Resolving Gas Bubbles Ascending in Liquid Metal from Low-SNR Neutron Radiography Images

Abstract

We demonstrate a new image processing methodology for resolving gas bubbles travelling through liquid metal from dynamic neutron radiography images with an intrinsically low signal-to-noise ratio. Image pre-processing, denoising and bubble segmentation are described in detail, with practical recommendations. Experimental validation is presented—stationary and moving reference bodies with neutron-transparent cavities are radiographed with imaging conditions representative of the cases with bubbles in liquid metal. The new methods are applied to our experimental data from previous and recent imaging campaigns, and the performance of the methods proposed in this paper is compared against our previously achieved results. Significant improvements are observed as well as the capacity to reliably extract physically meaningful information from measurements performed under highly adverse imaging conditions. The showcased image processing solution and separate elements thereof are readily extendable beyond the present application, and have been made open-source.

Magnetohydrodynamics Simulation of the Nonlinear Behavior of Single Rising Bubbles in Liquid Metals in the Presence of a Horizontal Magnetic Field

“…Apart from the metallurgical engineering applications, such a flow situation could also be a feature of nuclear fusion reactors, in which bubbles are injected into the liquid-metal coolant to enhance the efficiency of the heat transfer processes. Due to the opaqueness of the liquid metal, it is impossible to observe the bubbles directly using optical measurement techniques, and thus, indirect non-optical measures, such as local conductivity probes [1][2][3][4], Ultrasound Doppler Velocimetry (UDV) [5][6][7][8], X-ray radiography [9][10][11] and neutron radiography [4,[12][13][14][15], have been employed to "observe" bubble dynamics in the presence of a magnetic field in many related experiments. In parallel to the measurements, numerical Magneto-Hydro-Dynamics (MHD) simulations have been widely employed to better understand bubble dynamics [16][17][18][19], since with this approach, the distribution of all the variables related to the flow and electric field can, in principle, be obtained.…”