PULSATING GAS-SOLID FLOW INSIDE A BENCH-SCALE REACTOR

The gas-solid motion inside a laboratory-scale pulsating combustor was analyzed using numerical techniques. The gas flow was treated in an Eulerian frame of reference whereas the motion of representative coal particles were treated in a Lagrangian frame of reference. In most previous studies the particles had been exposed to regular, sinusoidal gas flow. Here the gas flow was obtained as part of the solution by solving the one-dimensional transient equations of motion. The driving force was the combustion heat release prescribed a priori. The resulting flow field is periodic but it cannot be described by a simple sine wave in time. It also varies significantly with the spatial coordinate. The motion of coal particles of various sizes (10-100-mu-m) with different initial conditions have been studied. The results provide more insight with regard to the aerodynamics of gas-solid flows in pulsating combustors. When released from rest, the larger particles, for example, have longer residence times than smaller particles. Particles with sizes less than about 10-mu-m follows the gas flow pulsation very closely. Particules larger than 100-mu-m are affected very little by the flow pulsation. Particle temperature history and heating rates were also calculated. In a pulsating flow the particle temperature oscillates about the gas temperature, resulting in periodic heating and cooling of the particle, but the convective heat transfer to the particle increases mainly because of the increased slip velocity.