科创中国

Cavitation of centrifugal blood pump is a serious problem accompany with the blocking failure of short inlet cannula.However,hardly any work has been seen in published literature on this complex cavitation phenomenon caused by the coupling effect of inlet cannula blocking and pumps suction.Even for cavitation studies on ordinary centrifugal pumps,similar researches on this issue are rare.In this paper,the roles of throttling,rotation speed and fluid viscosity on bubble inception and intensity in a centrifugal blood pump are studied,on the basis of experimental observations.An adjustable throttle valve installed just upstream blood pump inlet is used to simulate the throttling effect of the narrowed inlet cannula.The rotation speed is adjusted from 2 600 r/min to 3 200 r/min.Glycerin water solutions are used to investigate the influences of kinetic viscosity.Bubbles are recorded with a high-speed video camera.Direct observation shows that different from cavitation in industrial centrifugal pumps,gas nuclei appears at the nearby of vane leading edges while throttling is light,then moves upstream to the joint position of inlet pipe and pump with the closing of the valve.It's found that the critical inlet pressure,obtained when bubbles are first observed,decreases linearly with viscosity and the slope is independent with rotation speeds;the critical inlet pressure and the inlet extreme pressure which is obtained when the throttle valve is nearly closed,fall linearly with rotation speed respectively and the relative pressure between them is independent with rotation speed and fluid viscosity.This paper studies experimentally on cavitation in centrifugal blood pump that caused by the failure of assembled short inlet cannula,which may beneficial the design of centrifugal blood pump with inlet cannula.

Supercavitation in the diesel nozzle increases the instability of droplets in part due to the two-phase mixture,while the effect of cavitation bubbles on the instability of drops is still unclear.In order to investigate the breakup of cavitation bubbles within the diesel droplet,a new mathematical model describing the disturbance growth rate of the diesel bubble instability is developed.The new mathematical model is applied to predict the effects of fluids viscosity on the stability of cavitation bubbles.The predicted values reveal that the comprehensive effect of fluids viscosity makes cavitation bubbles more stable.Compared with the viscosities of air and cavitation bubble,the diesel droplet's viscosity plays a dominant role on the stability of cavitation bubbles.Furthermore,based on the modified bubble breakup criterion,the effects of bubble growth speed,sound speed,droplet viscosity,droplet density,and bubble-droplet radius ratio on the breakup time and the breakup radius of cavitation bubbles are studied respectively.It is found that a bubble with large bubble-droplet radius ratio has the initial condition for breaking easily.For a given bubble-droplet radius ratio(0.2),as the bubble growth speed increases(from 2 m/s to 60 m/s),the bubble breakup time decreases(from 3.59μs to 0.17μs)rapidly.Both the greater diesel droplet viscosity and the greater diesel droplet density result in the increase of the breakup time.With increasing initial bubble-droplet radius ratio(from 0.2 to 0.8),the bubble breakup radius decreases(from 8.86μm to 6.23μm).There is a limited breakup radius for a bubble with a certain initial bubble-droplet radius ratio.The mathematical model and the modified bubble breakup criterion are helpful to improve the study on the breakup mechanism of the secondary diesel droplet under the condition of supercavitation.

目的 探讨微泡增强的超声空化对兔脾脏微循环血流的阻断作用.方法 将15只新西兰白兔等分为微泡组(MB)、治疗超声组(TUS)和微泡超声组(MEUS),分别施以治疗超声或联合微泡.视觉评价和声学密度分析脾脏靶区的超声造影效果,最后做病理检查.结果 MEUS组治疗后造影增强程度降低,呈明显的低灌注区和负性显影区,随着时间推移灌注情况逐渐好转;TUS组及MB组治疗前后造影增强无明显变化.光镜下,MEUS组可见血窦扩张,细胞水肿,淤血及小血栓形成.结论 微泡增强的超声空化可阻断脾脏辐照区域的血流灌注,为今后应用于治疗脾肿大和脾亢提供依据.