A Comparative Study of Selected Models for Effective Thermal Conductivity

Abstract

This paper conducts a comparative evaluation of 22 models focusing on the effective thermal conductivity of two-phase porous materials. Calculations were performed for each model across a range of solid-to-fluid thermal conductivity ratios, spanning from 1 to 15,000, and for two different porosities: 0.1 and 0.2. The study advocates the use of dimensionless charts that normalised solid thermal conductivity (ks) and effective thermal conductivity (kef) concerning fluid thermal conductivity (kf) for qualitative analysis. Employing this approach, the examined models were categorised into four fundamental groups. The latter portion of the paper compares selected models with experimental data. These experiments involved testing eight porous media samples in the form of packed steel bars, arranged in two configurations: staggered and in-line. The tests were conducted over a temperature range of 75–400°C, corresponding to ks-to-kf ratios ranging from 1,800 to 855. Various graphical representations were used to compare measurement data with model calculations. The findings indicate that the most accurate comparisons can be made using linear charts, which present absolute values of the kef coefficient in relation to the thermal conductivity of the solid phase.