An investigation into pressure fluctuations and improved modeling of solids friction for dense-phase pneumatic conveying of powders
The aim of this paper is to investigate into flow mechanism with the help of pressure signal fluctuations analysis and modeling solids friction in case of solids-gas flows for fluidized-dense-phase pneumatic conveying of fine powders. Materials conveyed include fly ash (median particle diameter 30 μm; particle density 2300 kg m-3; loose-poured bulk density 700 kg m-3) and white powder (median particle diameter 55 μm; particle density 1600 kg m-3; loose-poured bulk density 620 kg m-3). These were conveyed in different flow regimes varying from fluidized-dense-to-dilute phase. To obtain information on the nature of flow inside pipeline, static pressure signals were studied using technique of Shannon entropy. Increase in the values of Shannon entropy along the flow direction through the straight-pipe sections were found for both the powders. However, drop occurred in the Shannon entropy values after the flow through bend(s). Change in slope of straight-pipe pneumatic conveying characteristics along the flow direction is another factor which provided indication regarding change in flow mechanisms along the flow. A new technique for modeling solids friction factor has been developed using a solids volumetric concentration and ratio of particle terminal settling velocity to superficial air velocity by replacing the conventional use of solids loading ratio and Froude number, respectively. The new model format has shown promise for predictions under diameter scale-up conditions.