High-Speed Laboratory Tomographic X-ray Particle Tracking Velocimetry*

Many flows are opaque due to the nature of the media or multiple refractive interfaces, making them difficult to measure with visible light techniques such as PIV and PTV. In a series of experiments, we show that advances in X-ray sources and imaging hardware are enabling rapid improvement in X-ray Particle Image Velocimetry and Particle Tracking Velocimetry (XPIV/XPTV). Using XPTV, we measure both Poiseulle pipe flow and a Taylor bubble at frame rates O(1kHz) with 50μm diameter tracers – two orders of magnitude faster the previous state of the art. Furthermore, we take advantage of the high-speed X-ray imaging setup to capture tomographic XPTV of both flows. We individually discuss the impact of the new tracer particles we designed, brighter liquid metal jet X-ray sources, and energy-resolving photon counting detectors (PCDs).

We further expand on the potential of PCDs in X-ray flow visualization. PCDs can nominally attain a higher signal-to-noise ratio than scintillating detectors. Most importantly, many new PCDs have two or more photon energy thresholds, enabling experimentalists to track multiple species at once, whether it be tracer particles, solvent concentration, or multiple fluid phases. This capability opens up a world of opportunity for X-ray flow visualization.