Abstract
Most of the pumps working under two phase flows conditions are used in petroleum industry applications, like electrical submersible pumps (ESP) for hydrocarbon fluids, in chemistry, nuclear industries and in agriculture for irrigation purposes as well. Two-phase flows always deteriorate overall pump performances compared with single flow conditions. Several papers have been published aiming to understand flow physics and to model all the main mechanisms that govern gas pocket formation and surging phenomena. These mechanisms depend on the pump type, the impeller geometry, the rotational speed, design and off-design liquid flow rate conditions, the volumetric gas fraction, the fluid properties and the inlet pressure. In the present paper, a review on two phase performances from various centrifugal pumps designs is presented, mainly based on experimental results. The main focus is devoted to detect the significant geometrical parameters that: (1) Modify the pump head degradation level under bubbly flow regime assumption; (2) Allow single stage centrifugal pumps keep working under two-phase flow conditions with high inlet void fraction values before pump shut down, whatever the pump performance degradations and liquid production rates should be. Because most of the published experimental studies are performed on dedicated laboratory centrifugal pump models, most of the present review is based on air-water mixtures as the working fluid with inlet pressures close to atmospheric conditions. The following review supposes that gas phase is considered as a non-condensable perfect gas, while the liquid phase is incompressible. Both phases are isolated from external conditions: neither mass nor heat transfer take place between the phases.
Highlights
Pump performance always decreases under two-phase flow conditions compared to single-phase ones
A small increase of inlet void fraction leads to a better head coefficient for a slightly higher flow coefficient compared to nominal conditions
For αi from 0 to 7%, degradation level is contribution means that inlet recirculation and pre‐swirl condition does not strongly depend on the increasing when the number of blades decreases except the particular case of Z = 3 for which initial inlet void fraction up to 8% and that disk friction losses are probably not modified inside hub and slope sign is positive
Summary
Pump performance always decreases under two-phase flow conditions compared to single-phase ones. The modification of two-phase flow patterns is driven by separation effects due to blade to blade pressure gradients as well as the Coriolis acceleration, coupled with additional strong radial pressure gradients due to centrifugal forces and local deceleration (Gülich [1]) These effects may be accentuated and reinforced in the axial-to-radial meridional inlet part of pump, because liquid is forced towards the hub, resulting in gas accumulation near the tip radius of the impeller eye. In 1974, Murakami and Minemura [2,3] presented what can be considered as the first and most basic important work on the effects of entrained air on the performance of a centrifugal pump They associated pump performance modifications with two-phase flow patterns inside the impeller and proposed a first approach for pump head drop evaluation. Considerations on different kinds of impeller design are proposed using a compilation of the best design rules found in the present review
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