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.
The current research of hydrodynamic bearing in blood pump mainly focuses on the bearing structure design.Compared with the typical plane slider bearing and Rayleigh step bearing,spiral groove bearing has excellent performance in load-carrying capacity.However,the load-carrying capacity would decrease significantly with increasing flow rate in conventional designs.In this paper,the special treatment is made to the upper spiral groove bearing to make sure that both the circulatory flowing and load-carrying capacity are high.Three-dimensional computational fluid dynamics(CFD) models in the space between rotor and shaft are developed by using FLUENT software.Effects of groove number,film height and groove depth on load-carrying capacity of the spiral groove bearings are investigated by orthogonal experiment design.The experimental results show that film height is the most remarkable factor to the load-carrying capacity.The variation tendency of load-carrying capacity reveals that the best combination of geometry is the one with groove number of 8,film height 0.03 mm and groove depth 0.08 mm.The velocity and pressure distributions in spiral groove bearings are also analyzed,and the analysis result shows that the distributions are in conformity with the design of the blood pump based on the principle of hydrodynamic bearing.The displacement of the rotor with the best combination parameters is tested by using laser displacement sensors,the testing result shows that the suspending performance is satisfactory both in axial and radial directions.This research proposes a bearing design method which has sufficient load-carrying capacity to support rotor as an effective passive hydrodynamic bearing.
