(78b) Transport of Water and Oil Droplets Entrained in Gas Phase for Larger Diameter Air-Oil-Water Low Liquid Loading Flow in Horizontal and Near-Horizontal Pipe

This paper describes a study on entrainment of oil and water in gas phase in case of air-oil-water three phase low liquid loading flows.  The experiments were carried out in a 6-in diameter pipe at inclinations of -2, 0 and +2 ° from the horizontal.  An isokinetic sampling probe system was used to measure flux of entrained droplets.  The distribution of entrained drops is highly asymmetric in horizontal flow.  Hence, droplet flux was measured at different locations along the vertical axis of the pipe.  The liquid superficial velocity (v_SL) and gas superficial velocity (v_SG) were varied between 0.005 m/s to 2.5 m/s and 10 m/s to 23 m/s, respectively.  All the three phase experiments were conducted for oil continuous phase and water cut of 0, 10, 20, 40 and 100 %.

The entrainment fraction was highly sensitive to gas flow rate.  The effect of liquid flow rate and inclination was less significant.  Although entrainment fraction tended to increase with change in inclination from -2 to +2°, the effect diminished as gas flow rate increased.  Entrainment of water was higher in air-oil-water three phase flow compared to air-water two-phase flow.  Thus, entrainment of water which is the dispersed phase was enhanced by the oil continuous phase.  The fraction of water in the entrained liquid decreased with increasing distance from bottom of the pipe due to higher settling velocity of water compared to that of oil.

An approach to modeling of the water and oil entrainment is presented assuming homogenous oil-water mixing in the liquid phase.  This approach assumes stratified atomization flow pattern, which is predominant flow pattern for low liquid loading flow conditions.  The approach suggested in current study for determination of entrainment fraction in low-liquid loading fairs better than the available correlations in describing the functional dependence of entrainment fraction on superficial liquid velocity.  This approach is extended to three-phase flow by assuming that the deposition of the entrained water and oil drops takes place independent of each other.  Uniform distribution of water in oil continuous phase is assumed to predict rate of atomization, which matches the experimental observations except at lower gas velocity.  For low gas flow rate (v_SG < 19 m/s) investigated in this study, the proposed correlation over predicts amount of water entrained in the gas phase.