Effective thermal conductivity heat transfer in an iron packed-sphere porous medium

Abstract

The investigation of an effective thermal conductivity (k_eff), influenced by conductive and radiative heat transfer, of the packed-sphere porous medium is the goal of this research. The globule iron having diameter of 5.55 mm and porosity (f) of 0.475 are examined. The experimental procedure is based on ASTM E1225. The tested porous sample is sandwiched by the references materials that a known thermal conductivity (k_solid), Brass solid (70%Cu, 30%Zn), is used. The energy heat rate supplied to system is obtained from electrical wire heater with a constant value of 350 W and the temperature of this position is defined as a higher temperature (T_H). To make sure the temperature gradient from T_H along the length of experiment, the end opposite side is cooled by water and thus the temperature of this position is called as a lower temperature (T_L). From the experiment, it was found that k_eff decreased with increasing T_H and the relation between k_eff and T_H can be appropriately proposed by a power equation (k_fit = 3880(T_H/100)^-2.77) owing to R² = 0.983. In addition, the average quantity of k_eff (k_avg) is slightly higher than the thermal conductivity combined by void and solid (k_f,s), i.e., k_avg > k_f,s, because of the effect of conduction and radiation is regarded in k_avg. However, the value of k_solid is highest owing to the solid materials not taken into account the effect of conduction from porosity or void volume.