曝气条件对等温层曝气器水力性能的影响

等温层曝气器内表观水流速度直接影响等温层曝气的充氧效果,针对表观水流速度难以准确计算的普遍问题,系统分析了曝气室内气水两相流运动所受的驱动能量与损失能量,提出了尾涡和顶部能量损失的无量纲表达式,建立了曝气室内水流的一维水动力学模型,以及基于MATLAB真域算法的模型求解方法.采用美国Prince湖等温层曝气器的实际运行数据,对该模型进行了验证,表观水流速度的预测误差在±8％以内,明显低于现有预测误差±20%.当曝气孔直径为2.6mm、曝气量从0.018m3/h增加到0.063m3/h时,曝气室内表观水流速度随曝气量的增加而增加;当曝气量固定,曝气孔直径从2.6mm减小至0.26mm时,表观水流速度随曝气孔直径的减小而增加,而当曝气孔直径进一步减小至0.026mm时,表观水流速度基本不受影响.计算了不同条件下的驱动能量和各项损失能量,揭示了引起表观水流速度变化的内因.建立的水动力学模型可用于指导等温层曝气器的设计和优化.

Effects of aeration conditions on the hydrodynamic performance of a hypolimnetic aerator

Superficial water velocity in a hypolimnetic oxygenator directly influences the oxygenation effectiveness of a hypolimnetic aerator. Aiming at the common problem of poor prediction of superficial water velocity, driving energy and energy losses of the gas-liquid two-phase flow in the aeration chamber were systematically analyzed, dimensionless formulas for calculating the energy losses due to wakes and top were particularly proposed, a one-dimensional hydrodynamic model for the water flow in the aeration chamber was developed, and a analytical solution to this hydrodynamic model was built using the real-domain method of MATLAB. The predicted superficial water velocities were validated against the operation data of hypolimnetic oxygenators installed in Lakes Prince, the United States, the prediction errors fell into the range of ±8%, which were much lower than the exiting prediction errors of ±20%. Under the orifice diameter of 2.6mm, the superficial water velocity increases with the air flowrate when the air flowrate increased from 0.018m3/h to 0.063m3/h; Under fixed air flowrate condition, the superficial water velocity increased when the orifice diameter decreased from 2.6mm to 0.26mm, but it remained unchanged when the orifice diameter further decreased to 0.026mm. Driving energy and energy losses under various conditions were calculated, the inherent factors causing the variations of superficial water velocity were revealed. This developed hydrodynamic model can be used to guide the design and optimization of a hypolimnetic oxygenator.