Two-phase flows in pumps Descriptions and consequences

Two-phase pumping is generally found in applications involving the pumping of hydrocarbons, chemically-charged fluids, foodstuffs, drinking water or irrigation. This is also the case with emergency pumping systems for nuclear safety, or when pumps are used in the event of flooding. In the case of more conventional pumps, this type of situation can arise, for example, when the bearings are in poor condition, allowing gas to pass through the seals.

This article does not deal with cavitating flows. Although the latter are part of two-phase flows within a pump, the physical phenomena that cause phase changes are associated with changes in local pressure within the pump. This is not taken into account in the present study, as the two-phase mixture is considered to already exist upstream of the pump, even at high initial pressures.

For the sake of simplicity, we have chosen to present the consequences of a two-phase flow, and more specifically of an initial immiscible liquid-gas mixture, in order to describe and understand the phenomena involved. These types of flows are always very difficult to grasp, given the diversity of geometries encountered (radial, mixed or axial machines), their configuration (single or multi-stage), the structures and interactions between phases, and also for the large number of variables involved. Approaches to modeling the behavior of mixtures in pumps exist, but are not presented in this article.