T h e velocity of a single bubble in quiescent and flowing liquid was studied to gain information on t h e structure of bubble-a n d slug-flows of gas-liquid two-phase flow.In t h e experiments, t a p water was used at room temperature and t h e bubbles were generated by injecting a i r with a syringe. T h e bubble velocities were evaluated from photographs taken by multiflash exposure. T h e tube diameters adopted were 5, 1 a n d 0.5 c m f o r t h e flowing liquid experiments a n d 1, 0.5 a n d 0.2 c m for t h e quiescent liquid experiments. T h e average liquid velocities varied from about 0 t o 2m/sec.T
h e results indicated t h a t t h e velocity of a single bubble in flowing liquid w a s t h e s u m of t h e local liquid velocity in t h e vicinity of t h e bubble and of t h e velocity of rise of bubble in quiescent liquid. For T a y l o r bubbles, t h e local liquid velocity is given by t h e maximum liquid velocity near t h e center of t h e channel.T h e velocities of spherical and ellipsoidal bubbles a r e determined by t h e balance of forces acting on them, but t h a t of t h e T a y l o r bubble appears to be determined by a different mechanism. A good explanation of such a mechanism is T a y l o r instability a t t h e gas-liquid interface well removed i r o m t h e channel wall.
The magnetic properties of A533B low alloy steel irradiated up to 3 x 1023 n/m2 in a nuclear reactor were measured using a SQUID sensor. The SQUID sensor used in the test is the type with a first-order axial gradiometer. Test specimens were irradiated to 0.5 x 1023 and 3.0 x 1023 n/m2, and then magnetized in a 0.2 T field until saturation before measurement. The specimens were put on a scanning table in a hot laboratory and the SQUID output was recorded while each specimen was gradually moved in a horizontal direction under the SQUID sensor. A superconducting magnet was used to put the test specimen under a magnetic field that changed from +0.01 T to -0.01 T to observe the relation between magnetic field intensity and coercive force (B-H curve). The B-H curve shows a definite tendency towards a higher coercive force for test specimens with higher neutron fluence. The test result also shows a good relation between mechanical properties, such as yield strength, tensile strength, and the Charpy impact test result, with SQUID output. This proves that there is a very good chance of developing a non-destructive evaluation system for nuclear reactor structure. This kind of evaluation system would be a great help in making plant life management even more reliable and reasonable.
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