A pore-scale visualized study of melting heat transfer of a paraffin wax saturated in a copper foam: Effects of the pore size

In this Technical Note, a visualized study at the pore-scale was carried out to explore the pore size effects on melting heat transfer of a paraffin wax saturated in a copper foam. Three types of copper foams having a pore size of 15 ppi, 30 ppi and 50 ppi were used. The pore-scale visualization of the melting process was enabled using an infrared video camera equipped with a macrolens. Thermocouples were also embedded in the melting system at different locations to monitor the local temperature variations. It was observed that at the wall superheat of 20 °C, the 30 ppi and 50 ppi copper foams lead to almost identical overall melting rates, which are both much faster than that for the 15 ppi one. However, when the wall superheat was increased to 30 °C, the 30 ppi copper foam appears to be the best filler that causes much faster melting than that of the 50 ppi one. In addition, transient evolutions of the pore-scale temperature field were observed through the infrared thermal imaging snapshots at representative time instants during melting. The local thermal nonequilibrium between the paraffin wax and its surrounding copper ligaments was clearly demonstrated to decrease with reducing the pore size. In sum, the use of copper foams with relatively small pores was deemed to be desirable, which may lead to both faster melting and less significant local thermal nonequilibrium effect.