Abstract: Mathematical models, combined with experimental evaluation, provide an approach to understand, design, and optimize food process operations. Magnetic resonance imaging (MRI), as an experimental technique, is used extensively in both medical and engineering applications to measure and quantify transport processes. Magnetic resonance (MR) was used in this study to assess a mathematical model based on Fourier's second law. The objective was to compare analytical solutions for the prediction of internal temperature distributions in foods during oven-based convective heating to experimental temperature measurements and determine at what point during the heating process a coupled heat and mass transport process should be considered. Cylindrical samples of a model food gel, Russet potato and rehydrated mashed potato were heated in a convection oven for specified times. Experimentally measured internal temperatures were compared to the internal temperatures predicted by the analytical model. Temperatures distributions in the axial direction compared favorably for the gel and acceptably for the Russet and mashed potato samples. The MR-acquired temperatures in the radial direction for the gel resulted in a shallower gradient than predicted but followed the expected trend. For the potato samples, the MR-acquired temperatures in the radial direction were not qualitatively similar to the analytical predictions due to moisture loss during heating. If temperature resolution is required in the radial direction, moisture losses merit the use of transport models that couple heat and mass transfer.
Abstract: Combination of heating modes such as microwaves, convection, and radiant heating can be used to realistically achieve the quality and safety needed for cooking processes and, at the same time, make the processes faster. Physics-based computational modeling used in conjunction with MRI experimentation can be used to obtain critical understanding of combination heating. The objectives were to: (1) formulate a fully coupled electromagnetics heat transfer model, (2) use magnetic resonance imaging (MRI) experiments to determine the 3D spatial and temporal variation of temperatures and validate the numerical model, (3) use the insight gained from the model and experiments to understand the combination heating process and to optimize it. The different factors that affect heating patterns during combination heating such as the type of heating modes used, placement of sample, and microwave cycling were considered. Objective functions were defined and minimized for design and optimization. The use of such techniques can lead to greater control and automation of combination heating process benefitting the food process and product developers immensely. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2468-2478, 2010
Abstract: Physics-based modeling complemented with magnetic resonance imaging (MRI) for validation can provide a novel means to understand and thereby optimize combination heating processes. The objectives of this study were to compare heating patterns in a combination of radiant, forced air and microwave oven measured by MRI with those predicted by coupled electromagnetics-heat transfer model; quantify speed and uniformity of heating for the different combination modes; determine the effect of food dielectric properties on heating patterns; and delineate the nature of individual heating modes and their combinations. The modes of radiant heating through heating elements and forced convection by fan led to a more uniform heating compared with the faster (but less uniform) heating method provided by the microwaves. Combination methods were faster than radiant, forced-air and microwave-only heating. Although the speed of heating increased appreciably for combination modes, the nonuniformity of heating did not increase as much.
Abstract: Many microorganisms such as bacteria and fungi possess so-called capsules made of polysaccharides which protect these microorganisms from environmental insults and host immune defenses. The polysaccharide capsule of Cryptococcus neoformans, a human pathogenic yeast, is capable of self-assembly, composed mostly of glucuronoxylomannan (GXM), a polysaccharide with a molecular weight of approximately 2,000,000, and has several layers with different densities. The objective of this study was to model pore-hindered diffusion and binding of the GXM-specific antibody within the C. neoformans capsule. Using the finite-element method (FEM), we created a model which represents the in vivo binding of a GXM-specific antibody to a C. neoformans cell taking into account the intravenous infusion time of antibody, antibody diffusion through capsular pores, and Michaelis-Menten kinetics of antibody binding to capsular GXM. The model predicted rapid diffusion of antibody to all regions of the capsule where the pore size was greater than the Stokes diameter of the antibody. Binding occurred primarily at intermediate regions of the capsule. The GXM concentration in each capsular region was the principal determinant of the steady-state antibody-GXM complex concentration, while the forward binding rate constant influenced the rate of complex formation in each region. The concentration profiles predicted by the model closely matched experimental immunofluorescence data. Inclusion of different antibody isotypes (IgG, IgA, and IgM) into the modeling algorithm resulted in similar complex formation in the outer capsular regions, but different depths of binding at the inner regions. These results have implications for the development of new antibody-based therapies.
Abstract: Combination heating of food using microwave and jet impingement has been simulated by coupling Maxwell's equations of electromagnetics with energy equation and using experimentally measured heat transfer coefficient values for jet impingement in a novel domestic oven. Transient food temperatures from the model and experiment for each separate heating mode and their combination revealed the characteristic nature of each of the heating modes. Contour plots of temperature show that with combination heating, surface can be heated faster (for crispness) and edge over-heating can be partially avoided. Measures of non-uniformity in temperatures in the heated food are developed using coefficient of variation and middle 80-percentile range as the parameters. Using these measures, it is shown that combination heating leads to more uniform heating, without compromising the speed or convenience. A 22-30% increase in uniformity has been observed for combination microwave-jet impingement heating over microwave-only heating. jet impingement is a good complement to microwave heating as it has different spatial and time variation of heating rates. During the initial period, jet impingement dominates over microwave heating near the Surface, with microwave heating being more significant in the interior. At later times, the roles switch with microwaves becoming more dominant on the surface while jet impingement takes a more significant role in heating the interior of the food. These findings should help the product, process and equipment designer achieve the balance between speed and uniformity of heating in a more precise manner. 0 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Abstract: Computational model for airflow through the upper airway of a horse was developed. Previous flow models for human airway do not hold true for horses due to significant differences in anatomy and the high Reynolds number of flow in the equine airway. Moreover, models that simulate the entire respiratory cycle and emphasize on pressures inside the airway in relation to various anatomical diseases are lacking. The geometry of the airway was created by reconstructing images obtained from computed tomography scans of a thoroughbred racehorse. Different geometries for inhalation and exhalation were used for the model based on the difference in the nasopharynx size during the two phases of respiration. The Reynolds averaged Navier-Stokes equations were solved for the isothermal flow with the standard k-epsilon model for turbulence. Transient pressure boundary conditions for the entire breathing cycle were obtained from past experimental studies on live horses. The flow equations were solved in a commercial finite volume solver. The flow rates, computed based on the applied pressure conditions, were compared to experimentally measured flow rates for model validation. Detailed analysis of velocity, pressure, and turbulence characteristics of the flow was done. Velocity magnitudes at various slices during inhalation were found to be higher than corresponding velocity magnitudes during exhalation. The front and middle parts of the nasopharynx were found to have minimum intraluminal pressure in the airway during inhalation. During exhalation, the pressures in the soft palate were higher compared to those in the larynx, epiglottis, and nasopharynx. Turbulent kinetic energy was found to be maximum at the entry to the airway and gradually decreased as the flow moved inside the airway. However, turbulent kinetic energy increased in regions of the airway with abrupt change in area. Based on the analysis of pressure distribution at different sections of the airway, it was concluded that the front part of the nasopharynx requires maximum muscular activity to support it during inhalation. During exhalation, the soft palate is susceptible to displacements due to presence of high pressures. These can serve as critical information for diagnosis and treatment planning of diseases known to affect the soft palate and nasopharynx in horses, and can potentially be useful for human beings.
Abstract: The role of a carousel in improving heating uniformity of food in a microwave oven is studied. A physics-based computational model is developed coupling the Maxwell's equations for electromagnetics and energy equation for heating inside a microwave oven with food load. The model is solved numerically using a finite element based computational software. Transient simulation of the heating process is done by considering the rotation of the turntable by repeating the computations for discrete angular positions of the turntable. The model is experimentally validated by measurements of point temperatures using fiber optic probes. Power absorbed in the food as a function of the angle of rotation of the turntable covering the entire cycle is available for the first time. Using various measures of heating uniformity, it is shown that the carousel helps in increasing the temperature uniformity of the food by about 40%. (C) 2007 Elsevier Ltd. All rights reserved.
Abstract: Physical properties of breads during baking were measured using three different heating modes of microwave plus infrared (MIR), microwave plus jet impingement (MJET) and jet impingement (JET) in two different commercially available microwave combination ovens. Breads baked in JET oven were significantly different from the breads baked in other ovens with respect to their specific volume and moisture content. Transient values of dielectric constant, dielectric loss factor, specific bulk volume, porosity, thermal conductivity and moisture content were determined. For all heating modes, thermal conductivity and dielectric properties of breads decreased sharply within the first 2-3 min of baking and then remained constant. Regression equations were developed to relate these properties to moisture content and porosity changes during baking. (c) 2006 Elsevier Ltd. All rights reserved.
Abstract: Metastatic melanoma is almost always deadly and new methods of treatment are urgently needed. Recently, we established the feasibility of radioimmunotherapy (RIT) for experimental melanoma in mice using a 188-rhenium (188Re)-labeled monoclonal antibody (mAb) 6D2 (IgM) to melanin. Our objective was to determine the effects of varying tumor melanin concentration and of different diffusivities and lymphatic clearance rates of the normal tissue, on the absorbed dose to the tumor in simulated therapy, in preparation for a clinical trial of RIT for melanoma. Using finite element analysis (FEA), we created a pharmacokinetic model that describes melanin-targeting RIT of a melanoma micrometastasis (1.3-mm radius) imbedded in normal tissue (14.3-mm radius). Our method incorporates antibody plasma kinetics, transcapillary transport, interstitial diffusion, and lymphatic clearance. Michaelis-Menten kinetics was used to model mAb binding to tumor melanin for melanin concentrations of 76, 7.6, 0.76, 0.076, and 0.0076 micromol/l. An absorbed dose was calculated, after accounting for direct and crossfire irradiation, on the basis of a 7.4-GBq intravenous dose of 188Re-6D2. The results showed that penetration of mAb into the tumor was inversely proportional to tumor melanin concentration. Decreased diffusivity and increased lymphatic clearance of the surrounding normal tissue decreased the dose to the tumor. The formation of mAb-melanin complex was remarkably similar within a 1000-fold range of melanin concentration, resulting in total doses of 2840, 2820, 2710, and 1990 cGy being delivered to tumors with melanin concentrations of 76, 7.6, 0.76, and 0.076 micromol/l, respectively. In conclusion, RIT of metastatic melanoma can be effective over a wide range of tumor melanin concentrations. The results can be useful in the design of a clinical trial of melanin-targeting RIT in patients with metastatic melanoma.
