Saturation boiling on MPC: Effects of thickness, inclination angle, transient bubble growth, and nucleation site density | Academic Article individual record
abstract

© 2013 by Begell House, Inc. Saturation pool boiling experiments of PF-5060 dielectric on micro-porous copper (MPC) near atmospheric pressure (∼0.085 MPa) have investigated the effects of the inclination angle (θ) and thickness (δMPC) on the nucleate boiling (NB) heat transfer coefficient (hNB) and critical heat flux (CHF). In the experiments, δMPCvaried from 80 to 230 μm and θ varied from 0° (upward facing) to 180° (downward facing). In addition to enhancing hNB, there was no (or a slight) excursion in the surface temperature (<5 K) prior to boiling incipience. Increasing ±MPCfrom 95 to 230 μm increased the CHF from 22 to 26 W/cm2. The highest [maximum nucleate boiling (MNB)] heat transfer coefficient (hMNB) near the end of fully developed NB region occurred at lower superheat than at the CHF. Both hNBand hMNBincreased with increasing ±MPC, peaking at ∼171 μm, and then decreased with a further increase in δMPC. They were highest in the upward-facing orientation. The hMNBvalue (up to ∼7.8 W/cm2· K) decreased slowly with increasing θ to 90°, and then decreased faster to the lowest value at 180°. In the upward-facing orientation hNBwas correlated in terms of the applied heat flux (hNB= AqB); coefficient A increased linearly from 0.427 to 1.143 as δMPCincreased from 80 to 230 μm, while B increased from 0.522 to a peak of 0.686 at δMPC∼ 162 μm, and then decreased to 0.573 at δMPC= 230 μm. The hNBcorrelation agreed with the data to within ±12%. Also developed was a correlation for the transient bubble growth on MPC at low heat flux (<0.48 W/cm2). This correlation agreed to within ±5% with measurements from footings recorded using a video camera at 210 frames per second. The bubble's departure diameter (Dd= 431 ± 7 μm) and detachment frequency (fd= 36 ± 2 Hz) in the upward-facing orientation were independent of δMPC. The active nucleation site densities on MPC, based on these values of Ddand fdand the boiling curves in the experiments, ranged from ∼725 to 1.07 × 104sites/cm2.

author list (cited authors)
El-Genk, M. S., & Ali, A. F.
publication date
2013
publisher
Begell House Publisher
citation count

2