The gas flow in and around once-through swirl tubes-also called axial flow cyclones-for gas demisting has been investigated by flow visualization using a neutrally boyant tracer and by computational fluid dynamics (CFD). The neutrally boyant tracer was helium-filled soap bubbles, which were made visible by illumination with sheets of white light and recorded by a variety of photographic techniques. The flowpatterns in the inlet swirl vanes, the separation space, and the core of the vortex are shown as streak patterns. Additionally, it was possible to study the breakdown of the vortex beyond the swirl tube outlet. Using high-speed photography and dedicated software, velocity information was gleaned from the experiments. The experimental results were compared with CFD simulations wherein the renormalization group k-epsilon turbulence model was used to simulate the flowpattern in the same configuration. The simulations matched the experimental results well in the separation space itself but could not properly reproduce the complicated flow around the tube outlet.