Using a visualization prototype built from original Electrical Submersible Pumps (ESP) components and with minimal geometrical modifications, a pioneer experimental procedure was developed and conducted to address the viscous effect on liquid-gas two-phase flow through these types of pumps.

Based on dimensionless groups that govern centrifugal pump single-phase performance, two-phase experiments were conducted at different shaft speeds (15, 25, 30 Hz), non-slip void fractions (up to 5%) and viscosity values (46 to 161 cP), while liquid rates were kept constant at 60% of the maximum rate at the defined shaft speed. High speed video footage was taken from the entire impeller flow channel and stage incremental pressure was measured.

The authors identified four liquid-air flow patterns inside the impeller channels: Agglomerated Bubbles, Gas Pocket, Segregated Gas and Intermittent Gas. By comparing the images with the differential pressure data, it was concluded that the Agglomerated Bubble pattern is responsible for the initial head degradation and that the surging event coincides with the Gas Pocket structure, indicating that this is an interface instability problem. Another conclusion made was that the increase in viscosity caused surging to occur at lower void fractions which could be compensated by increasing rotational speed.

The significance of this work is given by the fact that several authors have investigated centrifugal pump performance under two-phase flow; however, previous experiments have been conducted only with water as the liquid, thus neglecting the viscous effect on the two-phase flow mixture. In most of the petroleum industry's applications ESPs operate with oil and natural gas. Thus presenting a knowledge gap between scientific research and field applications, this starts to be addressed in this work.

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