Ian Bridle

Constructing an engineering model for moisture migration in bulk solids as a prelude to predicting moisture migration caking

The aim of this study was to examine one of the mechanisms behind moisture migration caking, where liquid solution bridges form between particles in a bulk solid system because of an increase in local relative humidity, and then solidify as the local relative humidity drops - the effect being increased as more cycles occur. The goal was to develop a one-dimensional model for the heat and mass transfer processes involved, based on established physics and the characteristic moisture sorption curve of the solid (in this case sugar). The model was verified using scaled-down equipment (a caking box) to simulate the caking in a big bag. The results of this study will assist in the prediction of caking produced in this way.

Computational model for prediction of particle degradation during dilute-phase pneumatic conveying: modeling of dilute-phase pneumatic conveying

A complete model of particle impact degradation during dilute-phase pneumatic conveying is developed, which combines a degradation model, based on the experimental determination of breakage matrices, and a physical model of solids and gas flow in the pipeline. The solids flow in a straight pipe element is represented by a model consisting of two zones: a strand-type flow zone immediately downstream of a bend, followed by a fully suspended flow region after dispersion of the strand. The breakage matrices constructed from data on 90° angle single-impact tests are shown to give a good representation of the degradation occurring in a pipe bend of 90° angle. Numerical results are presented for degradation of granulated sugar in a large scale pneumatic conveyor.

Measuring the tensile strength of caked sugar produced from humidity cycling

Abstract The aim of this study was to develop moisture migration modelling in stored sugar due to the temperature cycling of the storage environment. This was done by forming cake of sugar in a gas-bearing tensile tester. The sugar and tester were enclosed in a controlled humidity system and the relative humidity was cycled between four hours at 70 per cent relative humidity and four hours at 20 per cent relative humidity. Liquid bridges formed between the sugar particles at high relative humidity, with the bridges hardening subsequently when the humidity was reduced. It was found that the relationship between the tensile strength and number of cycles could be approximated by the relationship σT = K √N and the agglomerate tensile strength was in the order of 150Pa after 32 cycles. This suggests a soft cake rather than hard cakes with a tensile strength of twice this order of magnitude, which are formed, for example, in salt. A value of 1300kPa was obtained for the parameter representing the average strength of the bridge material in a simplified model of monosized spheres linked by pendular bridges in a system of uniform packing.

A hybrid numerical model for predicting segregation during core flow discharge

A continuum numerical model is presented that parameterizes the interactions between particles at the microscopic level and predicts the development of moving stagnant zone boundaries during core flow discharge of granular material. The model is then employed for the prediction of segregation of multi-component granular mixtures during discharge from core flow hoppers and its capability to accurately simulate the behavior of the granular mixture is demonstrated through comparisons with experimental data.

Assessing the potential of a fine powder to segregate using laser diffraction and sieve particle size measuring techniques

Abstract This paper describes a research programme undertaken with a view to solving a serious industrial powder handling problem. The aim of this research was to rationalize three grades of an additive fine powder used in the manufacturing of a mixed product to one grade, with the aim of reducing or eliminating the potential risk of particle segregation within the product. The use of a segregation tester, specifically to quantify the propensity of a sample of bulk solid to segregate when poured on to a heap, was central to this research. Particular attention was paid to the particle size distribution curves of the final product within different areas of the segregation tester. Two different techniques for characterizing particle size were used in the investigation — one based on size separation using sieving analysis and the other based on the laser diffraction technique. These techniques yield different measures of particle size distribution, resulting in different conclusions as to the feasibility of particle size analysis being a useful indicator of the propensity of a powder to segregate.

Utilising Computational Fluid Dynamics (CFD) for the Modelling of Granular Material in Large-Scale Engineering Processes

In this paper, the framework is described for the modelling of granular material by employing Computational Fluid Dynamics (CFD). This is achieved through the use and implementation in the continuum theory of constitutive relations, which are derived in a granular dynamics framework and parametrise particle interactions that occur at the micro-scale level. The simulation of a process often met in bulk solids handling industrial plants involving granular matter, (i.e. filling of a flat-bottomed bin with a binary material mixture through pneumatic conveying-emptying of the bin in core flow modepneumatic conveying of the material coming out of a the bin) is presented. The results of the presented simulation demonstrate the capability of the numerical model to represent successfully key granular processes (i.e. segregation/ degradation), the prediction of which is of great importance in the process engineering industry.

An investigation into the effect of product type when scaling for diameter in vertical pipelines

The prediction of pressure drop is important to pipeline design and it is often necessary to use data from one pipeline size to predict what will happen in another pipeline size. This paper looks at the effect of two different products when scaling for diameter in vertical pipelines. Data has been measured for cement and flour in two bore sizes. A means of modelling has been established to allow prediction of the operation of a pipeline of one bore size, from trials on another bore size in vertical sections. The model used to correlate pipeline diameter with pressure gradient data in vertical pneumatic conveying pipelines will be discussed along with the general data trends for the two materials.

Computational modelling of particle degradation in dilute phase pneumatic conveyors

The aim of this paper is to develop a mathematical model with the ability to predict particle degradation during dilute phase pneumatic conveying. A numerical procedure, based on a matrix representation of degradation processes, is presented to determine the particle impact degradation propensity from a small number of particle single impact tests carried out in a new designed laboratory scale degradation tester. A complete model of particle degradation during dilute phase pneumatic conveying is then described, where the calculation of degradation propensity is coupled with a flow model of the solids and gas phases in the pipeline. Numerical results are presented for degradation of granulated sugar in an industrial scale pneumatic conveyor.

Original paperAssessing the potential of a fine powder to segregate using laser diffraction and sieve particle size measuring techniques

Abstract This paper describes a research programme undertaken with a view to solving a serious industrial powder handling problem. The aim of this research was to rationalize three grades of an additive fine powder used in the manufacturing of a mixed product to one grade, with the aim of reducing or eliminating the potential risk of particle segregation within the product. The use of a segregation tester, specifically to quantify the propensity of a sample of bulk solid to segregate when poured on to a heap, was central to this research. Particular attention was paid to the particle size distribution curves of the final product within different areas of the segregation tester. Two different techniques for characterizing particle size were used in the investigation — one based on size separation using sieving analysis and the other based on the laser diffraction technique. These techniques yield different measures of particle size distribution, resulting in different conclusions as to the feasibility of particle size analysis being a useful indicator of the propensity of a powder to segregate.