Experimental Study and Numerical Simulation of Gas–Liquid Two-Phase Flow in Aeration Tank Based on CFD-PBM Coupled Model

Liang Dong,Houlin Liu,Jinnan Guo,Cui Dai,Jiawei Liu

doi:10.3390/w12061569

Abstract

Gas–liquid two-phase flow directly determines the efficiency and stability of the aeration tank. In this paper, a gas–liquid two-phase testbed is built to explore the aeration performance and internal flow in an aeration tank, including an inverted-umbrella impeller (immersion depth of 0 mm, rotational speed of 250 r/min). Also, the running process is simulated by computational fluid dynamics (CFD) with a population balance model (PBM), and mass transfer coefficient is compared to the experiment. The experimental results show that there is a big difference in bubble diameter, ranging from 0.4 to 1.6 mm. The simulation shows that the impeller intensely draws air above the free surface into the shallow liquid, and the circulation vortex entrains it to the bottom areas faster. Compared with the experiment, the simulated interfacial area and standard oxygen mass transfer coefficient is 12% more and 3% less, respectively. The results reveal that CFD-PBM coupled model can improve the accuracy of calculation, resulting in the simulation of gas–liquid two-phase flow.

Highlights

In urban wastewater treatment, the primary process for the treatment of nitrogen and organic compounds in wastewater is activated sludge
Coupled model can diameter scheme is much greater than the test value. It shows that the coupled model can improve the accuracy of calculation results in the simulation of gas–liquid two-phase flow
(1) The size of bubbles in the aeration tank was different at an immersion depth of 0 mm and a rotational speed of 250 r/min, ranging from 0.4 to 1.6 mm

Summary

Introduction

The primary process for the treatment of nitrogen and organic compounds in wastewater is activated sludge. Aeration consumes up to 70% of the total energy expenditure of the plant. The inverted-umbrella aerator has various advantages which include a simple structure, strong oxygenation capacity and high-power efficiency. It combines the use of oxygenation and stirring functions [1]. It has become one of the most widely used aeration equipment in oxidation ditch. The inverted-umbrella aerator throws the sewage into the air and is involved in air. The bottom of the impeller and suction side of blades generate negative pressure and suck air, which makes the bubble size in the aeration tank vary widely

Methods

Results

Discussion

Conclusion