P.C. Arnold

An analytical solution for the stress function at the wall of a converging channel

Abstract Presented is an analytical solution for the stress function S (α) at the wall of a mass flow hopper. Having an explicit expression for S (α) makes it possible to obtain analytical expressions for such parameters as the normal stress at the wall and the flow factors for arching, in a converging channel. Contours of ν w /γ B and ff determined from these expressions compare favourably with those obtained by Jenike using numerical solutions.

On improving scale-up procedures for pneumatic conveying design

Abstract The method of scaling-up test rig data to full-scale installations, previously used quite extensively in the design of pneumatic conveying systems, is shown to be inadequate in particular applications. Two popular forms of definition and three existing empirical relationships for the solids pressure drop component are modified to demonstrate the possible extent of this inadequacy. Steady-state pipeline conveying characteristics obtained from three products (fly ash/cement mix, PVC powder, screened coke) and four test rigs are used in the development of an improved scale-up procedure. Suggested methods to predict air-only pipeline pressure drop (for both single-and stepped-diameter pipelines) and to generalise pneumatic conveying characteristics for a particular material (applicable to any system of different length and/or diameter) are also included.

Prediction of the flowrate of bulk solids from mass flow bins with conical hoppers

Abstract A theoretical model based on continuum mechanics theory is developed for predicting the flowrate of bulk solids from mass flow bins with conical hoppers. Close agreement between theoretical predictions and experimental results is obtained. Both theoretical predictions and experimental results indicate that the flowrate of free flowing bulk solids increases rapidly at first and then more gradually as the bulk solid permeability constant increases. This dependence is reinforced by a sensitivity analysis which verifies that the air pressure gradient at the hopper outlet generated during flow has significant effect on the flowrate. The use of permeability enables the theory developed to be applied in describing the flow behaviour of both coarse and fine particle mixtures as well as size-distributed bulk solids. The use of consolidation-related bulk density and permeability relations enables the theoretical model to be applied to both compressible and incompressible materials. Results of both theoretical and experimental work relating to the effect of material surcharge level on th significant.

Consolidation-related bulk density and permeability models for bulk solids

Abstract This paper examines several consolidation-related bulk density and permeability models for bulk solids. Numbers of experiments have been performed to measure bulk density and permeability and, by using an optimization technique, the most suitable and accurate models for bulk density and permeability of bulk solids are identified.

Modelling of air pressure distributions in mass flow bins

Abstract The work in this paper develops a theoretical model for predicting the interstitial air pressure distribution for bulk solids flowing in a conical mass flow bin. The theoretical model is based on continuum mechanics theory. The boundary conditions are consistent with air pressure and bulk density continuity in the vertical direction. Close agreement between theoretical and experimental air pressure distribution is obtained. Both the theoretical model and experimental results indicate that the magnitude of air pressure increases with increasing the hopper outlet size, the surcharge level and/or decreasing the powder permeability.

Reducing hopper wall friction by mechanical vibration

Abstract Reduction of the effective wall friction in hoppers allows shallow core-flow hoppers to exhibit mass-flow characteristics. This paper presents theoretical and experimental evidence which indicates that a significant reduction in wall friction can be achieved by the proper use of applied vibrations. Some practical implications and applications of this reduced wall friction are discussed.

A simplified model for predicting the particle flowrate from mass flow bins

Abstract In this paper, a combination of Monte Carlo simulation and an optimization technique is used to simplify the model for predicting the dynamic deaeration coefficient K dea (Z. H. Gu, P. C. Arnold and A. G. McLean, Powder Technol., 72 (1992) 121 and 157). Sensitivity analysis indicates that the dynamic deaeration coefficient K dea mainly depends on bulk density constants (ϱ 0 , b 1 , b 2 ), the hopper outlet diameter D o , internal friction angle δ and surcharge level H/D . Based on the simplified K dea model, a simplified flowrate model is obtained, providing a very good agreement with the original flowrate model (Z. H. Gu, P. C. Arnold and A. G. McLean, Powder Technol., 72 (1992) 157) but without requiring the numerical analysis used to solve the integrations in the original model.

An alternative presentation of the design parameters for mass flow hoppers

Abstract The procedure for determining the critical hopper outlet dimension and wall slope for mass flow hoppers by the Jenike method is well established and documented. However, existing presentations relating the bulk solid flow properties of effective angle of internal friction and the kinematic angle of wall friction with the hopper wall slope and flow factor for mass flow are often inconvenient for manual use and present difficulties when included in design programs suitable for microcomputers. This paper details an alternative presentation of the original Jenike flow factor charts. These alternative charts have been abbreviated to display only the critical design values in the border region between mass flow and funnel flow. The charts eliminate the need for imprecise parameter interpolations by displaying the required design parameters in the form of contours of constant wall slope and critical flow factor as a function of the effective angle of internal friction and the kinematic angle of wall friction. An illustrative example is provided to demonstrate the inherent advantages of this presentation for the evaluation of mass flow hopper geometries.