水力旋流器细粒分离效率优化与数值模拟

Separation Efficiency Optimization of Liquid-solid Hydrocyclone and Numerical Simulation

水力旋流器内流体质点的切向速度、径向速度和轴向速度的分布规律及其流体动力学机理对于细粒分级粒径和效率具有决定性作用,并且受旋流器的结构参数、操作参数和物性参数等因素的影响。选用耐磨耐腐蚀的聚氨酯材料制造的不同规格固液分离水力旋流器,综合考虑分割粒径、处理流量、沉砂产率3项分离效率指标,通过多指标正交试验优化得到分离钙土的工作参数如下:旋流器直径50 mm,底流口直径10 mm,溢流口直径8 mm,并且在0.30 MPa给料压力下可达到分割粒径1.78μm,处理流量为2.39 m3/h的分离效率。同时针对优化后的旋流器工作参数,利用适用于旋流器湍流场的雷诺应力模型,运用FLUENT软件计算不同直径颗粒的亲水性固体在水动力中的速度场,得到分离介质的滞留时间为1.8×10 2s,反向轴速度最大可达3.08 m/s,最大切向速度半径为0.046 m,使得分离效率达到78.6%;从压力场的数值模拟结果看出,径向压强梯度从762.5 kPa/m增大到6 822.2 kPa/m,实现分割粒径达到1.78μm的效果。根据旋流器中压力场、速度场分布特征以及分离介质轨迹等数值模拟结果,提出延长分离介质的滞留时间、提高进料压力、降低中心准强制涡的速度梯度、减缓正向轴速度的径向变化梯度是提高分离效果的主要途径,从而通过试验与数值模拟对比,揭示出试验优化旋流器达到最佳分离效率的动力学机理。

In the separation process,the distribution rules of tangential velocity,radial velocity and axial velocity and the hydrodynamics mechanism could make the decisive effect on the particle cut size and the efficiency,which would also be impacted by the factors,such as structure,operating parameters of hydrocyclone and properties of treated object.The wear and corrosion-resistance material,polyurethane,has been used to manufacture the different specification liquid-solid hydrocyclone.Synthetically regarding with the particle cut size,the treatment capacity,and grit deposit efficiency,the optimization parameters of hydrocyclone separating calcium clay are diameter 50 mm,du=10 mm,do=8 mm,through the multi objective orthogonal experiment.Meanwhile,the particle cut size could be under 1.78μm at the pressure 0.30 mPa.And the processing capacity would reach 2.39 m3/h.According to the optimization parameters of hydrocyclone and the Reynolds stress model,which is suitable for rapids flow field in hydrocyclonee,the velocity field of pellet water affinity solid with different diameter is calculated by the FLUENT software.It is indicated that retention time of the separation medium is 1.8×10？2 s,the reverse axis speed may reach 3.08 m/s most greatly,and the radius of the most greatly tangential velocity is 0.046 m,so that the separation efficiency could reach 78.6%.Based on the numerical simulation result of pressure field,the pressure gradient of radial direction increases from 762.5 kPa/m to 6 822.2 kPa/m,in order to realize the particle cut size 1.78 μm.According to the numerical simulation results of distribution characters of the pressure field,speed field as well as separation medium path,it was proposed that the extending the retention time of separation medium,enhancing the feeding pressure,reducing the velocity gradient of the central accurate forced vortex,slowing down the forward axis speed gradient in the radial direction would be the main way to improve the separation effect.Therefore,through the comparison of the experiment and the theoretical calculation,it is revealed the dynamics mechanism of the hydrocyclone optimized to achieve the best separation efficiency by experiment.