Gravitational granular flow dynamics study based on tomographic data processing

This article presents capabilities of the application of electrical capacitance tomography (ECT) to hopper flow dynamics analysis. The two main goals are to demonstrate a number of tomographic data analysis methods in the application to core flow and to propose some simple parameters depicting this flow via funnel description. Experiments have been conducted for various diameters of hopper orifice using two types of materials with different physicochemical properties, rice and polyamide pellets. ECT allows noninvasive in situ measurement, visualization, and study to be carried out on nonconducting media such as particulate systems or powders. Tomographic images give valuable information about solids concentration distribution inside the measurement space delimited by electrodes. Proper interpretation of concentration changes during the hopper discharging allows the investigation of phenomenon dynamics to be performed. Data analysis consists of raw signal (the measured capacitances) interpretation and tomographic image post-processing manipulation. The present study focuses on the tracking of particulate concentration changes and the hopper discharge rate parameter proposition. Preliminary attempts at funnel propagation velocity measurements are presented here. On the other hand, funnel propagation velocity rate in the initial stage of hopper unloading is based on the calculation of transition time between characteristic points indicated on unloading dynamics diagram. Transition time is calculated using stochastic processes theory-based methods. The novel approach proposed by the authors is based on the estimation of velocity using just one plane of sensing electrodes in contrast to standard applied inter-plane correlation techniques. However, basic parameter estimators such as autocorrelation and variance are used in order to examine the gravitational flow as well.