Electrical Capacitance Tomography Measurements on the Pneumatic Conveying of Solids

Abstract

We have evaluated the usefulness of electrical capacitance tomography (ECT) as a tool for monitoring pneumatic conveying in horizontal ducts. Power spectra of solids concentration fluctuations obtained from single-plane ECT data were used to identify the various flow regimes, and these were confirmed through visual observation. From single-plane ECT data, the instantaneous and time-averaged distributions of particle concentration over the cross section of the conveying pipe have been determined in various flow regimes. Propagation velocities of patterns were evaluated from cross correlation of twin-plane ECT data. The solids mass flow rate, determined independently by load cell measurements, was found to be roughly proportional to the product of the pattern velocity, the particle density, and the average solids holdup in the pipe, and the proportionality factor depended on the material being transported through the pipe. In our experiments involving flows past a 90°smooth bend, ECT was able to detect significant temporal and spatial nonuniformity in particle concentration in the postbend region.

On the electrostatic equilibrium of granular flow in pneumatic conveying systems

“…By the same reasoning, granular flow in the vertical pipe was found to be more complex than that at the horizontal pipe so that it takes more time for the former to reach the electrostatic equilibrium. 22,23,31,32 This statement can also be verified in Table 2. Henceforth, it can be deduced that the electrostatic equilibrium involving granulewall collisions shows high relevancy to the granules' behavior and local flow characteristics (such as fluid turbulence): the more complex the granular flow, the longer to reach the electrostatic equilibrium state.…”

“…The instantaneous value of the cross-sectional average particle concentration ␣ s ( z, t) is defined as 22,23 : and the time-average value of ␣ s ( z, t) is denoted by Ͻ␣Ͼ(z):…”

Micromechanic modeling and analysis of the flow regimes in horizontal pneumatic conveying

“…This corresponds to an L/D ratio of about 124. This ratio is large enough to obtain developed flows according to the work of Rao et al, 23 who studied flow regimes in the horizontal pipe at the location 4 m (L/D ¼ 100) away from the solid feeding point using tomography techniques. The computational domain is meshed with body-fitted grids, as illustrated in Figure 1.…”

“…In the slug-flow regime, the entire cross area of the pipe is filled with particles in a slug, but with settled layers on the bottom in other parts of the pipe, as in the CCD camera records. 21,23,24 As a slug moves along the pipe, some particles are pushed ahead of the slug wave at the front, and this group of particles behave in a very dynamic and suspended fashion. This phenomenon has been experimentally confirmed in the work of Li et al, 70 by analyzing video footages from experiments in slug flows using similar particulate materials (3 mm spherical polymer pellets).…”

Circulating fluidized bed hydrodynamics experiments for the multiphase fluid dynamics research consortium (MFDRC).

“…For multiphase flows, the local material distribution can be determined from the local impedance using a mixture model if there is sufficient contrast between the electrical impedances of the materials. Several researchers have applied EIT systems to the study of gas-solid flows, including Halow et al (1993), Dyakowski et al (2000), Rao et al (2001), Warsito and Fan (2003), Makkawi and Wright (2003), and Pugsley et al (2003). These researchers have used a variety of data gathering and reconstruction methods to determine time-averaged and timevarying solids distributions.…”