Experimental Investigation of Two-Phase Subcooled Liquid Flow Structure under Preburnout Conditions

Abstract

The article presents the results from experimentally investigating the occurrence conditions and evolution with time of large vapor agglomerates in a rectangular channel during subcooled water boiling. The experiments were carried out at atmospheric pressure with a mass velocity of up to 1200 kg/(m² s) and subcooling equal to 30–75 K. Agglomerates emerge as a result of coalescence of small vapor bubbles, the merging of which becomes progressively more intense with increasing the heat flux density at the heating wall starting from approximately 0.75–0.80 of the critical flux value. Decreasing the boiling liquid subcooling value facilitates the occurrence of agglomerates. Nucleate boiling may take place, and burnout phenomena (dry spots) leading to wall burnout may emerge in the liquid film between the heating wall and the agglomerate surface. The vapor agglomerates emerging in the flow of subcooled boiling liquid in a channel are burnout onset precursors. When agglomerates emerge in a system of parallel channels with subcooled boiling liquid, the hydraulic stability of its operation is upset.