# Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

_{2}photocatalytic degradation of tetracycline by using a Venturi tube and found that hydrodynamic cavitation had a positive role and can prevent photocatalytic particles from agglomeration. Boczkaj et al. [18] indicated that the hydrodynamic cavitation can reduce the total pollution load in the effluent from the production of bitumens in advanced oxidation processes. Thanekar et al. [19] demonstrated that hydrodynamic cavitation combined with ozone can be effectively used as pretreatment for improving the biodegradability of Dichlorvos (DDVP). Hence, with the development of such technologies, the Venturi tube has already been widely used in wastewater treatment because of its cavitation characteristics.

## 2. Materials and Methods

#### 2.1. Physical Model

_{in}is inlet diameter (mm).

#### 2.2. Mesh Generation

#### 2.3. Numerical Approach

_{m}, u, p donate mixed medium density, velocity, and pressure, respectively. x and the subscripts i, j, k represent the coordinate direction. μ

_{m}is dynamic viscosity of the mixture. μ

_{t}is turbulent viscosity of the mixture. δ

_{ij}is the Kronecker delta.

_{v}is the vapor density, α

_{v}is the vapor volume fraction, and v

_{j}is a velocity component in x

_{j}direction, R

_{e}and R

_{c}are the mass transfer rates correspond to the evaporation and condensation during the cavitation process respectively. In this study, the Rayleigh-Plesset model was applied and the Rayleigh-Plesset equation describing the growth of a gas bubble in a liquid is given by:

_{B}is the bubble radius, p

_{v}is the pressure in the bubble (assumed to be the vapor pressure at the liquid temperature), p is the pressure in the liquid surrounding the bubbler, ρ

_{l}is the liquid density, α

_{n}is a nucleation site volume fraction, F is an empirical factor depend on condensation and vaporization designed for different rates.

^{−5}for all equations. According to mass conservation, the mass flow rates of inlet and outlet were both checked to ensure they were equal.

#### 2.4. Testing System

^{3}h

^{−1}and a lift head of 30 m delivered water to the testing system. The flow rate through the pipe was measured by an electromagnetic flowmeter with an accuracy of ±0.3%. Two pressure gauges with an accuracy of ±0.4% were installed at the upstream and downstream sections to monitor the differential pressure through the Venturi tube. Two gate valves were installed to adjust the differential pressure between the inlet and outlet sections of the Venturi tube.

## 3. Results and Discussion

#### 3.1. Verification of the Simulation Method

#### 3.2. Effects of Contraction Angle on Cavitation Characteristics

#### 3.3. Effects of Diffusion Angle on Cavitation Characteristics

#### 3.4. Effects of Contraction Ratio on Cavitation Characteristics

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 4.**Structural diagram of the experimental setup. 1. Electromotor 2. Pump 3. Electromagnetic flowmeter (50 mm) 4. Gate valve (50 mm) 5. Pressure gauge 6. Venturi tube 7. Pressure gauge 8. Gate valve (50 mm) 9. Water tank.

**Figure 6.**Average vapor volume fraction of cross-section form the throat in axial direction with different contraction angles.

**Figure 7.**Contour of vapor volume fraction in the throat and the diffusion section with different contraction angles, (

**a**) 15°, (

**b**) 30°, (

**c**) 45°, (

**d**) 60°.

**Figure 8.**Average vapor volume fraction of cross-section from the throat in the axial direction with different diffusion angles.

**Figure 9.**Contour of vapor volume fraction of the Venturi tube with different diffusion angles, (

**a**) 10°, (

**b**) 15°, (

**c**) 20°, (

**d**) 25°, (

**e**) 30°.

**Figure 10.**Average vapor volume fraction of a cross-section from the throat in the axial direction with different contraction ratios.

**Figure 11.**Contour of vapor volume fraction of the Venturi tube with different contraction ratios, (

**a**) 0.1, (

**b**) 0.2, (

**c**) 0.3, (

**d**) 0.4.

**Table 1.**Structural parameters of the Venturi model for computational fluid dynamics (CFD) analysis.

Group | α (°) | β (°) | γ |
---|---|---|---|

1 | 15, 30, 45, 60 | 20 | 0.28 |

2 | 30 | 10, 15, 20, 25, 30 | 0.28 |

3 | 30 | 20 | 0.2, 0.3, 0.4, 0.5 |

Scheme | Scheme 1 | Scheme 2 | Scheme 3 | Scheme 4 | Scheme 5 |
---|---|---|---|---|---|

Grid number | 101,342 | 154,683 | 201,679 | 284,813 | 349,866 |

Mass flow rate (kg s^{−1}) | 2.41 | 2.46 | 2.49 | 2.50 | 2.50 |

**Table 3.**Comparison between simulated and experimental values for mass flow rate under different differential pressures.

Inlet Pressure (MPa) | Outlet Pressure (MPa) | Mass Flow Rate | ||
---|---|---|---|---|

Measured (kg s^{−1}) | Simulated (kg s^{−1}) | Difference (%) | ||

0.15 | 0.10 | 1.64 | 1.70 | 3.66 |

0.20 | 0.10 | 2.38 | 2.49 | 4.62 |

0.25 | 0.10 | 2.43 | 2.53 | 4.12 |

0.30 | 0.10 | 2.42 | 2.54 | 4.96 |

0.35 | 0.10 | 2.43 | 2.55 | 4.94 |

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**MDPI and ACS Style**

Tang, P.; Juárez, J.M.; Li, H. Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method. *Water* **2019**, *11*, 2194.
https://doi.org/10.3390/w11102194

**AMA Style**

Tang P, Juárez JM, Li H. Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method. *Water*. 2019; 11(10):2194.
https://doi.org/10.3390/w11102194

**Chicago/Turabian Style**

Tang, Pan, Juan Manzano Juárez, and Hong Li. 2019. "Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method" *Water* 11, no. 10: 2194.
https://doi.org/10.3390/w11102194