Flow structure and distribution effects in gas-liquid mixture flows

Air-water mixtures which are assumed to flow homogeneously in a pipe are usually described by a one-dimensional momentum balance. This allows definition of a friction factor in a manner similar to single phase flows. By defining a momentum flux distribution parameter, the momentum balance has been modified to correctly include the etfects of phase and velocity distributions and the effect of these on calculated friction factors has been investigated. Resistivity probes were used to measure void fraction and gas phase velocity distributions for selected vertical and horizontal flow conditions, and these were combined with static pressure measurements to calculate friction factors. For bubbly flows, the inclusion of these distribution effects did not substantially alter friction factor estimates which are approximately 10% above single phase values (for Reynolds numbers based on liquid viscosity).

Friction factor values are shown to be related to flow development with higher values associated with deveioping flows. In particular, high friction factors are associated with the need to break-up bubbles to an “equilibrium” size. In order to experimentally simulate fully developed vertical flows, the highly turbulent nozzle mixer is most suitable while the less turbulent wall-injection type seems appropriate for horizontal flows.