Rao Yongchao, Li Lijun, Wang Shuli, Zhao Shuhua, Zhou Shidong
School of Petroleum Engineering, Changzhou University, Changzhou 213164, China.
Key Laboratory of Oil and Gas Storage and Transportation Technology of Jiangsu Province, Changzhou 213164, China.
Entropy (Basel). 2021 Apr 20;23(4):489. doi: 10.3390/e23040489.
The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3-4 times farther than that of the straight flow.
混合管道中的天然气水合物堵塞问题日益严重。水合物堵塞已逐渐成为确保管道运行安全的重要问题。研究了天然气水合物颗粒在螺旋流管道中的沉积和传热特性。采用离散相模型（DPM）模拟固体颗粒的运动，用于模拟含长扭曲带管道中水合物复杂的螺旋流特性。研究了螺旋流管道中气体水合物颗粒的沉积和传热特性。研究了管道内的速度分布、压降分布、传热特性和颗粒沉降特性。数值结果表明，与无长扭曲带的直流相比，有长扭曲带的流场中形成了两个明显的涡旋，涡旋中心速度最大。沿管道方向，两个涡旋从扭曲带附近向管壁移动，可有效携带沉积在壁面上的水合物颗粒。在相同雷诺数下，扭曲率越大，螺旋强度越小，切向速度越小，压降越小。因此，利用螺旋流的作用可尽可能降低压力损失。在直流光流中，努塞尔数呈开口向下的抛物线形状。在管道中心，努塞尔数向管壁方向逐渐减小至最大值，在近壁处，努数的衰减梯度较大。对于螺旋流，努塞尔数呈现的曲线在管道中心为低谷状，在管道直径的1/2处为峰值。随着扭曲率的减小，努塞尔数变大。因此，螺旋流可使温度分布更均匀，防止出现大温差，导致管道壁面大量形成水合物颗粒。螺旋流具有良好的携带效果。在相同条件下，螺旋流携带水合物颗粒的距离比直流远约3 - 4倍。
