Hydrogenated diamondlike carbon (H-DLC) coatings provide excellent wear resistance and low friction for bearing applications. However, the use of such coatings with aqueous lubricants could pose some difficulties due to the hydrophobic nature of the surface. A thrust bearing tribometer was used to compare performance of hydrophilic and hydrophobic surfaces in hydrodynamic lubrication with a mixture of water and glycerol as the lubricant. Hydrophobic surfaces on both runner and bearing were achieved with the deposition of H-DLC films on titanium alloy surfaces. Hydrophilic surfaces were created through modification of H-DLC surface with covalently bonded heparin. Several possible combinations of hydrophobic and hydrophilic surface conditions were used on the bearing and runner surfaces to provide full-wetting, partial-wetting, and half-wetting conditions. The experimental results confirmed that load support is still possible, when the bearing is half-wetted or partially wetted. However, the full-wetted bearing combination (i.e., Reynolds no-slip boundary condition) provided the highest load support. Introduction of slip at the surface resulted in a lower measured torque. Heparin treatment resulted in a lower than expected static friction and friction in full lubrication regime. The durability of coated surfaces was evaluated in a series of start–stop tests and in impact tests. The results confirmed that the coatings are stable and survive the test regiment that exceeded 50 test cycles; whereas the uncoated titanium alloy bearing surfaces were damaged after ten test cycles.

The MiTiHeart (MiTiHeart Corporation, Gaithersburg, MD, USA) left ventricular assist device (LVAD), a third-generation blood pump, is being developed for destination therapy for adult heart failure patients of small to medium frame that are not being served by present pulsatile devices. The pump design is based on a novel, patented, hybrid passive/active magnetic bearing system with backup hydrodynamic thrust bearing and exhibits low power loss, low vibration, and low hemolysis. Performance of the titanium alloy prototype was evaluated in a series of in vitro tests with blood analogue to map out the performance envelop of the pump. The LVAD prototype was implanted in a calf animal model, and the in vivo pump performance was evaluated. The animal's native heart imparted a strong pulsatility to the flow rate. These tests confirmed the efficacy of the MiTiHeart LVAD design and confirmed that the pulsatility does not adversely affect the pump performance.

For energy independence to become a reality, whether through the more effective use of US natural resources such as natural gas or through the continued development of the hydrogen economy, efficient and reliable large-scale compressors are needed to enhance the existing pipeline infrastructure that moves energy storing gases from production sites to end user locations. Oil-free, non-contacting seal and bearing technologies are critical to the successful development of new high efficiency and power dense compressors. Similarly with increasing emphasis on energy conservation, power and propulsion gas turbine engines will require advanced low leakage seals and may take advantage of efficiencies offered by compliant foil gas bearings. When properly applied these oil-free, non contacting technologies will have a positive impact on the operating efficiency and life of compressor and gas turbine engine systems. The overall objective of this paper is to present recent advances in compliant foil bearings and seals that make them attractive for a wide array of systems. The paper documents the design approach that includes analytical trade off studies to establish overall requirements followed by an experimental program to demonstrate the ability of the identified foil technology to meet the machine requirements. A summary of advancements in foil bearing load carrying capacity, size scaling from 6 mm to 150 mm in diameter, the ability to operate under shock loads greater than 40 g as well as under steady side loads with two different gases and finally the ability to operate at temperatures greater than 750 C will be presented. Data will also be presented showing the application of foil bearings to several different machines. Similarly, results from design, fabrication and testing of compliant foil radial and axial face seals will be discussed. Data from axial face seals testing at differential pressures, surface velocities, and normal loads greater than 675 kPa, 350 m/s, and 1100 N respectively will be presented to demonstrate non-contacting performance. Results of subcomponent testing will also be presented to demonstrate the capability of the face seal to accommodate axial excursions of up to 3.8 mm. Compliant foil radial seal testing in sizes ranging from approximately 60 to 215 mm in diameter under differential pressures to 690 kPa and surface velocities to 340 m/s will be presented and compared to prediction. The culmination of the work presented supports the application of compliant foil bearings and seals in a wide array of advanced machinery.

Design of a blood pump with a magnetically levitated rotor requires rigorous evaluation of the magnetic bearing and motor requirements and analysis of rotor dynamics and hydraulic performance with attention to hemolysis and thrombosis potential. Given the desired geometric dimensions, the required operating speed, flow in both the main and wash flow regions, and magnetic bearing performance, one of several design approaches was selected for a new prototype. Based on the estimated operating speed and clearance between the rotor and stator, the motor characteristics and dimensions were estimated. The motor stiffness values were calculated and used along with the hydraulic loading due to the fluid motion to determine the best design for the axial and radial magnetic bearings. Radial and axial stability of the left ventricular assist device prototype was verified using finite element rotor dynamic analysis. The analysis indicated that the rotor could be completely levitated and spun to the desired operating speed with low power loss and no mechanical contact. In vitro experiments with a mock loop test setup were performed to evaluate the performance of the new blood pump prototype.