Void fraction profile measurements in two-phase mercury — nitrogen flows using gamma-ray attenuation method

A nonintrusive measurement system using gamma rays from a 60Co source is developed to measure the void fraction profile in a two-phase flow of a high-density liquid metal and nitrogen. The method is based on the attenuation of gamma rays along various chord lengths in the cross section of a pipe line. Both the chord segment inversion (CSI) method and the least squares solution (LSS) method were applied to obtain void fraction profiles from the data. The CSI method gave spurious oscillations in the void fraction profiles, which could be attributed to the Poisson corruption due to low count rate. On the other hand, the LSS method did not contain any oscillations. Experiments were performed in the vertical riser pipe of a gravitational-type liquid metal magnetohydrodynamic loop with mercury-nitrogen two-phase flow. Void fraction profiles were obtained for various flow rates at two locations in the riser pipe. The average void fraction obtained from the profile data was compared with the values predicted by empirical relations developed for vertical two-phase flows.