Dynamic Drying Variables Evolution in Membrane Structure

Abstract

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.