Particle trajectories in a helixchanger

A 3D fluorescent PTV technique has been developped to measure particle trajectories in complex geometries. The technique has succesfully been applied in a mock-up of a helically baffled s&T heat exchanges, the Helixchanger, with a typical measuring accuracy of 0,02 mm. Particles with diameter 0,18-0,22 mm, injected at various locations in the wake of a tube (Reynolds numbers 420 and 1400), are found to be gradually accelerated to ca. one thirth of the water velocity outside the wake in 0,2 s. Their motion is slightly wobbling due to flow intermittency. Particles of 2,0 mm, accelerated in 10,3 m/s air-flow around a cylinder, have been found to stay in a plane. By comparison with FEM predictions, the apparent gravity, added mass and lift forces have been found to be significant. This analysis is used to generalize the findings in the Helixchanger.