Enhanced Boiling Heat Transfer on Super-Hydrophilic Surface with Porous Copper Layer
Saturation pool boiling of deionized water on a composite porous copper surface was investigated. SEM micrographs showed that the porous layer comprised three types of structures with macro pores above 200?m diameter, micro pores around 2?m diameter and dendritic structure in submicrometer size range. The porosity of the porous layer reached to as high as 94.4%. Contact angle of deionized water against the porous surface was less than 5°, indicating that it was of super-hydrophilic characteristic. The experimental results of pool boiling heat transfer revealed that the critical heat flux(CHF) of the porous surface reached up to 239 W/cm2, 101% higher than that of plain surface. Meanwhile, in order to investigate the mechanism of enhanced nucleate boiling high speed photography was employed to observe the bubble behaviors. Visualization data indicated that the coalescent bubble on porous surface grew more quickly and had larger size during high heat flux range. Consequently, the departure of bubble brought more liquid replenishment, resulting in continuous rise of heat transfer coefficient and higher CHF value.