Experimental Investigation of Intermittent Gas-Liquid Flows on Solid Particle Transportation in Inclined Pipelines

Solid particle transport in pipelines by fluids is widely encountered in energy industry processes, such as oil production, drilling of horizontal and inclined wells and mining. In contrast to the intensive research effort that has investigated solid transport in horizontal pipelines, limited studies have been published on solid transportation mechanism generated from an initial stationary particle bed in inclined pipes. Consequently the underlying mechanisms responsible for pipe inclination influence on bed-load transport phenomena have not been extensively assessed, particularly for gas-liquid conveying of solid particles. This paper presents an experimental investigation on the influence hydraulic and two phase (gas-liquid) flows on sand dune transportation resulting from a stationary flat bed as a function of (i) pipe inclination, (ii) gas liquid flow rate and (iii) initial sand bed thickness. Experiments were undertaken in a laboratory environment using a 14 m long transparent Plexiglas loop of 24 mm internal diameter to permit optical access. The three phases used were water, air and sand. High speed digital photography was employed to study the flow phenomenon and characteristics of sand bed transportation for the analysis variables (i) to (iii) under consideration. For hydraulic conveying of solid particles, it was found that 1° upward pipe inclination had negligible influence on both the flow phenomenon and solid-liquid flow pattern transition. In contrast, for gas-liquid conveying of solid particles, pipe inclination resulted in considerably different transport phenomena relative to that observed for the horizontal orientation. Differences such as backward bed movement and enhanced particle suspension were observed, and found to be highly gas-liquid ratio dependent. These measurements provide fundamental insights into the influence of upward pipe inclination on bed-load mode solid transportation in a closed conduit.