Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump units.The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model.UDF(User Define Function)programs such as structural dynamics equations,alternating load equations,and pressure disturbance equations are embedded in numerical calculations,and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology.The results show that when the pressure disturbance occurs at the inlet,as the amplitude and period of the disturbance increase,the film thickness gradually decreases.And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner.The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude.The mutual interference between enhanced waves does not have a significant impact on the film thickness,while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes,and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values.Compared with pressure disturbance conditions,alternating load conditions have a more significant impact on film thickness and leakage.During actual operation,it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

High-speed experimental photography of collapsing cavitation bubble between a spherical particle and a rigid wall

The synergetic effects between cavitation bubbles and silt particles on the damages of materials are essential problems in fluid machineries. For studying the underlying microscopic mechanisms, in the present paper, the dynamic behaviors of a single cavitation bubble between a spherical particle and a rigid wall are experimentally investigated with a high-speed camera. The results indicate that the existence of the particle can affect the bubble shape during collapse and significantly accelerate the collapse velocity of the bubble. The influences of the particle size, the distance between the bubble and the particle and the distance between the bubble and the rigid wall on the phenomena are qualitatively and quantitatively analyzed. These parameters can prominently affect the collapse velocity of the bubble(especially its maximum value).

Numerical investigation of the interactions between a laser-generated bubble and a particle near a solid wall

The interactions between the bubbles and the particles near structures are important issues for the applications of the cavitation in the fluid machinery.To study the hidden microscopic mechanisms,a numerical method for simulating the laser-generated bubble between the solid wall and a particle is developed in this paper with considerations of the viscosities and the compressibility of the gas and the liquid phases,as well as the surface tension between them.The gas-liquid interface is tracked by the coupling level set and the volume of fluid(CLSVOF)method.The numerical results clearly reveal that the particle can influence the cavitation bubble behaviors.The potential damage of the nearby structures is numerically quantified in terms of the wall pressure,which helps better understand the synergetic effects of the particle on the cavitation.The effects of three dimensionless parameters on the wall pressure are also investigated,especially,on the peak pressure,namely,γ1(defined as L_(1)/R_(max),where L_(1)is the distance from the center of the initial bubble to the solid wall and R_(max)is the maximum bubble radius),γ_(2)(defined as L_(2)/R_(max),where L_(2)is the distance from the lower surface of the spherical particle to the initial bubble center)andθ(defined as Rp/R_(max),where Rp is the spherical particle radius).Further numerical results show that these parameters play a dominant role in determining the peak pressure.When y_(1)<1.00,the peak pressure on the solid wall during the bubble collapse is mainly resulted from the liquid jet.Whenγ1>1.00,the peak pressure is caused by the shock wave.With the increase ofθor decrease ofγ_(2),the peak pressure increases.Whenγ_(2)>2.00,the effect of the particle on the bubble behavior can be neglected.

Dextran Gadolinium Complex Containing Folate Groups as a Potential Magnetic Resonance Imaging Contrast Agent

Folate-containing dextran ligand （FA-Dextran-DTPA） was synthesized by the incorporation of diethylenetriamine- pentaacetic acid （DTPA） and folate （FA） as a tumor-targeting group into dextran as a polymer carrier. This ligand was further reacted with gadolinium chloride to make a dextran gadolinium complex FA-Dextran-DTPA-Gd. The ligand and its gadolinium complex were characterized by 1H-NMR, FTIR, UV-Vis, average particle sizes and zeta potential, as well. In vitro properties including relaxivity, cytotoxicity assay, cellular uptake assay, and magnetic resonance imaging （MRI） were also evaluated. Compared with Gd-DTPA, FA-Dextran-DTPA-Gd possessed obviously higher relaxation effectiveness and lower cytotoxicity to HeLa cells. FA-Dextran-DTPA-Gd had a high affinity to the H460 and MDA-MB-231 tumor cells and can be taken up selectively by these tumor cells. Moreover, FA-Dextran-DTPA-Gd showed enhanced signal intensities （SI） of MRI and enhanced the contrast of MR images of tumor cells. These results indicated that FA-Dextran-DTPA-Gd showed the potential as a tumor-targeting contrast agent in MRI.