气凝胶
传质
超临界二氧化碳
自然对流
超临界流体萃取
材料科学
多孔介质
对流
质量通量
超临界流体
扩散
输运现象
超临界干燥
热扩散率
热力学
化学工程
多孔性
纳米技术
复合材料
物理
工程类
作者
Friday N. Abolorunke,Huu-Ba Dinh,Georgios Karamanis,Karthik S. Remella,Marc Hodes
标识
DOI:10.1115/ht2023-105770
摘要
Abstract In manufacturing silica aerogels, the alcohol solvent is often extracted from a wet gel via supercritical carbon dioxide (SCCO2) drying to avoid, during the majority of the drying process, crossing the liquid-vapor phase boundary and thus prevent capillary forces from collapsing the delicate mesoporous structure. Our understanding of the relevant physics is limited due to the complex phenomena involved in this transport process. Therefore, a rigorous model that captures the underlying physics is essential to understand the transport phenomena for scaling up the drying process and reducing overall manufacturing costs. Several studies that model the SCCO2 drying of aerogel have ignored the effect of natural convection on the extraction rate. Here, we developed a 3D model to capture the natural convective mass transfer due to variation in fluid density as the concentration of carbon dioxide CO2 changes in an ethanol-carbon dioxide mixture. The geometry is an annular gel concentric with an open region where SCCO2 flows. The aerogel is modeled as a porous medium where the flow is modeled using Darcy’s law. We solve the compressible forms of the momentum, continuity, and species equations that govern and couple the transport in the open region and the porous medium. Also, we account for the variation in molecular diffusivity in the species transport equation using a mass-fraction-dependent diffusion coefficient. We show the changes in the mass transfer rates relative to the case where natural convection is ignored to be substantive.
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