Abstract:
The mechanism of the formation of large vapor agglomerates was experimentally studied in a subcooled water flow boiling in a channel at a heat flux that approaches the critical value on a smooth or structured heated surface with high-speed video. The experiments were performed with distilled, deaerated water at atmospheric pressure and liquid subcooling of $\Delta t_{\text{sub}} = 20$–$75^{\circ}$Ñ in a mass flow rate range of $\rho w = 500$–$900$ kg/(m$^2$ s). Large agglomerates have been found to form as a result of the spontaneous coalescence of normal small vapor bubbles at a sufficiently high density on the heated surface. The presence of steam agglomerates induces dry spots on the heated surface, the enlargement of which in area is the direct cause of overheating of the heat-transfer surface and a boiling crisis. It has been demonstrated that structuring of the heating (boiling) surface via microarc oxidation has hardly any effect on the operating conditions upon the emergence of agglomerates.
Fulltext:
PDF file (5725 kB)
