基于两相两区模型的气固流化床DEM模拟

DEM Simulation of Gas-Solid Fluidized Beds Based on Two-Phase and Two-Region Model

气固流化床DEM模拟中,通常采用面积加权平均法计算局部空隙率,为了考虑网格中显著非均匀结构对局部空隙率的影响,提出一个计算局部空隙率的两相两区模型。该模型将网格中的非均匀结构虚拟划分为稀相和密相,将实际网格区域划分为稀区和密区,并采用时空关联性原理识别稀区和密区;模型还采用自适应方法计算网格中颗粒分布的非均匀度;将非均匀度作为非均匀结构的影响权重计算密区颗粒的局部空隙率。模拟了鼓泡流化床,模拟结果表明:与传统的DEM相比,基于两相两区模型的DEM能更好地模拟气泡形态,且能捕捉气泡冒出床层和气泡破裂的复杂现象。

Using discrete element method （DEM） to simulate the gas-solid fluidized beds, the area weighted averaging is usually adopted for calculating local voidage. This article developed a local voidage model named two-phase and two-region （P2R2） model to take into account the influence of the distinct heterogeneous structure on local voidage. The suppositional heterogeneous structure in a grid was divided into the dilute phase and the dense phase, while the grid zone was divided into the dilute region and the dense region. The dense region and the dilute region were recognized according to space-time relevance theory. An adaptive scheme was given to evaluate the heterogeneous degree for particle distribution in the grid. Local voidage in the dense region was then calculated in such a way that the heterogeneous degree was considered as the weighting coefficient for the effect of heterogeneity. Then the DEM simulations of a bubbling fluidized bed were performed. Simulations indicate that on the whole the result of using the DEM based on P2R2 model is better than that of using the traditional DEM. The bubble shape and size simulated with P2R2 model are much more consistent with the experiment results. Moreover, bubble eruption and bubble rupture can also be captured by simulations employing P2P2 model.