Research on Flow Control of Dense Gas-Solid Flows

本研究的目的是控制稠密气固两相流动中的细观结构。首先，通过数值和实验研究了气体脉动对床层中气泡运动的影响。计算和实验都发现，当注入气体的速度在一定的频带内脉动时，会产生特征气泡。当考虑气体分布器的压降时，计算得到的气泡运动与相应的实验结果相吻合。气体脉动是控制床层内气泡运动的有效方法之一，考虑气体分布板压力降的计算可以预测气体脉动对气泡运动的影响。在考虑壁面效应的情况下，修正阻力系数后，推力长度和推塞速度的预测值与相应的实验结果吻合较好。利用计算结果对堵塞的长度、速度、破裂频率等进行了统计分析。提出了一维恒定立管流动的推流模型，并提出了一种相似模型，该模型采用较大的颗粒模型来模拟颗粒的运动。将相似模型应用于沸腾床的数值模拟，考察了模型颗粒尺寸对气泡运动的影响。

The objective of this study is the control of meso-scale structures in dense gas-solid flows, First, the effect of gas pulsation on the bubble motion in a fluidized bed was investigated numerically and experimentally. It was found both in the calculation and the experiment that characteristic bubbles were generated when the injected gas velocity was pulsated at a certain frequency band. When the pressure drop through the gas distributor was considered the calculated bubble motion agree with that in the corresponding experiment. Gas pulsation is one of the promissing ways to control the bubble motion in the fluidized bed, and the calculation taking account of the pressure drop through the gas distributor can predict the effect of the gas pulsation on the bubble motion.Next, the plug motion in a standpipe flow was studied. When the drag coefficient is modified taking account of the wall effect the predicted pulg length and the plug velocity agree well with those in the corresponding experiment. The length, velocity, frequency of breakup of plugs are investigated statistically by using the calculated results. A plug flow model for a one-dimensional steady standpipe flow was proposed.Finally, a similarity model was proposed, in which the motion of particles are simulated by using larger model-particles. The similarity model was applied to the numerical simulation of a fluidized bed, and the effect of the model-particle size on the bubble motion was investigated.