# Prediction of a Visible Plume from a Dry and Wet Combined Cooling Tower and Its Mechanism of Abatement

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## Abstract

**:**

## 1. Introduction

## 2. Outline of a Cooling Tower

## 3. Numerical Calculation

#### 3.1. Governing Equations and Calculation Procedure

_{p}, K, and D mean specific heat, thermal conductivity and diffusion coefficient of air, respectively. In the model, the Reynolds stress term appearing in Equation (2) is assumed as follows:

_{t}means eddy viscosity of fluid and defined as follows:

_{t}means turbulent thermal conductivity, and D

_{t}means turbulent diffusion coefficient. In this calculation, the turbulent Prandtl number P

_{rt}= 0.9, and turbulent Schmidt number S

_{ct}= 0.9 were used. The abbreviations appeared in Equations (3) and (4) are shown as follows:

#### 3.2. Cooling Tower Model, Initial and Boundary Conditions

#### 3.2.1. Calculation Model

#### 3.2.2. Wet Operation

#### 3.2.3. Dry-and-Wet Combined Operation

#### 3.3. Calculation Conditions

## 4. Observations

## 5. Results and Discussion

#### 5.1. Validity of CFD Analysis

#### 5.2. Dry and Wet Combined Operation (without External Wind)

#### 5.3. Effect of Air Mixing on the Visible Plume

#### 5.4. Effect of the External Wind Velocity on the Visible Plume

## 6. Conclusions

- (1)
- The prediction of a visible plume rising from a cooling tower with dry and wet sections is possible employing CFD analysis and a turbulent model. The calculated results were validated with observed plumes, and the accuracy was found to be within the error range of 15%–20%, which is permissible for conducting practical design.
- (2)
- The mixing condition of heated air from the dry section and moist air from the wet section affects the scale of the visible plume. In the case of a mechanical-draft cooling tower, two streams of air are well mixed by the combined effect of twisting flow in the circumferential direction and radial outward flow due to the centrifugal force. A rotating fan is considered to function as a mixer. Therefore, in designing a cooling tower with a rotating fan, it is considered that the performance design for plume abatement can be conducted using the operating line on an air chart.
- (3)
- The effect of external wind on the scale of the visible plume under dry and wet combined operation is appreciable, and the visible plume becomes small as the external wind becomes stronger. These results are considered to suggest that the visible plume is relatively small and the diffusion effect of external wind thus reduces the extent of the visible plume.

## Supplementary Files

Supplementary File 1## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 1.**Schematics of cross flow cooling towers with a mechanical draft device (rotating fan): (

**a**) wet type; (

**b**) dry and wet combined type.

**Figure 3.**Analysis model and computed domain in the case of a single cooling tower (

**a**) and eight towers (

**b**).

**Figure 5.**Velocity distributions at the outlet of the exhaust fan measured using model equipment [8].

**Figure 6.**Schematic picture of observation and measuring condition of visible plume and external wind velocity and temperature.

**Figure 7.**Comparisons of (

**a**) calculated and (

**b**) observed visible plumes with external wind, and (

**c**) the calculated visible plume without external wind.

**Figure 10.**Trajectories of marked particles from dry and wet sections to outside the cooling tower: (

**a**) with a fan; (

**b**) without a fan.

**Figure 11.**Effect of the external wind velocity on the scale of the visible plume for dry and wet combined operation; wind velocity of (

**a**) 0 m/s, (

**b**) 1 m/s, (

**c**) 3 m/s, and (

**d**) 5 m/s.

Run-1 | Run-2 | Run-3 | Run-4 | Run-5 | Run-6 | Run-7 | Run-8 | |
---|---|---|---|---|---|---|---|---|

Mode of Operation | Wet | Wet | Wet | Wet/Dry | Wet/Dry | Wet/Dry | Wet/Dry | Wet/Dry |

Cooling Tower Size (m) | 15 × 10 × 15 H | 15 × 10 × 15 H | 15 × 90 × 18 H | 15 × 90 × 18 H | 12 × 10 × 15 H | 12 × 10 × 15 H | 12 × 10 × 15 H | 12 × 10 × 15 H |

Fan Diameter (m) | 5.49 | 5.49 | 7.42 | 7.42 | 5.49 | 5.49 | 5.49 | 5.49 |

Wind Velocity (m/s) | 6.8 | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 | 3.0 | 5.0 |

Number of Tower | 1 | 1 | 8 | 8 | 1 | 1 | 1 | 1 |

Observation Photo | Yes | None | Yes | Yes | None | None | None | None |

Outside Air Conditions | ||||||||

DBT (°C) | 1.8 | 11.4 | 10.2 | 10.2 | 11.4 | 11.4 | 11.4 | 11.4 |

WBT (°C) | 7.4 | 10.0 | 9 | 9 | 10.0 | 10.0 | 10.0 | 10.0 |

Fan Exit (Wet mode) | ||||||||

DBT (°C) | 30 | 30 | 26.5 | - | - | - | - | - |

WBT (°C) | 30 | 30 | 26.5 | - | - | - | - | - |

H/EX Exit (Wet/Dry mode) | ||||||||

DBT (°C) | - | - | - | 17 | 18 | 18 | 18 | 18 |

WBT (°C) | - | - | - | 12.5 | 11.5 | 11.5 | 11.5 | 11.5 |

Fill Exit (Wet/Dry mode) | ||||||||

DBT (°C) | - | - | - | 26.5 | 30 | 30 | 30 | 30 |

WBT (°C) | - | - | - | 26.5 | 30 | 30 | 30 | 30 |

Analysis Area | ||||||||

Mesh Numbers | 200 × 100 × 80 | 200 × 100 × 80 | 312 × 82 × 80 | 312 × 82 × 80 | 200 × 100 × 80 | 200 × 100 × 80 | 200 × 100 × 80 | 200 × 100 × 80 |

Analysis Domain (m) | 260 × 100 × 200 | 260 × 100 × 200 | 200 × 260 × 200 | 200 × 260 × 200 | 260 × 100 × 200 | 260 × 100 × 200 | 260 × 100 × 200 | 260 × 100 × 200 |

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## Share and Cite

**MDPI and ACS Style**

Takata, K.; Michioka, T.; Kurose, R.
Prediction of a Visible Plume from a Dry and Wet Combined Cooling Tower and Its Mechanism of Abatement. *Atmosphere* **2016**, *7*, 59.
https://doi.org/10.3390/atmos7040059

**AMA Style**

Takata K, Michioka T, Kurose R.
Prediction of a Visible Plume from a Dry and Wet Combined Cooling Tower and Its Mechanism of Abatement. *Atmosphere*. 2016; 7(4):59.
https://doi.org/10.3390/atmos7040059

**Chicago/Turabian Style**

Takata, Kazutaka, Takenobu Michioka, and Ryoichi Kurose.
2016. "Prediction of a Visible Plume from a Dry and Wet Combined Cooling Tower and Its Mechanism of Abatement" *Atmosphere* 7, no. 4: 59.
https://doi.org/10.3390/atmos7040059