Measurement and modelling of oil volume fraction and velocity profiles in vertical bubbly oil water flows

A series of experiments was carried out using a dual sensor conductance probe to measure the local axial oil velocity distribution and the local oil volume fraction
distribution in vertical, oil in water bubbly flows in an 80mm diameter vertical pipe.
Values of the water superficial velocity were in the range 0.276 ms-1 to 0.417ms-1,values of the oil superficial velocity were in the range 0.025ms-1 to 0.083ms-1 and
values of the mean oil volume fraction were in the range 0.047 to 0.205. For all of the flow conditions investigated it was found that the axial velocity profile of the oil droplets had a ‘power law’ shape which was very similar to the shape of the air velocity distributions previously observed for air-water bubbly flows at similar flow conditions. It was also found that the shape of the local oil volume fraction distribution was highly
dependent upon the value of the mean oil volume fraction. Mathematical modelling showed that the shapes of the observed local oil fraction distributions were a result of
diffusion and of hydrodynamic forces acting upon the oil droplets. For bref < 0.08 the net hydrodynamic force on the droplets was towards the pipe centre whilst for
bref > 0.15 the net hydrodynamic force on the droplets was biased towards the pipe wall. The nature, and relative strength, of each of the hydrodynamic forces acting on the oil droplets is discussed.