ICONE23-1467 Behavior of Entrainment Droplet formed by High Velocity Air Jet Flow in Stagnant Water

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A sodium-cooled fast breeder reactor (FBR) is now in a developing stage in Japan. A shell-and-tube type once-through heat exchanger is used to generate steam in the design. Low pressure hot sodium flows in the shell side and high pressure water flows in the tube side. Water is heated to generate steam in the tubes. It has been anticipated that a pin hole is formed on the tube wall and high pressure water or water-steam two-phase mixture blows out from the hole. When the high pressure water flows out from the hole of tube, flashing occurs and a high speed steam jet is formed in the sodium coolant. Small droplets of sodium are torn off from the sodium surface and entrained into the high speed steam jet. Water-sodium chemical reaction results an increase the entrained liquid droplet temperature. The hot and high speed sodium entrained liquid droplets attack the wall of a neighboring tube to damage and create a hole on the tube wall, which may result in the chain tube wall damage. The steam jet surface behavior, the sodium surface behavior, and the entrainment behavior are key issue to consider this occurrence. In the present paper, a two dimensional air jet was blown out vertically upward from a rectangular hole at the bottom of a thin rectangular test vessel into stagnant water of 80℃ in the vessel. This obtained results were compared with the former experiment results which obtained by using same vessel, on the other hand, water was used in normal temperature. The test vessel was 5 mm deep, 270 mm wide and 300 mm high. The stagnant depth of water in the vessel was 100 mm. The rectangular hole of air inlet was 1 mm × 5 mm. The air pressure at the upstream of the hole was at 115 〜 250 kPa. The air velocity at the outlet of the hole was 130 〜 300 m/s. The entrainment process and the air jet/water surface behavior were recorded with a high speed video camera. The trajectory of entrained liquid droplets and the velocity variation after entrained were examined from recorded pictures.

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