An analysis on flow modes in pneumatic conveying systems

In this study, an experimental investigation on flow mode analysis of pneumatic particle conveying was conducted. An experimental test set-up and coupled measurement system were constructed for the purpose. The measurements were conducted in three separate test cases consisted of which vertical, horizontal test pipelines and a horizontal continuous conveying with a particle feeder. The covered particles of semolina, wheat, sand, polyethylene, zeolite and tea with the ranges of loose poured bulk density, 200 kg/m3 ˂ ρblp ˂ 2400 kg/m3 and average particle diameter, 150 μm ˂ dp ˂ 2750 μm were used in the range of 21697 ˂ Re ˂ 156992. The measurements of the local static pressures, pressure drops, ∆P and pressure gradients ∆P/L were performed as a function of minimum fluidization velocity, Umf. The velocity and pressure measurements which were evaluated through a custom design program FDRIPCS.vi in LabView 2009 SP1® environment were carried out in the error margins of ± 1.16 % and ± 3.31 % respectively. The visual observation of the flow field through the functional relationships between P1 vs P2, ∆P vs Uair were used to determine Umf. The transported particles as a ratio of mass flow rate of air; Ṁp/Ṁa, calculated local permeability factors Pf and Pf mf and Remf corresponding to Umf were used to analyze the flow modes with the covered ranges of 21697 ˂ Remf ˂ 147600, 3.65 m/s ˂ Umf ˂ 24.83 m/s, 0.0052 m2/Pa.s ˂ Pf mf ˂ 0.92 m2/Pa.s and 0.25 % ˂ Ṁp/Ṁa ˂ 51.99 %. The functional relationship between Pf mf = f(Remf) was used to verify the flow mode analysis. The observed modes were defined as: unstable zone, transition of fluidized dense phase, fluidized dense phase, slug flow, transition of plug flow, plug flow and dilute phase. The defined flow modes were the severe function of experimental methodology besides particle characteristics. It is seen that the value of loose poured bulk density, ρblp is dominant to determine flow modes when it is compared with average particle diameter, dp in vertical test case. On contrary to this, dp of particles are found to be more significant in comparison with ρblp for investigation of flow modes in horizontal test case. It seems that fluidized dense phase is in the range of 0.0052 m2/Pa.s ˂ Pf ˂ 0. 2 m2/Pa.s, slug flow and plug flow are valid for 0.2 m2/Pa.s ˂ Pf ˂ 0.56 m2/Pa.s and dilute phase is inside 0.56 m2/Pa.s ˂ Pf.