Abstract
With the decrease of oil and gas resources on land, increased attention has been paid to multiphase oil–gas exploitation and the transportation technology represented by oil–gas multiphase pumps. The helical–axial multiphase pump has become the focus of research on oil and gas mixed transmission technology due to its relatively high operating efficiency and adaptability to a wide range of gas volume fraction changes. In order to investigate the thickness variation in the air foil from the hub to the shroud of the blade on the mixture transportation characteristics of the gas–liquid two-phase flow in a helical–axial pump, the thickness ratio coefficient ξ was introduced, and the hydraulic performance of the single compression unit with different thickness ratio coefficients was investigated. A single compression unit including an impeller, diffuser, inlet section and outlet section of a helical–axial multiphase pump. The hydraulic performance including the hydraulic head and efficiency was investigated by numerical simulation with the Eulerian multiphase model and the shear stress transport (SST) k-w turbulence model. In order to demonstrate the validity of the numerical simulation approach, the hydraulic head and efficiency of the basic model was measured based on a gas–liquid two-phase flow pump performance test bench. The simulation results agreed well with the experimental results; the error between the simulation results and experimental results of different inlet gas volume fractions was within 10% at the design point, which indicated the numerical simulation method can be used in the research. The thickness ratio coefficient ξ, which was taken as a variable, and the aggregation degree λ of the gas were introduced to analyze the gas–liquid mixture transportation characteristics of the pump. The thickness ratio coefficient was selected in a range from 0.8 to 1.8. The results showed that, for the same hub thickness, the head coefficient and efficiency increase, and the aggregation degree of gas decreases with the decreasing of the thickness ratio coefficient. The head coefficient of the modification multiphase pump was 5.8% higher in comparison to the base pump while the efficiency was 3.1% higher than that of the base pump, the aggregation degree of this model was the lowest, which was 30.3%; the optimal model in the research was the model of scheme 1 with ξ = 0.8. The accumulation of gas in the flow passage of the impeller could be delayed to the trailing edge of the blade by adjusting the thickness ratio coefficient, which produced a super-separated airfoil for helical–axial multiphase pumps and effectively ensured reliable operation under high gas volume fraction conditions. The accumulation area of gas was consistent with the area in which the gradient of turbulent kinetic energy was large.
Highlights
With the continuous development of society, oil field exploitation and transportation technology requirements in industrial applications are continually increasing
Lee et al [26] presented a procedure for the design optimization of a multiphase pump, with the evaluation of influences performed by using the 2K factorial method and the efficiency of multiphase pump derived by using the response surface approximation (RSA) model; the results showed the method was effective for improving the performance of multiphase pumps, which suggests guidelines for the high-performance design of a multiphase pump through numerical optimization techniques
Thickness schemes under the designed working condition when the inlet gas volume fraction was Figure 11 shows that when δhmax remained unchanged and δsmax increased—i.e., reducing the thickness
Summary
With the continuous development of society, oil field exploitation and transportation technology requirements in industrial applications are continually increasing. The first is the twin-screw multiphase pump; the advantage of this is that the gas–liquid two-phase medium is more stable and the change in gas volume fraction has little effect on the performance of the pump. The disadvantage is that the conveying flow is low, and it is sensitive to particles such as sediment This type of pump has low reliability, short lifespan and its maintenance is inconvenient [2]. When the centrifugal pump conveys the gas–liquid two-phase medium with a certain inlet gas volume fraction, the efficiency will drop sharply and it becomes difficult even to maintain the operation of the pump [3]. The application of multiphase pumps is an ideal choice for gas–liquid two-phase transportation in the petroleum industry.
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