Effect of low interfacial tension on flow patterns, pressure gradients and holdups of medium-viscosity oil/water flow in horizontal pipe

In most cited literatures, low-viscosity oils (1-10cP) or high-viscosity oils (greater than 100cP), which formed interfacial tension (IFT) of not less than 20mN/m with water were used in determining the characteristics of oil-water flows and very few studies used medium-viscosity and low-forming IFT oils. Therefore, this experimental study was carried out to investigate the flow characteristics such as pressure gradients, flow patterns and holdups/velocity ratios of medium viscosity oil/water flow with low IFT in horizontal pipe of 30.6mm-ID. The medium viscosity oil is a mineral oil with viscosity and density of about 24cP and 872kgm^-3 respectively at 25°C. Measurement of the flow characteristics covered the range of mixture velocities from 0.1 to 1.5m/s and input oil volume fractions from 0.1 to 0.9. Pressure gradients were found to increase with increase in mixture velocities and input oil fractions. Phase inversions were observed at mixture velocity as low as 0.6m/s where there were sharp increase in the pressure gradients and the phase inversion points occurred between 0.55 and 0.6 input oil fractions for the whole range of flow conditions. In addition, all the flow patterns identified using visual observation and high speed video camera can be grouped into three categories - stratified, dual continuous and dispersed flow. In terms of mixture velocity, the stratified flow was observed up to 0.2m/s, the dual continuous flow was between 0.2 and 0.5m/s and the dispersed flow was observed from 0.6m/s and above. The velocity ratios were found to increase with increase in mixture velocity except at high input oil fractions where oil was the continuous phase. It was also observed that water was the faster flowing phase at low and medium mixture velocities while the reverse was the case at high mixture velocity. Lastly, the results of the study were compared with existing results from previous works which used medium-viscosity but high-forming IFT oils.