EÚ-odbor termomechaniky a techniky prostředí
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- ItemHeat Flux Assessment in Reciprocating Compressor(EPJ Web of Conferences, 2024-07-04) Rapta, Patrik; Hejčík, Jiří; Jícha, MiroslavHeat transfer inside a cylinder and the cylinder head of a reciprocating compressor is responsible for the majority of thermodynamic losses in these devices. Both the magnitude and direction of the heat flux through the walls of those components change several times during a single revolution. They are directly dependent on the position of the piston and suction/discharge valves. A better understanding of these thermal processes could lead to better and more targeted cooling. This would result in higher efficiency of the reciprocating compressors. In this paper, two experimental methods for determining heat flux are used. The first method uses heat flux sensors to measure heat flux directly. The other one is focused on the indirect assessment of heat flux via surface-mounted thermocouples. To tie the measurement to the position of the crankshaft, both sensors are coupled to a rotary encoder. The rotary encoder sends a signal once per revolution when the piston is in the top dead center position to trigger signal acquisition. The results show signs of reaching a quasi-steady state and would most likely require sampling of the signal more times per revolution.
- ItemOptimal design of structure in rheological models: an automotive application to dampers with high viscosity silicone fluids(JVE International, 2017-10-09) Píštěk, Václav; Klimeš, Lubomír; Mauder, Tomáš; Kučera, PavelDynamic torsional vibration dampers are for a long time inherent integral components of internal combustion engines. One of the most common types of the dynamic dampers is a silicone damper. It has been, for many years, perceived as an exclusively viscous damper, thus it has been constructed and designed according to this perception. When compared to other types of dynamic dampers of the similar size with flexible components used for their construction, the standard iscous damper has a lower damping effect. Moreover, this damper type has been a significantly cheaper and simpler solution. Current silicone oils with high nominal viscosity, having not only the expected damping properties, but also significant elastic characteristics under alternate shear stress, enable construction of dynamic dampers with a higher damping effect than a viscous damper. Frequency and temperature dependent complicated rheological properties of high viscosity silicone fluids can only be identified experimentally using a suitable dynamic viscometer. However, the measured frequency dependencies of both components of the complex shear modulus are only defined for harmonic loading while internal combustion engine load is periodic and contains several tens harmonics. The key to the solution is therefore to find suitable multiparameter rheological models comprised of linear elastic and damping elements that would approximate in the specified frequency range both components of the complex shear modulus. Such a complicated task can be solved using efficient optimization algorithms. This article focuses on the mathematical description of convolute rheological properties of high viscosity silicone liquids and also contains an example of the application of created rheological models in the complex dynamic model of a V10 diesel engine. A computational tool for the determination of stiffness and damping coefficients of the multi-parameter rheological model was created and solved in the optimization software GAMS by means of the CONOPT solver. The possibility of these modern technologies is shown by the comparison of computation models and experimentally set torsional vibration spectres with standard viscous damper and damper utilizing a high viscosity silicone oil.
- ItemPrediction of localized aerosol deposition in a realistic replica of human airways using experimental data and numerical simulation(EDP Sciences, 2016-11-15) Lízal, František; Elcner, Jakub; Bělka, Miloslav; Jedelský, Jan; Jícha, MiroslavThe presence of aerosol deposition hot-spots in human airways presumably contributes to development of various diseases. The overall aerosol deposition in human lungs can be predicted with sufficient accuracy nowadays. However, the prediction of localized aerosol deposition poses arduous challenge, namely in diseased lungs. Numerical simulation is considered to be a promising tool for the successful prediction. Yet, the validation of such simulations is difficult to perform, as not enough experimental data acquired using realistic airway replicas is available. This paper presents a first comparison of localized deposition measurement and simulation performed on the identical realistic geometry. The analysis indicates that both approaches yield similar results for low Reynolds number flows.
- ItemImprovement of baffle type Rotating Packed Bed’s packing by visual study(Polish Academy of Sciences Committee of Chemical and Process Engineering, 2023-09-25) Zawadski, Dawid; Majdzik, Małgorzata; Hájek, Ondřej; Malý, Milan; Blatkiewicz, MichalProcess intensification is one of the key branches of process engineering. High gravity equipment achieves intensification by substituting gravity with much higher centrifugal force. Rotating Packed Bed is the leading example of high gravity solutions, strongly facilitating gas-liquid mass transfer. However, cylindrical packings come with certain drawbacks, such as dry spots, that can be overcome with new solutions, such as baffle-based packing geometries. However, when baffles are arranged too close to each other, liquid bridges are formed between them, which may lead to decrease in mass transfer efficiency. This work is concerned with improvement of a Zickzack-like internal by the means of visual studies with the use of high-speed camera. According to measured ligament break-up length, two new packings were designed for particular rotational speeds and tested experimentally for effective mass transfer area and wet pressure drop.
- ItemPerformance of Twin-Fluid Atomizers for Atomization of Viscous Solutions(EDP Sciences, 2014-11-18) Mlkvik, Marek; Stähle, Philipp; Gaukel, Volker; Zaremba, Matouš; Jedelský, Jan; Jícha, MiroslavThe article compares the performace of two twin-fluid atomizers with different desing and fluid mixing principles for atomiyation of viscous liquids.