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论文类型：期刊论文
发表时间：2019-12-10
发表刊物：DRYING TECHNOLOGY
收录刊物：EI、SCIE
卷号：37
期号：16
页面范围：2126-2136
ISSN号：0737-3937
关键字：Freeze-drying; desorption; drying time; initial saturation; sublimation
摘要：Porous frozen material with a certain initial porosity was prepared to explore its influence on freeze-drying experimentally. Soluble coffee was selected as the solute in aqueous solution and liquid nitrogen ice-cream making method was used to prepare the frozen materials. Results showed that freeze-drying can be significantly enhanced using the initially porous frozen material compared with the traditionally solid one. By keeping the same sample mass and moisture content with sole radiation heating, drying time of the porous frozen sample was about one third shorter than that of the solid one under the same tested operating conditions. SEM images of dried products revealed that the porous material had a loose and tenuous structure that was favorable to the transportation of sublimated vapor and the desorption of bound moisture. Appropriately increasing the chamber surface temperature benefited the freeze-drying process and changing the chamber pressure had little effect on the process. Combined radiation and conduction heating can further promote the freeze-drying process and save as much as 36.4% of the drying time. The porous frozen material was found to have a wider range of operating temperature and result in relatively lower residual moisture content.