High-speed PIV measurement of particle velocity near the minimum air velocity in a horizontal self-excited pneumatic conveying of using soft fins

摘要

In order to reveal the reduction mechanism of conveying velocity and pressure drops in a horizontal self-excited pneumatic conveying by using soft fins, the distributions of particle velocity and concentration were measured by the high-speed particle image velocimetry (PIV) and image process at the minimum air velocity. The study focuses on the effect of the different fin's lengths on the horizontal pneumatic conveying in terms of frequency features of fin's oscillation, time-averaged particle concentration and velocity, fluctuation intensity of particle velocity and power spectrum of particle fluctuating velocity. It is found that the particle concentration of the fins is lower than that of non-fin near the bottom and is higher than that of non-fin near the top of pipe even at low air velocity. In the acceleration regime, the normalized particle velocity of the long fins is higher than that of non-fin, implying the efficiency of the long fin on reducing pressure drop and conveying velocity. For conveying particles having the relatively large terminal velocity, however, there is little effect of fins on particle velocity. The fluctuating energy of particle velocity of fins are larger than that of non-fin near the bottom of pipe, and the long fins exhibit the largest value in the top part of pipe in the fully developed regime. Based on analyzing the power spectrum of particle fluctuation velocity, it is indicated that the fins generate the large peaks of power spectrum in the low frequency range, which is related to the reduction of pressure drop.