Fluidization by lift of 300 circular particles in plane Poiseuille flow bydirect numerical simulation

We study the transport of a slurry of heavier-than-liquid circular particle s in a plane pressure-driven flow in a direct simulation. The flow is calcu lated in a periodic domain containing 300 circular particles. The study lea ds to the concept of fluidization by lift in which all the particles are su spended by lift forces against gravity perpendicular to the flow. The study is framed as an initial-value problem in which a closely packed cubic arra y of particles resting on the bottom of the channel is lifted into suspensi on. All the details of the flow are resolved numerically without model assu mptions. The fluidization of circular particles first involves bed inflatio n in which liquid is driven into the bed by high pressure at the front and low pressure at the back of each circle in the top row. This kind of bed in flation occurs even at very low Reynolds numbers but it takes more time for the bed to inflate as the Reynolds number is reduced. It appears that the bed will not inflate if the shear Reynolds number is below the critical val ue for single particle lift-off. The flows with a single particle are compl etely determined by a shear Reynolds number and a gravity parameter when th e density ratio and aspect ratio parameters are specified. In the multi-par ticle case, the volume fraction and distribution also matters. The transiti on to a fully fluidized slurry by waves is discussed. An analytical model of the steady motion of a single particle dragged forwa rd in a Poiseuille flow is derived and compared with a simulation. The undi sturbed fluid velocity is always larger than the particle velocity, produci ng a fluid hold-up. The effect of the hold-up in the many particle case is to greatly reduce the velocity of the mixture which may be described by a t wo-fluid model in which the solid laden mixture is regarded as a second flu id with effective properties.