Abstract:

Liquid-solid separation is a common operation unit in coal chemical wastewater treatment. The material to be treated is tangentially inserted into the separation device against the inner wall surface of the cylinder to form a three-dimensional concave wall tangential jet. In order to compare the influence of the jet inlet structures on discrete particles, the liquid-solid separation experiment and discrete phase model are used to calculate the trajectory and Reynolds number of the particles. The continuous phase turbulence characteristics are investigated under the influence of the particles, and the distribution of wall shear stress was analyzed. The results show that the fit length between inlet and wall are shortened for semi-circular, square and circular. The radial distribution range of particles is sequentially widened, and the distance of flow direction is sequentially shortened. The particle residence time is shortened in the order of circle, semi-circular, and square inlets. The reason is that the maximum tangential velocity of the semi-circular inlet is 16.0% higher than that of the square, and the circular shape is reduced by 15.3%. The average value of the centrifugal force of the semi-circular inlet is increased by 59.9% and the circle is reduced by 43.5% than the square in the near wall. 97% of the particles Reynolds number is in the range of 40—400, and the number of particles with Re = 80 is the highest for three inlets. The particles are affected by the concave-wall jet, the impact and rolling is formed between the discrete particles and the wall. The first impact is in the range of 10°—35° in the inlet circumferential direction, the maximum wall shear stress appears to be flat. The wall shear stress gradually approaches zero after the particles roll along the wall surface and the circumferential direction exceeds 90°. After calculations, the turbulence intensity increased 27.1%, 8.8%, and 62.7%, and the wall shear stress increased 23.7%, 13.5%, and 15.2% for square, semi-circular and circular inlet, respectively.

Key words: concave-wall jet, discrete phase model, solid particle, turbulence intensity, wall shear stress

摘要：

液固分离是煤化工污水处理中的常规操作单元，待处理物料贴着圆筒体内壁面切向进入分离设备，形成三维凹壁面切向射流。为了比较射流入口结构对离散颗粒产生的影响，利用液固分离实验和离散相模型模拟研究了颗粒的轨迹和Reynolds数，并对加入颗粒前后凹壁面切向射流的湍动特性和壁面剪应力分布进行分析。研究结果表明，半圆形、方形、圆形入口与设备内壁面贴合长度依次缩短，颗粒沿径向分布范围依次加宽，流向行程依次缩短。而颗粒停留时间按照圆形、半圆形、方形依次缩短。其原因在于，半圆形入口切向最大速度比方形提高16.0%，圆形降低15.3%。近壁面一倍射流高度范围内的离心力平均值，半圆形入口比方形提高59.9%，圆形降低43.5%。三种入口结构下97%的颗粒Reynolds数在40～400范围内，Reynolds数为80的颗粒数量最多。颗粒受凹壁面切向射流的影响，入口周向10°～35°范围内，离散颗粒与壁面形成第一次冲击，最大壁面剪应力值出现持平趋势，超过 90°以后，颗粒沿壁面滚动下滑，壁面剪应力逐渐趋于0。经过计算，方形、半圆形、圆形三种入口结构加入离散颗粒后湍动强度分别提高27.1%、8.8%、62.7%，壁面剪应力分别提高23.7%、13.5%、15.2%。

关键词: 凹壁面切向射流, 离散相模型, 固相颗粒, 湍动强度, 壁面剪应力