Experimental Investigations on the Inner Flow Behavior of Centrifugal Pumps under Inlet Air-Water Two-Phase Conditions

Abstract

Centrifugal pumps are widely used and are known to be sensitive to inlet air-water two-phase flow conditions. The pump performance degradation mainly depends on the changes in the two-phase flow behavior inside the pump. In the present paper, experimental overall pump performance tests were performed for two different rotational speeds and several inlet air void fractions (αi) up to pump shut-off condition. Visualizations were also performed on the flow patterns of a whole impeller passage and the volute tongue area to physically understand pump performance degradation. The results showed that liquid flow modification does not follow head modification as described by affinity laws, which are only valid for homogeneous bubbly flow regimes. Three-dimensional effects were more pronounced when inlet void fraction increased up to 3%. Bubbly flow with low mean velocities were observed close to the volute tongue for all αi, and returned back to the impeller blade passages. The starting point of pump break down was related to a strong inward reverse flow that occurred in the vicinity of the shroud gap between the impeller and volute tongue area.

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

“…Inside the volute channel, the air with high air content is mainly distributed far from the impeller. Around the tongue area, the air with high air content is mainly distributed away from the tongue and finally flows to the outlet pipe, which is consistent with the flow pattern distribution observed in the literature [5]. Figure 19 shows the location of eight volute sections.…”

“…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.…”

Research Progress and Prospects of Multi-Stage Centrifugal Pump Capability for Handling Gas–Liquid Multiphase Flow: Comparison and Empirical Model Validation

“…In addition, the rotational speed does not really have any effect on the empirical models for the prediction of both pump performance and surging mechanism. However, the actual pump performance analyses on our two data sets [46] (Table 4) have shown that the performance degradation of the pump running at lower rotational speeds (1000 rpm) was worse compared to higher rotational speeds (1450 rpm). Furthermore, our study has proved that the rotational speed is an important parameter that permits the pump to work better when handling multiphase flow conditions.…”

“…Since then, many researchers, such as Patel [49], Kim [50], Furukawa [51], Sato [52], Andras [53], Takemura [54], Estevam [10], Thum [55], Izturitz [56], Barrios [3,17], Schafer [57,58], Shao [59], Si [46], Cubas [60], have put their efforts towards flow visualization, in order to achieve complete information about bubble behavior within impeller and gaspocket formation. Among these, Patel [49], Kim [50], and Takemura [54], Sato [52], and Thum [55] have discussed, in detail, the bubble agglomeration mechanism where Patel [49] and Kim [50] explained that the accumulation of the bubbles happens due to strong slippage effect between the liquid and gas phase which cannot be ignored inside the impeller flow channel.…”

“…The values of correlation coefficients for mixed-flow pump K-70. In order to analyze the validity and accuracy of previous correlation models, the pump performance test analysis performed by our research team [46] is used for comparison among different empirical models ( Table 2). The data sets shown in Table 4 are taken from a single-stage radial flow centrifugal pump at two different rotational speeds (1000 rpm and 1450 rpm) and gas void ratios (GVRs).…”