Annular synthetic jet used for impinging flow mass-transfer

An annular synthetic jet was investigated experimentally, both with and without an opposing impingement wall. The experiments involved smoke visualization and mass transfer measurement on the wall by means of naphthalene sublimation technique. Two qualitatively different flow field patterns were identified, depending upon the driving amplitude level. With small amplitudes, vortical puffs maintain their identity for a relatively long time. If the amplitudes are large, breakdown and coalescence of the vortical train is much faster. Also the resultant mass transfer to the impingement wall is then much higher. Furthermore, a fundamental change of the whole flow field was observed at the high end of the investigated frequency range, associated with radical reduction of the size of the recirculation bubble

On the design and simulation of an airlift loop bioreactor with microbubble generation by fluidic oscillation

Microbubble generation by a novel fluidic oscillator driven approach is analyzed, with a view to identifying the key design elements and their differences from standard approaches to airlift loop bioreactor design. The microbubble generation mechanism has been shown to achieve high mass transfer rates by the decrease of the bubble diameter, by hydrodynamic stabilization that avoids coalescence increasing the bubble diameter, and by longer residence times offsetting slower convection. The fluidic oscillator approach also decreases the friction losses in pipe networks and in nozzles/diffusers due to boundary layer disruption, so there is actually an energetic consumption savings in using this approach over steady flow. These dual advantages make the microbubble generation approach a promising component of a novel airlift loop bioreactor whose design is presented here. The equipment, control system for flow and temperature, and the optimization of the nozzle bank for the gas distribution system are presented. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V All rights reserved

Multi-parameter approximation of stress field in a cracked specimen using purpose-built Java applications

A quality of multi-parameter approximation of the stress and displacement fields around a crack tip in a non-brittle material test specimen is studied in the paper. The stress field approximation using Williams power series is intended to be utilized for estimation of the nonlinear zone extent which potentially plays a role within methods for determination of true values of fracture parameters of materials exhibiting nonlinear failure. Considering the fact that in the case of elastic-plastic and especially quasi-brittle materials the size of this zone is substantial in comparison to the specimen dimensions, it is necessary to take a large region around the crack tip into account for this task. An automatic utility created to determine the values of coefficients of the higher order terms of Williams power series by usage of over-deterministic method applied on results of finite element analysis of arbitrary mode I test geometry is one of the tested procedures. The second one provides a backward reconstruction of the crack-tip stress field analytically by means of truncated Williams expansion. The developed procedures are based on the support of Java programming language and considerably simplify analyses of the mechanical fields’ description in a farther distance from the crack-tip. The presented research is focused on optimization of selection of FE nodal results for improvement of accuracy of the approximation

Mikrofluidika v řízení živých tvorů

Microfluidics had recently interesting uses in biomedical sciences. Its development towards smaller scales has reached the stage making possible an interfacing with the brain cortex at the cellular level: reading and inputting the neural signals. The signals and their processing are mostly of electronic character, but fluidics plays in this application one of the key supporting roles. The contribution on the one hand lists therapeutical applications, but on the other hand notes current trend of military uses of insects or small rodents who can intrude into military establishments and gather there pictorial information

EXTRACTING INFORMATION ABOUT COHERENCE IN JET FLOWS

Several alternative approaches to processing jet flow visualization images were recently introduced by the authors. Common feature is processing a sequence of 2D images to detect presence and evaluate development dynamics of 3D vortical structures, which are recognised as regions that differ from the uncorrelated turbulent background in the processed pictures by their high negative values of correlation coefficient

Velocity spectra and transition into turbulence in synthetic jets

Paper investigates transition into turbulence in synthetic jet. The investigation was based on the quasi-similarity model with model parameter varying along the jet trajectory.The distance travelled from the nozzle to the location of the transition depends on the driving frequency – and hence on the size of the vortical structures, which were modelled by a sphetical vortex model. It appears the trasnsition takes placeat the distance equal to ~20 diameters of this model object

Fluidics: what it is, where it is heading - and how it will change the world we line in

Fluidics, technique of handling fluids, is usually meant to imply absence of moving components. It is less known and used than it deserves considering the advantages it offers. Recently its applications became more widespread thanks to two development directions. On one hand, it is the power fluidics, handling larger flow rates. Newly developed are no-moving-part fluidic pumps for dangerous liquids (in particular radioactive ones) — and fluidic oscillators for generation of microbubbles used in waste water processing and growth of unicellular plants. The other rapidly growing development direction is microfluidics, often integral with electronic circuitry on the same substrate. It has immense possibilities in sensors and also in handling small amounts of fluids e.g. in microchemistry

Fluidic Relaxation Oscillators for Microbubble Generation

Paper discusses low-frequency oscillators based on the unusual relaxation principle. In thefluidic version, the oscillator is suitable for supplying CO2 to cultivated unicellular algae