Streakline flow visualization with neutron radiography

Although flow visualization is an extremely useful tool in fluid mechanics research, many practical fluid flow problems have limited optical access for visualization. A technique has been developed which permits fluid flow to be visualized even in cases where the flow is completely shrouded by metal. The technique employs real-time thermal neutron radiography, which is similar to x-ray radiography except that a collimated beam of neutrons is used. Neutrons can easily penetrate metal casings, but are attenuated by elements such as hydrogen, boron, cadmium, and gadolinium. Various combinations of neutron-opaque tracer particles moving in neutron-transparent ambient fluids were tested for image contrast, resolution, and ability to accurately track the flow. Experiments in a simple pipe flow have demonstrated the feasibility of the technique. Namely, it was possible to visualize the motion of streaklines within a flow field shrouded by metal, which would not have been possible with any other technique.