Saturation boiling of PF-5060 on rough Cu surfaces: Bubbles transient growth, departure diameter and detachment frequency

摘要

Investigated is the transient growth of discrete bubbles in saturation nucleate boiling of PF-5060 liquid on rough Cu surfaces at an applied heat flux of ～0.5 W/cm~2. The uniformly heated 10×10 mm surfaces have an average roughness, Ra = 0.039 μm (smooth Cu), and 0.21-1.79 μm. The transient growth rate, departure diameter and detachment frequency of the discrete vapor bubbles are determined from images captured at 210 fps using high-speed video camera. On smooth Cu, the bubble departure diameter and detachment frequency are 655±40μm and 31 ±4Hz. On the other Cu surfaces (Ra = 0.21-1.79μm), the measured values of 438 ± 17 μm and 38 ± 3 Hz, respectively, are independent of surface roughness. Results, in conjunction with the experimental nucleate boiling curves, estimate the surface average density of active nucleation sites as a function of wall superheat For smooth Cu, the density of active sites ranges from 100 to 2000 cm~(-2), compared to 650-10,000 cm~(-2) for the rough Cu surfaces. For all surfaces, the active nucleation sites density increases with increasing the wall superheat and/or surface roughness.