| Drying consumes a large amount of energy and is a limiting step in industrial production. To cut down production cost and to improve the quality of products, it is important to study the effect of external heating conditions on the evaporation rate and the internal mechanisms of the heat and mass transfer in the heated products. This thesis is devoted to explore these two research areas.;In an experimental study of heating conditions a water-filled cylindrical sandstone was heated by hybrid energy (convective hot air and/or microwaves) in a sequence of increasing heating intensity. As the heating intensity increases, the evaporation rate increases and the evaporation-rate curve undergoes a series of shape changes. Based on the drying phenomena of the sandstone, an attempt was made to search optimum heating conditions for a cylindrical bovine muscle.;To investigate the heat and mass transfer mechanisms operative in porous media subjected to convective heating or microwave heating, we solved two slightly different mathematical models for the cylindrical sandstone. For the convective heating, the sample is hotter outside. In most of the heating period, water vapor condenses along its path as it flows toward the centerline of the sample and air also moves in the same direction but at smaller flux. Liquid water, however, migrates toward the surface with a flux 2 to 3 orders of magnitude larger than vapor flux. As for the microwave heating, the sandstone is hotter inside. During most of the heating period, air slowly flows to the sample's centerline, water vapor flows to the surface, and liquid vaporizes as it flows to the surface with higher flux than vapor.;For the first research area, a capillary-tube model was solved to examine the influence of mass transfer coefficient, sample temperature, and liquid front depth on the evaporation rate. It is found that the effect of front depth on the evaporation rate becomes increasingly significant and approaches a limit for mass transfer coefficients larger than 5 cm/sec, but this effect becomes insignificant for mass transfer coefficients much lower than 5 cm/sec. |
