# The Effect of Mixing Chamber Configuration and Submersion Depth on Centrifugal Aerator Performance

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

^{3}; ${\mu}_{m}$ is the mixing viscosity coefficient, Pa·s; ${\alpha}_{k}$ is the volume fraction of the kth phase; ${\rho}_{k}$ is the density of the kth phase, kg/m

^{3}; and ${v}_{dr,k}$ is the drift velocity of the kth phase, m/s.

## 3. Results and Discussion

#### 3.1. Numerical Simulation Accuracy Verification

_{2–}6H

_{2}O hexahydrate and Na

_{2}SO

_{3}anhydrous. The specific parameters of the instruments and reagents used in the centrifugal aerator test are shown in Table 2 and Table 3.

- (1)
- Add water to the aeration pool to record the height, H.
- (2)
- Turn on the dissolved oxygen meter and calibrate it; place the probe of the dissolved oxygen meter at 0.3 m from the liquid surface.
- (3)
- Put anhydrous sodium sulfite and cobalt chloride hexahydrate into the aeration tank to exclude dissolved oxygen in the water, observe the dissolved oxygen meter until the reading no longer drops, and record the value.
- (4)
- Start the centrifugal aerator.
- (5)
- Record the dissolved oxygen concentration, and thereafter record the data every 30 s; when the reading no longer changes, the dissolved oxygen in the water is considered to have reached saturation, therefore stop the experiment.

^{3}/h. The simulated gas flow velocity at the inlet port monitored by the numerical model with time changes is compared with the experimentally measured wind velocity, as shown in Figure 7, and the relative error of the numerical simulation is compared with the experimentally measured average wind velocity V = 5.646 m/s. The relative error is 2.28%.

^{3}/h obtained from the experimental test. Therefore, the numerical simulation shows good accuracy, and the results reflect the real aeration and oxygenation capacity of the centrifugal aerator.

#### 3.2. Verification of the Necessity of the Discharge Tube

#### 3.3. Variation of Relative Area Ratio (ð)

^{3}/h. According to the working experience of most domestic companies manufacturing centrifugal aerators of this power, the use of 4, 6, and 8 discharge tubes is a more common and efficient form. To explore a more suitable number of discharge tubes, 4, 6, and 8 discharge tubes were selected for numerical optimization simulations. Since the structural dimensions of centrifugal aerators with different power vary, to analyze the selection of a more suitable size of discharge tube to achieve a good aeration effect under different mixing chamber dimensions, a dimensionless parameter mixing chamber relative area ratio (ð) is defined to express the dimensional characteristics of the mixing chamber of centrifugal aerators; combined with Figure 13, ð is defined as follows:

^{2}in each mixing chamber, execpt the number of the discharge tubes is different, so the total discharge area of the mixing chamber is also different. The three schemes under the mixing chamber area and the discharge area are shown in Table 4.

#### 3.4. Variation of Submergence Depth

_{1}is the volume of water below the level of the centrifugal aerator discharge tube; V

_{2}is the volume of water above the level of the centrifugal aerator discharge tube. That is, when the greater the dive coefficient, the closer the working position of the aerator is to the top of the aeration pool; when the smaller the dive coefficient, the closer the working position of the aerator is to the bottom of the aeration pool. For example, when the aeration machine is in the aeration pool in the middle of the vertical direction, β = 0.5, and is located at the bottom of the aeration pool when β = 1.

^{3}/h for dip coefficients of 0.35, 0.25, 0.15, and 0.05. The gas flow rate pattern at the outlet is consistent with the pattern presented in the gas volume fraction diagram above for the entire aeration tank, which also better the reason for the different gas contents in the aeration tank. The flow rates at the outlet of the mixing chamber and the distribution of the gas phase throughout the aeration tank for different dive coefficients are presented in Table 6. After aeration and oxygenation, the most important performance indicator in the oxidation ditch is the dissolved oxygen rate, and more gas is delivered into the aeration tank to allow more oxygen to dissolve in the water. At the same air intake, the gas volume fraction increases by an average of 31.29% compared to the other three cases when the dip coefficient is 0.15, providing the most gas to the working aeration tank, and thus allowing more gas to be dissolved in the aeration tank.

## 4. Relationship between Oxygenation Capacity and Submersion Depth

- (1)
- Standard oxygen total transfer coefficient (Kla (20)):

_{1}and t

_{2}, mg/L, respectively.

^{−1}; and 1.024 is the correction factor.

- (2)
- Standard Oxygen Transfer Rate (SOTR)

- (3)
- Standard Aerator Efficiency (SAE)

## 5. Conclusions

- For centrifugal aerators, the installation of a discharge tube is necessary. When the discharge tube is installed, the average gas volume fraction in the mixing chamber is increased from 13.4% to 19.7%, an increase of 47%. The ratio of mixing chamber area to discharge area (ð) affects the performance of dissolving air inside the mixing chamber and discharging it to the aeration tank, which tends to increase and then decrease as ð increases. When ð = 12.57, ð = 8.38, and ð = 6.28, ð = 8.38 achieves the best performance and increases the outlet gas flow rate by 51.98% compared to the other two cases.
- The appropriate working depth enhances the amount of gas dissolved in the pool by the down-running centrifugal aerator, which helps to increase the dissolved oxygen rate of the pool. To be used to find the suitable submergence depth for different working environments, a dimensionless coefficient is proposed: the down-dip coefficient (β). When β = 0.15, the gas flow rate reaches 15.54 m
^{3}/h, which is an average increase of 3.69 m^{3}/h compared to the other three conditions. The volume fraction of gas in the aeration tank under this condition is 19.3%, which is 31.3% higher than the average volume fraction of gas in the other three conditions. - Experiments were conducted for different dive coefficients of centrifugal aerators. The maximum dissolved oxygen content (DO) increased by 25.16%, the maximum standard oxygen transfer coefficient (Kla(20)) increased by an average of 1.13 times, the standard oxygenation capacity (SOTR) increased by 56.6%, and the standard power efficiency (SAE) increased by 44.2% when β = 0.15 compared to the average of the results obtained in the other three cases. In conclusion, the efficient aeration and oxygenation performance of the centrifugal aerator can be achieved when β = 0.15.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

- Hosono, Y.; Fujie, K.; Kubota, H. Operational Characteristic Evaluation of Liquid-Pump type Deep Shaft Aerator. J. Chem. Eng. Jpn.
**1979**, 12, 136–142. [Google Scholar] [CrossRef] - Petrille, J.; Boyd, C.E. Comparisons of oxygen-transfer rates and water-circulating capabilities of emergency aerators for fish ponds. Aquaculture
**1984**, 37, 377–386. [Google Scholar] [CrossRef] - Shukla, B.K.; Sharma, P.K.; Goel, A. Study on Oxygenation Performance of Solid Jet Aerator having Circular Opening corresponding to Variable Jet Length and Flow Area. J. Phys. Conf. Ser.
**2020**, 1531, 012117. [Google Scholar] [CrossRef] - Shukla, B.K.; Goel, A. Study on oxygen transfer by solid jet aerator with multiple openings. Engineering science and technology. Int. J.
**2018**, 21, 255–260. [Google Scholar] - Bılek, M.; Štigler, J. Modelling of single-phase flow in the stator channels of submersible aerator. Eng. Mech.
**2014**, 21, 289–298. [Google Scholar] - Dong, L.; Guo, J.; Liu, J.; Liu, H.; Dai, C. Experimental study and numerical simulation of gas–liquid two-phase flow in aeration tank based on CFD-PBM coupled model. Water
**2020**, 12, 1569. [Google Scholar] [CrossRef] - Huang, W.; Li, K.; Wang, G.; Wang, Y. Computational fluid dynamics simulation of flows in an oxidation ditch driven by a new surface aerator. Environ. Eng. Sci.
**2013**, 30, 663–671. [Google Scholar] [CrossRef] [PubMed] - Dong, L.; Liu, J.; Liu, H.; Dai, C.; Gradov, D.V. Study on the internal two-phase flow of the inverted-umbrella aerator. Adv. Mech. Eng.
**2019**, 11, 1687814019871731. [Google Scholar] [CrossRef] - Patil, S.S.; Deshmukh, N.A.; Joshi, J.B. Mass-transfer characteristics of surface aerators and gas-inducing impellers. Ind. Eng. Chem. Res.
**2004**, 43, 2765–2774. [Google Scholar] [CrossRef] - Hu, S.; Dong, L.; Hua, R.; Guo, J.; Liu, H.; Dai, C. Experimental Study of a Gas-Liquid-Solid Three-Phase Flow in an Aeration Tank Driven by an Inverted Umbrella Aerator. Processes
**2022**, 10, 1278. [Google Scholar] [CrossRef] - Zhang, C.; Xu, S.; Yu, P. Numerical analysis of the effects of gas-phase properties on the internal characteristics and wear in a centrifugal pump. Aquac. Eng.
**2020**, 91, 102126. [Google Scholar] [CrossRef] - Liu, J.; He, X.; Shi, W.; Su, Q. Design and Experimental Research of Self-Suction Sprinkler Irrigation Jet Pump. In Proceedings of the Fluids Engineering Division Summer Meeting, Hamamatsu, Japan, 24–29 July 2011; Volume 44403, pp. 25–33. [Google Scholar]
- Zhang, B.; Pu, X.; Qi, Y.; Mao, S.; Wu, Z. Investigation on Oxygenation Performance and Numerical Simulation of Swirling Aerator. IOP Conf. Ser. Earth Environ. Sci.
**2019**, 295, 012053. [Google Scholar] [CrossRef] - Thakre, S.B.; Bhuyar, L.B.; Deshmukh, S.J. Effect of different configurations of mechanical aerators on oxygen transfer and aeration efficiency with respect to power consumption. Int. J. Aerosp. Mech. Eng.
**2008**, 2, 100–108. [Google Scholar] - Xing, P.; Zhang, A.M.; Deng, Z.X. The fluid-structure interaction analysis of the inverted umbrella aerator curved blade. In Applied Mechanics and Materials; Trans Tech Publications Ltd.: Wollerau, Switzerland, 2015; Volume 705, pp. 101–105. [Google Scholar]
- De Jesus, S.S.; Moreira Neto, J.; Santana, A.; Maciel Filho, R. Influence of impeller type on hydrodynamics and gas-liquid mass-transfer in stirred airlift bioreactor. AIChE J.
**2015**, 61, 3159–3171. [Google Scholar] [CrossRef] - Wang, C.L.; Zhang, J.L.; Zhang, M.Q. Hydrodynamics and oxygen mass transfer properties of the hemi-cambered pitched blade turbines. Chem. Ind. Eng. Prog.
**2018**, 37, 35–46. [Google Scholar] - Cheng, H.Y.; Ji, B.; Long, X.P.; Huai, W.X.; Farhat, M. A review of cavitation in tip-leakage flow and its control. J. Hydrodyn.
**2021**, 33, 226–242. [Google Scholar] [CrossRef] - Wang, Z.Y.; Cheng, H.Y.; Ji, B. Euler–Lagrange study of cavitating turbulent flow around a hydrofoil. Phys. Fluids
**2021**, 33, 112108. [Google Scholar] [CrossRef] - Wang, Z.Y.; Cheng, H.Y.; Ji, B. Numerical prediction of cavitation erosion risk in an axisymmetric nozzle using a multi-scale approach. Phys. Fluids
**2022**, 34, 062112. [Google Scholar] [CrossRef]

**Figure 3.**Schematic diagram of mesh topology. (

**a**) Grid of the mixing chamber; (

**b**) Grid of rotor blades.

**Figure 9.**Types of mixing chamber arrangement. (

**a**) Mixing chamber without discharge tube; (

**b**) Mixing chamber with discharge tube.

**Figure 10.**Contours of blade pressure. (

**a**) Internal rotor blade pressure cloud without discharge tube; (

**b**) Internal rotor blade pressure cloud with discharge tube.

**Figure 14.**Schematic diagram of mixing chamber structure. (

**a**) ð = 12.57; (

**b**) ð = 8.38; (

**c**) ð = 6.28.

**Figure 18.**Contours of the velocity of A–A sections at different β. (

**a**) β = 0.35; (

**b**) β = 0.25; (

**c**) β = 0.15; (

**d**) β = 0.05.

**Figure 19.**Contours of the velocity of the aeration tank at different β. (

**a**) β = 0.35; (

**b**) β = 0.25; (

**c**) β = 0.15; (

**d**) β = 0.05.

**Figure 21.**Streamlines on the Z–X central section. (

**a**) β = 0.35; (

**b**) β = 0.25; (

**c**) β = 0.15; (

**d**) β = 0.05.

**Figure 22.**The plot of gas volume fraction in aeration tank at different β. (

**a**) β = 0.35; (

**b**) β = 0.25; (

**c**) β = 0.15; (

**d**) β = 0.05.

Mesh | Rotation Domain | Total Number | Inlet Speed | Relative Error |
---|---|---|---|---|

1 | 1,213,758 | 2,184,764 | 5.428 | 3.86% |

2 | 1,577,885 | 2,840,193 | 5.479 | 2.96% |

3 | 2,051,251 | 3,692,251 | 5.506 | 2.48% |

4 | 2,666,626 | 4,799,927 | 5.517 | 2.28% |

5 | 3,466,614 | 6,239,904 | 5.526 | 2.13% |

Reagents | Chemical Formula | Function | Concentration | Characteristic |
---|---|---|---|---|

Sodium sulfite anhydrous | Na_{2}SO_{3} | Deoxidation | ≥97% | White crystal powder, easy to dissolve |

Cobalt chloride hexahydrate | CoCl_{2}·_{6}H_{2}O | Catalyst | ≥99% | Pink crystal, easy to dissolve |

Name | Type | Measurement Range | Error |
---|---|---|---|

Dissolved oxygen meter | MIK-DM3000 | 0~20 mg/L | ±0.2 mg/L |

Anemometers | AS-H5 | 0–30 m/s | ±0.5 m/s |

Four Drain Type | Six Drain Type | Eight Drain Type | |
---|---|---|---|

ð | 12.57 | 8.38 | 6.28 |

ð | 12.57 | 8.38 | 6.28 |
---|---|---|---|

Outlet flow (kg/s) | 16.155 | 16.617 | 5.713 |

β | 0.05 | 0.15 | 0.25 | 0.35 |
---|---|---|---|---|

Outlet gas flow (m^{3}·h^{−1}) | 12.25 | 15.54 | 11.35 | 11.95 |

Gas-phase volume fraction | 16.2% | 19.3% | 13.8% | 14.1% |

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**MDPI and ACS Style**

Zhang, Z.; Zheng, Y.; Xu, X.; Peng, B.
The Effect of Mixing Chamber Configuration and Submersion Depth on Centrifugal Aerator Performance. *Sustainability* **2022**, *14*, 11355.
https://doi.org/10.3390/su141811355

**AMA Style**

Zhang Z, Zheng Y, Xu X, Peng B.
The Effect of Mixing Chamber Configuration and Submersion Depth on Centrifugal Aerator Performance. *Sustainability*. 2022; 14(18):11355.
https://doi.org/10.3390/su141811355

**Chicago/Turabian Style**

Zhang, Zhen, Yuan Zheng, Xiwang Xu, and Bin Peng.
2022. "The Effect of Mixing Chamber Configuration and Submersion Depth on Centrifugal Aerator Performance" *Sustainability* 14, no. 18: 11355.
https://doi.org/10.3390/su141811355