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Recent advances in characterisation of subsonic axisymmetric nozzles
Tesař, Václav
Nozzles are devices generating jets. They are widely used in fluidics and also increasingly often in active control of flows past bodies. Being practically always a component of larger system, design and optimisation needs nozzle properties characterisation by an invariant quantity. Perhaps surprisingly, no suitableinvariant has been so far introduced. This article surveys approaches to characterisation quantities and presents several examples of their typical use such as parallel operation of two nozzles, matching a nozzle to its fluid supply source, apparent resistance increase in flows with pulsation, and the secondary invariants of a family of quasi-similar nozzles.
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Modeling two-phase bubble flow in microfluidics
Stehlík, Martin ; Kozák, Jiří (referee) ; Rudolf, Pavel (advisor)
The goal of submitted thesis is to perform a computer simulation of bubble creation in T-channel. In the first section of the paper, the theoretical applications of microfluidic bubble, micromachines and droplet formation are described. In the second part of the text, author uses cross flowing method for simulation od bubble creation. Furthermore, several settings in computer simulation software Fluent are mentioned. In addition, the influence of velocity at the T-channel inlet on surface tension and on bubble length is presented.
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Invariants of simple nozzles
Tesař, Václav
Paper presents a new concept: invariance of second order. The idea bypasses the necessity geometric similarity (known as allowing only a scaling up or down) in derivation of dimensionless criterial parameters. The approach is demonstrated on the case of family of simple nozzles, the members of the family differing in their lengths of exit channel. While each nozzle is characterised by its primary invariant, characterisation of the whole family leads to two secondary invariants.
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Viscosity-dominated regime of flow in fluidic devices at very low Reynolds numbers
Tesař, Václav
Because of their small size – and typically due to high viscosity of handled fluids - some microfluidic devices have to operate at very low Reynolds number levels. The devices based on using inertia of a deflected jet under these conditions losetheir efficiency and finally exhibit a phenomenon so far not discussed in literature: they enter a regime in which their behaviour is no more specified by Reynolds number value. Paper presents a detailed case description of a valve and itstransition into the sub-dynamic regime. Pressure-assisted flow into the device terminal is characterised by newly introduced pressure parameter.
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Verification of thermal-insulation properties of the foil materials
Šot, Petr ; TROJAN,, Karel (referee) ; Šťastník, Stanislav (advisor)
The master´s thesis deals with verification of thermal insulating property of thermoreflection foil insulations. The teoretical part of thesis focuses on the energy demand of buildings, the problems of heat transfer material, terms required for study of thermoreflection thermal insulation and experimental methods for determination of thermal insulating properties of insulators. In the next part the chapter is accompanied by an overview of the most common insulation materials which used in construction. The last part of teoretical part is devoted to the description of thermoreflect formation and analysis of the spread of thermal insulating layers of thermoreflection thermal insulation. The first part of thesis is devoted to the use of thermoreflection therm insulation in buildings. The second part of thesis is devoted to the design, assembly and calibration of the measuring device that uses a method of protected warm chamber. It is declared as a binding method of detection of the heat transfer performance of thermoreflection thermal insulation. The developed measuring device allows detection of endpoints in some direction of propagation of heat. Measurment of heat transfer coefficient devoted the third part of practical part. This part contains a description of the samples used for the measurement of the heat transfer coefficient. In the fourth chapter of the practical part are presented the results of the heat transfer coefficient measurments on selected samples of thermoreflection foil insulation. It is shown the characteristic of heat transfer coefficient of individual samples, the dependence of the heat transfer coefficient on the position of the sample in the measuring device and the recommendation of an appropriate use of sample in the works for the climatic conditions of the Czech republic. The work concludes the chapter of comparing and evaluating of all samples with practical recommendations.
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Laboratory Model of the Vortex Speed Indicator
Kazda, Ondřej ; Kolka, Zdeněk (referee) ; Biolková, Viera (advisor)
This work is concerned with posibility of measuring a wind flow by Von Karman vortex sheed structure. The bluff body is situated in the way of air flow propagation and consequentally vortexes will be appeared. Important part of speedmeter design is measurment chamber must allow to vortex sheed propagation. The transient and the reciever are situated vertically to propagation of flow.The Ultrasonic carrier is transmitted and modulated by freqency of vortex sheeding in measurment chamber.Demodulator uses PLL to “focusing“ detection of the ultrasonic beam. This can be indicated like lock and unlock phase loop. From known value of sheed frequency can be directly calculated speed of flow.
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