Critical heat flux in thin, uniform particle coatings

Pool boiling on thin, uniform porous coatings is examined experimentally using different copper particle diameters (between 40 and 80 mu m), fabrications (loosely packed, shaken, or pressed), and particle characteristics (solid or porous particle) with coating thickness varying between 3 and 5 particle diameters. The results show that the critical heat flux (CHF) is about 1.8 times for all the coatings, while the pre-CHF regime shows variations. We suggest that the presence of the thin, uniform porous coating influences the hydrodynamic (macroscale) stabilities such that statistically the critical Rayleigh-Taylor wavelength decreases and/or the vapor area fraction increases in a manner to statistically cause a decrease in the dominant interfacial wavelength. By the CHF experimental results, it is postulated that for a 2-fold increase in CHF, the wavelength-in the Zuber CHF model is nearly one-fourth of that for plain surface, or the area of the vapor channels increases by 2(2/3) (compared to plain surface). (c) 2005 Elsevier Ltd. All rights reserved.