Local Thermal Nonequilibrium During Melting of a Paraffin Filled in an Open-Cell Copper Foam: A Visualized Study at the Pore-Scale

In this technical brief, the application of infrared thermal imaging to investigate melting of a phase-change material (PCM) filled in an open-cell metal foam was proposed. Melting experiments in a rectangular cell were performed with paraffin/copper foam composite samples having a single pore size of 15 ppi. The visualized study at the pore-scale was enabled using an infrared video camera equipped with a macrolens, offering a resolution of 50 μm. The transient thermal imaging results were first validated against the temperature readings by a pre-installed thermocouple. A relative deviation below 4% was observed between the two methods over the entire course of melting. The local thermal nonequilibrium between a copper ligament and its surrounding paraffin was found to become more pronounced as melting proceeds, which could reach up to the order of 10 °C during the late stage of melting. The quantitative observation of the local thermal nonequilibrium effect may facilitate improvement of the existing two-temperature models for numerical simulations on melting of PCM enhanced by embedding metal foams.