TED-AJ03-159 EXPERIMENTAL STUDY ON THERMAL STRIPING PHENOMENA FOR A FAST REACTOR : TRANSFER CHARACTERISTICS OF TEMPERATURE FLUCTUATION FROM FLUID TO STRUCTURE

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A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes thermal fatigue in structural components, is of importance for integrity of reactor plant. It is necessary for the evaluation to investigate occurrence of temperature fluctuation, decay of temperature fluctuation near structures and transfer of temperature fluctuation from the fluid to the structures. Attenuation of temperature fluctuation should be considered in these elements of thermal striping phenomena. In this study, a sodium experiment of parallel triple jets configuration was performed in order to evaluate temperature fluctuation characteristics in the fluid, transfer characteristics of temperature fluctuation from the fluid to the structure and conduction in the structure. As for the experimental geometry, a cold jet on the center and hot jets on both sides flowed vertically and along the wall (wall jet). The experimental parameters were discharged velocities of the jets and the discharged velocity profile among the hot and cold jets. Two types of velocity profile were examined; isovelocity condition (the discharged velocities of three jets were identical) and non-isovelocity condition (the cold jet velocity was smaller than the two hot jet velocities). The temperature fluctuation intensity near the wall decreased as the discharged velocity of the jet decreased. The power spectrum density of the temperature fluctuation had a prominent frequency depending the discharged velocities of the jets under the isovelocity condition. This velocity dependency of the prominent frequency was evaluated using Strouhal number based on the discharged velocity. The conduction of random temperature fluctuation in the structure was predicted by the superposition of well-known non-stationary thermal conduction equation of a single period. The amplitude of the temperature fluctuation at the wall surface was smaller than that in the fluid. A frequency analysis showed that this decay rate increased as the frequency of the temperature fluctuation increased. The heat transfer coefficient from the fluid to the structure was obtained so as to fit a theoretical power curve using the heat transfer coefficient with the power of the transfer function based on the measured temperatures in the fluid and in the structure near the surface. Then, it was shown that the non-stationary heat transfer characteristics could be represented by a heat transfer coefficient, which was constant in time and independent of the frequency of the temperature fluctuation. Figure A-1 shows the relationship between the obtained heat transfer coefficients and Peclet number based on the discharged velocities in the cold jet in our wall jets geometry. The heat transfer coefficients were increased as Peclet number increased and independent of the two types of discharged velocity profiles. [figure]
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TED-AJ03-159 EXPERIMENTAL STUDY ON THERMAL STRIPING PHENOMENA FOR A FAST REACTOR : TRANSFER CHARACTERISTICS OF TEMPERATURE FLUCTUATION FROM FLUID TO STRUCTURE

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