Investigation of macrolayer thickness in nucleate pool boiling at high heat flux

Liquid–vapor structure near heating surface at high heat flux in subcooled pool boiling

“…(Fig.8) or the pulse frequency (Fig.7). Therefore, the paper determines the macrolayer thickness based on the The results reported for the correlations proposed by Rajvanshi et al [4], Kumada et al [10], and the correlation that Bhat et al [11] derived from the data of Iida et al [1] are also shown in Fig.17. The thickness of macrolayer at lower heat fluxes where the pulse spectrum has the single peak established here, and the thickness determined from the peak of the wider pulse width (longer hovering period) at higher heat fluxes where the pulse spectrum has two peaks agree with the correlation of Bhat et al However, the thicknesses corresponding to the peak of the narrower pulse width lie close to the Rajvanshi correlation.…”

“…It is generally accepted that this macrolayer is closely related to the occurrence of CHF in saturated boiling. Therefore, attempts have been made to determine the liquid-vapor structure under the vapor masses in saturated boiling, using electric conductance probes [1,2,3,4] and an optical probe [5] for the measurements because the vapor masses hovering on the heating surface make it impossible to conduct direct observations of the macrolayer from above the heating surface.…”

“…The heating surface was polished by #1000 emery paper before each experiment. 4 A conductance probe method was adopted for the measurements of the liquid-vapor behaviors very close to the heating surface. The sensing element of the conductance probe, which is a 90 µm diameter stainless steel wire, was inserted in a conical capillary quarts tube with very low thermal expansion coefficient.…”

CHF and near-wall boiling behaviors in pool boiling of water on a heating surface coated with nanoparticles

“…In Fig.17, the symbols are for the averaged values calculated using equation (1) and the vertical bars at each symbol indicate the minimum and 16 maximum values. The macrolayer thicknesses predicted with the empirical correlations proposed by Bhat et al [13] and Rajvanshi et al [14] for pool boiling of water on horizontal surfaces, and with the semi-theoretical correlation by Haramura and Katto [15] are also shown in Fig.17 3.7 Transient behavior of void fraction near heating surface before and after the CHF As shown in the previous section, the TiO2 coated surface is covered by a macrolayer that is not subject to dryout even at heat fluxes far higher than the CHF of the surface not coated by TiO2, and that the macrolayer formed on the TiO2 coated surface is thicker than that on the uncoated heating surface. The surface heat fluxes in Fig.18 are the values calculated from the readings of the two thermocouples embedded in the copper block.…”

“…The time-series data of the pulse signals were measured at various heights 14 over the heating surface (total number of pulses 4096 or 8192). Then, the pulses obtained at each height were classified into groups for every 2 ms of pulse width, and the frequency of the appearance of pulses of each pulse group was plotted.…”