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Application of the Electrodiffusion Method forNnear-Wall Flow Diagnostics
Tihon, Jaroslav
The electrodiffusion method is presented as a measuring technique suitable for the flow measurement done in close proximity of the wall, thus in the region difficultly accessible by standard anemometric techniques (e.g. PIV, LDA). The experimental results obtained in different flow configurations (backward-facing step flow, wavy film flow, turbulent channel flow, rising Taylor bubbles) document application capabilities of this technique, e.g. for mapping of wall shear stresses, delimitation of stable flowrecirculation zones, detection of short-time reversal of the near-wall flow, investigation of the near-wall turbulence, or detection of moving fluid particles. A new technology of sensor fabrication based on photolithography is introduced and possible applications of microsensors in microfluidic devices discussed.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22014011511300 - PDF
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Application of the Electrodiffusion Method for Near-Wall Flow Diagnostics
Tihon, Jaroslav
The electrodiffusion method is presented as a measuring technique suitable for the flow measurement done in close proximity of the wall, thus in the region difficultly accessible by standard anemometric techniques (e.g. PIV, LDA). The experimental results obtained in different flow configurations (backward-facing step flow, wavy film flow, turbulent channel flow, rising Taylor bubbles) document application capabilities of this technique, e.g. for mapping of wall shear stresses, delimitation of stable flow-recirculation zones, detection of short-time reversal of the near-wall flow, investigation of the near-wall turbulence, or detection of moving fluid particles. A new technology of sensor fabrication based on photolithography is introduced and possible applications of microsensors in microfluidic devices discussed.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22013110513500 - PDF
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Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels
Tihon, Jaroslav ; Pěnkavová, Věra ; Vejražka, Jiří
The motion of single air bubbles in flat channels is experimentally investigated. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large rising bubbles. The measurements are synchronized with the visual observation of bubble movement by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel configuration (with heights of 1.5, 4, and 8 mm), cover a wide range of channel inclination angles (from horizontal to vertical position), and dealing with both the bubbles in stagnant and in co-flowing water.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012112614030 - PDF
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Wall Shear Rate Components for Wavy Taylor-Couette Flow
Kristiawan, M. ; Jirout, T. ; El Faye, A. ; Sobolík, Václav
Experiments were carried out in the wavy flow between concentric cylinders with the inner cylinder rotating and outer cylinder fixed. The radius and aspect ratios were 0.8 and 44, respectively. The electrodiffusion method with a three-segment and simple micro-electrodes was used for study of the axial and azimuthal components of shear rate at the outer cylinder. The axial distributions of these components were obtained by sweeping the vortices along the probes using a slow axial flow. The wavelength and phase celerity of waves, height of vortices and their drifting velocity were calculated from the measured limiting diffusion currents.
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Vliv pulzací nátoku na strukturu toku v kanále za náhlým rozšířením.
Pěnkavová, Věra ; Tihon, Jaroslav
The wall shear rate profiles were measured along the bottom and roof walls of rectangular channel with backward-facing step. The profiles were measured by two-strip electrodiffusion probes. It is possible to see the strong effect of the inlet flow pulsations on the flow structure. The influence of the inlet flow pulsation was studied for various frequence and amplitude for water when the Reynolds number was ranging from 100 to 1500 and expansion ratio of the channel was 2.
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