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Modeling intermittent microwave-convective drying (IMCD) of food materials

Modeling intermittent microwave-convective drying (IMCD) of food materialsModeling intermittent microwave-convective drying (IMCD) of food materialsDrying of foodstuffs is an important and the oldest method of food processing. However, drying is a very energy-intensive process and consumes about 20–25% of the energy used by food processing industry. The energy efficiency of the process and the quality of the dried product are the two most crucial concerns in food drying. The global energy crisis and increasing demand for quality dried food further challenge researchers to explore innovative techniques in food drying to address these issues. Intermittent microwave-convective drying (IMCD) has proved to be an advanced technology, which improves both energy efficiency and food quality in drying. However, the physical understanding of the heat and mass transport mechanism of IMCD is still not understood properly. To understand and optimize IMCD, it is critical to developing mathematical models that can provide insight into the physics involved in the process. Although there are some experimental investigations of IMCD, there are until now no mathematical models to describe heat and mass transfer in IMCD process for food. 

This study aims to develop a mathematical model for IMCD of food materials. First diffusion based and then multiphase porous media based IMCD models have been developed in the study. The final model in this thesis is the first fundamental and the most comprehensive multiphase model for IMCD, which considers 3D electromagnetics coupled with multiphase porous media heat and mass transport. The 3D electromagnetics considered Maxwell’s equation and a multiphase transport model considering three different phases: solid matrix, liquid water and gas (water vapour and air) and considered pressure-driven flow, capillary diffusion, binary diffusion, and evaporation. Thus, the model provides an in-depth understanding of IMCD drying enabling investigation of moisture distribution, temperature distribution and redistribution, evaporation, and fluxes due to different mechanisms. Water and vapour fluxes obtained from the model showed that the pressure gradient flow of water and vapour in IMCD is about 5–20 times higher than convective drying, which significantly reduces the drying time in IMCD. Understanding of these factors can, in turn, lead to an improvement in the food quality, the energy efficiency, increased the ability to automation and optimization.

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