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The hygroscopic porous particle was used as the fluidizing particle for the superheated steam fluidized bed drying under reduced pressure. A relatively large material was immersed in the fluidized bed as the drying sample. The drying characteristics of the sample were examined experimentally and the results were compared with those in the case of inert particle fluidized bed.The water transfer from the sample to the fluidizing particle bed in the case of hygroscopic porous particle facilitated the drying regardless of pressure and temperature in the drying chamber. The increment degree of the sample temperature at the earlier period of drying was smaller in the case of hygroscopic porous particle than in the case of inert particle, and the phenomenon was more remarkable in the case of superheated steam than in the case of hot air. INTRODUCTIONThe quality of a dry product is strongly affected by the drying process. During the drying process, heat-sensitive materials such as food and pharmaceuticals must be kept at low temperature. The freeze dryer is used for such materials, but the long drying time and the large amount of energy are necessary for the drying. Therefore, the development of a dryer that has low drying temperature, high drying rate, and high energy efficiency is required for heat-sensitive materials.Under reduced pressure, the material temperature in drying becomes lower. Under extremely low pressure, however, the convective heat transfer rate from the drying gas to the material is low and the drying time becomes much

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