Đang chuẩn bị liên kết để tải về tài liệu:
Mass Transfer in Multiphase Systems and its Applications Part 17

Tham khảo tài liệu 'mass transfer in multiphase systems and its applications part 17', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Heat and Mass Transfer in Packed Bed Drying of Shrinking Particles 629 Fig. 4. Bulk shrinkage ratio Sb as function of dimensionless bed-averaged moisture content 1.0 0.8 0.6 T 30 C v 0.5 m s T 50 C v 1.5 m s 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 X X0 - Fig. 5. Shrinkage ratio Sb as a function of dimensionless moisture content for artificially coated seeds 3.5 Changes in structural properties during drying Physical properties of beds composed of very wet particles are clearly dependent upon reduction of both moisture content and volume. Any attempt to raise the shrinkage phenomenon to a higher level of understanding must address the structural properties of the material such as density porosity and specific area. Moreover porosity specific area and bulk density are some of those physical parameters that are required to build drying models they are particularly relevant in case of porous beds and as such plays an important role in the modelling and understanding of packed bed drying. Several authors Ratti 1994 Wang Brennan 1995 Koẹ et al. 2008 have investigated the changes in structural properties during drying. In what follows a discussion is directed to changes in physical properties during drying of single and deep bed of skrinking particles. Typical experimental data on changes in structural properties of mucilaginous and gel coated seeds during drying in bulk or as individual particles are presented in Figure 6. 630 Mass Transfer in Multiphase Systems and its Applications a Particle and bulk density versus dimensionless moisture content for mucilaginous seeds b Particle and bulk density versus dimensionless moisture content for gel coated seeds c Bed porosity versus dimensionless moisture content for mucilaginous seeds d bed porosity versus dimensionless moisture content for gel coated seeds 1.7 1.6- -1.5. e . 1.4- Ễ 1.3- s 1.2- 1.1 - 1.0 0.0 0.2 e Specific surface area versus dimensionless moisture content for the packed bed T 30oC v 0.5 m s T 50oC v 0.5 m s T 50oC v