(714c) Minimum Pickup Velocity

Aditya Anantharaman^a, J. Ruud van Ommen^b, Jia Wei Chew^a,c

^aSchool of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore

^b Chemical Engineering, Delft University of Technology, The Netherlands

^cSingapore Membrane Technology Center, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore

 

Pneumatic conveying is an important operation in a wide range of chemical industries from pharmaceutical to oil and gas. A critical parameter for ensuring the efficient operation of pneumatic conveying systems is the minimum pickup velocity, U_pu, defined as the minimum superficial gas velocity required to initiate rolling or suspend a particle initially at rest. Despite the growing popularity of nanoparticles, most of the past studies [1-3] on U_pu have focused on micron sized particles (0.5-3000 μm); with only a recent work [4] studying U_pu of nanoparticles in the particle diameter (d_p) range of 13-21 nm. This work is aimed at bridging the knowledge gap between the nano- and micro-scale particles by investigating the U_pu of particle diameters traversing both scales.

 Experiments were conducted to determine the U_pu of nine different particle diameters (d_p) of alumina (Al₂O₃) particles from 5 nm to 110 μm using the weight loss method and categorized according to the established pickup zones [3] (which is analogous to the Geldart Groups [5]). The following are the key findings. Firstly, U_pu varied non-monotonically (namely, increased, then decreased) with increasing particle diameter (d_p) in the range investigated, which spans the nano-scale and micro-scale. Secondly, while the larger micro-scale particles agreed well with the established zone, the smaller nano-scale particles agreed with a zone that they did not belong in. Thirdly, the intermediate particle diameter (d_p) of 200 nm did not correspond to any zone, and represented the transition between the nano- and micro-scales. Collectively, the results reveal the missing link on the pneumatic conveying behavior of particles between d_p = 21 nm [4] and d_p = 0.53 μm [2] in terms of U_pu trends.

References:

1. Cabrejos, F.J. and G.E. Klinzing, Incipient motion of solid particles in horizontal pneumatic conveying. . Powder Technology, 1992. 72: p. 51-61.

2. Hayden, K.S., K. Park, and J.S. Curtis, Effect of particle characteristics on particle pickup velocity. Powder Technology, 2003. 131(1): p. 7-14.

3. Kalman, H., et al., Pickup (critical) velocity of particles. Powder Technology, 2005. 160(2): p. 103-113.

4. Anantharaman, A., J.R. van Ommen, and J.W. Chew, Minimum pickup velocity (U pu) of nanoparticles in gasâ??solid pneumatic conveying. Journal of Nanoparticle Research, 2015. 17(12).

5. Geldart, D., Types of Gas Fluidization. Powder Technology, 1973. 7(5): p. 285-292.