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

Abstract

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 ∼0.5W/cm2. The uniformly heated 10×10mm surfaces have an average roughness, Ra=0.039μm (smooth Cu), and 0.21–1.79μm. The transient growth rate, departure diameter and detachment frequency of the discrete vapor bubbles are determined from images captured at 210fps 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±17μm and 38±3Hz, 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 2000cm−2, compared to 650–10,000cm−2 for the rough Cu surfaces. For all surfaces, the active nucleation sites density increases with increasing the wall superheat and/or surface roughness.