Showing papers in "Aiche Journal in 2006"

Fault detection and diagnosis based on modified independent component analysis

Abstract: A novel multivariate statistical process monitoring (MSPM) method based on modified independent component analysis (ICA) is proposed. ICA is a multivariate statistical tool to extract statistically independent components from observed data, which has drawn considerable attention in research fields such as neural networks, signal processing, and blind source separation. In this article, some drawbacks of the original ICA algorithm are analyzed and a modified ICA algorithm is developed for the purpose of MSPM. The basic idea of the approach is to use the modified ICA to extract some dominant independent components from normal operating process data and to combine them with statistical process monitoring techniques. Variable contribution plots to the monitoring statistics (T2 and SPE) are also developed for fault diagnosis. The proposed monitoring method is applied to fault detection and diagnosis in a wastewater treatment process, the Tennessee Eastman process, and a semiconductor etch process and is compared with conventional PCA monitoring methods. The monitoring results clearly illustrate the superiority of the proposed method. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Density functional theory for chemical engineering: From capillarity to soft materials

Abstract: Understanding the microscopic structure and macroscopic properties of condensed matter from a molecular perspective is important for both traditional and modern chemical engineering. A cornerstone of such understanding is provided by statistical mechanics, which bridges the gap between molecular events and the structural and physiochemical properties of macro- and mesoscopic systems. With ever-increasing computer power, molecular simulations and ab initio quantum mechanics are promising to provide a nearly exact route to accomplishing the full potential of statistical mechanics. However, in light of their versatility for solving problems involving multiple length and timescales that are yet unreachable by direct simulations, phenomenological and semiempirical methods remain relevant for chemical engineering applications in the foreseeable future. Classical density functional theory offers a compromise: on the one hand, it is able to retain the theoretical rigor of statistical mechanics and, on the other hand, similar to a phenomenological method, it demands only modest computational cost for modeling the properties of uniform and inhomogeneous systems. Recent advances are summarized of classical density functional theory with emphasis on applications to quantitative modeling of the phase and interfacial behavior of condensed fluids and soft materials, including colloids, polymer solutions, nanocomposites, liquid crystals, and biological systems. Attention is also given to some potential applications of density functional theory to material fabrications and biomolecular engineering. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Supercritical water oxidation: A technical review

Abstract: Supercritical water oxidation (SCWO) technology presents important environmental advantages for the treatment of industrial wastes and sludges. The homogeneous reaction that takes place between the oxidizable materials and oxygen, at temperatures and pressures above the critical point of the water (647.3 K and 22.12 MPa), is well known. Specific equations of state for water and aqueous mixtures, gases, and organics have been developed. The process is not having the expected industrial development. Some new plants have been closed by corrosion and operational problems related with high temperature, high pressure, and oxidative atmosphere inside of the equipments. To overcome these technical difficulties more research focused on solving operational problems is necessary. This article presents an overview of the technical aspects of the supercritical water oxidation process. Reactors design, construction materials, corrosion, salts precipitation problems, and industrial applications are discussed. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Liquid‐liquid two‐phase flow patterns in a rectangular microchannel

Abstract: In this work, the flow of immiscible fluids in a PMMA microchannel 300 mu m wide and 600 pm deep was investigated experimentally Dyed de-ionized water and kerosene were selected as the test fluids Flow patterns were observed by using a CCD camera and were identified by examining the video images Flow patterns obtained at the T-junction and in the microchannel are presented Superficial velocities varied between 926 x 10(-4) similar to 185 m/s for water and 926 x 10(-4) similar to 278 m/s for kerosene The formation mechanism of slug, monodispersed droplet and droplet populations at the T-junction was studied Weber numbers of water and kerosene, We(KS) and We(WS), were used to predict the flow regime transition and the flow patterns map The experimental data of volume of dispersed phase were successfully correlated as a function of We(KS), We(WS), and hold-up fraction Considering the uncertainty associated with experimental quantification of the process, the results are in satisfactory agreement over the wide range of 190 x 10(-3) < We(WS) < 3043 and 590 x 10(-6) < We(KS) < 013 with average absolute deviation of only 1618% (c) 2006 American Institute of Chemical Engineers

Characterization of gas crossover and its implications in PEM fuel cells

Abstract: With pure hydrogen as the fuel, PEM fuel cell operation at or near 100% fuel utilization is desirable to achieve a high stack efficiency and zero emissions. However, typical membranes used in PEM fuel cells allow a finite amount of permeation rates or crossover of hydrogen, oxygen, and nitrogen across the membrane. The hydrogen and oxygen that permeate through the membrane are consumed with the generation of heat and water but without the generating of useful work, leading to a fuel inefficiency. Nitrogen crossover, on the other hand, from the cathode side to the anode side accumulates at the exit of the anode flow fields, lowering the hydrogen concentration and resulting in local fuel starvation. In this study, an in-situ electrochemical technique has been applied to determine the magnitude of the hydrogen crossover over a range of relevant fuel cell operating temperatures and pressures. Permeability coefficients thus obtained are compared to values reported in the literature. A mathematical model is developed to predict the extent of nitrogen accumulation along the anode flow fields, and fuel recycle as a mitigation method is simulated by improving hydrogen distribution. The model results were validated by comparison with experimental results. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Preparation of highly monodisperse droplet in a T-junction microfluidic device

Abstract: In our previous work, a new flow route was developed—a so-called perpendicular shear force–induced droplet formation—in a self-designed simple T-junction microchannel device. In this work, the crossflowing rupture technique was used to prepare monodisperse droplets in a similar device and successfully prepared monodisperse droplets ranging from 50 to 500 μm with polydispersity index (σ) values of <2%. Two kinds of flow patterns of plug flow and drop flow in the T-junction microchannels could be formed. By changes in the surfactant concentration, the interfacial tension and the wetting ability varied, and the disordered or ordered two-phase flow patterns could be controlled. Evolutions of the contact angle of the oil in contact with the wall surface were explained by the adsorption of surfactant molecules to the solid–liquid interface. The increase of continuous phase flow rate and viscosity resulted in the decrease of the droplet size, and the droplet size was correlated with capillary number Ca. By comparing the variation range of drop size using the two methods, it was found that the method of perpendicular flow-induced droplet formation can control the drop size over a much wider range. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Solubility and diffusivity of hydrofluorocarbons in room-temperature ionic liquids

Abstract: Gaseous absorption measurements of hydrofluorocarbons (trifluoromethane, difluoromethane, pentafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1-trifluoroethane, and 1,1-difluoroethane) in l-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) were performed using a gravimetric microbalance at various isothermal conditions (temperatures between 283.15 and 348.15 K) and at pressures < 2 MPa. This report shows for the first time the solubility and diffusivity data for the hydrofluorocarbons in room-temperature ionic liquids and surprisingly large differences in the solubility among the hydrofluorocarbons. Experimental gas solubility data were successfully correlated with well-known solution models (Margules, Wilson, and NRTL activity coefficient equations). Diffusivities obtained from the time-dependent absorption data were well analyzed using a diffusivity model developed in this study. The present solubility and diffusivity data are also compared with those of CO2, studied in our previous study. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Unified conceptual approach to targeting and design of water and hydrogen networks

Abstract: An algorithm is proposed to target the minimum freshwater for fixed flow rate (FF) problems in single-contaminant water networks. The approach is based on an extension of the limiting composite curve concept proposed earlier for fixed contaminant-load (FC) problems. The targeting method is elegant, noniterative, and can be applied to FF problems involving regeneration to minimize waste discharge. To design networks that achieve the minimum freshwater targets set for FF problems, an algorithm is presented based on the principle of nearest neighbors. The principle simply states that the sources to be chosen to satisfy a particular water demand must be the nearest available neighbors in terms of contaminant concentration. A significant advantage of the approach is that the same targeting concepts can be profitably used to determine the minimum makeup utility in hydrogen networks. Furthermore, hydrogen networks may be designed by the unified conceptual approach using the nearest neighbors algorithm. The hydrogen networks may then be evolved to account for the pressure constraints imposed by compressors or improved by regeneration through purification processes such as pressure-swing adsorption. © 2005 American Institute of Chemical Engineers AIChE J, 2006

On the breakup of fluid particles in turbulent flows

Abstract: Dynamics of bubble and drop breakup in turbulent flows have been studied in detail, using a high-speed CCD camera. Analysis of breakup times, deformations, deformation velocities, number of fragments, and the resulting daughter size distributions show that there are several important differences in the breakup mechanism of bubbles and drops. It is shown that the increase in interfacial energy prior to breakup exceeds the increase after breakup. The use of an activation barrier that better describes the turbulent structures that can interact with fluid particles and also cause breakup is proposed. Measurements under identical hydrodynamic conditions reveal that an internal flow redistribution mechanism is responsible for generation of unequal-sized bubble fragments. Due to the three orders of magnitude higher density of liquids than of gases, this mechanism does not occur for drops. The measurements also show that assumption of binary breakup is reasonable for bubbles but not for drops.© 2006 American Institute of Chemical Engineers.

CFD predictions for chemical processing in a confined impinging‐jets reactor

Abstract: Confined impinging-jets reactors (CIJR) offer many advantages for the chemical processing of rapid processes, such as precipitation and the production of organic nanoparticles. Nevertheless, due to the lack of predictive design criteria, the use of such a reactor for a new process currently requires a significant experimental campaign before it can be used commercially. Experimentally derived scale-up rules for CIJRs have recently been reported. Using carefully controlled experiments with a fast parallel-reaction system, the conversion of 2,2-dimethoxypropane (DMP) for a wide range of jet Reynolds numbers have been measured. The experimental conversion data can be accurately predicted using computational fluid dynamics (CFD) for the range of jet Reynolds number where the flow is turbulent. In addition, the CFD provides a wealth of detailed information on the reacting flow inside of the CIJR. Such information provides excellent guidance for improving the performance of the reactor by, for example, changes in the geometry. By clearly illustrating the ability of CFD to reproduce (without adjustable parameters) the experimental data for a CIJR, this study makes a significant step in the direction of “experiment-free” design and scale-up of chemical reactors. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Biomass gasification in a bubbling fluidized bed reactor: Experiments and modeling

Abstract: A model is presented for the gasification of beech wood particles in a bubbling fluidized bed gasifier (BFBG). The model encompasses the hydrodynamics of the solid and gas phases as well as the different reaction kinetics. It also accounts for the freeboard where additional homogeneous reactions take place. The influential impact of the pyrolysis step on the final composition of produced fuel gas was demonstrated by applying two different kinetic models for pyrolysis. Model results are compared with the experimental work of this study and other published results on wood gasification in BFBG. Effects of equivalence ratio (ER), steam to biomass ratio (SB), bed temperature, feed location, and mass transfer between the countercurrent regions (Kw) on the gas composition of product fuel gas are studied. The model shows good agreement with the experimental results. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Dehydration of glycerol to acetol via catalytic reactive distillation

Abstract: Dehydration of glycerol was performed in the presence of various metallic catalysts including alumina, magnesium, ruthenium, nickel, platinum, palladium, copper, raney nickel, and copper-chromite catalysts to obtain acetol in a single-stage reactive distillation unit under mild conditions. The effects of operation mode, catalyst selection, glycerol-feed flow rate, catalyst loading, and initial water content were studied to arrive at optimum conditions. High-acetol selectivity levels (> 90%) were achieved using copper-chromite catalyst, and operating in semi-batch reactive distillation mode. A small amount of water content in glycerol feedstock was found to reduce the tendency for residue to form, therein extending catalyst life. The acetol from this reaction readily hydrogenates to form propylene glycol, providing an alternative route for converting glycerol to propylene glycol. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Design and scale‐up of chemical reactors for nanoparticle precipitation

Abstract: In recent years there has been a growing interest in production on an industrial scale of particles with size in the sub-micron range (40-200 nm). This can be done by controlling particle formation in order to nucleate very small particles and by tailoring the particle surface in order to avoid particle aggregation and produce stable suspensions. In this work we focus on the role of turbulent mixing on particle formation in confined impinging jet reactors. In particular, we show how computational fluid dynamics and simple precipitation models could be used to derive scale-up criteria for the production of nanoparticles. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Optimization strategies for simulated moving bed and PowerFeed processes

Abstract: Simulated moving bed (SMB) processes have been applied to many important separations in sugar, petrochemical, and pharmaceutical industries. However, systematic optimization of SMB is still a challenging problem. Two tailored approaches are proposed, full discretization and single discretization, where both the optimal operating condition and concentration profiles are obtained by a Newton-type solver. In a case study of fructose and glucose separation, it has been found that the full-discretization method implemented on AMPL with IPOPT is more efficient than single-discretization method on gPROMS with SRQPD. The reliability of the full-discretization method is also demonstrated with case studies of a bi-Langmuir isotherm and a PowerFeed optimization problem. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Simulation of binary mixture adsorption of methane and CO2 at supercritical conditions in carbons

Abstract: Knowledge of the adsorption behavior of coal-bed gases, mainly under supercritical high-pressure conditions, is important for optimum design of production processes to recover coal-bed methane and to sequester CO 2 in coal-beds. Here, we compare the two most rigorous adsorption methods based on the statistical mechanics approach, which are Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) simulation, for single and binary mixtures of methane and carbon dioxide in slit-shaped pores ranging from around 0.75 to 7.5 nm in width, for pressure up to 300 bar, and temperature range of 308-348 K, as a preliminary study for the CO 2 sequestration problem. For single component adsorption, the isotherms generated by DFT, especially for CO 2 , do not match well with GCMC calculation, and simulation is subsequently pursued here to investigate the binary mixture adsorption. For binary adsorption, upon increase of pressure, the selectivity of carbon dioxide relative to methane in a binary mixture initially increases to a maximum value, and subsequently drops before attaining a constant value at pressures higher than 300 bar. While the selectivity increases with temperature in the initial pressure-sensitive region, the constant high-pressure value is also temperature independent. Optimum selectivity at any temperature is attained at a pressure of 90-100 bar at low bulk mole fraction of CO 2 , decreasing to approximately 35 bar at high bulk mole fractions.

A CFD–PBM coupled model for gas–liquid flows

Abstract: A computational fluid dynamics-population balance model (CFD-PBM) coupled model was developed that combines the advantages of CFD to calculate the entire flow field and of the PBM to calculate the local bubble size distribution. Bubble coalescence and breakup were taken into account to determine the evolution of the bubble size. Different bubble breakup and coalescence models were compared. An algorithm was proposed for computing the parameters based on the bubble size distribution, including the drag force, transverse lift force, wall lubrication force, turbulent dispersion force, and bubble-induced turbulence. With the bubble breakup and coalescence models and the interphase force formulations in this work, the CFD-PBM coupled model can give a unified description for both the homogeneous and the heterogeneous regimes. Good agreement was obtained with the experimental results for the gas holdup, liquid velocity, and bubble size distribution.

NH3‐SCR of NO over a V‐based catalyst: Low‐T redox kinetics with NH3 inhibition

Abstract: We present transient kinetic data that demonstrate an inhibiting effect of ammonia on the NH3-selective catalytic reduction (SCR) of nitric oxide (NO) at low temperatures over a V2O5-WO3/TiO2 commercial catalyst for vehicles. This effect has significant mechanistic as well as practical implications. It cannot be reproduced by conventional or modified Eley–Rideal approaches used in the past for SCR-deNOx stationary applications, but is well described by a novel dual-site redox rate expression assuming that ammonia may block the vanadium-related catalyst sites for NO + NH3 activation. The same rate model also successfully represents the kinetic influence of the oxygen concentration. It is shown that account of ammonia inhibition at low temperatures is critical for simulating the highly transient operation of onboard SCR converters for diesel exhaust aftertreatment. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Global optimization of a combinatorially complex generalized pooling problem

Abstract: Global optimization strategies are described for a generalization of the pooling problem that is important to the petrochemical, chemical, and wastewater treatment industries. The problem involves both discrete variables, modeling the structure of a flow network, and continuous variables, modeling flow rates, and stream attributes. The continuous relaxation of this mixed integer nonlinear programming problem is nonconvex because of the presence of bilinear terms in the constraint functions. We propose an algorithm to find the global solution using the principles of the reformulation-linearization technique (RLT). A novel piecewise linear RLT formulation is proposed and applied to the class of generalized pooling problems. Using this approach we verify the global solution of a combinatorially complex industrial problem containing 156 bilinear terms and 55 binary variables, reducing the gap between upper and lower bounds to within 1.2%. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Diamine modification of P84 polyimide membranes for pervaporation dehydration of isopropanol

Abstract: The effectiveness of chemical crosslinking modification of P84 copolyimide membranes using diamine compounds for pervaporation dehydration has been investigated and the scheme to enhance separation performance of asymmetric polyimide membranes has been developed. Two diamine crosslinking agents, p-xylenediamine and ethylenediamine (EDA), were used in this study for both dense and asymmetric P84 membranes. Experimental results suggest that the crosslinking reaction induced by EDA is much faster than that by p-xylenediamine because the former has a smaller and linear structure than that of the latter. However, membranes crosslinked by p-xylenediamine are thermally more stable than those by EDA. Membranes modified by p-xylenediamine or EDA have increased hydrophilicity. An increase in the degree of crosslinking reaction initially results in an increase in separation factor with the compensation of lower flux for pervaporation dehydration of isopropanol (IPA). However, a further increase in the degree of crosslinking reaction may swell up the polymeric chains because of the hydrophilic nature of these diamine compounds, thus resulting in low separation performance. It is found that post treatment after crosslinking reaction can significantly enhance as well as tailor membrane performance because of the formation of charge transfer complexes (CTCs) and the enhanced degree of crosslinking reaction. A low-temperature heat treatment may develop pervaporation membranes with high flux and medium separation factor, whereas a high-temperature heat treatment may produce membranes with high separation factor with medium flux. © 2006 American Institute of Chemical Engineers AIChE J, 52: 3462–3472, 2006

Automatic reaction network generation using RMG for steam cracking of n-hexane

Abstract: A new reaction mechanism generator RMG is used to automatically construct a pressure dependent kinetic model for the steam cracking of n-hexane. Comparison between simulated and pilot plant data shows that RMG is able to generate detailed reaction networks that accurately predict the conversion and the yields of the major products although none of the kinetic parameters are fit to the experiments. RMG generates reaction networks based on minimal assumptions, making it possible to test commonly used assumptions such as the -hypothesis and the quasi steady-state approximation (QSSA) for -radicals, traditionally used in steam cracking, 1,2 as well as in pyrolysis. 3 The RMG-reaction network for n-hexane confirms that no bimolecular reactions of heavy radical species are important at the examined conditions (COT: 953 K 1090 K; COP: 0.20 MPa -0.24 MPa; 80% conversion), and that the QSSA for the group of -radicals leads to negligible errors. RMG also offers the possibility to estimate the error introduced by neglecting the pressure dependence of most of the reactions. In the case studied, this frequently made (but seldom tested) approximation appears to be justified. © 2005 American Institute of Chemical Engineers AIChE J, 52: 718 –730, 2006

Numerical simulation of behavior of gas bubbles using a 3‐D front‐tracking method

Abstract: In this paper a three-dimensional (3-D) front-tracking (FT) model is presented featuring a new method to evaluate the surface force model that circumvents the explicit computation of the interface curvature. This method is based on a direct calculation of the net tensile forces acting on a differential element of the interface. Our model can handle a large density and viscosity ratio and a large value of the surface tension coefficient characteristic for gas-liquid systems. First, the results of a number of test cases are presented to assess the correctness of the implementation of the interface advection and remeshing algorithms and the surface tension model. Subsequently, the computed terminal Reynolds numbers and shapes of isolated gas bubbles rising in quiescent liquids are compared with data taken from the bubble diagram of Grace. In addition drag coefficients for rising air bubbles in water were successfully computed, a system that has proven difficult to simulate by other methods, and showed good agreement with existing correlations. Finally, a number of sample calculations involving multiple bubbles are reported to demonstrate the capabilities of our three-dimensional FT model.

Integrated fault-detection and fault-tolerant control of process systems

Abstract: The problem of implementing fault-tolerant control to nonlinear processes with input constraints subject to control actuator failures is considered, and an approach predicated upon the idea of integrating fault-detection, feedback and supervisory control is presented and demonstrated. To illustrate the main idea behind the proposed approach, availability of measurements of all the process state variables is initially assumed. For the processes under consideration, a family of candidate control configurations, characterized by different manipulated inputs, is first identified. For each control configuration, a Lyapunov-based controller that enforces asymptotic closed-loop stability in the presence of constraints, is designed, and the constrained stability region, associated with it, is explicitly characterized. A fault-detection filter is used to compute the expected closed-loop behavior in the absence of faults. Deviations of the process states from the expected closed-loop behavior are used to detect faults. A switching policy is then derived, on the basis of the stability regions, to orchestrate the activation/deactivation of the constituent control configurations in a way that guarantees closed-loop stability in the event that a failure is detected. Often, in chemical process applications, not all state variables are available for measurement. To deal with the problem of lack of process state measurements, a nonlinear observer is designed to generate estimates of the states, which are then used to implement the state feedback controller and the fault-detection filter. A switching policy is then derived to orchestrate the activation/deactivation of the constituent control configurations in a way that accounts for the estimation error. Finally, simulation studies are presented to demonstrate the implementation and evaluate the effectiveness of the proposed fault-tolerant control scheme, as well as to investigate an application in the presence of uncertainty and measurement noise. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Experimental and numerical study of droplets hydrodynamics in microchannels

Abstract: This article reports on numerical simulations and experimental determination of the hydrodynamics of liquid–liquid flow in rectangular microchannels. The numerical method is an interface-capturing technique without any interface reconstruction. Microparticle image velocimetry (micro-PIV) measurements are used to obtain experimental velocity fields inside droplets that are compared to simulations. Finally, injecting a passive tracer in the simulated droplets also helps to obtain a better understanding of the mixing phenomenon. These results allow interpreting mixing defaults during bleaching experiments inside microdroplets. Furthermore, this study leads to important results about interface deformation and velocity fields inside the droplets and in the continuous phase for mass- and heat-transfer studies. 2006 American Institute of Chemical Engineers AIChE J, 52: 4061–4070, 2006

Chemical product engineering: An emerging paradigm within chemical engineering

Abstract: New product development is a crucial task for modern corporations. Facing an increasingly competitive and dynamic market, the ability to continuously identify customer needs and create products that meet such needs is essential to business success. As a result, researchers from fields such as management, marketing, industrial design and engineering have devoted their attention to new product development issues, and many references can be found in the literature covering this topic.1-5 New product development combines strategic and organizational actions with technical effort; the former dealing with the management of the development process, strategic placement and launch of the new product; the latter being chiefly concerned with the design of the product and its manufacturing process. While in some industrial and engineering sectors, such as mechanical and electronic, the technical side of the development process has always been appreciated as a major issue, in the chemical process industries the systematic and efficient design of new products is a relatively recent concern. However, these industries, with chemical engineering as their technical support, seem to be making up for lost time, and chemical product engineering is a fast developing concept among both industrial and scientific communities. The aim of this article is to provide a review of the scope of chemical product engineering by discussing its emergence within chemical engineering. Chemical Engineering: Present and Future

Effect of antifreeze protein on nucleation, growth and memory of gas hydrates

Abstract: The effect of Type I antifreeze protein (AFP) from winter flounder on the formation of propane hydrate and methane hydrate was studied. We show that the formation of both hydrates is inhibited significantly, with both nucleation and crystal growth being affected. Also, AFP showed the so-far unique ability to eliminate the "memory effect" in the reformation of gas hydrate. We have proposed a mechanism involving the interference of AFP with heterogeneous nucleation and subsequent growth of the hydrates. It is also shown that a number of samples must be studied in order to obtain meaningful statistics, and that magnetic resonance imaging provides a novel way of studying the nucleation and growth of hydrate in multiple droplets.

Poly(ethylene glycol)/acrylic polymer blends for latent heat thermal energy storage

Abstract: In the present study, polyethylene glycol (PEG) were blended with acrylic polymers like polymethyl methacrylate (PMMA), Eudragit S (Eud S), and Eudragit E (Eud E) as novel form stable phase change materials (PCMs) and characterized by optical microscopy, spectroscopy and viscosity techniques. Latent heat thermal energy storage (LHTES) properties of the blends were evaluated by using the differential scanning calorimetry (DSC) technique. In the form-stable blends, PEG acted like phase change-LHTES material when the acrylic polymers served as supporting material because of their adhesion property. The maximum percentage of PEG was found 80% w/w for any of the blend in which no leakage of PEG occurred for 100 heating/cooling cycles. The optical microscopy investigations revealed that the phase behavior of the blends was observed as self organized PEG distributed in the matrix of acrylic polymers rather than chain-like structures. The interactions between the blend components (PEG and one of the acrylic polymers) were analyzed by Fourier transform infrared (FT-IR) spectroscopy and the viscosimetry technique. The key LHTES properties (melting and freezing temperatures, and latent heats of melting and freezing of the blends) were evaluated by DSC. The DSC results indicated that PEG/PMMA, PEG/Eud S, and PEG/Eud E blends as form-stable PCMs were convenient materials for LHTES applications in terms of their satisfying thermal properties. Therefore, these form-stable PCMs could be incorporated into an LHTES system with the advantage of direct utility in order to store daytime solar energy for space heating. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Formation of monodisperse microbubbles in a microfluidic device

Abstract: The crossflowing rupture technique was first used in a microfluidic device to prepare microbubbles, and successfully prepared monodisperse microbubbles with polydispersity index (σ) values of <2%. The parameters affecting the microbubble-formation process, such as two-phase flow rates, continuous-phase viscosity, surface tension, and surfactants were investigated. The microbubble-formation mechanisms of the crossflowing rupture technique with those of the techniques of both flow-focusing rupture and geometry-dominated breakup were also compared. It was also found that the bubble size decreased with increasing continuous-phase rate and its viscosity, while independent of surface tension. The different species of surfactants also influenced the microbubble-formation process. Moreover, the bubble-formation mechanism by using the crossflow rupture technique was different from the techniques of both hydrodynamic flow focusing and geometry-dominated breakup. The microbubble-formation process using the crossflowing rupture technique is controllable.