ExperimentaI study on convective mixing for ThermaI Striping Phenomena; Mixing process among paralleI Triple-Jet and effect or discharged velocity

Kimura, Nobuyuki; Tokuhiro, Akira; Kamide, Hideki 

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing among jets causes thermal fatigue in structural components, is of importance for reactor safety. ln this study, a water experiment was performed using vertical and parallel triple jets, those are cold jet on center and hot jets on both side. The experimental parameter was discharged velocity of the triple-jet and local temperature and velocity were measured by ultrasound Doppler velocimetry and movable thermocouples. The objective is a quantification of the mixing process in the multiple-jet. Under isovelocity condition, the jets oscillated periodically and mixing among thejets was promoted by periodic oscillation. The periodic oscillation was dependent on the Strouhal number based on the discharged velocity. Under non-isovelocity condition, on the other hand, the jets did not oscillate periodically and mixing among the jets progressed more gentle compared with the case under isovelocity condition. The tempwrature fluctuation could be decomposed into coherent and random components using the phase averaging process. The rate of the coherent component in the temperature fluctuation increased and the rate of random component in temperature fluctuation decreased in proportion as the discharged velocity was increased.