In a steam generator of liquid sodium cooled fast breeder reactor, the occurrence of secondary heat transfer tube failure has been considered due to overheating in sodium-water reaction. A computer code SERAPHIM has been developed to analyze this kind of secondary heat transfer tube failure due to steam jet with heat generation and chemical reaction by Japan Atomic Energy Agency (JAEA). The detailed experimental data that verify the adequacy of SERAPHIM code and upgrade it, are now required. In ICONE13, the local and mean heat transfer coefficients around a horizontal heated rod (φ 15mm) immersed in a water pool and in a sodium pool with gas jet impingement without chemical reaction, were reported as the first step. It was confirmed in the water pool experiment that the local and mean heat transfer coefficients slowly increase with increasing the Ar jet velocity from 8.7m/s to 78m/s The local and mean Nusselt numbers almost keeps same values independent on the Ar gas velocity in the sodium pool experiment. From these results, we inferred that the ambient liquid is entrained inside and contributes to high heat transfer rates. A series of experiments that investigate the entrainment process of ambient liquid toward jet interior are carried out by using a laser-sheet visualization and a void meter in water pool in the present work. It was observed that the entrainment of water into Ar gas jet is constantly caused in two regions just above the nozzle and just below the single rod. In the region just above the nozzle, negative pressure causes the entrainment of water. In the region below the rod, the entrainment of water is caused because the preceding Ar gas jet is caught up by the succeeding gas jet. The basic behavior of Ar gas jet causing the entrainment of water was confirmed to be almost same over the Reynolds number range of Ar gas jet, 2.17×103 to 2.17×104, in the present study. In addition, the measurement of void fraction was performed to investigate the entrainment of water quantitatively and the behavior of local heat transfer coefficients around a single rod with gas jet impingement in water pool was made clear.

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