Sand Particle Erosion In Vertical Slug/Churn Flow

Solid particle erosion can result in major pipeline failures, economic losses and more importantly safety and environmental issues. Erosion in multiphase flow is not widely understood and previous work has mostly focused on cases where the carrier fluid is single phase. There are different multiphase flow regimes, and amid them, churn flow appears frequently in piping systems such as risers, jumpers and flow spools. Furthermore, elbows have broad applications in the oil and gas industry, and they are subject to sand particle erosion damage. Therefore, the study of erosion in elbows, while the superficial velocities of the carrier fluids are in the range so that the flow pattern is churn flow, is of utmost importance. Initially, experimental tests were carried out in order to investigate sand particle erosion in a 76.2 mm ID standard vertical-horizontal (V-H) elbow. A novel non-intrusive ultrasonic device was implemented to attain erosion patterns under different flow conditions. The effects of superficial gas and liquid velocities, particle size and liquid viscosity on erosion rate were investigated. The results were compared to the available data of erosion rates in a horizontal-horizontal (H-H) elbow with the same size of the elbow employed here. The most striking outcome to emerge from the comparisons was that erosion rates in the V-H elbow are significantly higher than those in the H-H elbow. A challenging area in the field of multiphase flow is the study of churn flow. According to the multiphase flow community, churn flow has not been widely investigated in intermediate and large diameter pipes at high gas and liquid flow rates. In order to better understand churn flow, a series of experiments was performed to study upward vertical air--water flow in a 76.2 mm I.D. pipe. Superficial gas velocities ranging from 10 to 38 m/s and four superficial liquid velocities (0.30, 0.46, 0.61 and 0.76 m/s) were employed. The experimental data points were mostly located in churn flow and at the transition between churn and annular flow. A dual 16x16 Wire Mesh Sensor (WMS) was used to obtain the temporal/spatial variations of phase distributions over the pipe cross-section at one specific axial location (L/D = 236). Sequences of phase distributions, axially sliced images, virtual 3-D images as well as void fraction time series were used to distinguish between different interfacial structures such as slugs and huge waves. Results showed that huge waves occur with either a continuous gas core with a distinct boundary between two phases or a core with a gas--liquid mixture. Furthermore, velocities and frequencies of interfacial structures were obtained. Results were qualitatively and quantitatively consistent with the previous findings available in literature. Undoubtedly, gas-liquid multiphase flow can be observed within different industrial processes. Hence, it is essential to have the ability of comprehensive analysis of gas-liquid flow. However, analyzing this kind of flow is not always simple because of the complex nature. In fact, gas-liquid multiphase flows can acquire different patterns and also are affected by various factors. Thus, from an experimental point of view, its investigation requires a great deal of endurance. Furthermore, through experiments, it is not always possible to obtain information regarding all parameters of interest, as they are numerous. An alternative method for scrutiny of gas-liquid flow can be Computational Fluid Dynamics (CFD). One key advantage of utilizing CFD is that it can deliver a great deal of information. Yet, compared to the experimental method, CFD is not a widely utilized tool due to the computationally-demanding aspect of CFD modeling of multiphase flow. But, the larger point is whether the available CFD multiphase flow models are able to deliver a realistic solution for a complex flow pattern like churn flow? And if yes, to what extent are the results accurate? To shed light on these issues, the Eulerian-Eulerian MultiFluid VOF model offered by ANSYS FLUENT 15 was used to simulate high flow rate air-water multiphase flow in a 76.2 mm pipe upstream of an elbow in the vertical-horizontal configuration. From the CFD simulations, data such as phase distributions, mean void fractions, and average void fraction time series were extracted. They were then compared to experimental Wire Mesh Sensor (WMS) data formerly obtained. Interestingly, evaluation of the model revealed that it was successful in terms of capturing different liquid structures present within the flow and delivering void fraction data which were in agreement with those of experiments. Finally, after validation of the CFD multiphase flow results, particle tracking in multiphase flow was performed to investigate sand particle erosion in churn flow. The obtained results, then, were compared with the erosion experimental data.