The objective of the current work is to investigate in detail the nature of particle velocity distribution in a horizontal pneumatic conveying system using flow visualization techniques. To that end, an experimental set-up consisting of a feeder hopper, a variable length test section, and a jet ejector pump and a collection bin, is fabricated. The test channel is made of boro-silicate glass and the height by depth ratio of the channel is maintained as 1:4. The collection bin is placed on the load cell to measure the solid mass flow rate. The air flow rate is determined using a rotameter (Eureka-PG). Solid mass flow rate is controlled by two ball valves V1 and V2 (Astron USA). The opening of the first valve, V1 is calibrated for the solid flow rate measured at open to atmospheric condition and act as the solid mass flow rate controller, whereas the second one acts as an on-off valve. This arrangement ensures less uncertainty in the solid mass flow rate during the experimental runs. Solid particles are carried by a jet ejector pump. More detail of the experimental set-up is discussed in .
The flow of particles in the channel is captured using a CMOS camera (Phantom V9.1) at a frame rate between 5000-14000 fps. NIKKOR (AF micro-Nikkor 60 mm f/2.8 D and AF Zoom-Nikkor 24-85 mm f/2.8-4D IF) lenses are used for the videography. A white translucent paper is taped on channel wall on side of light from Fiber-Lite MH100 illuminator. The images are sequentially stored and processed using the algorithms implemented on MATLAB platform as well as developed in-house.
Experiments are carried out for different mass loading ratios, defined as the mass flow rate of solid per unit of gas flow rate and particles diameters (465 µm and 106 µm). Measurements are carried out in the region where the flow is developed completely. It is observed that the solid particles have a tendency to accumulate at the bottom of the channel as the mass loading ratio increases. A similar observation is reported by Tsuji and Morikawa, where they determined the mean density of the particles using LDV . The velocity profile of the solid particles also depends on the mass loading ratio. The mean velocity of the solid phase decreases as the mass loading ratio increases.
The distribution of the fluctuating velocities in the stream-wise and the cross-stream directions are observed to be non-Gaussian in nature. The stream-wise velocity distribution is skewed but that of the cross-stream component is symmetric. In addition, numerical simulations based on coupled CFD-DEM method is also carried out using the open source software MFIX developed by NETL. The simulation results are found to be in good agreement with the experimental observations.
 Makwana, A. B., Patankar, A., Bose, M.: Effect of Dune Formation on Pressure Drop in Horizontal Pneumatic Conveying System. Part. Sci. Technol.33(1),59-66 (2015)
 Tsuji, Y., Morikawa, Y.: LDV measurements of an air-solid two-phase flow in a horizontal pipe, J. Fluid Mech. 120, 385–409 (1982)