基于VOF-DPM的气体辅助式污泥雾化破碎的数值模拟

为实现污泥雾化破碎的数值模拟，探究污泥雾化特征和操作参数对污泥雾化效果的影响，在污泥雾化试验平台试验的基础上基于Fluent软件对污泥在气体辅助式雾化器的雾化破碎进行模拟研究，模拟结果确定了污泥的雾化特征和最优操作参数。通过耦合流体体积法(VOF)与离散相模型(DPM)，对较大的液体团采用VOF方法直接求解，对小液滴采用双向耦合的离散相模型进行追踪，能最大程度地提高计算的准确性。结果表明，污泥的密度和黏度随着含水率升高逐渐降低，气体速度、气液比和雾化角度是影响污泥雾化破碎的最重要的三个操作参数。在雾化过程中，中心区域的雾滴密度大于边缘区域且有少量大颗粒的聚集。对于含水率为87%、密度为1.065×103 kg/m3的污泥，在风速为180 m/s，气液比为126.3，雾化角度为55°时雾化效果最佳，雾滴颗粒的平均粒径约为0.193 mm，试验结果与模拟结果的颗粒粒径吻合度较好，最大相对误差为5.80%。

Numerical investigation of gas-assisted sludge atomization and breakup based on VOF-DPM coupled model

Sewage sludge is an unavoidable by-product in the process of sewage treatment. Due to its characteristics of high pollution and difficult to treat, the efficient and harmless treatment of sludge is still facing certain challenges. A new sludge treatment technology, spray drying technology with relatively simple process and high value-added utilization after sludge atomization has a great promotion effect on sludge treatment. The gas-assisted atomizer has a good atomization effect on high-viscosity fluids, and can ensure a better atomization quality at a faster atomization rate. In the study of sludge atomization, many scholars have carried out certain researches, but there is no numerical simulation study of sludge atomization, and numerical simulation can be low-cost, more intuitive study of sludge atomization breakup, has certain advantages. In order to realize the numerical simulation of sludge atomization and breakup, computational fluid dynamics software is used to explore the influence of gas-assisted sludge atomization characteristics and operating parameters (gas velocity, gas-liquid ratio, spray angle) on the effect of sludge atomization. The results show that the density and viscosity of sludge gradually decrease with the increase of moisture content. Gas velocity, gas-liquid ratio and spray angle are the three most important operating parameters that affect sludge atomization and breakup. During the atomization process, the high-speed airflow makes the sludge vibrate and unstable at the front end of the atomizer, resulting in the tearing of the sludge and the breaking of the droplets. The density of droplets in the center area is greater than that in the edge area and there are a few large particles agglomerated. For sludge with moisture content of 87% and a density of 1.065×103 kg/m3, the atomization effect is the best when the gas velocity is 180 m/s, the gas-liquid ratio is 126.3, and the spray angle is 55°. The average particle size of the droplets is about 0.193 mm, and the experimental results are in good agreement with the simulated particle size, and the maximum relative error is 5.80%.