Pore-scale visualization and measurement of paraffin solidification in high porosity open-cell copper foam

In this work, a pore-scale experimental investigation on solidification of paraffin in high porosity open-cell copper foam is performed based on the visualization and measurement technique. With the use of high definition camera and infrared camera, the phase and temperature fields of the copper foam/paraffin sample are obtained to directly visualize the solidification process. Simultaneously, T-type thermocouples are employed to measure the local thermal response characteristic and thermal non-equilibrium effect of the copper foam/paraffin sample. For comparison, the corresponding solidification experiment with pure paraffin sample is also conducted. Local details of solidification phase change including the evolution of phase change interface within foam pore region, the liquid phase flow and air gap formation due to the volume shrinkage effect of paraffin are revealed. It is found that the highly conductive copper foam remarkably extends the phase change interface, avoids the formation of overlarge-size air gap that forms in the pure paraffin sample and enables a higher thermal response rate of the copper foam/paraffin sample. As a result, an attractive solidification enhancement (about 2.8 times) of paraffin in copper foam is achieved. Moreover, strong effect of local thermal non-equilibrium between copper foam and paraffin is detected during the solidification process. Finally, through generalizing the present experimental results, a correlation for dimensionless solidification time of the copper foam/paraffin sample is developed at pore scale.