A Comparative Study on Centrifugal Pump Designs and Two-Phase Flow Characteristic under Inlet Gas Entrainment Conditions

Abstract

Capability for handling entrained gas is an important design consideration for centrifugal pumps used in petroleum, chemistry, nuclear applications. An experimental evaluation on their two phase performance is presented for two centrifugal pumps working under air-water mixture fluid conditions. The geometries of the two pumps are designed for the same flow rate and shut off head coefficient with the same impeller rotational speed. Overal pump performance and unsteady pressure pulsation information are obtained at different rotational speeds combined with various inlet air void fractions (α 0 ) up to pump stop condition. As seen from the test results, pump 2 is able to deliver up to 10% two-phase mixtures before pump shut-off, whereas pump 1 is limited to 8%. In order to understand the physics of this flow phenomenon, a full three-dimensional unsteady Reynolds Average Navier-Stokes (3D-URANS) calculation using the Euler-Euler inhomogeneous method are carried out to study the two phase flow characteristics of the model pump after corresponding experimental verification. The internal flow characteristics inside the impeller and volute are physically described using the obtained air distribution, velocity streamline, vortex pattern and pressure pulsation results under different flow rates and inlet void fractions. Pump performances would deteriorate during pumping two-phase mixture fluid compared with single flow conditions due to the phase separating effect. Some physical explanation about performance improvements on handing maximum acceptable inlet two phase void fractions capability of centrifugal pumps are given.Energies 2020, 13, 65 2 of 25 of the flow pattern. The pump performance degrades as the α 0 increase and generates undesired pulsation problems, endangering the operation stability and reliability of the system [4,5]. Therefore, it is especially important to thoroughly study and reveal the internal flow characteristic of centrifugal pumps under gas entrainment conditions. Several pioneering relevant studies on the basic theory, numerical simulation and experiment of how gas-entrainment affects pump performance degradation have been done. Murakami and Minemura [6,7] firstly conducted experimental works and developed a two-phase, one dimensional, flow model. In their research hydraulic-head degradation and abrupt flow-pattern changes were observed as more air entered the system. Furukawa et al. [8,9] designed a centrifugal pump using an outlet impeller blade angle greater than 90 • with a set of tandem blades. They obtained rather good two-phase flow performances, but their design failed at low flow rates. It is also known that open impellers have better capabilities than shrouded ones with respect to two phase flows due to the stronger mixing created by tip blade leakage and induced vortex flows structures (Cappellino et al. [10], Mansour et al. [11]). Flow patterns play an important role affecting hydraulic performance and energy conversion, even in the single phase flow of centrifugal pumps [12]. Releva...

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