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In this paper, a dynamic biomass gasification model was developed based on the hybrid peripheral fragmentation and shrinking-core (HPFS) model. To improve the accuracy of syngas generation transient prediction, the chemical kinetic model was trained using global surrogate optimization techniques. The pre-exponential factors of kinetic reactions are calibrated under non-catalytic conditions, employing experimental transient data of syngas generation rate and compositions under different temperatures and gasifying agents. The DYCORS and GOMORS were employed as the numerical solvers for finding the global optimum solution of the pre-exponential factors. The calibrated kinetic models based on both single-objective and multi-objective approaches have been validated by experimental data in four different biomass gasification scenarios. The calibrated kinetic model shows an over 95% decrease in terms of integrated squared error (ISE)-based model mismatch when compared to the original kinetic model.

In this work, a double-nozzle coaxial electrohydrodynamic atomization (CEHDA) system was designed as an instructive case toward large-scale production of core-shell microspheres. The effect of nozzle-to-nozzle distance was investigated to reveal that the interference between neighboring nozzles significantly affect the product quality in terms of morphology and core-shell structure. Optimal spacing indicated that ∼3000 nozzle/m2 packing density may be achieved with minimum interference of electric field from neighboring nozzle by adjusting the nozzle-to-nozzle distance greater than 0.018 m. The proposed multi-scale model also showed that the X-component of electric field strength (Ex) at the region near side nozzles increases with increasing nozzle number, and the bending of jets/sprays at the side may be reduced by using dummy nozzle at the edge side. The model could guide the design of multi-nozzle CEHDA system for production of core-shell microparticles in large-scale. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5303–5319, 2017

In this study, a computational fluid dynamic (CFD) model was developed to simulate the liquid cone-jet and core-shell droplet formation in the Coaxial Electrohydrodynamic Atomization (CEHDA) process. Validation experiments were conducted using poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) solutions as core and shell materials, respectively. Good agreement was obtained between experimental results and simulation predictions in terms of both particle size and core-shell structure. Investigation of interfacial tension between core and shell fluids showed that a stable compound cone-jet and droplet can be easily formed using miscible or partially miscible liquids compared with immiscible liquids with higher interfacial tension. It was also found that the nozzle tip configuration has significant effects on droplet production due to differences in fluid motion. The results also showed that the productivity of the CEHDA process, that is, slow production of core-shell microparticles due to low flow rates, could be enhanced using optimal cone-shaped nozzle configuration. Overall, this computational model provided a means of designing and optimizing CEHDA processes for large-scale core-shell microparticle fabrication in pharmaceutical application, such as selections of materials and nozzle configuration. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4259–4276, 2016

Experimental and numerical studies of cogasification of woody biomass and sewage sludge have been carried out. The gasification experiments were performed in a fixed-bed downdraft gasifier and the experimental results show that 20 wt % dried sewage sludge in the feedstock was effectively gasified to generate producer gas comprising over 30 vol % of syngas with an average lower heating value of 4.5 MJ/Nm3. Further increasing sewage sludge content to 33 wt % leads to the blockage of gasifier, which is resulted from the formation of agglomerated ash. The numerical models were then developed to simulate the reactions taking place in four different zones of the gasifier (i.e., drying, pyrolysis, combustion, and reduction zones) and to predict the producer gas composition and cold gas efficiency. The deviation between the numerical and experimental results obtained was lower than 10%. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2508–2521, 2015

Electrohydrodynamic atomization (EHDA) is a promising method for the fabrication of micro- and nanosized particles with narrow-size distribution and better morphologies in comparison to conventional methods of particle fabrication. A computational model was developed in this study to simulate the fluid and particle dynamics in an EHDA chamber, and thereby providing a means of predicting particle collection efficiencies at various operating conditions. Experiments were also conducted using a new design of the EHDA chamber. It was found that nitrogen flow rate, solution flow rate and voltage difference between the nozzle and ring can significantly affect the particle collection efficiency of the EHDA process. Electric field and electric potential profiles in the chamber were significantly affected by the combined voltages of the nozzle and ring. In general, a good qualitative agreement in particle collection efficiencies was obtained from experiments and simulations. The computational model developed in this study provided a means of understanding the various processes involved in micro- and nano-sized particle fabrication using the EHDA methodology. © 2012 American Institute of Chemical Engineers AIChE J, 2012

The success of membrane-based, cell-encapsulating microcapsules depends on the membrane permselectivity that provides efficient inward transport of nutrients, therapeutic protein egress, and complete exclusion of immunoglobulins. Microcapsules with a calcium crosslinked alginate core and a genipin-crosslinked chitosan alginate (GCA) were prepared with good control over size, membrane thickness and density. Importantly, in this study, we report a novel approach of using three relevant biomolecules and investigating the effects of the membrane characteristics (thickness and density) and microcapsule size on biomolecular mass transport across the GCA microcapsules using mathematical models based on a balance of the chemical potential. Scaling analysis was used to interrelate the membrane thickness, chitosan–alginate reaction rate constant, and diffusion coefficient. The resistance to diffusion of the three biomolecules increased with membrane density and thickness. Interestingly, swelling in the large microcapsules resulted in an increase in permeability, allowing larger biomolecules (immunoglobulin and carbonic anhydrase) to diffuse more readily. In the case of the smaller biomolecule, vitamin B12, a shorter diffusion path length in smaller microcapsules allowed better ingress. When compared with other microcapsules, the GCA microcapsules possess improved permselectivity for them to allow diffusion of small nutrient molecules and proteins, whereas completely excluding antibodies. Also, these results elucidate the importance of membrane properties and microcapsule size to realize favorable transport of biomolecules. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Electrohydrodynamic atomization (EHDA) process has received more research attention in recent years due to its potential to generate monodisperse droplets of low electric conductivity. It is reported that the EHDA process can be fine-tuned by adjusting the electrical field strength by an additional ring electrode near the nozzle tip to control both the spray mode and the droplet size. In the present study, a computational fluid dynamic (CFD)-based front tracking/finite volume method has been used to investigate numerically the effect of the secondary electric field source and the ring electrode on the EHDA process. The full Navier–Stokes equations are solved for both the liquid phase and the ambient air near the nozzle tip, and the liquid–air interface is monitored using a front tracking approach. At the interface, both the surface tension and the electrical stress due to surface charging and the applied electric field are taken into account. Because of the large dimension difference between the Taylor cone and the liquid jet, the simulations involve two drastically different length scales for describing the dynamic of the entire process. To accurately include the effect of the ring electrode, the electrical field distribution is first calculated over a domain large enough to enclose all key components of the EHDA process. Subsequently, the calculated electrical field in the large domain is integrated with the detailed CFD analysis on a small domain near the region of the nozzle tip. The formations of the Taylor cone, liquid jet, and droplets are successfully simulated and compared with experimental results with reasonable agreement. The numerical simulation method proposed in this article can be used as a platform for the investigation, analysis, and optimization of electrohydrodynamic atomization process. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Photolithography, soft lithography, and ink jetting have been used for automated micropattern fabrication. However, most of the methods for microfabrication of surface pattern are limited to the investigation of material properties of substrates with high-cost and complex procedures. In the present study, we show a simple (single-step) yet versatile and robust approach to generate biodegradable polymeric particle patterns on a substrate using electrospray deposition through a mask. Various particle patterns including patterned dots, circles, squares, and bands can be easily formed and the features of particle patterns could also be tailored using different masks and electrostatic focusing effects. Furthermore, cell patterns can be achieved on the surface of particle patterns by blocking the areas without particle deposition on the substrate and culturing cells on the substrate. Polymeric particle patterns and cell patterns developed in this study could be used in the high throughput screening of sustained release formulations, cell-based sensing, and drug discovery. In addition to experimental results, an analysis of the associated electric field is used to investigate quantitatively the nature of focusing effect. Scaling analysis is also applied to obtain the dominate terms in electrospray deposition process. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Most aerosols found naturally in the ambient environment or those dispersed from artificial devices such as dry powder inhalers, are electrically charged. It is known that a strong electrostatic charge on aerosols can result in transport behavior dramatically different from that of uncharged aerosols, even in the absence of an external electric field. In the present work, we study pneumatic transport of corona-charged particles in bifurcated tubes. This is accomplished by tracking the motion of discrete particles numerically under the influence of drag, gravitational, and electrostatic forces. The model aerosol is fly ash powder, whose size and charge distributions have been determined experimentally. The electrical mobility of the charged particle cloud is modeled through coulombic interactions between discrete point charges. For the case of polydispersed particles electrically charged across a distribution, the deposition efficiency was found to be greater than what is indicated by the mean charge and size. In particular, use of negatively charged fly ash powder of mean size of 2 μm and mean charge of −1.5 C/kg led to significant increase in deposition efficiency (∼29%) compared with uncharged fly ash powder of the same size distribution (∼8%). Analysis of particle residence times suggests significant interaction between electrical and drag forces. These findings could have implications for pneumatic powder conveying or pulmonary drug delivery applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009

An analytical methodology involving the concept of “electrostatic equilibrium” is developed for granular flow in pneumatic conveying systems. The methodology can be used for estimation of the electrostatic field distribution at various sections of the system and explanation of the mechanisms involved for various electrostatic phenomena observed. For all cases conducted in the conveying system, there was a “charging time” required for the system to reach the state of “electrostatic equilibrium.” Experiments conducted at different sections of the system showed that the time required increased in the order: horizontal pipe, vertical pipe, and pipe bend. Through a physical analysis, it is deduced that electrostatic equilibrium is related to the granules' behavior and local flow characteristics. In general, a longer time duration taken to reach equilibrium corresponds to a process with more complicated granular flow patterns. In the electrostatic equilibrium state, the field distribution shows the highest electrostatic field strength near the pipe wall, and this field strength degrades from the pipe wall to the pipe center. At various pipe sections, the highest strength occurs at the bend, in accord with observations that electric sparking first occurs at that location within the entire pneumatic conveying system. In the vertical pipe, granular distribution was measured using electrical capacitance tomography (ECT), and granular velocities were cross-referenced with those using particle image velocimetry (PIV). The electrostatic force at low air flow rates is found to be the primary cause for granules sticking to the pipe wall and results in the formation of the half-ring or ring structure. The state of electrostatic equilibrium is physically influenced by several elements in conveying systems. In a cyclic conveying system, a new pipe (or low humidity or no antistatic agent) tends to expedite the process to reach electrostatic equilibrium and attain high magnitude of electrostatic current at the state. In a non-cyclic horizontal conveying system, a thin film (pipe) is found to prolong the process duration to reach equilibrium, while the case with charged film (pipe) takes shorter duration to do so. © 2006 American Institute of Chemical Engineers AIChE J, 2006

The pneumatic transport of granular material is a common operation frequently employed to transport solid particles from one location to another. It is well established in the literature that different flow regimes can arise in such transportation processes depending on the system geometry and operating conditions used. In this study, the pneumatic transports of solid particles in both vertical and horizontal conveying lines were studied numerically using the discrete element method coupled with computational fluid dynamics. The simulation outputs corresponded well with reported experimental observations in terms of the different flow regimes obtained at different operating conditions. In the vertical pneumatic conveying simulations, two different flow patterns corresponding to the experimentally observed dispersed flow and plug flow regimes were obtained at different gas velocities and solid concentrations. Similarly, the homogeneous flow, stratified flow, moving dunes, and slug flow regimes previously reported to occur in horizontal pneumatic conveying were also reproduced computationally in this study. Solid concentration profiles obtained by spatial averaging along the length of the pipe showed a symmetrical but non-uniform distribution for dispersed flow and an almost flat distribution for plug flow in vertical pneumatic conveying. The profile for stratified flow in horizontal pneumatic conveying showed higher solid concentration near the bottom wall due to the effects of gravitational settling, while that for slug flow was flat. Hysteresis in solid flow rates was observed in vertical pneumatic conveying near the point where transition between the dispersed and plug flow regimes was expected to occur. Solid flow rates were also found to be more sensitive towards the coefficient of friction than the coefficient of restitution of particles and the pipe walls in a sensitivity analysis study of these parameters. © 2005 American Institute of Chemical Engineers AIChE J, 2006