螺带式混凝土搅拌机混合特性及DEM模拟

采用离散单元法模拟新拌混凝土于搅拌机中的混合过程，研究了双筒螺带式混凝土搅拌机的混合效率。 用Hertz-Mindlin with JKR接触方法建立新拌混凝土离散元模型，模拟了坍落度实验、L箱实验和流变仪实验，将模拟结果与实验结果进行对比，校准模型参数，采用混合系数定量研究了不同初始装填方式下搅拌机的混合效率。结果表明，采用上下装填方式时搅拌机混合效率较高；对任一初始装填方式，左部区域与右部区域、前部区域与后部区域间混合效率无明显差别，而上部区域混合效率比底部区域高，底部出料口处存在搅拌盲区，采用舍弃初始出料的方法可提高新拌混凝土性能。转速较高时混合效率较高，相同旋转圈数时，混合效率基本相同。

Mixing efficiency of a concrete ribbon mixer and DEM simulation

The ribbon concrete mixer with double barrels is commonly used to improve the uniformity of the fresh concrete in construction industry. In order to investigate the mixing efficiency of this kind of ribbon concrete mixer, a discrete element method was used to simulate the mixing process of fresh concrete. Firstly, a discrete element model of the fresh concrete was established by using the Hertz?Mindlin with JKR contact method. The experiment processes, i.e. slump test, L box test and rheometer test were simulated by using this discrete element model and its parameters, and the simulation results were compared with the experimental ones to verify these model parameters. Afterwards, the mixing efficiencies under different initial loadings were investigated and the mixing efficiency under top?bottom loading was highest. Under each initial loading, the mixing efficiency of the fresh concrete in mixer's left region and front region was almost the same as that in their opposite regions respectively, while the mixing efficiency in the upper region was much higher than that in the lower one. Besides, a mixing blind area was found near the outlet in the bottom of the mixer, and the method of discarding the initial concrete discharge was proposed to improve the uniformity of fresh concrete. In addition, the effects of rotational speed on the mixing efficiency were investigated, and it was found that the mixing efficiency with a larger rotational speed tended to be higher. However, their mixing efficiencies were almost the same at the same rotation number of impeller. This numerical model and results provided an effective approach to solve the concrete mixing problems in industry and some scientific references for improving the mixing efficiency of a double ribbon concrete mixer.