Effect of the bileaflet inlet valve angle on the flow of a pediatric ventricular assist device: Experimental analysis.

BACKGROUND: Mechanical heart valves (MHV) and its fluid dynamics inside a pulsatile pediatric ventricular assist device (PVAD) can be associated with blood degradation. In this article, flow structures are analyzed and compared by an experimental investigation on the effect of bileaflet MHV positioned at varying angles in the inlet port orifice of a PVAD. METHODS: Time-resolved particle image velocimetry was applied to characterize the internal flow of the device. St Jude Medical bileaftlet valves were used on the inlet orifice and positioned at 0°, 15°, 30°, 45°, 60°, and 90° in relation to the centerline of the device. Three planes with bidimensional velocity magnitude fields were considered in the analysis with visualization of diastolic jets, device wall washing patterns and flow circulation during emptying or systole of the pump. Also, the washing vortex area, and vertical velocity probabilities of regurgitant flows in the inlet valve were evaluated. RESULTS: The results show that a variation in the angle of the MHV at the inlet port produced distinct velocities, fluid structures, and regurgitant flow probabilities within the device. MHV positioned at an angle of 0° generated the strongest inlet jet, larger vortex area during filling, more prominent outgoing flow, and less regurgitation compared to the angles studied. The presence of unfavorable fluid structures, such as small vortices, and/or sudden flow structure interruption, and/or regurgitation, were identified at 45° and 90° angles. CONCLUSIONS: The 0° inlet angle had better outcomes than other angles due to its consistency in the multiple parameters analyzed.

Effect of SWCNT volume fraction on the viscosity of water-based nanofluids.

Nanofluids have received a great deal of interest in recent years because of their various unique features. According to the findings, the addition of nanotubes to the base materials can drastically alter their properties. In the present work, the viscosity of a typical water-based nanofluid containing single-walled carbon nanotubes is estimated using the molecular dynamics simulation for different volume fractions ranging between 0.557 and 3% at two temperatures (298 K and 313 K). The temperature of the systems is controlled using a Nose-Hoover thermostat. For calculating viscosity, the Green-Kubo equilibrium method is used. The enthalpy, potential, kinetic, and total energies are calculated to determine the system's stability. In addition, the influence of molecular mass on these energies is studied. The nanotube under investigation is an armchair(6,6)-type single-walled carbon nanotube. The results highlight the promise of the molecular dynamics simulation technique as a powerful tool in the prediction of nanofluid properties besides the experimental results. The value of viscosity will decrease as the temperature rises, much like the base fluid. Furthermore, it is shown that the viscosity is proportional to the volume fraction of water-SWCNT nanofluid. According to the results, a new viscosity relationship for volume fractions in the range of ϕ ≤ 3% is proposed. The viscosity, temperature, and volume fraction are all linked together in this equation.