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Předběžné výsledky měření na HVAC jednotce pro H2-Bus s chladivy R454C a R513A
Blahut, Aleš ; Kordík, Jozef ; Šulc, V. ; Vinš, Václav
Technická zpráva shrnuje předběžné vyhodnocení experimentálních zkoušek chladící jednotky a tepelného čerpadla (HVAC) pro vodíkový autobus s chladivy R454C a R513A. V klimakomoře Elektrotechnického zkušebního ústavu, s. p. v Praze Troji byla v říjnu 2023 podrobně testována zkušební HVAC jednotka v režimech klimatizace a tepelného čerpadla při teplotách okolí od -25 °C do +45 °C. Ve zprávě jsou analyzovány základní výkonové parametry HVAC jednotky zahrnující topný a chladící výkon na kondenzátoru, resp. výparníku, topné a chladící faktory okruhu a izoentropickou účinnost kompresoru.
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Design analysis of the heat exchanger between the primary and the intermediate circuits of the small modular reactor DAVID
Kobylka, D. ; Hrubý, Jan ; Kordík, Jozef ; Gabriel, Dušan ; Marek, René ; Isoz, Martin
The report summarizes the joint results of the Department of Nuclear Reactors FNSPE, CTU and IT CAS, in the area of thermal and hydraulic calculations of the heat exchanger between the primary and intermediate circuits of the developed small modular reactor (SMR) DAVID. The assignment parameters were further specified during control days and with updated documentation. During the analysis of the initial system parameters, it was found that the original geometric configuration of the exchanger had a completely insufficient surface for heat transfer. A decision was made, several parameters were modified and based on a series of calculations using two independent simplified models, a reasonable configuration with a significantly smaller diameter of the tubes in a significantly larger number was chosen. The pressure losses on both sides of the heat exchanger are within normal ranges and will not cause problems with the construction of these circuits. Although there are differences between the results from both used models, their comparison shows that the chosen different calculation methods lead to approximately the same results and the models do not show fundamental errors.
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Liquid thermal conductivity measurement of based on laminar convection
Kordík, Jozef ; Hrubý, Jan
This research report describes a device for liquid thermal conductivity measurement, which was designed within the internal project no. 902156. The principle of measurement is based on known heat transfer parameters in laminar flow regime. An experimental rig with a precise mass flow regulation and temperature measurements was designed for this purpose. The rig was tested with a pure water and based on measured quantities its thermal conductivities were obtained at several liquid temperatures. The resultant conductivities were compared with known values for pure water and a good agreement was achieved.
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Effect of Aero-Therm insulation layer on the overall heat transfer coefficient
Kordík, Jozef
The aim of this work was to test the properties of Aero-Therm insulation layer by determining overall heat transfer coefficients for selected cases of flow past a sphere. The material of the sphere was copper to minimize uncertainties due to internal temperature gradients. Three variants were examined, which differed in sphere surface thermal insulation. In the first variant, the sphere with a diameter of 40 mm had no insulation; only a thin layer of a copper oxide was present on the surface only. In the second variant, the sphere was coated with Aero-Therm insulating layer with a thickness of about 1.5 mm. The third variant differed from the second one in the thickness of the insulating layer, which was 2.9 mm in this case. The overall heat transfer coefficients were determined for cooling the sphere by a forced convection by air at various flow velocities.
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Experimental evaluation of the gear windage loss and thermal load of a gear tooth
Kordík, Jozef ; Dobiáš, Jiří ; Hrubý, Jan
The report is written for the needs of the project no. TA04011656 (Research and development of new type of high-speed planetary gear unit with the flexible pin technology to support the planet wheels enabling the transmission of high outputs.). The first part of the report targets the topic of windage losses of a rotating toothed wheel, the experiments with testing gearbox Alfa II are introduced here, as well. The experiments included measurements of windage losses and temperature measurements along a wheel tooth width. Three geometrical configurations differing in wheel enclosure distance were tested, the case without the enclosure was tested too. The outcome of this part is an extension of the previous windage loss model for real geometry configuration: a wheel with an enclosure opened at place of oil outflow and at place of meshing with pinion.\nThe second part of the report targets the thermal load of a wheel tooth and presents experimental results of measurements of temperature distribution along the tooth. This part also contains the details concerning the numerical modeling of this problematic. The numerical analysis included (i) development of methodology for modeling of tooths meshing, (ii) development of the computational model, (iii) development of methodology for assessment of unknown values of some parameters of the model, (iv) development of algorithm. \n
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Synthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement
Kordík, Jozef ; Trávníček, Zdeněk
The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet momentum flux (the jet thrust) by means of precision scales. The second method is a standard one, it is based on spatial-temporal integration of the velocity profile at the synthetic jet actuator nozzle exit. The velocity profile was obtained here using hotwire measurements in air. Comparison of the methods is based on dimensionless stroke length of the synthetic jet. It is confirmed that the results of both methods are nearly the same for higher dimensionless stroke length. On the other hand, if the jet regime approaches to the synthetic jet criterion threshold (i.e. to the dimensionless stroke length of 0.5) the results of both methods diverge. Using the current results a correction is suggested for the momentum-flux-based method to match the standard one.
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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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Methodology for evaluation of the gear windage loss and thermal load of a tooth
Bauer, Petr ; Bartoš, Ondřej ; Hrubý, Jan ; Kordík, Jozef ; Krátký, Tomáš ; Sedlář, Milan
This report contains results of experiments identifying thermo-physical properties of a gearbox oil mist. The main part of the report studies a dependency of a gear wheel windage power loss on the radial and axial gap between the wheel and its enclosure. This parametric study relies primarily on the results coming from numerical simulations (CFD analysis). For the default enclosure configuration the evaluated power dissipation is compared with the values obtained using theoretical relationships. The theory is based on one-dimensional turbulent velocity profiles over smooth and rough surfaces. A summary of the theoretical analysis and the derivations are also included in the report.\nThe influence of a tooth shape on the windage power loss is also studied using the numerical simulations. A change of a tooth top surface angle is technologically easily realizable adjustment, and can have a positive effect on the power loss reduction. In the report there are performed simulations for varying angles of this surface and the expected improvements in aerodynamic properties are confirmed.\nThe last part of the report contains the formulation of boundary conditions for numerical evaluation of gear wheel heat balance. This information is documented more in detail in related research reports.\n
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Generalization of the methodology for evaluation of the gear windage loss
Bauer, Petr ; Kordík, Jozef ; Krátký, Tomáš ; Sedlář, Milan
The first part of the report proposes a methodology for gear windage loss evaluation using CFD analysis. The methodology includes simplification of gearbox complex geometry and the toothed wheel and pinion are replaced by a rough-walled disks with additional braking volume forces. The values of volume forces were determined using auxiliary computations with a real gear geometry (a gear segment with periodical boundary conditions). The computations included configuration of the gear wheel meshing with the pinion, while distance of wheel enclosure was a variable parameter (the case without enclosure was tested as well). The cases without pinion were computed too, they were compared with earlier results obtained with the gear segment geometry.\nThe second part of the report contains a revision of the earlier proposed analytical approach. The approach can serve for approximate gear windage loss evaluation and its idea dwells in smooth connection of logarithmic velocity profiles. The gear windage loss values obtained from the analytical approach were compared with the results based on CFD analysis. A good agreement between both methods was concluded.\n
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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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