Bulk Solids In Silos Research Articles

A MIMO Radar System based on Fractal Antenna Arrays for Level Measurement Applications

Abstract. In this contribution, the design of a multiple-input multiple-output (MIMO) radar system in 77–81 GHz range with 18 transmitting antennas and 24 receiving antennas for measuring the height profile of bulk solids in silos, is presented and discussed. The antenna array topologies are optimized by utilizing space filling fractals in order to approximate a circular shaped antenna array on a hexagonal grid. The proposed MIMO radar system achieves an angular resolution of 3.1∘ for a maximum scanning angle of ±45∘ and a side lobe suppression of 12.6 dB. The performance of the system has been evaluated by test measurements on a sand heap, showing an improved measurement accuracy compared to conventional radar level systems.

Modelling of full-scale silo experiments with flow correcting inserts using material point method (MPM) based on hypoplasticity

Flow patterns in bulk solids in silos are of importance for stresses exerted on silo walls. They may be changed by using different inserts. The paper discusses numerical results on confined granular flow of cohesionless sand in a full-scale metal silo with different symmetrically placed inserts, used for correcting a flow pattern (double cone, cone-in-cone and inverted cone). The material point method (MPM) was employed to simulate the dynamic flow of sand in a silo. To describe the flow behaviour of cohesionless sand, a hypoplastic constitutive model was adopted. The emphasis was on flow patterns and pressures on both silo walls and inserts. The numerical outcomes were directly compared with the corresponding experiments in a full-scale silo. A satisfactory agreement was achieved between numerical and experimental outcomes. In MPM calculations, the effect of initial void ratio of sand, wall friction angle, insert position and grid cell size was also studied.

Determination of the flow/no-flow transition from a flat bottom hopper

Hoppers and silos are widely used in storing powders in various industries, such as agricultural, chemical, food and pharmaceutical industries. It is of practical importance to design hoppers and silos to ensure smooth discharge of bulk solids from these devices, and to minimise the occurrence of arching, blockage and build-up of materials around the walls. However, due to the complex nature of bulk solids, arching behaviour of bulk solids in silos and hoppers is still not well understood. In this study, a combined experimental and numerical study was performed to explore the transition from non-flow to flow of bulk solids from a flat bottom hopper. Glass beads of various sizes were considered and the minimal orifice size through which these materials can be discharged was determined experimentally using a Flodex™ tester and numerically with discrete element modelling (DEM). The dependency of the minimal orifice size on the particle size was explored. Both the experimental and numerical results showed that the minimal orifice size is a function of the particle size, which can be well described using a modified Beverloo equation. It was also interesting to find that, even for spherical particles, dead zones could be formed during the discharge from the flat bottom hopper. Moreover, mono-layered dead zones were created when large particles were used.

PARAMETRIC METHODS FOR ECT INVERSE PROBLEM SOLUTION IN SOLID FLOW MONITORING

The article presents the parametrisation-based methods of monitoring of the process of gravitational silo discharging with aid of capacitance tomography techniques. Proposed methods cover probabilistic Bayes’ modelling, including spatial and temporal analysis and Markov chain Monte Carlo methods as well as process parametrisation with artificial neural networks. In contrast to classical image reconstruction-based methods, parametric modelling allows to omit this stage as well as abandon the associated reconstruction errors. Parametric modelling enables the direct analysis of significant parameters of investigated process that in turn results in easier incorporation into the control feedback loop. Presented examples are given for the gravitational flow of bulk solids in silos.

FE-studies on rapid flow of bulk solids in silos

This paper contains results of numerical modelling of the onset of silo flow for granular material in a model silo with convergent walls. The calculations were performed with a finite element method based on a polar elasto-plastic constitutive relation by Muhlhaus. It differs from the conventional theory of plasticity by the presence of Cosserat rotations and couple stresses using a mean grain diameter as a characteristic length. The characteristic length causes that numerical results do not depend upon the mesh discretisation. The model tests on rapid silo flow of glass beads performed by Renner in a glass hopper with a large wall inclination from the bottom were numerically simulated. The FE-calculations were performed for plane strain by taking into account inertial forces and linear viscous damping. A satisfactory agreement between numerical and experimental results was obtained. In addition, the FE-calculations were performed for very rough walls. Advantages and limitations of a continuum approach for simulations of rapid silo flow were outlined.

Bedding effects in bulk solids in silos: experiments and a polar hypoplastic approach

This paper is concerned with bedding effects in granular bulk solids in silos. Finite element (FE)-analyses were performed for a cylindrical thin-walled steel model silo with imperfections containing dry sand. Numerical calculations were carried out for an axisymmetric case with a polar hypoplastic constitutive relation which can capture the salient properties of granular materials. In the FE-calculations, different types of wall displacements along the silo height were taken into account to model roughly the formation of buckles due to initial imperfections of the silo wall. The effects of the initial void ratio and mean grain diameter of bulk solids, initial stress state, wall roughness, and size and form of buckles were studied. The numerical results clearly show that the modelling of a bedding effect of bulk solids in silos by means of springs is too simple and can lead to strongly unrealistic predictions of the bedding modulus.

Loads of stored bulk solids in silos

The design of silos has been the object of scientific and technical research for a whole century and this has led to great advances in the field. The results have not always been adequately disseminated among the technicians. The aim of this paper is to present the techniques for calculation of the loads of the materials stored in silos, inform about and comment on the standards, introduce the latest works carried out worldwide based on the finite elements method and, lastly, venture an opinion on the changes this may cause in the future.

Verfahrenstechnische und statische Aspekte der Siloauslegung

AbstractProcess Engineering Aspects and Statics of Silo Design. Design of silos for flow is described, starting from the flow profiles developing during discharge. The respective flow profile depends on the flow properties of the bulk solids and on the silo geometry. Based on measured flow properties the determination of the maximum permissible hopper wall inclination to achieve mass flow and of the minimum dimension of the outlet to prevent arching and ratholing is demonstrated, taking into account time consolidation aspects. This yields the size of a feeder and the position of discharge aids. The flow properties are required additionally for structural design of silos. Flow of bulk solids in silos, especially the development of asymmetric flow channels, has a significant influence on the pressure distribution.

Austragorgane und Austraghilfen

AbstractFeeders and Discharge Aids. Feeders and discharge aids have an influence on the flow behaviour of bulk solids in silos. Together with the geometric form of the silo, they are responsible for the operating conditions of a silo. Therefore, feeders and discharge aids have to be chosen and installed under consideration of the flow properties of the bulk solid to be stored. The necessary information is obtained by using the silo design method due to Jenike. This method yields the geometrical data of the hopper (wall steepness, outlet diameter) necessary for a troublefree operation (no doming and ratholing; mass flow; no segregation; uniform flow). Furthermore, the design of feeders and discharge aids plays an important role in determining their function. For example, stagnant zones will build up and cause flow problems on protruding edges and on walls which are not steep enough. For the correct function of the hopper/feeder combination it is important to make sure that the feeder fully activates the hopper outlet and stagnant zones cannot build up. This can be ensured by an appropriate feeder design (increasing capacity in direction of conveying). The driving power of a feeder has to be calculated also on the basis of the flow properties of the bulk solid to be stored.