Abstract
The current work studies a swirling laminar viscous pipe flow with a controllable swirl number and varying pipe divergence cone angle. Such flows are widely used in various engineering ...applications. When a certain level of flow swirl is reached, a phenomenon called vortex breakdown occurs, the characteristics of which depend on the intensity of swirling of the flow and the Reynolds number. However, in addition to these two parameters, an important influence is exerted by the pipe opening angle, which often does not allow generalizing the results obtained in the pipe flow with even slightly different angles. Since experimentally it is quite difficult and expensive to change the pipe angle, especially considering the water as working fluid, this issue could be solved using CFD techniques. Using the design study, 63 different combinations of S and α are considered. The effect of the pipe divergence angle on the position of the bubble vortex breakdown and its properties is demonstrated. It is shown that there is a nonlinear relationship between the position of the bubble breakdown onset and the minimum value of the axial velocity at the axis depending on the opening angle of the cone.
Abstract
An experimental study of a cavitating NACA0012 hydrofoil with aspect ratio 0.02 in a slit channel was carried out using a high-speed visualization at sampling rate more than 100 kHz. The ...features of the formation and development of cavities in a quasi-two-dimensional turbulent flow were studied. The most energetic modes of unsteady cavitation flow around the hydrofoil were obtained using dynamic mode decomposition. The presence of the second and third modes in the cavitation flow is shown here for the first time. It was shown that each of these modes corresponds to a certain period of development of the unsteady cavity. Experimental data on the reverse motion of the vapor–gas mixture into the inner region of supercavitation are presented.
Looking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere (tornado) ...and ocean (waterspout). To better understand the flow nature and topology, this experimental study explores the development of vortex breakdown (VB) in a lab-scale swirling flow of two immiscible fluids filling a vertical cylindrical container. The rotating bottom disk drives the circulation of both fluids while the sidewall is stationary. The container can be either sealed with the still top disk (SC) or open (OC). As the rotation strength (Re) increases, a new circulation cell occurs in each fluid-the dual VB. In case SC, VB first emerges in the lower fluid at Re = 475 and then in the upper fluid at Re = 746. In case OC, VB first emerges in the upper fluid at Re = 524 and then in the lower fluid at Re = 538. The flow remains steady and axisymmetric with the interface and the free surface being just slightly deformed in the studied range of Re. Such two-VB swirling flows can provide efficient mixing in aerial or two-fluid bioreactors.
Conflicting data exist on the effect of dexmedetomidine on delirium. For the present study, a randomized trial was performed to investigate the effect of perioperative dexmedetomidine on the rate of ...postoperative delirium after cardiac surgery.
A randomized controlled trial.
University hospital.
Patients (n = 169) undergoing elective cardiac surgery (coronary artery bypass graft surgery, valve surgery, or combined surgery) with cardiopulmonary bypass.
Patients received a sevoflurane-based general anesthesia and were randomly assigned 1:1 to receive a dexmedetomidine infusion that started in the operating room (0.7 μg/kg/h) and continued into the intensive care unit (0.4 μg/kg/h) or an equivolume infusion of placebo.
A decrease in the rate of delirium in the dexmedetomidine group compared with the placebo group was demonstrated (6 of 84 7.1% v 16 of 85 18.8%; p = 0.02; odds ratio OR 0.33 95% confidence interval {CI} 0.12-0.90). Reduced intensive care unit and hospital lengths of stay also were observed (18 18-22 hours v 22 18-39 hours; p = 0.002 and 17 7-20 days v 19 8-21 days; p = 0.04, respectively). Mortality at 30 days was 2 (2.4%) in both groups. On multivariate analysis, only dexmedetomidine administration (OR 0.24 95% CI 0.08-0.74) and cardiopulmonary bypass time (OR 1.02 95% CI 1.01-1.03 for increases of 1 min) were independent predictors of delirium development.
Dexmedetomidine administered during and after general anesthesia for cardiac surgery with cardiopulmonary bypass decreased the rate of postoperative delirium and intensive care unit and hospital lengths of stay.
Aim. To assess whether plasma mitochondrial DNA (mtDNA) levels in the early postoperative period can predict the development of systemic inflammatory response syndrome (SIRS) and multiple organ ...failure in patients undergoing cardiac surgery. Methods. This pilot, prospective, observational, cohort study included 85 patients undergoing cardiac surgery. Plasma mtDNA levels were determined immediately after the surgery, and the development of SIRS, acute kidney injury, acute heart failure, and adult respiratory distress syndrome was assessed. Results. The mtDNA levels showed good potential for predicting the development of SIRS within 1-2 days after the surgery (area under the curve = 0.74). Regarding the cut-off point, a mtDNA level of >0.54 ng/mL predicted the development of SIRS in the early postoperative period with a sensitivity of 73.7% and a specificity of 66%. The odds ratio for the development of acute kidney injury with/without SIRS was 3.4 confidence interval (CI) = 1.27–9.08; p = 0.0149; acute heart failure, 5.7 (CI = 2.20–14.84; p = 0.0003); and adult respiratory distress syndrome, 3.6 (CI = 1.01–11.10; p = 0.047). Conclusion. The plasma mtDNA levels in the early postoperative period can be used as a predictive marker for the development of SIRS and multiple organ failure in patients undergoing cardiac surgery. Moreover, SIRS is associated with the development of acute kidney injury, acute heart failure, and adult respiratory distress syndrome. Received 25 March 2019. Revised 3 April 2019. Accepted 8 April 2019. Funding: The study did not have sponsorship. Conflict of interest: Authors declare no conflict of interest.
A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (EuxLu1−x)2bdc3·nH2O, was synthesized using a direct reaction in a water ...solution. At the Eu3+ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (EuxLu1−x)2bdc3 and (EuxLu1−x)2bdc3·4H2O crystalline phases, where the Ln2bdc3·4H2O crystalline phase was enriched by europium(III) ions. At an Eu3+ concentration of more than 40 at %, only one crystalline phase was formed: (EuxLu1−x)2bdc3·4H2O. All MOFs containing Eu3+ exhibited sensitization of bright Eu3+-centered luminescence upon the 280 nm excitation into a 1ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu3+ 5D0-7FJ (J = 0–4) significantly depended on the Eu3+ concentration. The luminescence quantum yield of Eu3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu3+ due to the absence of Eu-Eu energy migration and the presence of the Ln2bdc3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln2bdc3·4H2O.
•The double helix vortex structure in a tangential chamber was obtained by means of numerical simulation.•Three regimes were simulated according to different swirl numbers.•Several recirculation ...zones were formed in the tangential chamber near its axis.•The frequency of the pressure pulsation was approximately twice the rotational frequency of the double helix structure.•The vorticity redistributes between branches of the double helix structure during its rotation and evolution.
The paper investigates the flow structure in a tangential vortex chamber based on numerical simulation of unsteady turbulent flow by the LES method. The swirl flow in a cylindrical chamber was organized using 12 nozzles, supplying the flow tangentially. Three regimes were considered with different design swirl number S = 5.78, 8.67, and 17.34, which was varied by closing one or two nozzle rows. The unsteady computation shows the formation of a rotating double helix vortex structure in the regimes with S equal to 8.67 and 17.34, which is also verified by experimental observations. Several recirculation zones were formed in the tangential chamber near its axis, as well as along the wall at the lower part, and on the axis near the top lid. A dominant frequency was observed in the pressure pulsation spectrum, which increased with increasing swirl parameter, and for the S = 8.67 regime, it was approximately twice the rotational frequency of the double helix structure. In the course of rotation of the double helix structure, the vorticity redistributed between its branches from an approximately symmetric pattern and up to approaching a single-vortex structure at certain points in time.
Luminescent, heterometallic terbium(III)–lutetium(III) terephthalate metal-organic frameworks (MOFs) were synthesized via direct reaction between aqueous solutions of disodium terephthalate and ...nitrates of corresponding lanthanides by using two methods: synthesis from diluted and concentrated solutions. For (TbxLu1−x)2bdc3·nH2O MOFs (bdc = 1,4-benzenedicarboxylate) containing more than 30 at. % of Tb3+, only one crystalline phase was formed: Ln2bdc3·4H2O. At lower Tb3+ concentrations, MOFs crystallized as the mixture of Ln2bdc3·4H2O and Ln2bdc3·10H2O (diluted solutions) or Ln2bdc3 (concentrated solutions). All synthesized samples that contained Tb3+ ions demonstrated bright green luminescence upon excitation into the 1ππ* excited state of terephthalate ions. The photoluminescence quantum yields (PLQY) of the compounds corresponding to the Ln2bdc3 crystalline phase were significantly larger than for Ln2bdc3·4H2O and Ln2bdc3·10H2O phases due to absence of quenching from water molecules possessing high-energy O-H vibrational modes. One of the synthesized materials, namely, (Tb0.1Lu0.9)2bdc3·1.4H2O, had one of the highest PLQY among Tb-based MOFs, 95%.
Numerical modeling and experimental investigation of hydrodynamic cavitation on a microcylinder located in a microchannel were carried out. The Zwart–Gerber–Belamri cavitation model was employed to ...simulate cavitation processes, and turbulence was simulated using the LES model. Experimental studies were performed by visualization with a shooting frequency of 960 Hz. Fluid pressure at the channel inlet ranged from 2 to 30 bar. Time dependences of pressure, velocity and vapor volume fraction, as well as their average values, were obtained at five points. Stable developed cavitation was found to exist for inlet pressures above 18 bar; no cavitation at all was observed for inlet pressures below 8 bar as confirmed by experimental studies. A fairly good agreement was revealed between the calculated and experimental data. The cavitation pulsation frequency (480–2200 Hz) and hydrodynamic pulsation frequency values (26–96 kHz) were obtained. The presence of cavitation was shown to shift the frequency of hydrodynamic pulsations towards larger values. Dependence of the relative drag coefficient on the inlet pressure, well approximated by a correlation ζr = (2Δp)0.5, was obtained.
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