A comparative analysis of upward and downward pressure gradient behaviour in vertical gas-liquid two-phase flows in a large diameter pipe facility

Pressure gradient (PG) is vital in the design/operation of process equipment e.g. in determining pumping requirements and has direct effect on capital and running costs. Here, we report a gas-liquid experimental study using a large diameter pipeline system. Pressure was measured at two locations of each section of the upward and downward flowing sections. PG was then determined for a wide range of superficial velocities: usg = 0-30 m/s and usl = 0.07-1.5 m/s. We found varying trends in pressure gradient behaviour between upward and downward flow under similar conditions: from bubbly to annular flow. We give a theoretical account due to the different physical mechanisms. PG values based on prevailing conditions and flow direction were compared. We show that the satisfactory prediction of PG is highly dependent on flow direction and limits of experimental conditions. These factors can have important implications for the design and operation of fluid pipelines in the process, nuclear and oil and gas industries.