Experimental investigations of pool boiling heat transfer on horizontal plate sintered with metallic fiber felt

In this study, pool boiling heat transfer performance of de-ionized water on horizontal plates sintered with copper fiber of various geometries was experimentally investigated under atmospheric pressure. Copper fiber felt with different structural parameters was proposed to provide artificial nucleate sites to improve heat transfer performance. A high-speed camera was used to photograph bubble growth processes. Pool boiling curves were obtained. Effects of fiber felt porosity and fiber diameter on the onset of nucleate boiling (ONB) and boiling heat transfer coefficient were investigated. It was revealed that copper fiber felt surfaces can reduce wall superheat at boiling incipience and exhibit significant enhancement of heat transfer compared with smooth surface. The influence of porosity on heat transfer performance for metal fiber felts was more sensitive than fiber diameter. A bubble with an average diameter of less than 0.3 mm was defined as a small-sized bubble (SSB) from visualization photograph by high-speed camera, and pool boiling heat transfer performance was highly dependent on the percentage of small-sized bubbles (PSSB) to help illustrate enhancement mechanisms between bubble size distribution and boiling heat transfer performance. Smaller mean pore diameter can be achieved through decreasing either porosity or fiber diameter, as it allowed the fiber felt to create stronger capillary force to form bigger size bubble and lower PSSB to result in improved heat transfer coefficient.