A liquid-fluidized bed of inert particles was used to separate a pure object from a mixture. One (binary solid-liquid-fluidized bed) or two (tertiary solid-liquidfluidized bed) types of objects with relatively large-sized particles were immersed in an inert-particle bed, and the bed behavior was observed for different liquid velocities. The void fraction and apparent density of the inert-particle suspension were predicted by considering the effect of the change in object position for different liquid velocities. The prediction method, which considers the change in the minimum fluidization velocity, accurately expressed the changes in the void fraction and the apparent density of the bed with the position of the objects in the bed. Using this method, the liquid velocity required to separate a certain kind of object from a mixture can be predicted.
A solid‐liquid fluidized bed of inert particles can be used to separate pure objects from a mixture. Pieces of plastic sheet were selected as the objects to be separated. To estimate the separation characteristics, the behavior of pieces of plastic sheet in the bed was examined experimentally. Slow stirring was used to improve the fluidization state of the bed. The object size and the volume ratio of objects to inert particles were varied. The use of stirring of the bed was effective in improving the fluidization state of the bed, and the objects, which sank in the bed without stirring, moved from the bottom to the upper portion of the bed at a certain liquid velocity. This liquid velocity increases with decreasing object size, and it also increases as the volume ratio of objects to inert particles in the bed increases. When the volume ratio of objects to inert particles is too high, the objects are distributed throughout the entire bed, regardless of the liquid velocity.
The drying characteristics and properties (color and shrinkage) of carrots (as a representative agricultural product) were experimentally examined in a fluidized bed under reduced pressure. Dry hot air and superheated steam were used as the drying gases. Rice and carrot powders (0.125-0.355 mm in diameter) were used as the fluidizing particles, in addition to glass beads (0.12 mm in diameter).It was confirmed that the drying rate using a fluidized bed was much higher than without a fluidized bed (hot-air drying), regardless of the type of fluidizing particles used. Under reduced pressure, both with and without a fluidized bed, the drying rate was higher than that at atmospheric pressure using hot air. The drying rate was sufficiently high for fluidized-bed drying with superheated steam, though the drying rate was higher with hot air than with superheated steam. As the drying temperature increased, the volume ratio (befor/after drying) of the sample increased. At high drying temperatures (373 and 423 K in the present study), the color of the sample changed; in other words, a heat-induced change in the properties of the carrot was observed. At a low drying temperature (333 K in the present study), the drying method did not affect the color of the carrot; i.e., the color of the dried material was maintained even in a fluidized bed under reduced pressure when the drying rate was higher. INTRODUCTIONThe drying process affects the quality of a dried product. In particular, heat-sensitive materials such as food, agricultural products, and pharmaceuticals need to be kept at a low temperature while being dried. Vacuum and freeze dryers have been used for the low-temperature drying of such materials. However, these dryers have certain problems; a long drying time and a large amount of energy are required for drying. It is necessary to manufacture a dryer that has a low drying temperature, high drying rate, and high energy efficiency for drying heat-sensitive materials.
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