Thermal conduction model of asymmetric structural aramid nanofiber aerogel membranes based on fractal theory

Asymmetric structural aramid nanofiber aerogel membranes (ASAAMs) have been considered ideal thermal insulators due to their unique characteristics, such as dense surface layers and nanoscale 3D fibrous body components. Fractal theory has been used in studying the pore size distribution of fibrous aerogels with symmetrical structures but is rarely used in studying the thermal conductivity of asymmetric structural aerogels. In this work, two basic fractal units are used to simulate the pore size distribution of ASAAMs. The models are transformed into series and parallel fractal resistance networks using the equivalent resistance method. Additionally, a marginal weighting function is proposed to modify the heat transfer model, which is applied to calculate the total effective thermal conductivity of ASAAMs. Results showed that: (1) The correlation between the porosity and the effective thermal conductivity of ASAAMs is negative. (2) The basic fractal units of 7 × 7 size selected in this paper could be described the pore size distribution of ASAAMs well. (3) The modified model demonstrates only 2.58% error, which is closer to the experimental data.