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The material pulse flow structure within the fluidized dense phase pneumatic conveying of flyash powder was studied using the Electrical Capacitance Tomography (ECT). Decomposition of the bulk density levels within the pipe cross-sectional area were obtained and statistical analysis of bulk density waves were performed. The results suggest that the pulse amplitude and duration obeyed the Weibull and lognormal distributions. In addition, bulk density factor was found to have a linear relationship with pulse amplitude; however, it is independent of pulse duration.

The material pulse flow structure within the fluidized dense phase pneumatic conveying of flyash powder was studied using the Electrical Capacitance Tomography (ECT). Decomposition of the bulk density levels within the pipe cross-sectional area were obtained and statistical analysis of bulk density waves were performed. The results suggest that the pulse amplitude and duration obeyed the Weibull and lognormal distributions. In addition, bulk density factor was found to have a linear relationship with pulse amplitude; however, it is independent of pulse duration.

Abstract This study used a 3D coupled CFD–DEM model to assess how slugs tend towards steady state in single slug horizontal pneumatic conveying. Initial slug length, inlet velocity and initial stationary layer fractions were systematically varied for a total of 72 simulations. Previously made observation that slugs tend towards a steady state was confirmed via a theoretical derivation. The derivation shows that slugs move towards their steady state lengths exponentially. This allowed for a calculation of a characteristic time scale which is a measure of how quickly a slug tends towards the steady state. The theoretical estimate which is a function of slug porosity, steady length, velocity and stationary layer fraction has good agreement with simulated results. A link between steady slug length and solids loading ratio was also shown.

Abstract This study used a 3D coupled CFD–DEM model to assess how slugs tend towards steady state in single slug horizontal pneumatic conveying. Initial slug length, inlet velocity and initial stationary layer fractions were systematically varied for a total of 72 simulations. Previously made observation that slugs tend towards a steady state was confirmed via a theoretical derivation. The derivation shows that slugs move towards their steady state lengths exponentially. This allowed for a calculation of a characteristic time scale which is a measure of how quickly a slug tends towards the steady state. The theoretical estimate which is a function of slug porosity, steady length, velocity and stationary layer fraction has good agreement with simulated results. A link between steady slug length and solids loading ratio was also shown.

Abstract Due to their differences, predictive methods suitable for dilute and dense phase pneumatic conveying are rare in the literature. Conveying trials are often required to characterise a given system, where pressure drop measurements are plotted against gas mass flow rate for various solids flow rates. Empirical curves of constant solids flow are overlaid with measurements and resemble a ‘J’ shape. This paper presents a model for these curves based on the assumption that the pressure drop is a sum of two terms relating to the gas only influence and a combined gas and solids term. The model is validated for slug flow capable materials, where excellent agreement is obtained. However, it is concluded that the procedure is suitable for fluidised dense-phase capable materials as well. The developed model has the potential to significantly reduce the number of conveying trials required to characterise a pneumatic conveying system.

Abstract Due to their differences, predictive methods suitable for dilute and dense phase pneumatic conveying are rare in the literature. Conveying trials are often required to characterise a given system, where pressure drop measurements are plotted against gas mass flow rate for various solids flow rates. Empirical curves of constant solids flow are overlaid with measurements and resemble a ‘J’ shape. This paper presents a model for these curves based on the assumption that the pressure drop is a sum of two terms relating to the gas only influence and a combined gas and solids term. The model is validated for slug flow capable materials, where excellent agreement is obtained. However, it is concluded that the procedure is suitable for fluidised dense-phase capable materials as well. The developed model has the potential to significantly reduce the number of conveying trials required to characterise a pneumatic conveying system.

The many advantages of slug flow pneumatic conveying are outweighed by the lack of understanding of the flow mechanisms. For horizontal slug flow, the unique feature is the stationary layer of material found between the travelling slugs, which was recently shown to be characterised by two constants. This paper looks to utilise the vast data available in the literature, which is representative of the entire mode of flow, and relates the stationary layer and slug velocity to predict the two constants from only these inputs. It was found that, even for the vast range of materials and systems considered, slug flow encompasses a narrow bound of the two constants. Furthermore, an empirical approach that was developed to relate the layer fraction and particle velocity was found to provide good agreement to measurements and may be of use in other investigations that require an additional equation for modelling.

The many advantages of slug flow pneumatic conveying are outweighed by the lack of understanding of the flow mechanisms. For horizontal slug flow, the unique feature is the stationary layer of material found between the travelling slugs, which was recently shown to be characterised by two constants. This paper looks to utilise the vast data available in the literature, which is representative of the entire mode of flow, and relates the stationary layer and slug velocity to predict the two constants from only these inputs. It was found that, even for the vast range of materials and systems considered, slug flow encompasses a narrow bound of the two constants. Furthermore, an empirical approach that was developed to relate the layer fraction and particle velocity was found to provide good agreement to measurements and may be of use in other investigations that require an additional equation for modelling.

This paper considers the particle exchange between a slug and its stationary layers to propose a limiting case for slug stability. It is shown that a stable slug must have a length that is greater than the product of its velocity and the time taken to accelerate particles from the stationary layer into the slug. Theoretical analysis and experimental results are utilised to derive an expression for the acceleration time – resulting in an inequality relating slug length and velocity, layer fraction and pipeline diameter. Single slug, horizontal conveying trials of five bulk materials are used for validation, after which the inequality is generalised to a function of only operating conditions using expressions and observations from the literature. The paper concludes with a case study demonstrating the ability of the resulting method to predict the area of the operating conditions space for which slugging can occur.