| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 98 === Vacuum drying can be operated at a relatively low temperature and is one of a few drying methods which can be applied for drying the temperature-sensitive materials such as health foods, drugs and other bio-active materials. To maintain a low pressure inside the vacuum chamber, the vaporized steam is usually expelled out by a vacuum pump. Since the specific volume of vapor is very large (about 40000 times of liquid water), the operation energy for a pump is very energy intense. In addition, the very fine dried product may be entrained into the exhausted system flow and loss to (or contaminate) the environment. There for, our research team used the concept from lithium bromide absorption chiller to create an absorber/desorber system, which can continuously absorb the vaporized steam inside the vacuum chamber and desorbs it outside the chamber.
The construction of this absorber/desorber system includes conception design, system simulation and analysis by a computer code, manufacture and setup of a test facility and the functional test of absorption/desorption processes. In this thesis, the focuses are placed on the configuration design of experimented facility and the material selection for system components in order to maintain a low pressure environment inside the vacuum chamber and to achieve the continuity of absorption/desorption processes.
To assist in promoting the absorption capacity, the absorption tests carried out in this study used two different kinds of cooling tube; one without fin and the other with plat-fin connected vertically along a tube array. The test results indicated that the heat transfer rate and the vapor absorption rate of finned tube were respective about 8~35% and 16~21% higher than that of plain tube.
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