并列和错列纤维过滤器稳态除尘过程的 格子Boltzmann模拟

大部分纤维捕集效率和压降的理论模型认为纤维性能仅取决于来流速度、颗粒粒径、纤维体积分数、过滤层厚度、纤维直径等因素。实际上,布袋除尘器的性能还与纤维配置方式直接相关。利用LB(lattice Boltzmann)两相流模型对多层纤维捕集颗粒物过程进行了数值模拟,研究了不同纤维配置方式下系统压降与捕集效率的变化。结果表明,错列纤维的性能参数优于并列纤维;纤维排列间距增大,压降增幅大于捕集效率,导致性能参数下降。通过比较不同位置纤维的捕集能力发现,在布朗扩散和拦截捕集机制主导下,前方纤维捕集能力略强于后方纤维;而在惯性碰撞捕集机制主导时,对捕集贡献最大的主要是前两排纤维,后方纤维对捕集效率的贡献非常小,可以忽略。这些研究结果可以对布袋除尘器的多层纤维配置方式的优化提供理论依据和工程建议。

Simulation of steady filtration process for parallel and staggered fibrous filter by lattice Boltzmann method

Fibrous filter with the advantage of high capture efficiency of sub-micro particles is widely used in coal-fired power plants, mineral engineering, cement industry and other fields.The filtration process is very complex because of various capture mechanisms and the interactions among airflow, particles and fibers.Up to now, many researchers have investigated the filtration process of fibrous filter, especially the single fiber condition.A series of theories or equations have been presented to calculate pressure drop and filtration efficiency for the single fiber.By contrast, studies for multi-fiber condition are fewer than the single fiber condition.The existing studies of multi-fiber filtration process often focus on the factors(velocity of airflow, volume fraction, particle diameter, etc.)which may affect capture efficiency.It is worth noting that, the ultimate purpose for the study of filtration process should be optimization of fiber configuration for multi-fiber filter, and then a filter with high capture efficiency and low pressure drop can be obtained.However, there is no report about optimization for fiber configuration.In this paper, the lattice Boltzmann-cell automata(LB-CA)probability model was used to simulate the filtration process of multi-fiber filter.The pressure drop and capture efficiency with different mechanisms and fiber configurations were investigated, and the results obtained from the LB-CA model were in good agreement with existing results.The quality factor defined as ratio of capture efficiency and pressure drop was also introduced to weigh the fibrous filters.In order to present the optimization method for different particles, the capture ability of each fiber was first defined and calculated.Parallel model and staggered model for fiber configuration were presented.The quality factor of the staggered model was greater than that of the parallel model because of higher capture efficiency although its pressure drop was also larger.Through comparison of capture ability of fibers in different positions, it was found that the fore fibers were more efficient than the rear ones, especially in the inertial impaction capture mechanism.In the diffusional and interception mechanisms, the similar situation also existed but the contribution of rear fibers could not be neglected.The results showed that a filter with diminishing volume fraction along the depth direction might perform well in the filtration process with the diffusional and interception mechanisms; in the inertial impaction mechanism, the row number of fibers should not exceed two.