Streakline flow visualization with neutron radiography.

Although flow visualisation is an extremely useful tool in fluid mechanics research, many practical fluid flow problems have limited optical access for visualisation. A technique was 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 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.