EÚ-odbor termomechaniky a techniky prostředí

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Detailed spray analysis of airblast atomization of various fuels in a reacting environment
(Elsevier, 2024-08-01) Kardos, Réka Anna; Rácz, Erika; Malý, Milan; Jedelský, Jan; Józsa, Viktor
Understanding spray evolution in a reacting environment is critical to designing advanced, clean combustion systems. The processes in the upstream region determine flame shape, stability, ignition characteristics, pollutant emission, and combustion efficiency. The developed spray is never achieved in combustion since the early regions feature primary and secondary atomization, while droplets evaporate as they approach the flame. Consequently, there is no thermodynamic equilibrium before the flame front. The principal goal of this paper is to provide detailed information to model developers on various sprays measured by a Phase Doppler Anemometer; the processed measurement data is available as supplementary material, while the raw data will be provided upon request. Four different fuels were tested: diesel fuel, aviation kerosene type JP-8, biodiesel, and a 50 % biodiesel-diesel blend by volume. The plain -jet airblast atomizer was tested at four atomization gauge pressures (0.3, 0.45, 0.6, 0.75 barg). Therefore, sixteen different sprays were measured along one spray diameter at each of four downstream distances of 15, 25, 35, and 45 mm, measured from the nozzle tip. The paper details the droplet size distribution, droplet axial velocity, fluctuations, and correlation between size and velocity to facilitate a comprehensive understanding of liquid fuel sprays. This latter measure helps identify the overshooting phenomenon, i.e., localizing the regions where the large droplets move faster than the gas phase.
Heat Flux Assessment in Reciprocating Compressor
(EPJ Web of Conferences, 2024-07-04) Rapta, Patrik; Hejčík, Jiří; Jícha, Miroslav
Heat 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.
Flow Behaviour of Inhaled Fibres – Equations of Motion and Preliminary Results of Real Trajectories Recorded by a High-Speed Camera
(EDP Sciences, 2020-11-18) Lízal, František; Bělka, Miloslav; Malý, Milan; Cabalka, Matouš; Jedelský, Jan; Jícha, Miroslav
The ability to precisely predict the fate of inhaled fibres is important for toxicologists as well as for pharmaceutists struggling to utilize fibres as carriers of a medication. However, the complexity of fibre movement in human airways still represents a significant challenge for programmers of codes for simulation of fibre flow. This conference contribution introduces the theoretical equations of fibre motion which can be used for calculation of the fate of inhaled fibres, and also, in the second part, first results of high-speed camera recorded trajectories of fibres downstream of a realistic human airway bifurcation are presented as an illustration of the real behaviour of fibres in the lungs.
Lagrangian tracking of fibres in a channel flow
(EDP Sciences, 2018-11-13) Volavý, Jaroslav; Farkas, Árpád; Lízal, František; Elcner, Jakub; Jícha, Miroslav
Tracking of fibres in a fluid flow is much more complicated than tracking of spherical particles. In fibre motion, the orientation of fibre against the flow direction plays a very important role. In addition to the standard equation of motion, additional equations for orientation and angular velocity must be solved during the tracking of fibres. A mathematical model describing fibre motion is introduced in this work. Capabilities of this model are demonstrated through simulations of fibre transportation by air in a channel flow. The importance of the terms in the equation of angular velocity are discussed.
High Quality Steel Casting by Using Advanced Mathematical Methods
(MDPI, 2018-12-04) Mauder, Tomáš; Štětina, Josef
The main concept of this paper is to utilize advanced numerical modelling techniques with self-regulation algorithm in order to reach optimal casting conditions for real-time casting control. Fully 3-D macro-solidification model for the continuous casting (CC) process and an original fuzzy logic regulator are combined. The fuzzy logic (FL) regulator reacts on signals from two data inputs, the temperature field and the historical steel quality database. FL adjust the cooling intensity as a function of casting speed and pouring temperature. This approach was originally designed for the special high-quality high-additive steel grades such as higher strength grades, steel for acidic environments, steel for the offshore technology and so forth. However, mentioned approach can be also used for any arbitrary low-carbon steel grades. The usability and results of this approach are demonstrated for steel grade S355, were the real historical data from quality database contains approximately 2000 heats. The presented original solution together with the large steel quality databases can be used as an independent CC prediction control system.

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