(83d) Modelling Solids Friction Factor for Dense-Phase Pneumatic Conveying of Powders

The power function approach to modelling particle-wall friction factor for the prediction of pressure drop in pneumatic conveying has been used widely by researchers and designers for many years. More fundamental methods based on powder mechanics have been developed for certain products and modes of flows, such as the low-velocity slug-flow of granular products. However, the pneumatic conveying of powders, especially under dense-phase conditions, has been far more difficult to model at a similar level of detail. For this reason, the more empirical power function approach has been employed widely to avoid the need to develop fundamental relationships between friction factor and the relevant particle and bulk properties. Despite the apparent accuracy of the developed power functions, these empirical relationships occasionally and unexpectedly become unreliable or even unstable under certain scale-up conditions. This paper presents results from an investigation into power-function modelling of solids friction factor for the dilute-phase and fluidised dense-phase (FDP) conveying of powders. Three different diameters/lengths of pipeline were used to generate a wide range of steady-state data and also explore important scale-up issues. The effect of pressure tapping locations on the data and derived models also was investigated. Different sets of power-function model solutions were used for comparison purposes and also to check scale-up stability and accuracy. Comparisons with predictions from recent models developed by other researchers are included. It is concluded that certain forms of the power function model are more stable (in terms of scale-up) than others. The paper also demonstrates how existing models can go unreliable or unstable under certain scale-up conditions and discusses possible causes of such problems.