Effective thermal diffusivity and conductivity of a fluid-saturated solid foam

Abstract

The thermal properties of composite materials, such as fluid-saturated solid foams, can be estimated in two ways: using equivalent models based on both the thermal properties of the liquid and solid phases or by direct measurements, which, however, are not always straightforward. In this paper, we provide a new experimental device based on the four-layer (4L) method to measure the effective thermal diffusivity of a solid foam filled with different fluids (glycerol and water). The specific heat of the solid part is measured using differential scanning calorimetry, and the volumetric heat capacity of the composite system is estimated using an additive law. The effective thermal conductivity deduced from experiments is then compared with the maximum and minimum values obtained from the parallel and series equivalent models. The proposed 4L method is first validated by measuring the thermal diffusivity of pure water and then used afterward to measure the effective thermal diffusivity of the fluid-saturated foam. Experimental results converge with those obtained from equivalent models in the case where the different components of the system have similar thermal conductivities (e.g., glycerol-saturated foam). On the other hand, when the liquid and solid phases have very different thermal properties (e.g., water-saturated foam), the experimental results differ from what equivalent models predict. This highlights the need to make appropriate experimental measurements to estimate the overall thermal properties of these latter multicomponent systems or to consider more realistic equivalent models.