This study was carried out to understand the particle-particle interaction in multiphase flows. We used light polstyrol particles (density 0.05 g/cm3) which were colored to detect the particles at higher void fractions. To investigate the influence of the shape on the particle interaction spherical as well as ellipsoidal particles were used. The polystyrol particles behave similar as air bubbles in water because of their relative low density. This was documented by several experiments of the motion and wake structure with single rising bubbles and particles [1]. The particles were studied in a water tank in counter-flow. A stereoscopic three-dimensional PTV systems was built up to record the particle motion. By using different concentration of water/glycerine mixture we are able to simulate different Reynolds-numbers. The results demonstrates that the shape of the particles plays a dominant role on the interaction, see the particle pair distribution shown in Fig. 1. In case of the spherical particles, most of the particle pairs are horizontally aligned which is a clear trend of bubble pairing. This agrees with the observations made by Fortes et al. (1987). In contrast, the prolate spheroids show a different distribution which can only be attributed to the different shape. It is likely, that the additional degree of freedom of the prolate spheroids to tilt or to align with the flow is the main reason which has also great influence on the drag and lift-forces.

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