变截面流化床理论模型及数值模拟

Theoretical model and numerical simulation of variable section fluidized bed

基于双流体模型,在一定假设的条件下推导得到了用于描述变截面床流化过程的局部平衡模型。对于局部平衡模型,空间导数项的离散采用五阶精度的WENO有限差分格式,时间导数项的离散采用TVD Runge-Kutta型的离散格式,对流量突变后的瞬态过程进行了模拟,得到固相体积分数在整个变化过程中沿床高的分布以及床高变化规律和床层表面颗粒速度变化曲线。对于流量突增过程,在床内不同位置形成了一系列的连续波,当所有的连续波到达床面整个变化过程结束。而对于流量突然减小过程,将会有固相体积分数间断在分布板处形成,当所有间断到达床面时,塌落过程结束。

Based on the Two-Fluid Model,under some hypotheses,the Local Equilibrium Model（LEM） was developed.Using the model,the bed height and concentration distributing in liquid-solid variety section bed were studied by numerical simulation method.The fifth-order WENO scheme was used for spatial derivative and third-order TVD Runge-Kutta method for time derivative.The laws of the bed height change,the particle velocity,the particle volume fraction distributing were gotten.The simulation results show that during the process of expansion,there always exists a progressively broadening and upward-propagating continuous transition zone,but during the collapse process a solid-phase volume fraction discontinuity propagating upward from the distributor appears.