Measurement of Carrier Bead Velocity Distribution in Cascade Flow

A miniature piezoelectric impact probe is described for measuring the impact velocity of carrier beads in a cascade flow. The probe can sense a force of a few dynes. It has a response time of about 1 ?s and a total settling time of less than 40 ?s. The impacts of a few microgram particles due to a free-fall under gravity of a distance of about 50 ?m and at a count rate in excess of 20 000/s have been measured. The probe has been used in measuring the impact velocity distribution of carrier beads in a cascade flow. The impact velocity distributions have been measured at different flow conditions and compared with theoretical predictions. The characteristics of the cascade flow are briefly discussed in terms of the two parameters: the number density of the carrier beads in the flow and the diffusion constant of the flow.