Taylor-Couette flow control by amplitude variation of the inner cylinder cross-section oscillation

The hydrodynamic stability of a viscous fluid flow evolving in an annular space between a rotating inner cylinder with a periodically variable radius and an outer fixed cylinder is considered. The basic flow is axis-symmetric with two counter-rotating vortices each wavelength along the whole filled system length. The numerical simulations are implemented on the commercial Fluent software package, a finite-volume CFD code. It is aimed to make investigation of the early flow transition with assessment of the flow response to radial pulsatile motion superimposed to the inner cylinder cross-section as an extension of a previous developed work in Oualli et al. [H. Oualli, A. Lalaoua, S. Hanchi, A. Bouabdallah, Eur. Phys. J. Appl. Phys. 61, 11102 (2013)] where a comparative controlling strategy is applied to the outer cylinder. The same basic system is considered with similar calculating parameters and procedure. In Oualli et al. [H. Oualli, A. Lalaoua, S. Hanchi, A. Bouabdallah, Eur. Phys. J. Appl. Phys. 61, 11102 (2013)], it is concluded that for the actuated outer cylinder and relatively to the non-controlled case, the critical Taylor number, Tac1, characterizing the first instability onset illustrated by the piled Taylor vortices along the gap, increases substantially to reach a growing rate of 70% when the deforming amplitude is ε = 15%. Interestingly, when this controlling strategy is applied to the inner cylinder cross-section with a slight modification of the actuating law, this tendency completely inverts and the critical Taylor number decreases sharply from Tac1 = 41.33 to Tac1 = 17.66 for ε = 5%, corresponding to a reduction rate of 57%. Fundamentally, this result is interesting and can be interpreted by prematurely triggering instabilities resulting in rapid development of flow turbulence. Practically, important applicative aspects can be met in several industry areas where substantial intensification of transport phenomena (mass, momentum and heat) is needed such as in chemical reactors, combustors, heat exchangers and cylindrical water filters

Cardiac surgery in patients on hemodialysis: Eight years experience of the Tunisian military hospital

End-stage renal disease (ESRD) is known to be an important risk factor for cardiac operations performed with cardiopulmonary bypass. We investigated the influence of preoperative status on perioperative mortality and morbidity. We retrospectively analyzed data from 26 patients with ESRD, who were on maintenance dialysis and underwent a cardiac surgical procedure bet-ween 2000 and 2007. Of them, 61.5% of the patients had isolated coronary artery bypass grafting (CABG) and 38.5% had replacement or reconstruction of one or two valves. The perioperative mortality rate was 26% with five deaths occurring in patients undergoing CABG procedure. We found CABG procedure, being female and left ventricular (LV) function < 30% to be associated with a higher relative risk for perioperative death. In conclusion, our data suggest that both indi-cations and referral for surgical intervention for coronary artery disease may be delayed in pa-tients who have ESRD, contributing to the relatively high perioperative mortality