﻿ 压载水旋流预处理单元的优化设计与数值模拟
 舰船科学技术  2016, Vol. 38 Issue (3): 73-78 PDF

Optimal design and numerical simulation of cyclone pretreatment unit in ballast water system
MENG Meng, BAO Guo-zhi, ZHAO Yu-yu, CHEN Ning
School of Energy and Power Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
Abstract: The ballast water management standard D2 established by IMO has made clear rules for the range of particles size and content in the ballast water. In order to meet the rules, the hydrocyclone has begun to be widely applied in treatment of ship's ballast water. However, in order to improve the separation property of the hydrocyclone, optimize the hydrocyclone by changing its entry structure. The cyclone entry structure is designed as Archimedes spiral entrance to increase fluid rotational speed, reduce the energy consumption and finally improve the separation efficiency. Using Fluent software and combining with the Reynolds stress model and the mixture multiphase model to simulate the solid-liquid multiphase of the two structures of Archimedes entrance and tangential entrance hydrocyclone. The simulation includes the fluid field distribution and solid volume fraction distribution inside the hydrocyclone and the separation efficiency. The simulation results show that:compare to the tangential entrance, the tangential velocity and separation efficiency both increased, achieved the goal of optimization.
Key words: ballast water    hydrocyclone    optimal design    solid-liquid multiphase    numerical simulation
0 引言

1 旋流器的优化设计

 图 1 水力旋流器结构参数 Fig. 1 Structural parameters of hydrocyclone

2 固-液两相流的数值模拟 2.1 湍流模型

 $\frac{{\partial {U_i}}}{{\partial {x_i}}} = 0\text{，}$ (1)

 $\begin{array}{l} \rho (\displaystyle\frac{{\partial {U_i}}}{{\partial t}} + {u_j}\frac{{\partial {U_i}}}{{\partial {x_j}}}) = - \frac{{\partial P}}{{\partial {x_i}}} + \frac{\partial }{{\partial {x_j}}}[\mu (\frac{{\partial {U_i}}}{{\partial {x_j}}} + \frac{{\partial {U_j}}}{{\partial {x_i}}}) - \\ \quad\quad\quad\quad\quad\quad\quad\quad \rho \overline {{{u'}_i}{{u'}_j}}] + \rho {g_i}\text{。} \end{array}$ (2)

 $\rho \displaystyle\frac{{{\rm d}\overline {{{u'}_i}{{u'}_j}} }}{{{\rm d}t}} = \frac{\partial }{{\partial {x_i}}}(\frac{{{\mu _t}}}{{{\sigma _k}}} + \mu \frac{{\partial \overline {{{u'}_i}{{u'}_j}} }}{{\partial {x_i}}}) + {p_{ij}} - \frac{2}{3}{\delta _{it}}\rho \varepsilon + {\varPhi _{ij}}\text{，}$ (3)

 $\rho \frac{\text{\rm d}k}{\text{\rm d}t}=\frac{\partial }{\partial {{x}_{l}}}[\frac{{{\mu }_{t}}}{{{\sigma }_{k}}}+\mu \frac{\partial k}{\partial {{x}_{l}}}]-\rho \overline{{{u}_{i}}{{u}_{l}}}\frac{\partial {{U}_{i}}}{\partial {{x}_{l}}}-\rho \varepsilon \text{，}$ (4)

 $\begin{array}{l} \rho \displaystyle\frac{{{\rm{d}}\varepsilon }}{{{\rm{d}}t}} = \frac{\partial }{{\partial \mathop x\nolimits_l }}\left[{\left( {\frac{{\mathop \mu \nolimits_t }}{{\mathop \sigma \nolimits_\varepsilon }} + \mu } \right)\frac{{\partial \varepsilon }}{{\partial \mathop x\nolimits_l }}} \right] - \\ \quad\quad\quad \mathop C\nolimits_{\varepsilon 1} \displaystyle\frac{\varepsilon }{k}\frac{{\mathop \mu \nolimits_t }}{2}\left( {\frac{{\partial \mathop u\nolimits_i }}{{\partial \mathop x\nolimits_j }} + \frac{{\partial \mathop u\nolimits_j }}{{\partial \mathop x\nolimits_i }}} \right){}^2 -\mathop C\nolimits_{\varepsilon 2\rho } \displaystyle\frac{{\mathop \varepsilon \nolimits^2 }}{k}\text{。} \end{array}$ (5)

2.2 固-液两相流模型

2.3 三维模型及网格划分

 图 2 几何模型 Fig. 2 The geometric model

 图 3 网格图 Fig. 3 Mesh diagram
2.4 边界条件及其他设置

1）液相边界条件：入口边界采用速度入口，取垂直于入口端面的平均速度 ul,为 6.57 m/s；底流和溢流出口边界采用压力出口；固壁边界采用无滑移边界条件。

2）固相边界条件：入口边界采用速度入口，入口速度 us = ul；底流和溢流出口边界采用压力出口；固壁边界采用无滑移边界条件。

3）其他：设定水的密度：998.2 kg/m3，粘度：0.001 003 Pa·s；设定砂粒密度为 3 000 kg/m3，将离散相砂粒粒径分别设为 30 μm，40 μm，50 μm，60 μm，70 μm，80 μm，粘度 10 mPa·s，入口体积分数为 5%，质量流率为 8.327 kg/s。首先运用 RSM 模型对流体相做定常流动计算，待其结果收敛后，添加混合模型，完成对固-液两相流的数值模拟计算。

3 结果与分析

 图 4 旋流器轴截面简图 Fig. 4 Sketch of axial cross-sections in hydrocyclone
3.1 切向速度对比分析

 图 5 旋流器不同截面切向速度分布图 Fig. 5 Tangential velocity distribution of different sections in hydrocyclone
3.2 轴向速度和径向速度的对比分析

 图 6 旋流器不同截面轴向速度分布图 Fig. 6 Axial velocity distribution of different sections in hydrocyclone

 图 7 旋流器不同截面径向速度分布图 Fig. 7 Radial velocity distribution of different sections in hydrocyclone
3.3 固相体积分数的对比分析

 图 8 砂相体积分数分布云图 Fig. 8 Distribution contours of sand fraction

 图 9 旋流器不同截面砂相体积分布图 Fig. 9 Sand fraction distribution of different sections in hydrocyclone
3.4 分离效率的对比分析

 $E = \frac{{{M_u}}}{{{M_i}}} \times 100\% \text{。}$ (6)

 图 10 不同直径砂粒的分离效率 Fig. 10 Separation efficiency of the sand in different diameters

4 结语

1）将旋流器入口结构优化为阿基米德螺线形后，其各截面的切向速度、轴向速度和径向速度均有所增加，其中切向速度增加的幅度较大，对提高对旋流器的分离效果起到促进作用。

2）与切向入口结构的旋流器相比，阿基米德螺旋线入口旋流器对不同直径砂粒的分离效率均有所增加。当粒径大于 5 0 μm 时，阿基米德螺旋线入口旋流器的分离效率均达到了 95% 以上，其中对直径为 50μm，60 μm，70 μm，80 μm 砂粒的分离效率分别为 89.47%，95.42%，98.23% 和 99.08%。

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