An investigation into pressure fluctuations for fluidized dense-phase pneumatic transport of fine powders
This paper presents results of an ongoing investigation into the flow mechanism for the pneumatic conveying of fine powders conveyed from fluidized dense phase mode to dilute-phase. Three different techniques of signal analysis (i.e. rescaled range analysis, phase space method and technique of Shannon entropy) have been applied to the pressure fluctuations obtained during the solids-gas flow of fly ash (median particle diameter 30μm; particle density 2300kgm-3; loose-poured bulk density 700kgm-3) through a 69mm I.D.x168m long pipeline and also white powder (median particle diameter 55μm; particle density 1600kgm-3; loose-poured bulk density 620kgm-3) through a 69mm I.D.x148m long test rig. Results show that with increasing conveying distance (and conveying velocity in the direction of flow), there is an overall decrease in the values of Hurst exponent, an increase in the area covered by the phase-space diagram and an increase in the Shannon entropy values, indicating an increase in the degree of complexity of flow mechanism (or turbulence) along the length of the conveying pipeline. All the three methods have revealed that the closely coupled bends reverse the trend of change of Hurst exponent, phase-space diagram area and Shannon entropy values. This is due to the slowing down of particles caused by the friction of particles along the bend wall resulting in dampened particle turbulence.