Mathematical modeling and experimental study on water condensation in nanopores of calcium carbonate
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摘要: 岩石纳米孔隙中的凝聚水与许多水文地质工程地质问题关系密切:干旱区凝聚水是维持当地生态平衡的重要水资源,石雕石刻文物保护中凝聚水问题是需要考虑的关键因素之一,页岩气工程中页岩纳米孔隙中的凝聚水对页岩气的聚集和流动有重要影响,全球碳循环问题中凝聚水会影响C02与碳酸盐岩的作用。本文给出了单位体积岩石形成的凝聚水的质量与温度、相对湿度、孔隙度、颗粒大小之间数学关系式。在这一关系式中,通过分离压理论计算吸附水,通过开尔文方程考虑了毛细作用。把解析计算结果与三个平行样四个不同湿度下的凝聚水量实验值对比,对所提出的数学表达式进行了验证。实验时选取直径500 nm的碳酸钙球形颗粒,采用夯实的办法加工成样,把样品置于恒温恒湿环境中令水汽在孔隙中凝聚,定期对样品称重计算凝聚水质量,直到凝聚过程达到平衡。Abstract: Condensed water in nanopores of rocks is closely related to many hydrogeological and engineering geological issues. In arid areas, condensed water is an important resource to maintain local ecological balance. For the protection of stone carvings cultural relics, condensed water is one of the key factors to be considered. Condensed water in nanopores of shale has an important influence on the accumulation and flow of shale gas in the project of shale gas engineering. In global carbon cycle problems, condensed water affects the interaction between CO2 and carbonate rocks. This paper presents the mathematical relationship between the amount of condensed water and temperature, relative humidity, porosity and particle size. In this relationship, the adsorption water is calculated based on the disjoining pressure theory, and the role of capillary condensation is considered by Kelvin equation. The analytical results are compared with measured values of three parallel experiments on condensed water at four different relative humidity to verify the proposed mathematical expression. In the experiment, spherical particles of calcium carbonate with diameter of 500 nm were selected and processed into samples by tamping. The samples were placed in a constant temperature and humidity environment to condense water vapor in the pores. The samples were weighed periodically to determine the quality of the condensed water until the condensation process reached equilibrium.
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