Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band
Abstract
:1. Introduction
2. Numerical Simulation Method
2.1. Physical Model
2.1.1. Geometric Model
2.1.2. Boundary Conditions
2.2. Meshing
2.3. Mathematical Model
2.3.1. Governing Equations
2.3.2. Discrete Phase Model
2.4. Calculation Method
2.5. Grid Independence Test
2.6. Experimental Verification
3. Results and Discussion
3.1. Velocity Distribution
3.2. Turbulence Intensity
3.3. Temperature Distribution
3.4. Vortex Line Distribution
3.5. Attenuation Law of Wall Shear Stress
3.6. Attenuation Law of Swirl Number
3.7. Deposition Law of Hydrate Particles
4. Conclusions
- The swirl flow velocity presents a symmetrical bimodal structure. The two velocity centers gradually move closer to the center of the pipeline and finally merge together with the attenuation of the swirl flow. The axial velocity is an “M” shape in the twisted segment, the peak value is 1/2r away from the pipeline wall, and the axial velocity is a parabolic shape in the rear pipeline segment. The absolute value of radial velocity is relatively small, which is the result of the redistribution of velocity by twisted band and it rapidly drops to 0 m/s in the posterior segment. The tangential velocity is the “M” shape in the twisted band section and the back pipe section. The peak value appears 1/6~1/7r away from the pipe wall.
- Swirl flow can improve the heat transfer efficiency between the pipeline wall and the fluid, which is mainly related to Reynolds number, twist rate, and particle concentration. In the twisted band section, the Nu increases firstly, and it is removed after the twisted band. The Nu decreases and the slowing rate decreases continuously. The increase in Re has a more obvious induction effect on the motion of solid particles, thus Nu increases. With the increase in the volume fraction of particles, the increase rate of Nu number on the wall slows down. The twist rate is smaller, the Nu is larger, and the heat efficiency is higher.
- The turbulence intensity distribution in the twisted band section shows a “W” shape at the center of the rigid main vortex. The vortex in the free vortex area near the twisted band has a small scale and large unstable velocity pulsation, so the turbulence intensity is large. In the merging process of two symmetric vortexes outside the twisted band, the pulsation velocity at the central vortexes is increased, and the turbulence intensity distribution curve shows a “U” shape.
- The swirl direction of hydrate particles is the same as that of the twisted band. The vortex line swirl center begins to appear at both ends of the proximal twisted band, then it moves to the center of the proximal twisted band, and it finally moves to the edge of the pipeline to achieve stability. After leaving the twisted band, the vortex attenuates rapidly. The twist rate Y is smaller, the Re is larger, and the vortex attenuates more slowly. The attenuation rate of vorticity is mainly affected by Re, while the twist rate mainly affects the initial vorticity size. The shear stress is the main reason for the decrease in swirl strength, and the shear stress decreases exponentially in the pipe section with strong swirl flow. The twist rate mainly affects the initial swirl number, but it has little influence on the attenuation rate of swirl flow. The twist rate is smaller, the initial swirl number is larger. The attenuation of swirl flow is mainly related to Re, and the Re is larger, and it is slower. The swirl flow decreases exponentially, and the relation expression between swirl flow attenuation exponent and Re is obtained.
- The hydrate particles are distributed near the pipe wall under the action of centrifugal force generated by the swirl flow. The hydrate particles do not enter the forced vortex region. Due to the effect of shear force, the carrying distance of particles is increased. However, the swirl flow rapidly attenuates with the increase in carrying distance, the swirl radius of the particles decreases, and deposition occurs at the end of the pipe. The twist rate is larger, the swirl flow intensity is smaller, the attenuation is faster, and the particles are more likely to accumulate. In addition, the Re is larger, the cross-section particle distribution is more uniform, and the particle concentration is smaller.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Particle Concentration (%) | Particle Size (mm) | Twist rate Y | Initial Velocity (m/s) |
---|---|---|---|
1~8 | 0.001 | 6.2/7.4/8.8 | 0.5~12 |
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Rao, Y.; Liu, Z.; Wang, S.; Li, L.; Sun, Q. Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band. Entropy 2021, 23, 913. https://doi.org/10.3390/e23070913
Rao Y, Liu Z, Wang S, Li L, Sun Q. Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band. Entropy. 2021; 23(7):913. https://doi.org/10.3390/e23070913
Chicago/Turabian StyleRao, Yongchao, Zehui Liu, Shuli Wang, Lijun Li, and Qi Sun. 2021. "Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band" Entropy 23, no. 7: 913. https://doi.org/10.3390/e23070913
APA StyleRao, Y., Liu, Z., Wang, S., Li, L., & Sun, Q. (2021). Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band. Entropy, 23(7), 913. https://doi.org/10.3390/e23070913