Use of Large Plastic Beads to Follow Slow Flow of Water in a 7 Ft Diameter Vessel

Abstract

To measure water velocities of the order of a few inches per minute in a 7 ft diameter vessel, half-inch diameter plastic beads were ballasted to be neutrally buoyant and after release at various points, photographed at intervals. Mismatching the coefficients of expansion of the plastic and water proved an unexpectedly serious problem, as did tiny air bubbles and solid particles adhering to the beads.