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Analysis of non-harmonic excitation of synthetic jet actuators
Kordík, Jozef ; Trávníček, Zdeněk
Axisymmetric synthetic jet actuator based on a loudspeaker was tested experimentally. The actuator was driven by a voltage waveform, whose shape was derived from a pulse-width modulated signal. While the duty cycle and frequency of the excitation signal were varied the outlet velocities were measured by a hot-wire probe. Integral quantities such as characteristic velocity, momentum flux, and kinetic energy flux were evaluated from the outlet velocities. Their maxima were located as functions of frequency and the duty cycle. The found maximal values were compared with results obtained for harmonic excitation. The highest improvement (about 18%) was achieved for kinetic energy flux.
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Phosphinoferrocene ligands with polar amide substituents
Charvátová, Hana ; Štěpnička, Petr (advisor) ; Trávníček, Zdeněk (referee) ; Jambor, Roman (referee)
Title: Phosphinoferrocene ligands with polar amide substituents Author: Hana Charvátová Department: Department of Inorganic Chemistry Supervisor: prof. RNDr. Petr Štěpnička, Ph.D. Abstract: This thesis is focused on phosphino-urea ferrocene ligands that are still rather neglected in the literature. It describes the synthesis of novel polar amides and hydrazides of 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) with or without ethylene linker bearing various urea and guanidine terminal functional groups. Urea and guanidine derivatives with ethylene bridge can be prepared from Hdpf and appropriate amine with amidation agents. Phosphine ureas without the linker are accessible from reactions of primary amide of Hdpf with suitable acylation agents while analogical guanidine is obtained from guanylation of amide-amine generated from Hdpf acylbenzotriazole and ethylenediamine. Reaction of the acylbenzotriazole with free guanidine leads to [1-(diphenylphosphino)ferrocenecarbonyl]guanidine hydrochloride. These ferrocene ligands were used to prepare four types of palladium(II) complexes, viz. where L denotes the newly synthesized ligands and LNC is 2- [(dimethylamino)methyl]phenyl-C,N auxiliary chelating ligand. Catalytic efficiency of complexes with ethylene bridge was tested on reactions of aromatic...
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Condensing steam turbine
Trávníček, Zdeněk ; Fiedler, Jan (referee) ; Kracík, Petr (advisor)
The aim of the master’s thesis is to design a condensing steam turbine based on given inputs. Firstly, a design and computation of heat balance is made, followed by thermodynamic calculation of steam turbine channel and a design of compensatory piston of axial forces. Last part of the thesis consists of a review of a change of cooling water temperature in condensator on last turbine stages. The structural drawing of longitudinal section of turbine is included as well.
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Anion receptors based on symmetrically tetrasubstituted calix[4]arenes
Klimentová, Jana ; Lukeš, Ivan (advisor) ; Budka, Jan (referee) ; Trávníček, Zdeněk (referee)
The submitted Ph.D. thesis concerns anion receptors based on symmetrically tetrasubstituted cone calixf4]arenes. These receptors are easily synthesized and display sufficient water solubility to function as receptors for tetrahedral oxoanions. The thesis starts with a brief survey of literature on calix[4larene anion receptors and sensors. The theoretical part of the thesis deals with a stereochemical investigation of calixf4]arenes from the Cambridge Structural Database (CSD) with emphasis on the influence of inter- and/or intramolecular interactions on the geometry and rigidity of the calix[4]arene scaffold. In order to describe the geometry of the calixf4]arene moiety, it was necessary to introduce new stereochemical parameters cr, B and 5. The utility of these parameters in evaluating the geometry of the calixf4]arene base frame was confirmed. The stereochemical investigation formed the basis for design of new potential anion receptors based on symmetric al ly tetrasub stituted c o n e calixl4 ] arene s. The experimental part of this work started with synthesis of symmetrically tetrasubstituted calixf4]arene derivatives containing 1-propoxy groups at the lower rim and synthesis of calixf4]arene derivatives with carboxymethoxy groups at the lower rim and enhanced water solubility. Identity and...
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Comparison of synthetic jet actuators based on sharp-edged and round-edged nozzles
Kordík, Jozef ; Trávníček, Zdeněk
Axisymmetric synthetic jet actuators based on a loudspeaker and on two types of flanged nozzles were tested and compared experimentally. The first type of the nozzle was a sharp-edged circular hole. The second one had a special design with fillets at inner and outer nozzle exit and with a small step in the middle of the nozzle. The function of the step was to prevent the flow reattachment during the extrusion stroke. The actuators with the two types of nozzles were operated at resonance and were compared first qualitatively using a simple phase locked flow visualization. Then the hot-wire anemometer was used to measure velocity \ndistributions along nozzle axis and velocity profiles at the nozzle exit. Comparison of the nozzles was based on evaluation of the characteristic velocity and integral quantities (volumetric, momentum, and kinetic energy fluxes). It was found out that these quantities, which were evaluated at the nozzle exit, differ substantially for both nozzles. On the other hand the velocity flow field in farther distances from the nozzle exit area did not exhibit such prominent differences.
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PIV and LIF study of flow and thermal fields of twine plumes in water
Broučková, Zuzana ; Trávníček, Zdeněk
Flow and thermal fields of a pair of plane plumes in water are investigated using PIV and LIF experiments. The plumes are generated from thermal line sources (electrically heated cylinders, diameter D = 1.21 mm). Either continuous or pulsating heating were used with the same heating input power. For a continuous heating, low frequency oscillations were identified and the natural frequency was evaluated as 0.5 Hz. Pulsating heating was used at frequency of 0.25 Hz. The maximum time-mean velocity magnitude at the continuous and pulsating heating were commensurable, approximately 0.007 m/s. Temperature fields reasonably agree with these findings.
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Active control of the wake behind the cylinder
Broučková, Zuzana ; Flídr, Erik ; Šafařík, P. ; Trávníček, Zdeněk
Active control of the flow around a cylinder using synthetic jet (SJ) array was experimentally investigated. The prevailing method was flow visualization. Modification of the wake was investigated at two values of a dimensionless momentum coefficient (Cμ = 0.21 and 1.02). Various α and Cf parameters were tested (where α is the angle between SJs and the main flow direction and Cf is the frequency ratio). The control moves separation point more downstream. Increasing frequency ratio Cf causes refining of the vortex structure. When SJs are placed at the front or rear stagnation points, wake tends towards the symmetrical pattern.
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Natural gas
Trávníček, Zdeněk ; Moskalík, Jiří (referee) ; Pospíšil, Jiří (advisor)
The aim of the bachelor thesis is to collect facts about natural gas, focusing mainly on the situation in the Czech Republic. Firstly, the thesis discusses the natural gas in general - its properties, world resources, ways of production and usage. The main part of the thesis deals with supply and accumulation of natural gas in the Czech Republic. Secondly, enumeration and brief description of possibilities of natural gas substitution is presented. Finally, comparison of usage of classic non-condensing and condensing boiler for a family house heating is introduced. Recommendation of boiler type based on the model example is included as well.
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Jet flow issuing from an axisymmetric pipe-cavity-orifice nozzle
Broučková, Zuzana ; Pušková, P. ; Trávníček, Zdeněk ; Šafařík, P.
Axisymmetric air jet flow is experimentally investigated under passive flow control. Jet issues from a pipe (inner diameter 10mm, length 150 mm) equipped with an axisymmetric cavity at the end. Cavity operates as resonator creating self-sustained acoustic excitations. Mechanism of excitations is complex. Experimental methods were: flow visualization, microphone measurements and velocity measurements by the Pitot probe. Power spectral density (PSD) and sound pressure level (SPL) were evaluated from microphone measurements. Jet Reynolds number ranged Re = 1600–18 000. Peaks in PSD indicated a function of the resonator. The most effective acoustic response was found at higher Re. Results demonstrate effects of the control: mixing and velocity decay along the axis are intensified. It causes shortening of the transition region. However, an inverse proportionality of the velocity decay in the fully developed region is not changed. Momentum and kinetic energy fluxes decrease more intensively.
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