This research presents theoretical analysis and numerical simulation of combined valves' dynamic characteristics in reciprocating oil-gas multiphase pump. Based on the mathematical model describing valves' motion, a geometric model of pump cavity and combined valves is put forward for numerical simulation in multiphase pump. The simulation is conducted by computational fluid dynamics (CFD) method with its dynamic grid technique. The motion process of suction valve and discharge valve are obtained on the basis of boundary conditions and optimized numerical approaches. And the effects of gas volume fraction (0.1 ∼ 0.9), suction pressure (0.20 ∼ 0.40 MPa) and discharge pressure (1.0 ∼ 3.0 MPa) on valves' motion are reported. The results of pressure distribution, and valves' lift and velocity show that valve plates may cling or rebound and then vibrate after reaching the lift limiter, and the lag angle of one cycle remains 3°under different working conditions. The study could lay theoretical foundation for the design of new type of multiphase pump. ARTICLE HISTORY

In petroleum industry, the stability of multiphase pumping is highly disturbed by the gas' presence with high content and variable working conditions. This paper is focused on studying the whole working cycle of the novel three-cylinder double-acting reciprocating multiphase pump. Based on the theoretical analysis, the method of computational fluid dynamics (CFD) is adopted to simulate the oil–gas flow in reciprocating multiphase pump. The numerical methodology, involving multiphase model, dynamic grid technique and user defined functions (UDF), is used to deal with in the calculation. The transient flow characteristics in pump cavity are obtained, and the flow ripples of reciprocating multiphase pump are analyzed. Furthermore, the effects of different operating parameters, such as suction and discharge pressures, inlet gas volume fraction (GVFi) on the capacity, and stability of pump, are studied. The results could help to develop and optimize the high-efficiency multiphase pump system.

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