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

In this paper, a visualization and measurement investigation is performed on melting phase change of paraffin in high porosity open-cell copper foam at pore scale. With the aid of high definition camera and infrared camera, the phase and temperature fields of paraffin-foam and pure paraffin samples are captured to visualize the detailed melting phenomena. The local temperatures of both paraffin and copper foam matrix are measured by the thermocouples to study the thermal response characteristic and local thermal non-equilibrium effect. The experimental results reveal multiple pore-scale physical processes including the evolution of solid-liquid phase change interface, volume expansion of paraffin, motion of solid paraffin and release of air bubbles from paraffin. Under the combined influences of these physical processes, it shows that copper foam with a high porosity of 0.974 effectively extends the phase change interface and improves the thermal response rate of paraffin. As a result, the melting rate of paraffin has increased by more than two times, while the reduction in the amount of latent heat is only 2.6%. Moreover, significant effect of local thermal non-equilibrium between paraffin and copper foam is found during the melting process of paraffin-copper foam sample. Finally, through generalizing results from present experimental measurements, a correlation for dimensionless melting time of the paraffin copper foam sample at pore scale is developed. The present investigation can contribute to a better understanding of melting in metal foam and provide guidance for the application and performance analysis of paraffin/metal foam composite. (C) 2017 Elsevier Masson SAS. All rights reserved.