# A Perforated Baffle Design to Improve Mixing in Contact Tanks

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## Abstract

**:**

## 1. Introduction

## 2. Methods

#### 2.1. Computational Model

#### 2.1.1. Flow Model

_{i}and x

_{j}are Cartesian coordinates. Reynolds-averaged Navier–Stokes (RANS) equations are closed using a k-ε turbulence closure model for the solution of turbulent flow in the contact tank. Reynolds stresses are approximated by the following Boussinesq hypothesis:

_{ij}is the Kronecker delta, k is the turbulence kinetic energy, and ${v}_{t}$ is the turbulent viscosity, which is defined as,

_{μ}is the model constant and selected as 0.09. Two transport equations are sequentially solved for $k$ and $\epsilon $ using appropriate boundary conditions.

#### 2.1.2. Conservative Tracer Model

_{init}is the injected tracer concentration (C

_{init}= 1), T

_{injection}is the injection time, Ɵ = t/τ is the dimensionless time and τ is the MRT.

#### 2.1.3. Computational Domain and Boundary Conditions

_{average}= Q/A for a given flow rate Q and applied as a constant value along the flow direction. The following boundary conditions are used for the turbulence quantities at the inlet:

#### 2.2. Experimental Method

^{3}/day in the prototype was converted to the laboratory model as 2.9 lt/s, according to the Froude similitude $\left(\frac{{Q}_{model}}{{Q}_{prototype}}={\left(\frac{1}{10}\right)}^{2.5}\right)$, which was appropriate to characterize the flow in the contact tank. Experimental studies were conducted using the flow conditions shown in Table 1 on a laboratory model which was 4 m long, 66 cm in width and 75 cm in height. The flow rate was adjusted manually using a valve and measured with an ultrasonic flow meter mounted on the feeding pipe. The water depth in the tank was measured as 48.5 cm under steady-state flow conditions. As seen in Figure 3a, the laboratory-scale contact tank consists of ten chambers and baffles are removable to test different baffling configurations on the same experimental setup in [4].

## 3. Results and Discussion

#### 3.1. Perforated Baffle Structures

#### 3.2. Numerical Results

_{10}, as given in Table 3.

#### 3.3. Experimental Results and Model Validation

_{90}value in the CRTD curve (Figure 6b). The differences between CRTD curves are such that they do not contain significant deviations in hydraulic and mixing efficiency indexes.

#### 3.4. Flow Analysis

#### 3.5. Performance Analysis of the Perforated Baffle Design

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**Computational mesh generated using blockMesh and snappyHexMesh: (

**a**) wall boundaries of the contact system; (

**b**) zoomed view of the hexahedra mesh over the perforated baffles.

**Figure 3.**Snapshot of the experimental setup during tracer studies in the laboratory: (

**a**) front view; (

**b**) plan view.

**Figure 5.**Sketch of the manufactured baffles showing the hole distribution on the baffle: solidity ratio decreases in the flow direction (

**a**) Design 2; (

**b**) Design 7.

**Figure 6.**Comparison of numerical and experimental tracer results for Design 2 and Design 7: (

**a**) RTD; (

**b**) CRTD.

**Figure 7.**Velocity vectors on a horizontal plane located at the mid-depth of the tank: (

**a**) conventional design; (

**b**) Design 2; (

**c**) Design 7.

**Figure 8.**Visualization of three-dimensional streamlines for (

**a**) conventional design; (

**b**) Design 2; (

**c**) Design 7.

**Figure 9.**Variation of efficiency indexes with the number of holes for the constant solidity ratios of 95% in Section 1, 80% in Section 2 and 65% in Section 3: (

**a**) baffling factor, (

**b**) Mo index, (

**c**) dispersion index and (

**d**) AD index.

**Figure 10.**Comparison of tracer results for the conventional and optimized designs: (

**a**) RTD; (

**b**) CRTD.

Discharge (lt/s) | Water Depth (cm) | Wet Volume (m^{3}) | MRT (s) | Injection Time (s) |
---|---|---|---|---|

2.93 | 48.5 | 0.63 | 215 | 10 |

Design | Solidity Ratio (%) | Hole Diameter (cm) | Number of Holes | ||
---|---|---|---|---|---|

Design 1 | Open Area | Section 1 | 90 | 1 | 110 |

Section 2 | 80 | 1.3 | 130 | ||

Section 3 | 70 | 1.6 | 128 | ||

Design 2 | Open Area | Section 1 | 95 | 1 | 54 |

Section 2 | 80 | 1.3 | 132 | ||

Section 3 | 70 | 1.6 | 128 | ||

Design 3 | Open Area | Section 1 | 95 | 1 | 55 |

Section 2 | 85 | 1.2 | 114 | ||

Section 3 | 75 | 1.4 | 140 | ||

Design 4 | Open Area | Section 1 | 95 | 1 | 55 |

Section 2 | 85 | 1.2 | 114 | ||

Section 3 | 70 | 1.6 | 128 | ||

Design 5 | Open Area | Section 1 | 95 | 1 | 55 |

Section 2 | 75 | 1.4 | 140 | ||

Section 3 | 70 | 1.6 | 128 | ||

Design 6 | Open Area | Section 1 | 96 | 1 | 44 |

Section 2 | 80 | 1.4 | 130 | ||

Section 3 | 70 | 1.6 | 128 | ||

Design 7 | Open Area | Section 1 | 95 | 1 | 55 |

Section 2 | 80 | 1.4 | 130 | ||

Section 3 | 65 | 1.6 | 152 |

**Table 3.**Baffling classifications and factors [23].

Baffling Condition | θ_{10} |
---|---|

Unbaffled | 0.1 |

Poor | 0.3 |

Average | 0.5 |

Superior | 0.7 |

Perfect (plug flow) | 1.0 |

Design | θ_{10} | θ_{90} | Mo | σ | AD |
---|---|---|---|---|---|

Conventional | 0.547 | 2.486 | 4.545 | 0.14293 | 3.203 |

Design 1 | 0.768 | 1.894 | 2.466 | 0.08597 | 3.853 |

Design 2 | 0.8 | 1.914 | 2.392 | 0.07553 | 5.097 |

Design 3 | 0.784 | 1.885 | 2.404 | 0.07719 | 4.097 |

Design 4 | 0.798 | 2 | 2.506 | 0.07874 | 4.95 |

Design 5 | 0.797 | 1.895 | 2.378 | 0.07439 | 4.409 |

Design 6 | 0.799 | 1.968 | 2.463 | 0.07822 | 4.816 |

Design 7 | 0.807 | 1.838 | 2.277 | 0.07454 | 4.342 |

Design | Hole Diameter (cm) | Number of Holes | θ_{10} | Mo | σ | AD |
---|---|---|---|---|---|---|

Design 7 | 1 | 55 | 0.807 | 2.2776 | 0.07454 | |

1.4 | 130 | 4.342 | ||||

1.6 | 152 | |||||

Design 7.1 | 1.51 | 25 | 0.7911 | 2.4544 | ||

1.86 | 64 | 0.0806 | 4.507 | |||

2.19 | 80 | |||||

Design 7.2 | 0.54 | 192 | 0.8235 | 2.2745 | ||

1.1 | 182 | 0.0718 | 4.960 | |||

1.35 | 210 | |||||

Design 7.3 | 0.54 | 192 | 0.8456 | 2.2776 | ||

0.9 | 270 | 0.0698 | 6.013 | |||

1.12 | 306 | |||||

Design 7.4 | 0.47 | 250 | 0.8491 | 2.2346 | ||

0.83 | 320 | 0.0692 | 5.947 | |||

1.05 | 350 |

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## Share and Cite

**MDPI and ACS Style**

Nasyrlayev, N.; Kizilaslan, M.A.; Kurumus, A.T.; Demirel, E.; Aral, M.M.
A Perforated Baffle Design to Improve Mixing in Contact Tanks. *Water* **2020**, *12*, 1022.
https://doi.org/10.3390/w12041022

**AMA Style**

Nasyrlayev N, Kizilaslan MA, Kurumus AT, Demirel E, Aral MM.
A Perforated Baffle Design to Improve Mixing in Contact Tanks. *Water*. 2020; 12(4):1022.
https://doi.org/10.3390/w12041022

**Chicago/Turabian Style**

Nasyrlayev, Nazhmiddin, M. Anil Kizilaslan, A. Tolga Kurumus, Ender Demirel, and Mustafa M. Aral.
2020. "A Perforated Baffle Design to Improve Mixing in Contact Tanks" *Water* 12, no. 4: 1022.
https://doi.org/10.3390/w12041022