In a previous work we have demonstrated the feasibility of high-frame-rate,fast-neutron radiography of generic air-water two-phase flows in a 1.5 cmthick, rectangular flow channel. The experiments have been carried out at thehigh-intensity, white-beam facility of the Physikalisch-TechnischeBundesanstalt, Germany, using an multi-frame, time-resolved detector developedfor fast neutron resonance radiography. The results were however not fullyoptimal and therefore we have decided to modify the detector and optimize itfor the given application, which is described in the present work. Furthermore,we managed to improve the image post-processing methodology and the noisesuppression. Using the tailored detector and the improved post-processingsignificant increase in the image quality and an order of magnitude lowerexposure times, down to 3.33 ms, have been achieved with minimized motionartifacts. Similar to the previous study, different two-phase flow regimes suchas bubbly slug and churn flows have been examined. The enhanced imaging qualityenables an improved prediction of two-phase flow parameters like theinstantaneous volumetric gas fraction, bubble size and bubble velocities.Instantaneous velocity fields around the gas enclosures can also be morerobustly predicted using optical flow methods as previously.
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