Enhanced fractal capillary bundle model for effective thermal conductivity of composite-porous geomaterials

A good knowledge of the effective thermal conductivity (ETC) of geomaterials is required to achieve accurate study on heat transfer in a variety of earth-contact engineering applications. On account of composite-porous characteristic of geomaterials, the thermal conductivity of each component is the foundation while the porous structure is the key influence factor. Accordingly, a fractal capillary bundle model at pore scale is proposed in this paper to predict the ETC of saturated/unsaturated composite-porous geomaterials. The combination of fractal theory and capillary bundle model hypothesis is used to describe the random, disordered and extremely complicated microstructure of geomaterials. The analytical solution of the ETC is obtained by using the thermal-electrical analogy technique, which demonstrates that the proposed model is a function of variety of composition and microstructure parameters. Both the effects of these two types of parameters on the ETC of geomaterials are analyzed theoretically. Compared with other models, the present model represents specific physical meaning and shows acceptable accuracy and performance. The model predictions are further compared with the available experimental data for three types of concrete, and a good agreement between them can be found in most of saturation degrees (0.2 < S-r < 0.8).