Investigation on the pressure pulsation characteristics in a twin-screw multiphase pump

A three-dimensional gas-liquid two-phase transient numerical model for a twin-screw multiphase pump based on dynamic grid technology was established and validated with experiments. The pump's simulated pressure distributions, velocity fields, and pressure pulsations were analyzed to reveal the mechanisms of pressure transmission and pressure pulsation characteristics. The results indicated that the flow rate of the pump fluctuated twice due to the discharge of the male and female rotors in one cycle. As the inlet gas volume fractions increased, the flow rate decreased, but the pressure pulsations increased. At the engaging positions of the two rotor tips, a sudden pressure drop happened due to the combined effect of both tooth-tip and tooth-flank leakage. When the discharge port opened, the backflow happened; the flow rate and the pressure in the discharge chamber decreased, but the pressure in the working and suction chambers increased. When the suction port closed, a slight compression of the fluid in the low-pressure working chamber occurred, causing a pressure increase in the working chamber. The working chambers inhaled and discharged once in one cycle, so the first harmonic of pressure pulsations at the suction and discharge chamber was two times the running speed. The transient flow due to the simultaneous closing and opening of the suction and discharge ports at both sides of the male and female rotors generated a harmonic of four times the running speed. This study would help to improve the operational stability of twin-screw multiphase pumps.