| A modelling method by molecular dynamics simulation was proposed to construct the three dimensional porous structure of silica aerogel. Further, we built contact secondary particles which were consist of full-density silica and defects. Size effect was observed when the particle chain length was under 8nm, which was a bit of shorter than the one of bulk silica. The influence of contact area proportion and defects concentration on the heat transport between adjacent particles were investigated. Lastly, the solid-gas coupling heat transport in the contact particles unit was discussed.The porous structure was obtained by deleting atoms randomly first, then melting and quenching the whole system to simulate the diffusion cluster limited aggregation process. The thermal conductivity and density followed the scaling theory, and the scale factor was 1.5 in our results, well falling in the range of 1.2-2 obtained by other similar researches.Then adjacent silica particles were modelled. Size effect in heat transport was observed when the particle chain length was under 8nm, which was a little shorter than the one of bulk silica (10nm). The contact length and defect concentration had significant effects in the heat transport of the contact particles. And the smaller the fraction of solid conduction path or the bigger the defect concentration was, more significant the reduction effect could be. The share of contact thermal resistance became smaller as the contact length increased, but showed no correlations with defect concentration.The solid gas coupling effect in the contact particle units was investigated. In our result, the noticeable enhancement by this coupling effect was not observed as the theory predicted. We thought this coupling effect related to the mean free path lgas(P) and particle diameter (D). Only when D >> lgas(P), this coupling effect in enhancement of heat transport could be considered, or it did not increase the thermal conductivity in a visible amount. |
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