转盘表面黏性薄液膜稳态流动特性数值模拟

Numerical simulation of stable flow dynamics of viscous film on spinning disk surface

转盘表面薄膜流广泛存在于转盘反应器、造粒和分子蒸馏等化工领域,其流动特性对造粒、反应以及热质传递具有重要影响。建立了稳态薄膜流动特性理论模型,并对比实验数据与数值模拟结果,研究了等效Froude数Fr、量纲1特征厚度与长度比值ε和浇注尺寸r_i对薄膜厚度分布的影响,导出了水跃和同步区半径模型并通过实验验证。结果表明:等效Froude数Fr不会对薄膜厚度分布产生明显影响;量纲1ε和浇注尺寸r_i是水跃发生与否的决定条件,增大ε或缩小r_i有助于水跃出现,水跃半径稳定于r=0.85;平均径向速度呈典型三分区特征,缩小浇注尺寸r_i将引起浇注区范围加大而加速区范围显著缩小,导致薄膜无明显加速现象而直接进入同步区,但同步区半径维持在r=1.53。研究结果为转盘反应器以及离心粒化器等的设计与优化提供了可借鉴的理论与应用基础。

Film flow on spinning disk surface exists extensively in chemical engineering operations, such as centrifugal graining, molecular distillation and spinning disk reactors. Flow dynamics of the film flow has a major impact on graining, reaction, heat and mass transfer rate. Theoretical model of stable film flow dynamics was established and verified by comparison of experimental results and numerical simulations. The effect of equivalent Froude number, dimensionless ratio of characteristic thickness over length e, and casting size ri on dimensionless film thickness distribution was studied, which a model of dimensionless hydraulic jump and synchronized zone radius was derived and verified by experiments. The results show that equivalent Froude number has little effect on film thickness distribution and occurrence of hydraulic jump phenomenon mainly depends upon e and ri. Increasing ε or decreasing ri leads to appearance of hydraulic jump with a dimensionless hydraulic jump radius always at r=0.85. Mean radial velocity exhibited features of typical three zone distribution. Reducing casting size would extend injection zone and shrink acceleration zone, such that film flow goes directly to synchronized zone at dimensionless synchronized radius of 1.53 without evident acceleration. The results will provide theoretical reference for design and optimization of spinning disk reactors and centrifugal pelletizers.