Experimental investigation of spray cooling on micro-, nano-and hybrid-structured surfaces

摘要

The heat transfer during spray cooling was studied experimentally using deionized water to investigate the spray characteristics and the differences between spray cooling on a smooth silicon surface and micro-, nano- and hybrid microano-structured surfaces. The spray cooling experiments show that the heat transfer rates were better for the nano-structured surface, followed by the smooth surface coated with the SiO_2 film and the pure silicon surface since the contact angle was smallest on the nano-structured surface and increased on the latter two. The droplet parameter results show that most droplets were 40-60 μm in size. The heat transfer coefficient increased and the wall temperature decreased on the 25G × 25S surface coated with the SiO_2 film compared with the 50G × 50S surface coated with the SiO_2 film as the heat transfer moved into the partial dryout region due to the SiO_2 film's stronger hydrophilicity so the heated area was more fully utilized, while the CHF was larger for the 50G × 50S surface. Coating the micro-structured surfaces with carbon nano-tube (CNT) films having characteristic sizes smaller than the droplet size was more effective than on the surfaces with larger characteristic sizes. The CHF was largest on the 25G × 25S surface coated with 4 carbon nano-tube films with a 75.3% increase over the smooth surface. The wall temperature increase and the temperature fluctuations were small in the boiling regime as the power increases for the enhanced surfaces.