An investigation into modeling of solids friction for dense-phase pneumatic conveying of powders
This article presents results from an investigation into the modeling of solids friction factor for fluidized dense-phase pneumatic conveying of powders. A fundamental design approach was pursued by employing “straight pipe” and “back calculation” techniques for modeling and using two types of power function formats. The “straight pipe” models were found to be unexpectedly different depending on the selected location of pressure-measuring tapping points (even for the same product). An attempt to explain this variation by studying the “straight pipe” conveying characteristics suggested significant changes in flow mechanisms along the pipe. The derived models were evaluated for scaleup accuracy and stability by predicting for larger and longer pipes. The results showed significant variations in predictions. One format of power function model was found to result in more stable predictions than the other. Possible explanations for the causes of such variations are provided. Physical observations of the flow phenomena of dense-phase conveying for different powders showed the products were mostly conveyed as a dense non-suspension liquid-type-layer along the bottom of the pipe. This mechanism does not seem to be correctly represented by the existing design approach of using a Froude number term in the solids friction factor models, thus initiating a search for suitable alternative dimensionless grouping(s) that can adequately represent the non-suspension flow phenomena. In this study, Steady-state conveying data of three different powders conveyed in various pipes (diameter/lengths) were used for the purpose of modeling and scaleup investigations.