Abstract
(1) This experiment was conducted to observe some physical and thermal characeristics of rolled hay wafer dried by the micro-wave heating.
(2) The drying process was divided into three periods; pre-heating period, constant drying-rate peried, and falling drying-rate period. The pre-heating time was in proportion to the initial water equivalent of the material. The drying process of the material shifted sharply from the pre-heating period to the constant-rate drying, and changed to the falling-rate drying at the moisture content about 8.7% (w, b.), and finally became to the bone-dry condition. Comparing with the heated-air drying, the constant drying-rate period occupied the major portion of drying process.
(3) During the constant drying-rate period, the material was isothermally dried, approxmiately 100°C, the moitsure was evaporated by boiling, and then moved out. In this experiment, it seemed that the drying-rate of the material did not depend on the apparent density of the dry matter and the initial moisture content of the material, and it was mainly influenced by the micro-wave out put of the energy source.
(4) Moisture at any position of the material, center, medium, and surface, was evaporated uniformly, and moved out. However it seemed that a little variance existed because of the nonuniformity of the energy field in the cavity, and it could not be measured.
(5) The vapor transfered in the material and moved out by the gradient of the partial pressure of the vapor so it was considered that the resistance to the vapor transfer was ver ylow. The resistance to the vapor transfer in the axial direction was lower than that in the radial one.
(6) The heat does not transfer easily from the surface to the center of the material by the heated air drying. But by the micro-wave heating, the heat is generated uniformly was the material, so the amount of moisture which was equivalent to the micro-wave out put could be evaporated.
