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Prague, Czech Republic

Tesar V.,Czech Institute of Thermomechanics
Chemical Engineering Journal | Year: 2010

Flow control valve containing no moving components was developed for switching fluid flow passing through it into a parallel secondary path once the conditions in the main path reach a certain limit. No sensors or actuators are involved; the switching is caused by the inability of the Coanda effect to keep the flow attached to a wall that leads it into a particular outlet once a large resistance is met in this outlet. So far, there has been no method for designing such valves. To provide a guidance, this paper summarises experimental evidence about loading characteristics obtained with a considerable number of tested valve geometries. © 2010 Elsevier B.V.

Tesar V.,Czech Institute of Thermomechanics
Flow Measurement and Instrumentation | Year: 2013

This paper presents a simple sensor for measuring shear stress in fluid flow adjacent to a wall. Experiments and numerical flowfield computations have shown no measurable disturbance of the flowfield and the sensor may thus be well suited to conditions in which the invasive character of known sensors causes premature transition to turbulence or flow separation. The sensing part occupies a minimum surface area on the wall. In principle, the sensor is capable of detecting individual vortices in near-wall turbulence. Accuracy and sensitivity are comparable to known sensors of the sublayer-fence type. © 2013 Elsevier Ltd.

Heczko O.,ASCR Institute of Physics Prague | Straka L.,Aalto University | Seiner H.,Czech Institute of Thermomechanics
Acta Materialia | Year: 2013

The morphology and microstructure of a single, macroscopically straight twin interface with a twinning stress of about 1 MPa was analysed in detail by differential interference contrast optical microscopy and X-ray diffraction. The interface was identified as a Type I macrotwin boundary between two variants with a/b-laminates and constant modulation direction, in contrast with a highly mobile twinned interface consisting of Type II macrotwin boundary segments with changing modulation direction and a/b-laminate reported earlier. Theoretical analysis using elastic continuum theory shows that only pure Type I or Type II boundaries are fully compatible with a/b-laminate. Other hypothetical twin microstructures combining these two mobile interfaces are shown to be incompatible to various degrees. A weakly incompatible combination of Type I and II boundaries was experimentally observed. The large difference in mobility between Type I and Type II macrotwin boundaries created at the same location of the same sample indicates that the mobility depends on the internal structure of these boundaries. A possible origin of this different mobility is discussed. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tesar V.,Czech Institute of Thermomechanics
Chemical Engineering Research and Design | Year: 2014

Efficient generation of sub-millimetre microbubbles was recently made possible by pulsating the flow of gas supplied into a parallel-exits aerator, using a fluidic oscillator for the purpose. Without moving parts, it can generate oscillation at high frequency, an important factor due to bubble natural frequency rapidly increasing with the desirable decrease of their size. This paper discusses development of an unusual oscillator - a part of an integral oscillator/aerator unit - capable of generating a particularly high driving frequency, in the kilohertz range, in a layout that promotes a strong third harmonic frequency of the basic oscillation. © 2014 The Institution of Chemical Engineers.

Tesar V.,Czech Institute of Thermomechanics
Chemical Engineering Journal | Year: 2014

Microbubbles - gas bubbles of diameter less than 1. mm - became currently of considerable importance for chemical and process engineering applications, mainly because of the recent discovery of an energetically efficient method of their generation with a fluidic oscillator in the gas supply into an aerator. The oscillation should be applied at the microbubble resonant conditions, about which there has been so far known very little. The key problem is the unknown and difficult to evaluate extent of the surrounding liquid that takes part in the microbubble oscillatory motions and represents the inertia term in the governing equation. The oscillation of microbubbles also influences their ascent, which is slow and puts them often into mutual proximity causing their conjunctions. Author evaluated basic data on oscillating microbubbles from high-speed camera frames and used them to setup a simple model, suitable for engineering design purposes. © 2013 Elsevier B.V.

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