in Wiley Online Library (wileyonlinelibrary.com).Phase-resolved PIV measurements were carried out to provide a thorough characterization of the flow and mixing dynamics occurring in a cylindrical shaken bioreactor when operating conditions such as medium height h, shaking rotational speed N, orbital shaking diameter d o , and cylinder inner diameter d i , are varied. A scaling law based on the aspect ratio h/d i , on the orbital to cylinder diameter ratio d o /d i , and on the Froude number Fr = 2(N) 2 d o /g, is derived to predict the incipience of flow transition occurring when the free surface orientation starts to exhibit a phase delay to the shaker table position along its orbit; depending on the combination of Fr, d o /d i and h/d i the transport phenomena in the bioreactor are controlled by a horizontal toroidal vortex, or by a vertical one precessing around the cylinder axis. The free surface interfacial area was directly measured by image analysis to assess oxygen transfer potential and compared to an analytical solution valid for low Fr.

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PurposeThe physiological flow dynamics within the Valsalva sinuses, in terms of global and local parameters, are still not fully understood. This study attempts to identify the physiological conditions as closely as possible, and to give an explanation of the different and sometime contradictory results in literature.MethodsAn in vitro approach was implemented for testing porcine bio-prosthetic valves operating within different aortic root configurations. All tests were performed on a pulse duplicator, under physiological pressure and flow conditions. The fluid dynamics established in the various cases were analysed by means of 2D Particle Image Velocimetry, and related with the achieved hydrodynamic performance.ResultsEach configuration is associated with substantially different flow dynamics, which significantly affects the valve performance. The configuration most closely replicating healthy native anatomy was characterised by the best hemodynamic performance, and any mismatch in size and position between the valve and the root produced substantial modification of the fluid dynamics downstream of the valve, hindering the hydrodynamic performance of the system. The worst conditions were observed for a configuration characterised by the total absence of the Valsalva sinuses.ConclusionThis study provides an explanation for the different vortical structures described in the literature downstream of bioprosthetic valves, enlightening the experimental complications in valve testing. Most importantly, the results clearly identify the fluid mechanisms promoted by the Valsalva sinuses to enhance the ejection and closing phases, and this study exposes the importance of an optimal integration of the valve and root, to operate as a single system.

in Wiley InterScience (www.interscience.wiley.com).The precession of macroinstability (MI) vortices in stirred vessels has been investigated with vortex tracking methodologies, and utilized to enhance mixing performance. The techniques used are presented and employed to determine the instantaneous and average location, size and vorticity of the MI vortex for Re ¼ 3,200 and 32,000 in 80 and 294 mm dia. vessels stirred by a Rushton impeller. Measurements of mixing time are performed in a 588 mm dia. vessel with surface insertion of a passive scalar tracer either inside or outside the precessing MI vortex. The data indicate that in-vortex insertion can result in a mixing time reduction of 20%, and even possibly 30%.