Liu Jing, Buahom Piyapong, Lu Chang, Yu Haiyan, Park Chul B
College of Vehicle and Traffic Engineering, Henan University of Science and Technology, Luoyang, 471003, China.
Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, ON, M5S 3G8, Canada.
Sci Rep. 2022 Dec 5;12(1):21034. doi: 10.1038/s41598-022-24133-5.
As a star insulation material, aerogel plays a significant role in saving energy and meeting temperature requirements in industry due to its extremely low thermal conductivity. The prediction of aerogel's thermal conductivity is of great interest in both research and industry, particularly because of the difficulty in measuring the separated gas conductivities directly by experiment. Hence, the proportions of separated gas conduction and solid-gas coupling conduction are debatable. In this work, molecular dynamics simulations were performed on porous silica aerogel systems to determine their thermal conductivities directly. The pore size achieved in the present study was improved significantly, making it possible to include the gas phase in the investigation of aerogel thermal conductivity. The separated solid conductivity [Formula: see text] and the separated gas thermal conductivity [Formula: see text] as well as the effective solid conductivity [Formula: see text] and the effective gas conductivity [Formula: see text] were calculated. The results suggest that the solid-gas coupling effect is negligible in rarefied gas because the enhancement of thermal conduction due to the short cut bridging effect by gas between gaps in the solid is limited. The gas pressure is the most significant factor that affects the solid-gas coupling effect. The large differential between the prediction and the actual value of the thermal conductivity is mainly from the underestimate of [Formula: see text], and not because of ignoring the coupling effect. As a conclusion, the solid-gas coupling effect can be neglected in the prediction of silica aerogel's thermal conductivity at low and moderate gas pressure, i.e., decreasing the gas pressure is the most efficient way to suppress the coupling effect. The findings could be used in multi-scale simulations and be beneficial for improving the accuracy of predictions of aerogel thermal conductivity.
作为一种明星保温材料，气凝胶因其极低的热导率，在工业领域节能和满足温度要求方面发挥着重要作用。气凝胶热导率的预测在研究和工业中都备受关注，尤其是因为直接通过实验测量分离气体的热导率存在困难。因此，分离气体传导和固 - 气耦合传导的比例存在争议。在这项工作中，对多孔二氧化硅气凝胶系统进行了分子动力学模拟，以直接确定其热导率。本研究中实现的孔径有了显著改善，使得在气凝胶热导率研究中纳入气相成为可能。计算了分离的固体热导率[公式：见原文]、分离的气体热导率[公式：见原文]以及有效固体热导率[公式：见原文]和有效气体热导率[公式：见原文]。结果表明，在稀薄气体中固 - 气耦合效应可忽略不计，因为固体间隙间气体的捷径桥接效应导致的热传导增强有限。气体压力是影响固 - 气耦合效应的最显著因素。热导率预测值与实际值的较大差异主要源于[公式：见原文]的低估，而非忽略了耦合效应。总之，在中低压下预测二氧化硅气凝胶的热导率时，固 - 气耦合效应可以忽略不计，即降低气体压力是抑制耦合效应的最有效方法。这些发现可用于多尺度模拟，有助于提高气凝胶热导率预测的准确性。
