Plasma skimming efficiency of human blood in the spiral groove bearing of a centrifugal blood pump

This work investigates the plasma skimming effect in a spiral groove bearing within a hydrodynamically levitated centrifugal blood pump when working with human blood having a hematocrit value from 0 to 40%. The present study assessed the evaluation based on a method that clarified the limitations associated with such assessments. Human blood was circulated in a closed-loop circuit via a pump operating at 4000 rpm at a flow rate of 5 L/min. Red blood cells flowing through a ridge area of the bearing were directly observed using a high-speed microscope. The hematocrit value in the ridge area was calculated using the mean corpuscular volume, the bearing gap, the cross-sectional area of a red blood cell, and the occupancy of red blood cells. The latter value was obtained from photographic images by dividing the number of pixels showing red blood cells in the evaluation area by the total number of pixels in this area. The plasma skimming efficiency was calculated as the extent to which the hematocrit of the working blood was reduced in the ridge area. For the hematocrit in the circuit from 0 to 40%, the plasma skimming efficiency was approximately 90%, meaning that the hematocrit in the ridge area became 10% as compared to that in the circuit. For a hematocrit of 20% and over, red blood cells almost completely occupied the ridge. Thus, a valid assessment of plasma skimming was only possible when the hematocrit was less than 20%.

Reducing friction power losses of flywheel energy storage systems using PTFE composites: A technical note

This technical note aims to reduce friction power loss of flywheel energy storage system (FESS) supported by hydrodynamic spiral groove bearing and permanent magnetic bearing (PMB). An approach is proposed to fabricate the spiral groove bearing using polytetrafluoroethylene (PTFE) composite. A test rig is developed to test tribological properties of the spiral groove PTFE bearings. Also, two PTFE composites (C-PTFE: 80 vol.% PTFE filled with 20 vol.% graphite; C-Cu-PTFE 50 vol.% PTFE filled with 20 vol.% graphite and 30 vol.% copper powder) are tested. Results show that the friction power losses of the C-PTFE and C-Cu-PTFE bearings are lower than that of the traditional albronze (CuAl) bearing in the whole speed range. In addition, the spiral groove PTFE bearings show an excellent friction-reducing property under boundary or mixed lubrication condition. Finally, a case study is given to show the spiral groove PTFE bearing is capable of reducing the friction power loss of the FESS.

Dynamics of Flywheel Energy Storage System With Permanent Magnetic Bearing and Spiral Groove Bearing

Developing a flywheel energy storage system (FESS) with permanent magnetic bearing (PMB) and spiral groove bearing (SGB) brings a great challenge to dynamic control for the rotor system. In this paper, a pendulum-tuned mass damper is developed for 100 kg-class FESS to suppress low-frequency vibration of the system; the dynamic model with four degrees-of-freedom is built for the FESS using Lagrange's theorem; mode characteristics, critical speeds, and unbalance responses of the system are analyzed via theory and experiment. A comparison between the theoretical results and the experiment ones shows that the pendulum-tuned mass damper is effective, the dynamic model is appropriate, and the FESS can run smoothly within the working speed range.