Hamidreza Karami

Experimental Investigation of Three-Phase Low-Liquid-Loading Flow

Although many different studies have been conducted on gas/ liquid multiphase flow, only a very small number of three-phase flow studies, especially for low-liquid-loading flows, can be found. These studies are mainly experimental, and focused on two-phase flow in small-diameter pipelines. The coexistence of thin films of water along with oil in production systems is very commonly observed in wet-gas pipelines. The existence of the second liquid phase influences all of the flow characteristics. The three-phaseflow behavior can be considered as a combination of gas/liquid and oil/aqueous phase interactions. Meng et al. (2001) conducted two-phase-flow experiments for oil/air flow in a 2-in.-ID pipe. They observed a surprising decrease in liquid holdup and pressure gradient when the vSL was increased. They attributed this decrease to the increase in droplet entrainment. They also developed a correlation for interfacial friction factor. Fan (2005) used two experimental facilities with IDs of 2 and 6 in., respectively, to conduct two-phase water/air low-liquid-loading experiments. Fan observed stratified smooth and stratified wavy flow patterns in his experiments with the 6-in.-ID facility. With the 2-in.-ID facility, in addition to stratified flow patterns, an annular flow pattern was observed. Fan used the acquired experimental data to develop new closure relationships for mechanistic modeling. These closure relationships included wetted-wall fraction, liquid-wall friction factor, and interfacial friction factor. Later, Dong (2007) modified the 6-in.-ID facility of Fan (2005) to conduct low-liquid-loading three-phase-flow experiments. Water, air, and oil with a viscosity of 13 cp were the flowing fluids. This is a relatively high oil viscosity compared with the commonly observed values in wet-gas pipelines, and the results may not be representative for wet-gas pipeline systems. The distribution of oil and water in liquid phase for different flowing conditions was observed and categorized. In addition, a model comparison was provided for flow characteristics. Recently, Gawas (2013) used the same 6-in.-ID facility of Dong (2007) to investigate the characteristics of three-phase low-liquidloading flow. Gawas conducted his experiments by use of an oil with a viscosity of 1.3 cp for different values of water cut, and developed correlations for entrainment of liquid droplets in gas phase for twoand three-phase flows. He also analyzed the droplet-size distribution and developed a correlation for interfacial wave celerity. In addition, several studies have been conducted in other research centers to analyze low-liquid-loading flow. A summary of these studies is presented in Gawas (2013). In the current study, the facility of Gawas (2013) is used. The main objective of this research is to study low-liquid-loading threephase flow, and the targeted flow parameters are liquid holdup, water holdup, wave pattern, and pressure gradient. The experimental results for different flow characteristics are analyzed and evaluated to improve understanding of the flow phenomena. In addition, the commonly used models are evaluated by use of the acquired experimental data.

CFD Simulations of Low Liquid Loading Multiphase Flow in Horizontal Pipelines

Low Liquid Loading is a very common occurrence in wet gas pipelines where very small amounts of liquid flow along with the gas, mainly due to condensation of hydrocarbon gases and water vapor. The effects of low liquid loading on different flow characteristics, and flow assurance issues such as pipe corrosion prove the necessity of analyzing the flow behavior in more depth. In this study, CFD simulations are conducted for a horizontal pipe where liquid and gas are supplied at separate constant rates at the inlet. The liquid is introduced at the bottom to help shorten the developing section. The simulations are conducted with Ansys Fluent v14.5 using Volume Of Fluid (VOF) as the multiphase model. The analysis targets, mainly, the shape of the interface, velocity fields in both liquid and gas phases, liquid holdup, and shear stress profile. On the other hand, experiments are conducted in a 6-inch ID low liquid loading facility with similar testing condition. Experiments are conducted with water or oil as the liquid phase for a liquid volume fraction range of 0.0005–0.0020 of the inlet stream. For all cases, several flow parameters are measured including liquid holdup and interface wave characteristics. A comparison is conducted between CFD simulation results, model predictions, and experimental results, and a discussion of the sources of discrepancy is presented. Overall, the results help understand the low liquid loading flow phenomenon.Copyright