Numerical heat and mass transfer analysis for moisture adsorption / desorption in porous silica-gel packed beds

• Main Authors: Ting-HsuanHsu, 許庭瑄
• Other Authors: Tian-Shiang Yang
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/5f77ud

碩士 === 國立成功大學 === 機械工程學系 === 107 === Silica-gel packed bed systems are extensively used in various industrial processes for dehumidification or adsorption of volatile organic compounds. In order to improve the design of the system, understanding the heat and mass transfer mechanism during moisture adsorption/desorption process is important. Recently, a solid-side resistance model (SSR), which consider the resistance of solid part of silica gel, has better computation performance. In our group, we did both experiment and numerical work for the system.In previous work, we built the one-dimensional (1-D) and two-dimensional (2-D) model and found that the 2-D model has better result of simulations because it considered temperature and humidity distribution in radial direction. But the model neglects the nonhomogeneous velocity field of a porous medium, so the total water adsorption will be overestimated. To consider the non-homogeneous pressure and velocity field, we add Darcy’s law into our models. During our work, we found that there was some problems of velocity field for just adding the Darcy’s law inside our previous model. So, we also use the first order correction of Darcy’s law to have a better velocity field and also build a model for the pressure inside the silica gel. After the computation of the process, we found that pressure is an important factor of water adsorption. Higher pressure will cause higher water content of silica gel when reaction reaches steady state. Moreover, we analyzed the effect of geometry and other parameters, we found that, big caliber size comparing to the packed bed radius, smaller length, and bigger radius will cause higher speed of adsorbing water vapor at the beginning of reaction. And high inlet velocity, and bigger size of packed bed will lead to more water vapor adsorption.