一种多孔介质有效扩散系数和孔隙率的测定方法
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摘要
依据拟稳态扩散原理,通过物料衡算,建立了用蒸发管法测定多孔介质有效扩散系数及孔隙率的实验方法。在水—空气系统、乙醇—空气系统拟稳态扩散模型的基础上,分别对水蒸汽、乙醇蒸汽通过玻璃管内自由空气段和多孔介质段的扩散进行物料衡算,得到在常压下液体蒸汽在自由空气中和在多孔介质内的扩散系数,进而计算得到多孔介质的孔隙率。实验结果表明:蒸发管法测定的有效扩散系数及孔隙率与文献值的平均相对误差小于4%,这是一种简单有效地测定多孔介质扩散系数的方法,具有无毒、成本低,无需特殊设备等优点,为后续有效扩散系数的测定奠定了坚实的基础,有很强的实用性。
Based on the quasi steady-state diffusion theory, a new way of determining the effective diffusivity and porosity of the porous materials was established through the evaporation tube method and the mass balance calculations. The diffusion process has two steps, one is the free diffusion in the binary-component gas systems, and the other is the diffusion in the porous medium. In the H2O- Air and Ethanol-Air systems, the mass balance of water or ethanol was calculated for the diffusion process in the free air or the porous medium, then the effective diffusivities of the vapor of water or ethanol in air and porous medium were obtained, and the porosity of the porous materials can be calculated. The average relative error of the effective diffusivity between the values measured by evaporation tube method and the literature values is less than 4%. The results show that, this new method is simple, effective and reliable for the measurements of the effective diffusivity and porosity of the porous materials. Comparing with other diffusivity and porosity measurements, this new method has some advantages of low cost, non-toxic and no need of special equipments. The proposed new method also set a solid foundation for the subsequent research of the effective diffusion coefficients and porosity measurements of the porous mediums.
Based on the quasi steady-state diffusion theory, a new way of determining the effective diffusivity and porosity of the porous materials was established through the evaporation tube method and the mass balance calculations. The diffusion process has two steps, one is the free diffusion in the binary-component gas systems, and the other is the diffusion in the porous medium. In the H2O- Air and Ethanol-Air systems, the mass balance of water or ethanol was calculated for the diffusion process in the free air or the porous medium, then the effective diffusivities of the vapor of water or ethanol in air and porous medium were obtained, and the porosity of the porous materials can be calculated. The average relative error of the effective diffusivity between the values measured by evaporation tube method and the literature values is less than 4%. The results show that, this new method is simple, effective and reliable for the measurements of the effective diffusivity and porosity of the porous materials. Comparing with other diffusivity and porosity measurements, this new method has some advantages of low cost, non-toxic and no need of special equipments. The proposed new method also set a solid foundation for the subsequent research of the effective diffusion coefficients and porosity measurements of the porous mediums.
引文
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[2]Yang Xiaoxu,Li Yu,Gustaaf Van Tendello,et al.Nanoparticles within a hierarchically macroporous core@ordered mesoporous shell system[J].Adv Mater,2009,21(13):1368-1372.
[3]WU Ming(吴明),WU Jian-min(邬建敏).Preparation and characterization of porous silicon-supported bilayers lipid membranes(多孔硅支撑磷脂双层膜的制备与表征)[J].J Chem Eng of Chinese Univ(高校化学工程学报),2011,25(5):816-821.
[4]Colin S Cundy,Paul A Cox.The hydrothesis of zeolites:history and development from the earliest days to the present times[J].Chem Rev,2003,103(3):663-701.
[5]YANG Jing-biao(杨景标),CAI Ning-sheng(蔡宁生).Effects of catalysts on the structure and morphology of a lignite char(粉煤灰结构和形态对催化性能的影响)[J].Proceedings of the CSEE(中国电机工程学报),2008,28(11):24-29.
[6]Sepulveda P.Gelcasting foams for porous ceramics[J]The American Ceramic Society Bulletin,1997,76(10):61-65.
[7]Kolaczkowski S T.Measurement of effective diffusivity in catalyst-coated monoliths[J].Catal Today,2003,83(1-4):85-95.
[8]Nijhuis T A,Van Den Broeke L J P,Van De Graaf J M,et al.Bridging the gap between macroscopic and NMR diffusivities[J].Chem Sci,1997,52(19):3401-3404.
[9]CHEN Tao(陈涛),ZHANG Guo-liang(张国亮).Basis For Chemical Engineering Transport(化工传递过程基础)[M].2nd ed(第2版).Beijing(北京):Chemical Industry Press(化学工业出版社),2002.
[10]LEI Hua(雷华),LU Yang(鲁阳),PAN Qin-min(潘勤敏).Visualization of diffusion process in polymer system(高分子体系中扩散过程的可视化研究)[J].J Chem Eng of Chinese Univ(高校化学工程学报),2004,18(1):1-6.
[11]R Byron Bird,Warren E Stewart,Edwin N Lightfoot.Transport Phenomena[M].2nd ed.Beijing:Chemical Industry Press,2002:673.
[12]WANG Cheng(王诚),MAO Zong-qiang(毛宗强).Influnce of carbon paper on self-humidifying performance of PEMFC[J].Chemical Journal of Chinese Universities(高等学校化学学报),2005,26(1):125-128.
[13]Denis Kramer,Stefan A,Freunberger,et al.Electrochemical diffusimetry of fuel cell gas diffusion layers[J].Electroanalytical Chemistry,2008,612(1):63-77.
[14]LIU Guang-qi(刘光启),MA Lian-xiang(马连湘),LIU Jie(刘杰).Chemical and Physical Manual(化学化工物性数据手册)[M].Beijing(北京):Chemical Industry Press(化学工业出版社),2002.