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Multiphase Science and Technology
SJR: 0.183 SNIP: 0.483 CiteScore™: 0.5

ISSN Imprimer: 0276-1459
ISSN En ligne: 1943-6181

Multiphase Science and Technology

DOI: 10.1615/MultScienTechn.v25.i2-4.80
pages 201-236

SATURATION BOILING ON MPC: EFFECTS OF THICKNESS, INCLINATION ANGLE, TRANSIENT BUBBLE GROWTH, AND NUCLEATION SITE DENSITY

Mohamed S. El-Genk
Institute for Space and Nuclear Power Studies; Mechanical Engineering Department; Nuclear Engineering Department, Chemical & Biological Engineering Dept., University of New Mexico, Albuquerque, New Mexico, 87131 USA
Amir F. Ali
Institute for Space & Nuclear Power Studies, University of New Mexico, Albuquerque, New Mexico, USA; Mechanical Engineering Department, University of New Mexico, Albuquerque, New Mexico, USA

RÉSUMÉ

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, δMPC varied 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 δMPC from 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 hNB and hMNB increased with increasing δMPC, peaking at ~171 µm, and then decreased with a further increase in δMPC. They were highest in the upward-facing orientation. The hMNB value (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 hNB was correlated in terms of the applied heat flux (hNB = AqB); coefficient A increased linearly from 0.427 to 1.143 as δMPC increased 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 hNB correlation 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 Dd and fd and the boiling curves in the experiments, ranged from ~725 to 1.07 × 104 sites/cm2.


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