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Academic Editor:Ningbo Liao
Department of Industrial Engineering, University of Naples Federico II, Via Claudio 21, 80125 Naples, Italy
Received 23 April 2014; Accepted 27 May 2014; 7 July 2014
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
The analysis of bubbles behavior inside centrifugal pumps is a fundamental issue in several engineering applications. This often represents a bad working condition with respect to single phase one, causing head reduction, efficiency decrease, and higher operational costs in terms of energy and money. Moreover, when gas fraction becomes too high, a gas locking condition is reached, when pump flow rate falls down to zero, and pump doesn't pump.
Petroleum production and nuclear plants are the most typical situation where two-phase flow can occur within centrifugal pumps. In the first case electrical submersible pumps (ESP) show head decrement due to slippage, that is, a difference between gas and liquid velocities. In the last case, for example, in loss of fluid conditions, stream pressure goes down and a two-phase mixture is generated during expansion. In particular in nuclear plants, such as PWR, loss of coolant accident (LOCA) is very dangerous because of liquid radioactivity. The behavior of pumps working with two-phase flow generated by accidental conditions must be studied in order to know pumps limits in anomalous conditions and in order to design pumps that are suitable for working in anomalous conditions.
Another typical situation where two-phase flow can occur is related to geothermal plants exploiting hot water with a considerable content of noncondensable gas, like carbon dioxide, nitrogen, and oxygen.
Several studies are reported in literature dealing with this topic, often based on major assumptions, neglecting the bubble effect on pressure field or liquid phase velocity, moreover, regardless to possible bubble fragmentation or coalescence phenomena.
One of the first studies was performed numerically and experimentally by Schrage and Perkings [1], considering the single bubble motion in a rotating annulus, subject to buoyancy, virtual mass, and drag forces, and neglecting bubble interaction. Experimental results showed a satisfactory agreement with numerical results.
Other studies followed by Runstadler [2], Mikielewicz et...