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Water oxygenation by fluidic microbubble generator
Tesař, Václav ; Peszyński, K.
Oxygenation of water by standard means is rather ineffective. The classicalapproach to improvements – decreasing the size of the aerator exits - have already reached their limits. Recent idea is to decrease the size of the generated air bubbles by oscillating the supplied air flow using fluidic oscillators. Authors made extensive performance measurements with an unusual high-frequency fluidic oscillator, designed to operate within the submersed aerator body. The performance was evaluated by the dynamic method of recording the oxygen concentration increase to saturation in the aerated water. Experiments proved the fluidic generator can demonstrably increase the aeration efficiency 4.22-times compared with the aeration from a plain end of a submerged air supply tube.
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Integral fluidic generator of microbubbles
Tesař, Václav ; Jílek, Miroslav
Very small gas bubbles dispersed in liquid are desirable in many applications. If smaller than 1 mm in diameter, they are called microbubbles. Until recently, the advantages they offer have been little usedbecause of generally low efficiency of microbubble generation methods. A solution was found in pulsating the gas flow into the submerged aerator by a fluidic oscillator. At present, the oscillator and aerator are separate devices. The flow pulsation is strongly damped in the connecting tubes. New solution presented in this paper relies on oscillator robustness and no need for maintenance, which allows integrating it with the aerator into a single body submerged in the liquid. Small bubble size requires driving frequency much higher than has been so far applied. The present paper shows some of the ways leading to high frequencies – in particular the use of dominant third harmonic of the basic switching frequency.
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Near-exit coalescence – a so far unknown limit to microbubble smallness
Tesař, Václav ; Šonský, Jiří
Gas bubbles in a liquid are required in applications to be of the smallest possible bubble size. Authors studied microbubble formation using a high-speed camera and discovered that bubbles increase their volume near the aerator exits by mutual coalescence. This effect presents a limit to how small microbubbles can be produced. The discovered conjunction effects are very fast and this is probably the reason why they have so far escaped attention.
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Microfluidics in search for catalysts for biomass conversion into liquid fuels
Tesař, Václav
Paper surveys recent developments of combinatorial chemistry characterised by testing many substances and their mixtures simultaneously. Attention focuses on the progress made possible by applying small-scale no-moving-parts fluidics. Encountered problems like small Re and their solutions are demonstrated on author's development of a microfluidic unit for parallel testing of catalysts improving effectiveness of Fischer-Tropsch synthesis of liquid fuels from biomass.
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Role of microfluidics in discovering new marketable substances – a survey
Tesař, Václav
Paper surveys developments in combinatorial chemistry and related search for new medicaments and biomedical procedures, characterised by simultaneous testing of many substances (and their mixtures). Attention is focused on advantages offered in this field by small-scale no-moving-part microfluidics. Typical problems and their solution are then demonstrated on author’s development of a microfluidic unit for parallel tests of catalyst having potential to improve the effectiveness of Fischer-Tropsch synthesis of liquid fuels from biomass.
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Fluidics: what it is, where it is heading - and how it will change the world we line in
Tesař, Václav
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.
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Interesting properties of microbubbles
Tesař, Václav
Paper investigates properties of very small, sub-millimetre sized gas bubbles in liquids,which are generated by oscillation produced by a fluiidic no-moving-part oscillato in the gas supply into the aerator. Of particular interest is the tendency of microbubbles to coalesce already while in immediate neighbourhood of the aerator exit. Another investigated property is oscillation driven by released surface energy. Autorr derived an equation describing the natural frequencty of the oscillation and with the help of this equation found interesting parameters of the processes, such as the amount of outside water that takes part in the oscillation and has a decisive role in the inertial properties of the variations of the microbubble shape.
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Large-amplitude pulsatile nozzle flow
Tesař, Václav ; Kordík, Jozef
Flowfield inside a simply-shaped nozzle with periodic unsteadiness of so large amplitude that a flow reversal occurs during a part of the cycle was investigated. The range of frequencies was from 20 Hz to 320 Hz, and ratios of the pulsation amplitude to the steady flow were from 1.0 to 4.0. Anemometric velocity measurements were combined with numerical flowfield computations.
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Microbubble Generation by Fluidics. Part II: Bubble Formation Mechanism
Tesař, Václav
Author develops a facility for generation of sub-millimetre sized air bubbles in water. A promising and economically viable method, based on author's earlier experience, is fragmentation of bubbles by oscillation while they are still at the aerator exit locations. Understanding the mechanism by which the oscillation affects bubble formation is a pre-requisite to new aerator design. Results obtained so far reveal a strange bubble size independence on the applied acoustic power, frequency of oscillation and the character of aeratoir body.
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Microbubble generation by fluidics. Part I: Development of the oscillator
Tesař, Václav
Author investigates generation of sub-millimetre air bubbles in water. An economical alternative is pulsating the supplied air flow, using a no-moving-part fluidic oscillator. The paper summarises the existing oscillator principles and discusses the author's development of the chosen oscillator – which resulted in a device with behaviour different from what has been so far described in literature.
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