A Study of the Interface Fluctuation and Energy Saving of Oil–Water Annular Flow

Oil–water annular flow is an efficient method of heavy oil transportation for energy-saving. To deeply study the influencing factors of the energy savings of oil–water annular flow, this paper compares the interface fluctuation and energy-saving situation of oil–water annular flow under different pipe structures (such as straight pipe, sudden-contraction pipe, and elbow pipe), flow parameters, and fluid properties. In the straight pipe, the flow parameters can impact the oil–water annular flow pattern and the energy savings, and the interface fluctuation is consistent with the energy savings. The stable oil–water core annular flow has slight interface fluctuation and significant energy savings. At the same time, the influences of pipe structure and fluid properties on energy saving are also analyzed. In the sudden-contraction pipe, the oil–water interface fluctuates, largely due to the sharp changes in flow cross-section, which leads to reduced energy savings. In the elbow, the oil–water interface fluctuates greatly due to the influence of centrifugal force caused by flow direction variation, and also leads to a decline in energy savings. The effects of oil property or annulus liquid property on the interface fluctuates, and the energy savings are analyzed; reducing surface tension is an effective measure to provide an energy-saving effect. These results can provide a reference for the design of heavy-oil-transportation pipelines, the analysis of interface fluctuation, and the energy-saving evaluation of oil–water annular flow.