Design of aerogel granule size for thermal insulation of petroleum pipelines

Silica aerogel granules possess low thermal conductivity and inherent hydrophobicity; however, the influence of granule size on thermal insulation performance has not been sufficiently investigated. In this study, silica aerogel granules with controlled sizes (0.04–3.33 mm) were prepared by mechanical or jet grinding, and a parallel thermal resistance network model was established to predict the effective thermal conductivity measured using the heat flow meter method. The results indicate that granules with an average diameter of 0.61 mm achieved the lowest thermal conductivity of 0.0173 W·m^{− 1}·K^{− 1}. This optimal performance originates from a balance between solid-phase conduction (reduced contact points) and gas-phase conduction (relatively compact packing density). COMSOL simulations further demonstrated that applying this material in a 2 km U-shaped geothermal well maintained the outlet fluid temperature at 99.38 °C. In addition, the intrinsically low density of the aerogel reduces the self-weight of the pipeline, thereby alleviating mechanical fatigue in long-distance transportation systems. This study provides an experimentally supported framework for understanding heat-transfer mechanisms in granular aerogel systems and offers guidance for improving the design and application of silica aerogels in geothermal and petroleum energy infrastructures.