Dynamic drying variables evolution in membrane structure
A rigorous and comprehensive coupled mathematical model of mass, heat and dry gas transfer was implemented to analyze the variables variations in convective drying of porous materials. The governing system of nonlinear partial differential equations were derived where conservation laws were applied...
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| Main Authors: | , |
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| Format: | Book Section |
| Published: |
Springer International Publishing Switzerland
2016
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/8626/ |
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| Summary: | A rigorous and comprehensive coupled mathematical model of mass,
heat and dry gas transfer was implemented to analyze the variables variations in
convective drying of porous materials. The governing system of nonlinear partial
differential equations were derived where conservation laws were applied and
implemented to finite element method in two dimensional system. Further, Skyline
solver was used to capture highly nonlinear transient process. The characteristic of
hygroscopic and nonhygroscopic materials on the drying variables variation was
clearly distinguished in this works. The model was further improved in the application
of multilayer membrane structure. Investigation of the dominant variables in
this structure during the drying show that liquid diffusivity induced by capillary
mechanism is dominant in the constant rate period (CRP) before vapour diffusivity
caused by diffusion of vapour pressure and bulk flow gas take place in first falling
rate period (FRP1). Subsequently, when drying reaches the second falling rate
period (FRP2), the bound water mechanism is activated for hygroscopic zone
whereas drying is almost accomplished for nonhygroscopic materials. At the shift to
a multilayer structure system, top hygroscopic layer exhibits a slower drying rate
due to higher water retention associated with its material characteristic compared to
nonhygroscopic layers. The model is able to predict proper results with reasonable
accuracy at any times. Knowledge gained from this study can be used to assist with
the optimization of a given dryer design during drying process of ceramic membrane
fabrication. |
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