This study presents a systematic experimental method of estimating the extent of the phase front under the local thermal non-equilibrium condition in porous media saturated with phase change materials (PCM). It describes a comparison of measured temperature of the solid matrix at pre-selected sites with the average pore temperature in order to substantiate the existence of the local thermal non-equilibrium condition. Also, the measured data are compared with the theoretical predictions reported in the literature. The agreement between the experimental and theoretical prediction is highly satisfactory. The results clearly show that, early during the phase change process, the Sparrow number is relatively small and the solid matrix is not at the local thermal equilibrium with the pore materials. At larger time, the Sparrow number rapidly increases and the system approaches the local thermal equilibrium condition.
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