63 Monitoring of solids behaviour during gravitional flow in rectangular silo M. Niedostatkiewicz 1 , Z. Chaniecki 2 , K.Grudzień 2 , A. Romanowski 2 , R.Banasiak 2 , J.Betiuk 2 1 Department of Fundamentals of Building and Material Engineering, Technical University of Gdańsk mniedost@pg.gda.pl 2 Computer Engineering Department, Technical University of Łódź zch@kis.p.lodz.pl Reviewer: H. Wang (Tianjin University, China) Summary: This paper is focused on the application of Electrical Capacitance Tomography (ECT) to gravitational flow of bulk solid in rectangular silo investigation. In order to measure the materials distribution inside a vessel, a dedicated, spatial 16 electrode sensor is designed. Reconstructed images are presented in 3D domain space. The investigated silo model consists of rectangular bin and a cone-like hopper section. The flow behaviour of material (friable sand) is studied for two silo model configurations having different lower section slopes. The slope angle is a silo geometrical parameter affecting the type of the flow regime - mass or funnel type. Keywords: ECT, bulk solid concentration measurement, rectangular silo investigation, processes monitoring, 3D imaging 1. Introduction The behaviour of granular materials during confined silo flow is very complex among others due to appearance of localization of deformation in the form of narrow zones of intense shearing (Tejchman et al., 2000). The shear zones occur along silo walls, as well, as inside flowing (initially dense) granular material for both: bin section (Fig. 1) with rough walls and hopper section no matter of the wall roughness (Tejchman 1997). The presence of wall shear zones significantly influences stresses along the walls. In turn, the appearance of shear zones inside of the flowing material causes significant quasi-static fluctuations of wall stresses and a flow asymmetry (Rechenmacher, 2006). The width of shear zones depends on many factors such as: initial solid density, mean grain diameter of solid, wall roughness, specimen size, pressure level, direction of deformation and flow velocity (Tejchman et al., 2000; Yoshida et al., 1994; Nübel, 2002). The knowledge of the deformation field in the silo fill is very important in order to explain the mechanism of the granular flow behaviour in silos. At present, the Particle Image Velocimetry (PIV) is one of the non-invasive methods to quantify local displacements in solids. This technique is used for measuring surface displacements on the basis of the numerical analysis of digital photographs successive pairs. Photographs pairs of the side of deformed specimen are taken with a CCD-camera (charge couple device). PIV method was also used for observation of bulk solid behaviour in rectangular model silo. Shear zones, along the silo vertical walls and inside the flowing material were detected on the basis of deviatoric and volume strains (Niedostatkiewicz and Tejchman, 2005; Slominski et al., 2006, 2007). The main aim of this paper is to present the preliminary results of the 3D concentration distribution of bulk solid during rectangular silo discharging (Wajman et al., 2007; Romanowski et al., 2006, 2007; Chaniecki et al., 2006). The prepared measurement computer system based on ECT unit makes it easier to investigate the physical phenomena which take place in the rectangular silo. The description of the shear zone is very important. The concentration measurement of solid (porous) is crucial to control the silo loading and emptying for both, model (laboratory) scale, as well, as for industrial application. The knowledge of the porous spatial distribution is decisive for the determining of the real distribution of solid pressure in silo. The accurate analysis of the spatial distribution may allow to diagnose the adverse phenomena, especially the dynamics effects, which take place during silo discharging. The understanding of dynamic effects enables to eliminate or minimize their dangerous occurrence. The conducted experiments concerned the investigation of influence the following considerations on material behaviour during silo discharging process.: • the regime flow (mass flow or funnel flow); • the initially packing slid density; • the wall roughness; The presented results concern the case of mass flow with initially dense sand. Two types of wall roughness are analysed; smooth and rough wall silos. 2. Experimental setup The model tests were carried out with two rectangular perspex symmetric model silos (mass flow silo and funnel flow silo) consisting of a bin and a hopper (Fig. 1). The same models were used both for PIV and ECT tests. The height of a mass flow silo was h=0.32 m, the width b=0.09 m, the depth d=0.07 m. In turn, the height of a funnel flow silo was h=0.29 m, the width b=0.15 m, the depth d=0.07 m. The width of the rectangular outlet along the silo depth in both models was 5 mm. The wall thickness was 0.01 m. The tests were performed with a dry, cohesionless sand with a mean grain diameter d50=1.0 mm and uniformity coefficient U=5. An initially dense sand (γ=16.5 kN/m3, e0=0.61) was obtained by filling the silo using a so-called “rain method” (through a vertically movable sieve located always 25 mm above the upper sand surface in the symmetry-axis). In turn, an initially loose sand (γ=15.5 kN/m 3 , e 0 =0.70) was