Diagnostics of Two-Phase Flows in Vertical Channels During the Natural Circulation by Near-Wall Pressure Pulsations

The paper discusses natural circulation of two-phase fluids, which is of particular interest for cooling systems of the reactor cores. The information about structural and integral characteristics of two-phase flows is necessary for verification of the computed thermal-hydraulic codes used in designing and safety justification of the nuclear power plants with two-phase cooling systems. The paper considers diagnostics of two-phase flows as well as an identification of the flow motion regimes inside the vertical channels in the natural circulation. The offered diagnostics is based on the analysis of measuring the near-wall pulsed pressure. The paper presents the results of measuring the near-wall pressure pulsations of two-phase air-water flows in the vertical channels of a circular cross section in the mode of natural circulation. It occurs at relatively low mass velocities of circulation for various flow regimes considering a superficial air velocity in the range of 1.95 to 9.18 m/s and a consumption gas content up to 0.4. Based on the analysis of both spectral-response characteristics and autocorrelation functions of the near-wall pressure pulsations, the spectral characteristics, the longitudinal distance between the occluded gas (bubbles), their sizes and speeds in two-phase flow were obtained.

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