MODELING MOISTURE TRANSPORT ACROSS PORCINE SKIN USING REACTION ENGINEERING APPROACH AND EXAMINATION OF FEASIBILITY OF THE TWO-PHASE APPROACH

The present study is an amendment to previous approaches to modeling moisture transport across porcine skin. The previous models were semi-empirical or based on the Fickian liquid diffusion equation. Effective liquid diffusivity was dependent on sample thickness, masking its dependence on temperature. From the modeling perspective, this can be a drawback. Therefore, use of two simultaneous equations to represent liquid and vapor transport would be fundamentally correct. A source term representing phase change has been introduced and their parameters established experimentally and correlated using the reaction engineering approach. The two-phase approach was implemented previously to model moisture transport for drying of porous biological materials. The current study checks the feasibility of this approach for modeling moisture transport across skin. A comprehensive model for moisture transport across skin could be of significance to researchers working in the areas of transdermal drug delivery, toxicology, and process applications such as leather drying.     

Mathematical analysis of transport properties of polymer films for food packaging. VII. Moisture transport through a polymer film with subsequent adsorption on and diffusion through food

A system of partial differential equations was developed to describe the transient, three-step transport of moisture through packaged food products. The steps included (i) Fickian diffusion through the polymer package film; (ii) Langmuirian adsorption upon the food surface; and (iii) Fickian diffusion through the food material. A set of finite difference equations was derived to approximate the continuous model. These equations were solved for standard boundary conditions in each section of the food packages. The results can be used for the determination of the food package shelf life.     

Mathematical Modeling of Kiln Drying of Softwood Timber: Model Development, Validation, and Practical Application

Mathematical modeling of wood drying is a powerful tool to better understand and quantify the effects of wood properties as well as the effects of drying and post-drying treatment conditions on drying and thus the wood drying models can be used to improve drying quality. The models that have been developed can be divided into three categories: models for drying a single board, models for drying a kiln-wide stack, and models for drying stress and deformation. The single-board drying model employs comprehensive heat and moisture mass transfer equations and can be used to investigate the influence of wood variability. The kiln-wide drying model, which is based on the transfer processes between wood and the drying medium, is able to examine the influence of drying schedules and wood properties. The stress model can predict stress development in drying and stress relief in final steam conditioning and post-kiln treatment. An integrated model can be used to optimize drying schedules and develop strategies for high-quality dried timber.     

Hybrid mixture theory based modeling of transport mechanisms and expansion‐thermomechanics of starch during extrusion

Water, vapor, and heat transport mechanisms and thermomechanical changes occurring inside the expanding extrudate were described using hybrid mixture theory‐based unsaturated transport equations. Transport equations were transformed from the Eulerian coordinates to the Lagrangian coordinates. Good agreements between the predicted and experimental values of surface temperature, moisture content, and expansion ratio of the extrudates were obtained. The model was also used to calculate temperature, moisture content, pore‐pressure, and viscoelastic‐stress distribution in the extrudate. Matrix collapse and glassy crust formation under the surface was calculated as a function of extrusion conditions. Expansion behavior of the extrudate was described using the difference between stress due to pore pressure and viscoelastic stress. The modeling results can serve as a guide for predictably modifying the extrusion parameters for obtaining specific textural attributes of expanded starch for various food, feed, and biomedical applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4517–4532, 2015     

Multi-Scale Multiphase Modeling of Transport Phenomena in Spray-Drying Processes

Spray drying is an extensively used technology in process engineering for receiving small particles by rapid moisture evaporation from a spray of droplets. This contribution summarizes achievements and results of the comprehensive scientific research on multi-scale multiphase modeling of transport phenomena in spray-drying processes undertaken by our research group: (1) study of particle formation on the scale of an individual droplet; (2) modeling and simulation of droplet–droplet and particle–particle collisions in a spray; (3) study of gas-spray mixing; (4) 2D and 3D study of spray drying by an innovative multi-scale simulation tool coupled to a commercial CFD software. The proposed multi-scale multiphase model of transport phenomena in a spray-drying process has been developed based on a thorough analysis of previously published experimental and theoretical works. The content of this paper will be useful for both academia and industry; e.g., pharmaceutical, biotechnology, chemical, ceramics, materials, nutrition, and other applications of spray drying.     

Modeling of the Seedless Grape Drying Process using the Generalized Differential Quadrature Method

Mathematical modeling of the grape drying process is important in understanding the transport phenomena involved in the production and processing of dried grapes. Drying models proposed in the literature have simplifying assumptions, and thus ignore important phenomena such as shrinkage and changes in transport properties which occur during the drying process. Consequently, a mathematical model is developed for the seedless grape drying process, which considers the effects neglected in previous models. Since an analytic solution to this nonlinear model is impossible, the generalized differential quadrature method is used to solve the models' equations. The model is validated with experimental data obtained from a laboratory scale convective tray dryer operating at 50–70 °C and an air velocity of 1.5 m/s. Model predictions are in close agreement with experimental data due to the inclusion in the model of shrinkage and variation in moisture diffusivity. Model results can serve as a framework to improve the performance of existing and novel dryers, and also in the design of process simulators for dryers.     

AN ANALYSIS OF MASS TRANSFER IN AIR-DRYING OF FOODS

A theoretical model for the convective drying of food materials was developed. These materials shrink considerably, as moisture content decreases; for this reason, the proposed model takes shrinkage into account as a fundamental part of the drying operation. This is accomplished by modeling the movement of dry solids and the consequent movement of bound substance during drying. The resulting system of three non-linear partial differential equations is solved numerically and the predicted values of moisture content and temperature are compared with experimental data for the drying of Sultana grapes. The effective moisture diffusivity in the mass of grapes was described by an Arrhenius-type equation. A sensitivity analysis of the predicted values and the examination of the confidence regions of the estimated parameters showed that the activation energy for mass transfer was estimated with a high degree of precision. The agreement between the calculated results and the experimental measurements, using various criteria, was very satisfactory.     

Analysis of fractured rock and gas flow interaction in explosion simulations

In this study, an attempt has been made to adopt a combined finite discrete element methodology to couple gas dynamics equations and solid deformation states to develop a numerical tool for simulation of blast damage in brittle solid media such as rocks. A standard finite-element method is used, accompanied by strain softening behavior for modeling initiation and propagation of solid cracks due to high gas pressures. This variable high pressure is governed by the gas mass and momentum conservation equations. The gas behavior is fully coupled by the solid deformation which changes the density and porosity required in the gas dynamics equations and is based on new modifications to the recently proposed approach by the same authors. The proposed model for the flow of the detonation gas allows for evaluation of the spatial distribution of pressure and mass of the detonation gas over a complex geometry of cracked/fragmented solid (rock) model. Full geometric and material nonlinearities are taken into account by using a fully deformable finite-element mesh and cracked/fragmented discrete elements. Local adaptive remeshing (enrichment) techniques are used to geometrically simulate the crack propagation. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 127–137, July–August, 2007.     

AN ANALYSIS OF MASS TRANSFER IN AIR-DRYING OF FOODS

A theoretical model for the convective drying of food materials was developed. These materials shrink considerably, as moisture content decreases; for this reason, the proposed model takes shrinkage into account as a fundamental part of the drying operation. This is accomplished by modeling the movement of dry solids and the consequent movement of bound substance during drying. The resulting system of three non-linear partial differential equations is solved numerically and the predicted values of moisture content and temperature are compared with experimental data for the drying of Sultana grapes. The effective moisture diffusivity in the mass of grapes was described by an Arrhenius-type equation. A sensitivity analysis of the predicted values and the examination of the confidence regions of the estimated parameters showed that the activation energy for mass transfer was estimated with a high degree of precision. The agreement between the calculated results and the experimental measurements, using various criteria, was very satisfactory.     

Modeling the Electrokinetic Decontamination of Concrete

Abstract

The decontamination of concrete is a major concern in many Department of Energy (DOE) facilities. Numerous techniques (abrasive methods, manual methods, ultrasonics, concrete surface layer removal, chemical extraction methods, etc.) have been used to remove radioactive contamination from the surface of concrete. Recently, processes that are based on electrokinetic phenomena have been developed to decontaminate concrete. Electrokinetic decontamination has been shown to remove from 70 to over 90% of the surface radioactivity. To evaluate and improve the electrokinetic processes, a model has been developed to simulate the transport of ionic radionuclei constituents through the pores of concrete and into the anolyte and catholyte. The model takes into account the adsorption and desorption kinetics of the radionuclei from the pore walls, and ion transport by electro-osmosis, electromigration, and diffusion. A numerical technique, orthogonal collocation, is used to simultaneously solve the governing convective diffusion equations for a porous concrete slab and the current density equation.

This paper presents the theoretical framework of the model and the results from the computation of the dynamics of ion transport during electrokinetic treatment of concrete. The simulation results are in good agreement with experimental data.

     

Modeling of fast pulse responses in the Multitrack: an advanced TAP reactor

A detailed transport model for the Multitrack setup, a TAP-like system, has been developed, which allows further analysis of adsorption, diffusion and catalysis phenomena. This includes the transport in the void part between the pulse valve and the reactor inlet. The effects of viscous flow and thermal transpiration, aspects that have not been studied in detail before for this type of setup, have been analyzed. A new expression for the modeling of the output signal is proposed depending on the positioning of the MS detector used in the study. The transport parameters of the model have been estimated by the analysis of the experimental pulse responses of the empty reactor system and the reactor charged with an inert packed bed. The proposed model reproduces the experimental pulse responses very well, and therefore can be extended to study systems with reacting or adsorbing beds by including the corresponding rate equations for the processes occurring in the bed of particles.     

Transport in deformable hygroscopic porous media during microwave puffing

Microwave puffing is a process used to obtain low‐fat healthy foods by rapid heating of food products to develop high internal pressures in the material that cause significant structural changes. Two‐way coupling of complex multiphase transport and large deformations in the material, which is critical to simulate the puffing process accurately, was implemented. A porous media model that includes different phases, solid, liquid water, and gas, and incorporates pressure driven flow and evaporation was used to describe the transport processes in the material. Large deformations were included to model structural changes, with the material treated as hyperelastic. Arbitrary Lagrangian–Eulerian (ALE) framework was used. The model was validated using experimental temperature, moisture, and volume measurement and used to comprehensively understand the puffing process. Uncertainty analysis was carried out to estimate uncertainty in model prediction due to the choice of critical input parameters such as bulk modulus and permeabilities. © 2012 American Institute of Chemical Engineers AIChE J, 59: 33–45, 2013     

FLASH DRYING OF FISH MEALS WITH SUPERHEATED STEAM: ISOTHERMAL PROCESS

The work considers the application of the flash drying to the moisture removal of fishmeal using superheated steam as transport medium. Heat, momentum and mass transfer equations were applied and an algorithm based on these equations was developed and solved. The model was validated using experimental data obtained in a pilot pneumatic dryer ( total length 60 m) provided with a steam jacket to maintain the superheated steam at a constant temperature. The drying time was less than 10 s to decrease the fish meals moisture content from 53.5% to 28% d.b. and in a second pass by the dryer the moisture down to 16.9% using superheated steam at It 1 ° C and 130 ° C in the jacket. The computational results are in agreement with the experimental data.     

Water transport in cellular tissues during thermal processing

Accurate modeling of water transport in food materials requires knowledge of how transport properties depend on the material structure. Water transport in a cellular tissue depends on its pathway (intracellular versus extracellular), which in turn depends on temperature. Using a combination of permeability measurement, pore‐size distribution analysis and bioimpedance analysis, it is shown that water in a cellular tissue (e.g., potatoes) is mostly intracellular at lower temperatures at which cell membranes are intact. During drying at high‐temperatures, cell membranes in potatoes are damaged, and the moisture transport pathway is primarily extracellular (through intercellular spaces and the lacunae created by the killed cells), with a much lower resistance to water transport. The difference in moisture diffusivity in potatoes for the two pathways has been estimated to be three orders of magnitude. Therefore, transport properties measured or predicted at low temperatures cannot be used for high temperatures because they correspond to different moisture migration pathways. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Some Considerations in Modeling of Moisture Transport in Heating of Hygroscopic Materials

Hygroscopic materials are those in which the equilibrium pressure of water vapor changes with moisture content and temperature, such as food, soil or wood, etc. Heat and moisture transports are coupled in heating of hygroscopic materials. One of the major links between temperature and moisture changes is water evaporation. There have been different formulations on modeling of evaporation in the past. A typical approach (Model 1 in this article) is to equate the evaporation rate to the rate of local moisture loss. The first part of this paper illustrates that such an approach is physically incorrect based on fundamental conservation relationships. A conservation-based coupled heat and moisture transfer model (Model 2) is presented here based on previous multiphase transport models. It shows that total evaporation rate over the entire material is included in Model 1 while the local evaporation rate is not. The situations when Model 1 may or may not generate large errors are discussed. The second part of this article completes the modeling of evaporation using Model 2. Two types of formulations are given depending on the phase equilibrium of moisture in the hygroscopic materials. When phase equilibrium between water and vapor is assumed for any location at any time, vapor pressure is provided as known variables. In a nonequilibrium approach, evaporation rate needs to be provided. The latter poses numerical difficulties near the material surface, which arises from the possibility that equilibrium state may have a large change near the surface. Further discussions were made on the physical and numerical considerations in using both approaches.     

Determination of appropriate effective diffusivity for different food materials

Effective diffusivity is the most important key parameter needed in the analysis, design, and optimization of heat and mass transfer during food drying process. In general, two types of effective diffusivities are used to develop the mathematical modeling of food drying, namely, moisture-dependent effective diffusivity (MDED) and temperature-dependent effective diffusivity (TDED). However, no study has extensively investigated which effective diffusivity is more accurate in predicting drying kinetics. The main goal of this study is to determine the appropriate effective diffusivity for predicting the drying kinetics. Drying models were developed for different fruits and vegetables based on moisture-dependent and temperature-dependent effective diffusivities. COMSOL Multiphysics, a finite element-based engineering simulation software is used to solve the coupled heat and mass transfer equations. 3D moisture profiles were developed to investigate the spatial moisture distribution during drying. Extensive experimental investigation on five types of fruits and vegetables was conducted and results were compared with the simulated results. The experiments were repeated thrice, and the average of the moisture content at each value was used for constructing the drying curves. Close agreement between experimental and simulated results validates the models developed. It was observed that the moisture profile and temperature profile in case of MDED were more closely fitted with the experimental results. For all fruits and vegetables, the moisture ratio with MDED was significantly lower than moisture ratio with TDED. This finding confirms that the MDED is more accurate for predicting kinetics in food drying. Moreover, the moisture ratio of apple was lowest whereas pear showed the highest moisture ratio. On the other hand, carrot showed a considerably lower moisture ratio compared to potato.     

Numerical Investigation of Case Hardening of Plant Tissue During Drying and Its Influence on the Cellular-Level Shrinkage

Dried plant food materials are one of the major contributors to the global food industry. Widening the fundamental understanding of different mechanisms of food material alterations during drying assists the development of novel dried food products and processing techniques. In this regard, case hardening is an important phenomenon, commonly observed during the drying processes of plant food materials, which significantly influences the product quality and process performance. In this work, a mesh-free-based 2D numerical model developed by the authors is further improved and used to simulate the influence of case hardening on shrinkage characteristics of plant tissues during drying. In order to model the fluid mechanisms of plant cells, smoothed particle hydrodynamics (SPH), which is a popular mesh-free technique used to solve hydrodynamics problems, is used. The cell wall mechanisms are modeled using the discrete element method (DEM). The model is fundamentally more capable of simulating large deformations of multiphase materials compared to conventional grid-based modeling techniques such as finite element methods (FEM) or finite difference methods (FDM). Case hardening is implemented by maintaining distinct moisture levels in the different cell layers of a given tissue. In order to compare and investigate different factors influencing tissue deformation under case hardening, four different plant tissue varieties (apple, potato, carrot, and grape) are studied. The simulation results indicate that the inner cells of any given tissue undergo limited shrinkage and cell wall wrinkling, compared to the case-hardened outer cell layers of the tissues. For a given dried tissue condition, the case-hardened cellular deformations are highly influenced by the unique characteristics of the different tissues, such as cell size, cell fluid turgor pressure, and cell wall properties.     

Objects for MWR

A computational framework has been developed for step-by-step implementation of global spectral projection methods used for solving boundary-value problems and for subsequent analysis of solutions produced using the numerical techniques of this framework. A set of matlab-based functions corresponding to each step in a Galerkin discretization procedure has been developed with emphasis on simplifying the implementation of discretization methods for nonlinear, distributed-parameter system models in up to three-dimensional physical domains. A key feature of this computational approach is that a set of object classes were developed to facilitate implementation of the weighted residual methods (MWR) in an effort to make the connection between the solution procedures and modeling equations as clear as possible. The utility of the computational procedures is demonstrated through applications to two-dimensional reaction-diffusion and fluid flow problems, and a three-dimensional heat transfer model relevant to semiconductor manufacturing.     

Numerical simulation of atomic layer deposition for thin deposit formation in a mesoporous substrate

ZnO deposition in porous γ-Al₂O₃ via atomic layer deposition (ALD) is the critical first step for the fabrication of zeolitic imidazolate framework membranes using the ligand-induced perm-selectivation process (Science, 361 (2018), 1008–1011). A detailed computational fluid dynamics (CFD) model of the ALD reactor is developed using a finite-volume-based code and validated. It accounts for the transport processes within the feeding system and reaction chamber. The simulated precursor spatiotemporal profiles assuming no ALD reaction were used as boundary conditions in modeling diethylzinc reaction/diffusion in porous γ-Al₂O₃, the predictions of which agreed with experimental electron microscopy measurements. Further simulations confirmed that the present deposition flux is much less than the upper limit of flux, below which the decoupling of reactor/substrate is an accurate assumption. The modeling approach demonstrated here allows for the design of ALD processes for thin-film membrane formation including the synthesis of metal–organic framework membranes.     

Coupled heat and mass transport phenomena in siliceous aggregate concrete slabs subjected to fire

A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum and energy, and including the effects of evaporation and dehydration processes on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Siliceous aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions. © 1997 John Wiley & Sons, Ltd.