Abstract
1) The process of freeze-drying was analyzed quantitatively using a manifold-type apparatus newly designed. It was found that the process is generally devided into the following stage and periods: the preliminary stage, the constant rate period, and the falling rate period.2) The preliminary stage begins immediately after the beginning of drying, and may take various velocities of drying according mainly to the surface temperature of material pre-frozen at the beginning of drying.3) The constant rate period follows the preliminary stage with a constant drying velocity. In this period, the velocities of various materials were noticed to be almost the same as that of pure distilled water. It was also recognized that in this period the values of the drying velocities computed from the radiation-heat coincided well with those actually measured.4) The falling rate period which follows the constant rate period might be composed of three sub-processes, namely the first, the second and the third stage. The mechanism of transition from the constant rate period to the falling rate period might be explained that the resistance of the superficial portion of material which had become porous by drying against water molecules evaporating from the undried portion changed from very weak to strong.
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