorption rate constant that characterizes the relationship between sorption rate and solute concentration, thereby resolving the issues associated with the original approach where the specific rate constant was found to depend on solute concentration and sorption time. This article is protected by copyright. All rights reserved.
Limiting Flux in Microfiltration of Colloidal Suspensions by Focusing on Hydrodynamic Forces in Viscous Sublayer AlChE J. (IF 2.836) Pub Date : 2017-12-08 Ryo Makabe, Kazuki Akamatsu, Shin-ichi Nakao
Cross-flow microfiltration tests were performed on colloidal suspensions under turbulence conditions. By changing the particle diameter, flow rate, and channel height in the membrane housing to measure limiting fluxes, the influence of each parameter on the limiting flux was assessed from the viewpoint of hydrodynamic forces exerted on a particle in the viscous sublayer. In analyzing all the data taken, we found that the particle Reynolds number calculated from the limiting flux is proportional to the 1.5-power of that calculated from the flow rate at the boundary between the viscous sublayer and the intermediate layer. This fact indicates that the limiting flux can be determined in situations where the drag force exerted by the flux is balanced by the lift force in the viscous sublayer. This article is protected by copyright. All rights reserved.
Enhanced CO2 separation performance for tertiary amine-silica membranes via thermally induced local liberation of CH3Cl AlChE J. (IF 2.836) Pub Date : 2017-12-07 Liang Yu, Masakoto Kanezashi, Hiroki Nagasawa, Norihiro Moriyama, Toshinori Tsuru, Kenji Ito
A facile method for the fabrication of amine-silica membranes with enhanced CO2 separation performance was proposed via the thermally induced liberation of small molecules from quaternary ammonium salt. Quaternary ammonium-silica (QA-SiO1.5) xerogel powders/films were fabricated via sol-gel processing and their thermal stability was systematically studied using thermogravimetric mass spectrometer, Fourier transform infrared, energy dispersive spectroscopy, and positron annihilation lifetime spectroscopy analysis. CO2 sorption performances of QA-SiO1.5 derived xerogel powders were quantitatively compared after assigning their relevant parameters to a dual-mode sorption model. The gas permeation performances of membranes derived from QA-SiO1.5 were evaluated in terms of kinetic diameter and temperature dependence of gas permeance, and activation energy (Ep) required for gas permeation. The results indicate that liberation of the CH3Cl molecules from these membranes significantly improved both CO2 permeation and CO2/N2 separation capabilities. Therefore, the present study provides insight that should be useful in the development of high-performance CO2 separation membranes via the effect of the thermally induced liberation of small molecules. © 2017 American Institute of Chemical Engineers AIChE J, 2017
Stem cell biomanufacturing under uncertainty: A case study in optimizing red blood cell production AlChE J. (IF 2.836) Pub Date : 2017-12-07 Ruth Misener, Mark C. Allenby, María Fuentes-Garí, Karan Gupta, Thomas Wiggins, Nicki Panoskaltsis, Efstratios N. Pistikopoulos, Athanasios Mantalaris
As breakthrough cellular therapy discoveries are translated into reliable, commercializable applications, effective stem cell biomanufacturing requires systematically developing and optimizing bioprocess design and operation. This article proposes a rigorous computational framework for stem cell biomanufacturing under uncertainty. Our mathematical tool kit incorporates: high-fidelity modeling, single variate and multivariate sensitivity analysis, global topological superstructure optimization, and robust optimization. The advantages of the proposed bioprocess optimization framework using, as a case study, a dual hollow fiber bioreactor producing red blood cells from progenitor cells were quantitatively demonstrated. The optimization phase reduces the cost by a factor of 4, and the price of insuring process performance against uncertainty is approximately 15% over the nominal optimal solution. Mathematical modeling and optimization can guide decision making; the possible commercial impact of this cellular therapy using the disruptive technology paradigm was quantitatively evaluated. © 2017 American Institute of Chemical Engineers AIChE J, 2017
Numerical and experimental evaluation of heat transfer in helically corrugated tubes AlChE J. (IF 2.836) Pub Date : 2017-12-06 David J. Van Cauwenberge, Jens N. Dedeyne, Kevin M. Van Geem, Guy B. Marin, Jens Floré
The enhancement of convective heat transfer in single-phase heat transfer through the use of helicoidally corrugated tubes has been studied numerically. By comparing the large eddy simulation (LES) results with detailed Stereo-PIV and Liquid Crystal Thermography measurements obtained at the von Karman Institute for Fluid Dynamics (VKI), a validated numerical framework was obtained. Heat transfer enhancements of 83–119% were seen, at the cost of pressure losses that were approximately 5.6 to 6.7 times higher than for a bare tube. To extrapolate the results to industrial Reynolds numbers at which experimental data is scarce, the simulation data was used to develop an improved near-wall Reynolds stress transport model (RSTM) that more accurately describes the heat flux vector. Comparison of both global and local flow characteristics at different Reynolds numbers confirms that the approach allows more accurate predictions over a wider range of design and operating parameters than using two-equation turbulence models, while the computational cost is still significantly lower than LES. © 2017 American Institute of Chemical Engineers AIChE J, 2017
A Full-condition Monitoring Method for Nonstationary Dynamic Chemical Processes with Cointegration and Slow Feature Analysis AlChE J. (IF 2.836) Pub Date : 2017-12-06 Chunhui Zhao, Biao Huang
Chemical processes are in general subject to time variant conditions because of load changes, product grade transitions, or other causes, resulting in typical nonstationary dynamic characteristic. It is of a considerable challenge for process monitoring to consider all possible operation conditions simultaneously including multifarious steady states and dynamic switchings. In the present work, a novel full-condition monitoring strategy is proposed based on both cointegration analysis (CA) and slow feature analysis (SFA) with the following considerations: (1) Despite that the operation conditions may vary over time, they may follow certain equilibrium relations that extend beyond the current time; (2) there may exist certain dynamic relations that stay invariant under normal process operation despite process may operate at different operating conditions. To monitor both equilibrium and dynamic relations, in the proposed method, nonstationary variables are separated from stationary variables first. Then by CA and SFA, the long-term equilibrium relation is distinguished from the specific relation held by the current conditions from both static and dynamic aspects. Various monitoring statistics are designed with clear physical interpretation. It can distinguish between the changes of operation conditions and real faults by checking deviations from equilibrium relation and deviations from the specific relation. Case study on a chemical industrial scale multiphase flow experimental rig shows the validity of the proposed full-condition monitoring method. This article is protected by copyright. All rights reserved.
Modeling of circulating fluidized beds systems for post-combustion CO2 capture via temperature swing adsorption AlChE J. (IF 2.836) Pub Date : 2017-12-06 Stefano E. Zanco, Marco Mazzotti, Matteo Gazzani, Matteo C. Romano, Isabel Martínez
The technology of circulating fluidized beds (CFBs) is applied to temperature swing adsorption (TSA) processes for post-combustion CO2 capture employing a commercial zeolite sorbent. Steady state operation is simulated through a one-dimensional model, which combines binary adsorption with the CFB dynamics. Both single step and multi-step arrangements are investigated. Extensive sensitivity analyses are performed varying the operating conditions, in order to assess the influence of the main operational parameters. The results reveal a neat superiority of multi-step configurations over the standard one, in terms of both separation performance and efficiency. Compared to fixed-bed TSA systems, CFB TSA features a high compactness degree. However, product purity levels are limited compared to the best performing fixed-bed processes, and heat management within the system appears to be a major issue. As regards energy efficiency, CFB systems place themselves in between the most established absorption-based technologies and the fixed-bed TSA. © 2017 American Institute of Chemical Engineers AIChE J, 2017
Combined Effects of Soot Load and Catalyst Activity on the Regeneration Dynamics of Catalytic Diesel Particulate Filters AlChE J. (IF 2.836) Pub Date : 2017-12-05 Valeria Di Sarli, Almerinda Di Benedetto
These findings highlight the importance of avoiding the cake formation, while properly optimizing the catalyst activity, to conduct an effective regeneration of catalytic filters. This article is protected by copyright. All rights reserved.
Optimal operation of batch enantiomer crystallization: From ternary diagrams to predictive control AlChE J. (IF 2.836) Pub Date : 2017-12-05 Caio Felippe Curitiba Marcellos, Helen Durand, Joseph Sang-Il Kwon, Amaro Gomes Barreto, Paulo Laranjeira da Cunha Lage, Maurício Bezerra de Souza, Argimiro Resende Secchi, Panagiotis D. Christofides
In this work, the modeling and control of batch crystallization for racemic compound forming systems is addressed in a systematic fashion. Specifically, a batch crystallization process is considered for which the initial solution has been pre-enriched in the desired enantiomer to enable crystallization of only the preferred enantiomer. A method for determining desired operating conditions (composition of the initial pre-enriched solution and temperature to which the mixture must be cooled for maximum yield) for the batch crystallizer based on a ternary diagram for the enantiomer mixture in a solvent is described. Subsequently, it is shown that the information obtained from the ternary diagram, such as the maximum yield attainable from the process due to thermodynamics, can be used to formulate constraints for an optimization-based control method to achieve desired product characteristics such as a desired yield. The proposed method is demonstrated for the batch crystallization of mandelic acid in a crystallizer with a fines trap that is seeded with crystals of the desired enantiomer. The process is controlled with an optimization-based controller to minimize the ratio of the mass of crystals obtained from nuclei to the mass obtained from seeds while maintaining the desired enantioseparation. © 2017 American Institute of Chemical Engineers AIChE J, 2017
Feedback control of proppant bank heights during hydraulic fracturing for enhanced productivity in shale formations AlChE J. (IF 2.836) Pub Date : 2017-12-05 Prashanth Siddhamshetty, Joseph Sang-Il Kwon, Shuai Liu, Peter P. Valkó
In hydraulic fracturing of shale formations, compared to conventional reservoirs, the fracturing fluid injected is of low-viscosity and hence during pumping the proppant settles significantly, forming a proppant bank. Motivated by this consideration, we initially develop a high-fidelity process model of hydraulic fracturing to describe the dominant proppant settling behavior during hydraulic fracturing process. Second, a novel remeshing strategy is developed to handle the high computational requirement due to moving boundaries. Third, a section-based optimization method is employed to obtain key fracture design parameters for enhanced productivity in shale formations subject to given fracturing resources. Fourth, a reduced-order model is constructed to design a Kalman filter and to synthesize a real-time model-based feedback control system by explicitly taking into account actuator limitations, process safety and economic considerations. We demonstrate that the proposed control scheme can regulate the uniformity of proppant bank heights along the fracture at the end of pumping. © 2017 American Institute of Chemical Engineers AIChE J, 2017
Simulation and modeling of segregating rods in quasi-2D bounded heap flow AlChE J. (IF 2.836) Pub Date : 2017-12-05 Yongzhi Zhao, Hongyi Xiao, Paul B. Umbanhowar, Richard M. Lueptow
Many products in the chemical and agricultural industries are pelletized in the form of rod-like particles that often have different aspect ratios. However, the flow, mixing, and segregation of non-spherical particles such as rod-like particles are poorly understood. Here, we use the discrete element method (DEM) utilizing super-ellipsoid particles to simulate the flow and segregation of rod-like particles differing in length but with the same diameter in a quasi-2D one-sided bounded heap. The DEM simulations accurately reproduce the segregation of size bidisperse rod-like particles in a bounded heap based on comparison with experiments. Rod-like particles orient themselves along the direction of flow, although bounding walls influence the orientation of the smaller aspect ratio particles. The flow kinematics and segregation of bidisperse rods having identical diameters but different lengths are similar to spherical particles. The segregation velocity of one rod species relative to the mean velocity depends linearly on the concentration of the other species, the shear rate, and a parameter based on the relative lengths of the rods. A continuum model developed for spherical particles that includes advection, diffusion, and segregation effects accurately predicts the segregation of rods in the flowing layer for a range of physical control parameters and particle species concentrations. © 2017 American Institute of Chemical Engineers AIChE J, 2017
Magnetic resonance imaging of gas–solid fluidization with liquid bridging AlChE J. (IF 2.836) Pub Date : 2017-12-05 C. M. Boyce, A. Penn, K. P. Pruessmann, C. R. Müller
Magnetic resonance imaging is used to generate snapshots of particle concentration and velocity fields in gas–solid fluidized beds into which small amounts of liquid are injected. Three regimes of bed behavior (stationary, channeling, and bubbling) are mapped based on superficial velocity and liquid loading. Images are analyzed to determine quantitatively the number of bubbles, the bubble diameter, bed height, and the distribution of particle speeds under different wetting conditions. The cohesion and dissipation provided by liquid bridges cause an increase in the minimum fluidization velocity and a decrease in the number of bubbles and fast particles in the bed. Changes in liquid loading alter hydrodynamics to a greater extent than changes in surface tension or viscosity. Keeping U/Umf at a constant value of 1.5 produced fairly similar hydrodynamics across different wetting conditions. The detailed results presented provide an important dataset for assessment of the validity of assumptions in computational models. © 2017 American Institute of Chemical Engineers AIChE J, 2017
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