Ashish Dhall

Modeling Transport in Porous Media With Phase Change: Applications to Food Processing

Fundamental, physics-based modeling of complex food processes is still in the developmental stages. This lack of development can be attributed to complexities in both the material and transport processes. Society has a critical need for automating food processes (both in industry and at home) while improving quality and making food safe. Product, process, and equipment designs in food manufacturing require a more detailed understanding of food processes that is possible only through physics-based modeling. The objectives of this paper are (1) to develop a general multicomponent and multiphase modeling framework that can be used for different thermal food processes and can be implemented in commercially available software (for wider use) and (2) to apply the model to the simulation of deep-fat frying and hamburger cooking processes and validate the results. Treating food material as a porous medium, heat and mass transfer inside such material during its thermal processing is described using equations for mass and energy conservation that include binary diffusion, capillary and convective modes of transport, and physicochemical changes in the solid matrix that include phase changes such as melting of fat and water and evaporation/condensation of water. Evaporation/ condensation is considered to be distributed throughout the domain and is described by a novel nonequilibrium formulation whose parameters have been discussed in detail. Two complex food processes, deep-fat frying and contact heating of a hamburger patty, representing a large group of common food thermal processes with similar physics have been implemented using the modeling framework. The predictions are validated with experimental results from the literature. As the food (a porous hygroscopic material) is heated from the surface, a zone of evaporation moves from the surface to the interior. Mass transfer due to the pressure gradient (from evaporation) is significant. As temperature rises, the properties of the solid matrix change and the phases of frozen water and fat become transportable, thus affecting the transport processes significantly. Because the modeling framework is general and formulated in a manner that makes it implementable in commercial software, it can be very useful in computer-aided food manufacturing. Beyond its immediate applicability in food processing, such a comprehensive model can be useful in medicine (for thermal therapies such as laser surgery), soil remediation, nuclear waste treatment, and other fields where heat and mass transfer takes place in porous media with significant evaporation and other phase changes.

Modeling of Multiphase Transport during Drying of Honeycomb Ceramic Substrates

Multiphase transport model to simulate drying of honeycomb ceramic substrates in a conventional (hot air) drier is developed. Heat and moisture transport in the honeycomb walls as well as channels is modeled. The model predictions are validated against experiments done for drying of cylinder-shaped substrates by comparing histories and axial profiles of moisture loss and point temperature histories at various locations. Drying experiments are performed at two different values of air temperature, 103°C and 137°C, at a relative humidity value of 5%. Sensitivity analysis reveals that the drying process is controlled by heat and water vapor transport. External heat transfer is the dominant resistance mechanism for energy transport, whereas internal convection and binary diffusion dominate the resistance to vapor transport.

Modeling Food Process, Quality and Safety: Frameworks and Challenges

Physics-based models provide increased understanding and predictive capabilities that can increase efficiency in food product, process, and equipment design; they also improve quality and safety. However, certain key food-specific developments are needed to enable widespread use of simulation technology in the food sector. First and foremost is the need to develop concise modeling frameworks (formulating various food-processing situations in mathematical models) for various classes of processes, as opposed to a custom model for each process, as mostly exists today. Deformable porous media with multiphase transport can provide such a framework, as will be discussed through examples of various processes that have been modeled by many researchers. The next critical piece is to have easy access to the properties that needed to be model. State-of-property prediction, starting from simple correlations and proceeding to multiscale modeling and thermodynamics-based and molecular dynamics, as is being pursued by researchers around the world, will be shared. Prediction beyond process to quality and safety is the third topic, where various approaches to modeling quality in a diffusion-reaction modeling framework will be presented. For safety, a practical approach that groups various food products, and thus provides an avenue to simulate safety for a large number of situations, will be shared. Finally, efforts to integrate modeling components into a novel, user-friendly software for increased use of modeling will be described.