Study On The Polypropylene Membrane And The Hollow Fiber Membrane Contactor

A membrane contactor is a device that achieves gas/liquid or liquid/liquid mass transfer without dispersion of one phase within another. The main studies of this thesis have been focused on the mass transport phenomenon in the hollow fiber membrane contactor, including the development of the model of the gas diffusion through the microporous membrane, the analytical solution of the shell side mass transfer differential equation in an orderly packed parallel flow module, the calculation of the shell side flow distribution in a randomly packed module, the estimation of the influence of the random arrangement of the fibers on the shell side mass transfer, and the experiments of the absorption of CO2 into water. At the same time, the microporous membrane made by stretching method was characterized, and the effect of the choice of pore morphological model upon the determination of the pore size and its distribution was discussed. And the relationship between the pore structure and the performance of the membrane contactor was also presented.Firstly, the microporous polypropylene membrane was characterized by SEM and liquid displacement method. In displacement technology, the determination of the pore size and its distribution was greatly affected by the choice of the pore model. The related physical equations (Yang-Laplace equation and Hagen-Poiseuille equation) were re-derived for different pore shapes. And the effect of using different pore model such as circle, elliptical and slit pore model to determine pore size and its distribution was investigated. The results showed that with different pore models leaded to significantly different pore size distributions. It was concluded that the pore shape should be chose with caution for membrane characterization.The stomatal diffusion model was adopted to describe the gas diffusion through the microporous membrane. For membrane contactor process, the binary gas mixture diffusion through the pore channel should be considered as a transition diffusion of the absorbed momentum A through the stagnant momentum B. And the process would consist three steps: transitiondiffusion through the pore channel, Stephen diffusion in the pore edge, and the pore interaction in the membrane surface. Generally, the membrane thickness is much larger than the pore dimension. Therefore, the resistance of the pore channel was the control resistance of the membrane diffusion process. While the existences of the Stephen diffusion and pore interaction well explained the reason why the total membrane surface would be used as the interfacial area through where the mass transport took place. Another question discussed was the pore shape correction. The equivalent pore radius of the elongated microcrack membrane pore was corrected by the correlation present in the study on the stomata diffusion of monocotyledons. An analytical solution on the shell side mass transfer in a parallel flow hollow fiber membrane module was carried out. A uniform fiber arrangement and a uniform concentration on fiber wall were assumed. And the shell side flow was described by Happel's free surface model. The analytical solution showed that the shell side Sherwood number was the function of Graetz number and the module packing density. The exponents of Graetz in the correlation gradually increased with the increasing of packing density, and the coefficients decreased at the same time. Compared with the numerical results presented by Miyatake and Iwashita, together with the experimental correlations in literatures, the results indicated that the model developed in this thesis was reasonable and it could be used in the description of the characterization of the shell side mass transfer.The shell side flow distribution in a randomly packed hollow fiber module was analyzed using the random cell model and free surface model. The module was divided into sub-channels, and the hydrodynamics in each channel was just the function of the local cell packing fraction. Based on the theoretical probability density distribution...