800 fps neutron radiography of air-water two-phase flow

We have demonstrated dynamic cold neutron imaging of air-water two-phase flows up to 800 frames per second imaging rates. This has been achieved by using a high-efficiency (relatively thick) scintillator screen in combination with the highest available flux on a continuous spallation source and a high-speed sCMOS camera. This combination renders the spatial resolution to relatively modest value of about 0.5 mm, which is nevertheless sufficient for resolution of bubbles of the size down to about 1.0 mm in motion with unprecedented framerate using neutron imaging. We show the feasibility of the technique on the two-phase flow at ambient temperature and atmospheric pressure conditions, with the foreseen aim of measurements of two phase flows at high-temperatures and high pressures. It is also foreseen that the technique will be further utilized for quantification of the time-resolved instantaneous gas fraction and the gas phase velocity. • Demonstration of up to 800 frames per second dynamic cold neutron radiography.• Application of such technique for non-periodic (transient) process of bubbly flow in water.• Potential for quantification of (i) instantaneous gas volume fraction in dynamic two-phase flow and (ii) instantaneous gas phase velocimetry.