Effect of the inlet gas volume fraction on the turbulent dissipation characteristics in the multiphase pump

The internal flow of the multiphase pump is complicated owing to its specific structure. To reveal the effect of the inlet gas volume fraction (IGVF) on the turbulent dissipation characteristics, the method of combining numerical simulation based on k-ε turbulence model with experiment was adopted, and the turbulent dissipation of the multiphase pump was quantitatively and qualitatively analyzed in both the pure water and gas-liquid two phases condition. Results showed the vortexes were primarily distributed in the diffusers at different inlet gas volume fractions (IGVFs), near the middle of the first diffuser and the outlet of the next diffuser. At the same time, the larger value of the turbulent dissipation than that in the impellers was concentrated in the inlet and outlet of the impellers and diffusers. In addition, the effect of IGVFs on the turbulent dissipation increased gradually from the hub to the shroud at the inlet section of the first impeller. Moreover, the turbulent dissipation became increasingly unsymmetrical from the hub to the shroud at the outlet section of the first impeller.

Research on cooperative optimization of multiphase pump impeller and diffuser based on adaptive refined response surface method

Multiphase pumps play an important role in the exploitation of natural gas hydrate. Compared with ordinary pumps, they can handle fluids with higher gas volume fraction (GVF). Therefore, it is important to improve the performance of the pump under high GVF. A model pump is designed based on the design theory of axial flow pump and centrifugal pump inducer. The hydraulic performance of the model pump is verified by numerical simulation and experiment. The Sparse Grid method is applied to the design of experiment (DOE), and three different adaptive refined response surface methods (RSM) are applied to the build the approximate model. Refinement points and verification points are used to improve and verify the precision of the response surface, respectively. The model with high precision and high computational efficiency is obtained through comparison and analysis. The multi-objective optimization of the optimal response surface model is carried out by MOGA (Multi-Objective Genetic Algorithm) method. The pressure increment of the optimized model is increased by 38 kPa. The efficiency is significantly improved under large mass flow conditions. The hydraulic performance of the optimized model is compared with that of the basic model. And the reasons that affect the performance of the multiphase pump are analyzed.

Experimental Study of Gas-Liquid Pressurization Performance and Critical Gas Volume Fractions of a Multiphase Pump

Gas entrainment may cause pressurization deterioration and even failure of pumps under conditions of high inlet gas volume fraction (GVF). When the inlet GVF increases to a critical value, an obvious deterioration performance of pump occurs. Air-water pressurization performance and inlet critical GVFs of a centrifugal multiphase pump are investigated experimentally under different inlet pressures and gas-liquid flow rates. To determine the first and second critical GVFs, a new method is proposed by computing the local extreme points of the second derivative of performance curves. New prediction correlations for two critical GVFs are established with relative errors lower than ±10% and ±8%. Boundaries of three different flow patterns and the transition flow rates are determined and presented by critical GVFs on the flow pattern diagram. Moreover, boundaries of maximum pressurization are determined by performance curve clusters and a power function correlation of gas-liquid flow rates when reaching the maximum pressurization is established. With the increase of inlet pressure from 1MPa to 5MPa, two-phase pressurization performance is significantly increased; occurrences of pressurization deterioration are obviously delayed with the first and second critical GVFs increasing by maximums of 8.2% and 7.1%.

Establishing & Estimating Gas-Liquid Performance Characteristics of Multiphase Pumps

Multiphase electric submersible pumps (ESPs) are used to produce gas and liquid in wells with high gas content. These pumps are operated at different speeds, and designed to handle flows with various gas volume fractions (GVFs). This study uses gas-liquid dimensionless parameters to obtain and compare the performance of conventional multiphase pumps. Knowledge of such techniques is important for production engineers, field operators and application engineers to ascertain pump performance for given gas-liquid operating conditions. Gas-liquid performance data for two multiphase pumps with 8.00-inch and 8.62-inch housing diameters were obtained from open literature. The inlet pressure, GVF and rotational speed ranges were 100 to 300 psig, 0 to 0.57, and 3000 to 3600 revolutions per minute (RPM), respectively. The total flow rates varied from 15000 to 60000 barrels per day (BPD). Euler turbomachinery principles for gas-liquid flows were applied to the data to obtain required dimensionless parameters and two-phase dimensionless performance curves for the pumps. The method was tested using dimensionless curves for a given operating condition to obtain pump performance at another operating condition. The results showed that for each rotational speed, the difference in dimensionless pressure between the multiphase pump discharge and inlet decreased with increasing mass-quality-weighted volume flow rate. For each weighted volume flow rate, the difference in pump discharge and inlet dimensionless pressures decreased with increasing intake GVF. The decrease with increasing intake GVF can range between a factor of 3 and 4, depending on the magnitude of the weighted volume flow rate. Using the 3000 RPM data, a two-phase (gas-liquid) dimensionless performance curve was obtained for one of the multiphase pumps with intake GVF and dimensionless volume flow rate parameter as the independent variables. The curve was used to estimate pump performance at 3600 RPM and then compared with the actual reference test data. For the second multiphase pump, two datasets at different intake pressures were used to obtain the effects of intake pressure. The performance for this multiphase pump was a function of dimensionless volume flow rate, intake GVF and intake gas-liquid density ratio. The maximum error in the estimated performance data was within 7%. Overall, the performance of multiphase pumps can be estimated using the technique in this study for the flow conditions analyzed. This study highlights the importance of obtaining dimensionless two-phase performance characteristics of multiphase pumps. Given that these pumps are frequently used in oilfield production operations, capability to determine the pressure boosting performance of the pumps, for given operating conditions, is important to field operating personnel and design engineers. This knowledge benefits the operator to optimally produce hydrocarbons from high gas-content wells and maximize the economic bottom line from the field asset.

Effect of Gas Volume Fraction on the Energy Loss Characteristics of Multiphase Pumps at Each Cavitation Stage

In the process of conveying a medium, when the inlet pressure is low, the cavitation phenomenon easily occurs in the pump, especially in the gas–liquid two-phase working condition. The occurrence of the cavitation phenomenon has a great impact on the performance of the multiphase pump. In this paper, the SST (sheard stress transport) k-ω turbulence model and ZGB (Zwart–Gerber–Belamri) cavitation model were used to simulate the helical axial flow multiphase pump (hereinafter referred to as the multiphase pump), and the experimental verification was carried out. The effect of gas volume fraction (GVF) on the energy loss characteristics in each cavitation stage of the multiphase pump is analyzed in detail. The study shows that the critical cavitation coefficient of the multiphase pump gradually decreases with the increase in GVF, which depresses the evolution of cavitation, and the cavitation performance of the multiphase hump is improved. The ratio of total loss and friction loss to total flow loss in the impeller fluid domain gradually increases with the development of cavitation, and the pressurization performance of the multiphase pump gradually decreases with the development of cavitation. The results of the study can provide theoretical guidance for the improvement of the performance of the multiphase pump.

Transport Performance Improvement of a Multiphase Pump for Gas–Liquid Mixture Based on the Orthogonal Test Method

To improve the transport performance of a rotodynamic multiphase pump for a gas–liquid mixture, we took the head and efficiency index at rated flow rate with 15% inlet gas volume fraction as the indices, and used the orthogonal test design method and CFD technology to optimize. We selected the blade shroud angles at the leading edge and trailing edge, and axial length of the impeller, as well as the inlet incidence angle and blade number of the diffuser, and a total of five factors were used for the orthogonal test. The weight function was used to determine the final trial protocol. The results showed that the blade shroud angle at the trailing edge had the greatest influence on the head and efficiency indices. Under the rated flow rate with a 15% inlet gas volume fraction, the head and efficiency of the optimized pump were increased by 2.81 m and 5.6%, respectively, in comparison to the base pump. After the optimization, the partial fast-speed regions at the inlet of the impeller passage and the partial low-pressure regions on the blade suction side of the impeller disappeared, the accumulation of the gas phase on the blade suction side at the impeller outlet was suppressed, and the pumping performance of the impeller using the gas–liquid mixture was improved greatly. This study provides an important theoretical basis for the optimization and design of a multiphase pump.