Experimental study of two and three-phase steady flows in inclined rising pipes

Abstract

This paper presents, interrelates, and discusses the main experimental results that have been obtained in three experimental campaigns performed in the Laboratory of Hydraulics, Water Resources and Environment (LHWRE) of Coimbra University in three different configurations of an installation that was built and developed for the study of steady multiphase flows in inclined rising pipes. The first and second configurations, working in pipe steady flow, were prepared to allow original measurements and innovative studies about the liquid flow rate increase, keeping the total head at an upstream inlet chamber of a subsystem initially ruled by gravity, and the gain of total head at the chamber, for given initial liquid flow rates, both due to the air-lift effect caused by gas–liquid two-phase flows in two inclined rising conduits of 35 mm transparent plasticized PVC and of 94.5 mm LDPE. The third configuration was prepared to allow original and innovative measurements and studies about the solids transport in liquid–solids two-phase flows and gas–liquid–solids three-phase flows, both accomplished in an inclined rising 84 mm transparent acrylic pipe, simulating both steady turbulent flows initially governed by gravity and forced in conventional pumping systems. The results of the experiments performed with air, water, sand and fine gravel, with air flow rates between about 0.5 and 4.5 L/s, water flow rates up to about 9 L/s and granular material between 0.425 mm and 7.20 mm show that the presence of a gas phase in steady upward multiphase flows in an inclined pipe improves expressively both the flow performance of the liquid phase and the solids transport, avoiding, in particular, the sedimentation of solid particles. In large municipal or intermunicipal wastewater systems, the gas phase may be the air or oxygen required for sulfide control, which may be injected in steady flow in the base of the rising pipes. The installation may be adapted to transport other fluids, like hydrocarbons, muds from mining or dredging works, for example, or sludge from wastewater treatment plants, developing and expanding the main basic conclusions obtained to a relevant and wide field of several practical applications.