Numerical study on pressure prediction and its main influence factors in pneumatic conveyors

摘要

The flow characteristics of multiphase gas-solid flow in a pneumatic conveyor were investigated numerically and experimentally to predict the important pressure within the pipeline. The effects of particle size, particle density, and bend radius ratio on pressure drop over the bend pipeline were also analysed. Experiments were conducted to obtain the static pressure at certain cross-sections of a fine powder pneumatic conveying pipeline with a length of 26. m and an inner diameter of 53. mm. The conveyed material was flyash with a mean particle size of 30 μm and the solids loading ratio was in the range 20-70. A numerical study of gas-solid flow in complex three-dimensional systems was undertaken by means of commercial CFD software Fluent 6.3. The simulation was performed using the Euler-Euler approach, accounting for four-way coupling. The calculated results of pressure gradient were found to be in good agreement with the measured data, with a fitting slope of 0.781 for the first horizontal straight pipeline and 1.017 for horizontal bend. It was also found that the pressure gradients increase with increase in particle diameter rapidly and reach the peak value when particle diameter is 150 μm, and then begin to decrease and show a slight steepening with increase in particle diameter with a value greater than 150μm. An increase in particle density results in increase in pressure gradient. The pressure drop is much smaller when the roughness height is zero. The pressure gradient over the horizontal bend increases gradually with the increase of roughness height. The larger the roughness constant is defined, the greater the pressure drop will be. The bend pressure gradient decreases significantly when the bend radius ratio increases from 1 to 3, and then much slowly for bend radius ratios 3-6. With the increase of velocity difference, the pressure drop decrease is different at first, after 0.2-0.3. m, the pressure reduces the same.