Case Study of Granular Flow in Silo Based on ECT and Optical Images
K. Grudzień, Z. Chaniecki, L. Babout
Institute of Applied Computer Science, Lodz University of Technology, Stefanowskiego 18/22, 90-924 Lodz, Poland
This paper presents a comparison between optical images and two different modalities of Electrical Capacitance Tomography (ECT), in order to analyse the degree of accuracy of the latter ones in the case of estimating flow boundaries during silo discharging. In that respect, thanks to a specially designed transparent rectangular silo that allows one to set independently hopper angles and outlet width, different types of funnel flow, i.e. concentric and eccentric, have been produced to analyse whether ECT measurements do identify the concentration changes induced by the outlet positioning with respect to the centre of the silo bin. In these experiments, non-cohesive, dry rice has been used because of its good dielectric properties for capacitance measurements. Moreover, CMOS camera recording the granular flow at the front side of the rectangular bin has been considered as reference images for comparison with ECT measurements. Moreover, another level of comparison has been studied by investigating the electrical signal difference between a commercial ECT system and a model ECT system combining a LCR meter and a multiplexer, the latter being considered as the most accurate of the two. Because of the presence of the sensor layer around the silo bin, funnel flow boundaries have been interpolated from the optical images after special image processing involving 0-entropy calculation. Then these boundary positions have been both compared qualitatively and quantitatively with the ones that can be deduced from the permittivity maps. A good agreement has been shown for three different hopper settings between the two different modalities, especially for the model ECT system that shows a larger reconstructed image contrast.
Keywords silo discharging, asymmetric flow, electrical capacitance tomography, CMOS camera
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