Experimental study on thermal-hydraulic for thermal striping phenomena; Results of temperature and velocity measurement among parallel triple jets

Miyakoshi, Hiroyuki; Nagasawa, Kazuyoshi*; Kimura, Nobuyuki; Miyake, Yasuhiro*; 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 structural integrity and also reactor safety. The reasonable and safety design could be approved by taking account of decay of temperature fluctuation in fluid, during heat transfer from fluid to structure surface and thermal onduction in the structure. In this study, water experiment was performed for vertical and parallel triple jets along wall, those are cold jet in the center and hot jets on both sides. The local temperature and velocity were measured by movable thermocouples and particle image velocimetry(PIV). The both hot jets flowed leaning to the cold jet. The lean of the jets increased as the jets approached the wall. So the convective mixing region among the jets was shifted upstream near the wall. Temperature fluctuation intensity was dependent of the distance from the wall. Under isovelocity condition, prominent frequency component was observed in the power spectrum density of the temperature fluctuation at the furthest position from the wall. The power at the prominent component decreased as the jets approached the wall. Under non-isovelocity condition, on the other hand, the power spectrum density of temperature fluctuation was independent of the distance from the wall. Comparison of the second moment between of velocity PIV and laser Doppler velocimetry showed that the PIV system had high measurment accuracy. Under non-isovelocity condition, the normal components in the second-order moments of fluctuation were smaller than those under isovelocity condition. Normal components in the second-order moments in turbulence was dependent of the distance from the wall."