Abstract
Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method—coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.
Highlights
Drag reduction by polymers was first discovered by Toms in 1948 [1]
The above numerical framework is used to do the direct numerical simulation (DNS) of the gas-liquid drag-reducing flow in
We wish to analyze the mechanism of drag reduction by polymer in gasliquid two-phase flow
Summary
Drag reduction by polymers was first discovered by Toms in 1948 [1]. It can largely reduce frictional forces in pipe flow by adding only a small amount of macro-molecular polymers, that the polymeric drag reduction can greatly save pumping energy (as high as 80%~90%) [2]. Due to the attractive energy-saving effect, drag reduction by polymer drag-reducing agents (DRAs) has received a lot of attention in the past several years in single-liquid turbulent flow systems. Reported the first commercial application for high polymer drag reduction in a Trans-Alaska oil pipeline. Virk obtained a quantitative relation between polymer concentration and drag reduction rate [4].
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