Energetický ústav

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Structure of Flow Fields Downstream of Two Different Swirll Generators
(2012-05-14) Štefan, David; Rudolf, Pavel
This paper discusses the comparison of the flow fields downstream of two different swirl generators. Both swirl generators are used to imitate the flow at the exit of the hydraulic turbine runner and study spatio-temporal behaviour of the swirling flow in the draft tube (i.e. outlet diffuser part of the hydraulic turbine), which undergoes breakdown into vortex rope. Unsteady CFD computations are carried out for identical Reynolds number. Resulting velocity and vorticity profiles are correlated with the structure of the vortex rope. Difference in excited pressure pulsations is illustrated on amplitudefrequency spectra of static wall pressure.
Development of an Effervescent Atomizer for Industrial Burners
(American Chemical Society, 2009-11-09) Jedelský, Jan; Jícha, Miroslav; Sláma, Jaroslav; Otáhal, Jan
The present work is conducted with the aim of developing an effervescent atomizer for industrial burners that will generate a fine and steady spray in large turn-down ratio. The atomizer is fed with light heating oil (LHO) and uses air as an atomizing medium. First, a basic classification is made of the published design concepts of effervescent atomizers investigated by different researchers. Three distinct types of such atomizers are recognized. A single-hole, plain-orifice atomizer with an "outside-in" gas injection configuration was chosen for this study. The basic geometric parameters that may significantly influence atomizer performance are described. An experimental study of the effervescent atomizer was conducted to evaluate the influence of operational conditions and of several geometric parameters on the drop size in the spray. The Sauter mean diameter of drops was measured using a Phase/Doppler Particle Analyser. The study covers the size and number of aerator holes, their location, and the diameter of the mixing chamber. The influence of these parameters on the spray quality was evaluated at atomizing pressures of 0.1, 0.3 and 0.5 MPa and gas to liquid mass flow-rate ratios (GLR) of 2, 5 and 10 %. The main goal of this work is to develop a new procedure for the design of effervescent atomizers. This procedure is based upon our experimental results and it is also supported by the findings of other authors. It allows for the determination of the key geometric parameters of the atomizer to achieve sprays of minimum mean drop size for defined values of liquid flow rate, air supply pressure and GLR. The article also studies the optimization of the exit orifice size and of other parameters, such as the size of the mixing chamber (internal diameter and length), and the number, size, and position of aeration holes.
Hydrodynamic cavitation-enhanced activation of sodium percarbonate for estrogen removal
(IWA Publishing, 2023-12-01) Odehnalová, Klára; Přibilová, Petra; Maršálková, Eliška; Zezulka, Štěpán; Pochylý, František; Rudolf, Pavel; Maršálek, Blahoslav
The present paper investigated the potential of hydrodynamic cavitation (HC) as an effective tool for activating sodium percarbonate (SPC). The method's efficiency was demonstrated by effectively removing estrogens, which are pollutants that have adverse impacts on aquatic ecosystems. The effects of the SPC concentration, temperature of solution, and cavitation time were evaluated. After SPC/HC treatment, the removal of estrogens was monitored by LC-MS/MS. Already after 4 s of treatment and 24 h of reaction time, more than 97% of estrogens (initial concentration of 300 ng/L) were removed. The effect of post-treatment time is not considered in several papers, even though it seems to be crucial and is discussed here. The results were supported by the values of degradation rate constants, which fit the pseudo-first-order kinetic model. We also verified that HC alone was not effective for estrogen removal under the selected conditions. The sustainability of the SPC/HC system was evaluated based on electric energy per order calculation. The combination of SPC and HC is a promising approach for rapidly degrading micropollutants such as estrogenic compounds without the need for additional technological steps, such as pH or temperature adjustment.
Applicability of Human Thermophysiological Model for Prediction of Thermal Strain in PPE
(MDPI, 2023-06-15) Lunerová, Kamila; Řehák Kopečková, Barbora; Pokorný, Jan; Mašín, Michal; Kaiser, David; Fialová, Vladimíra; Fišer, Jan
The use of personal protective equipment (PPE) is essential to protect the human body in hazardous environments or where there is a risk of CBRN agents. However, PPE also poses a barrier to evaporative heat dissipation, therefore increasing heat accumulation in the body. In our research, we investigated the applicability of thermophysiological models for the prediction of thermal strain and the permissible working time in a contaminated environment when the usage of protective ensembles is required. We investigated the relationship between the thermal insulation characteristics of four types of PPE against CBRN agents and the induced thermal strain in a set of real physiological strain tests with human probands wearing the PPE in a climatic chamber. Based on the results, we compared the predictions using two thermophysiological models-Predicted Heat Strain Index (PHS) and FIALA-based model of thermal comfort (FMTK)-with the experimental data. In order to provide a user-friendly platform for the estimation of thermal stress in PPE, a user-friendly computational tool, Predictor of Thermal Stress (PTS), was developed. The PTS tool is based on an extensive database of simulated calculations using an FMTK model based on PPE characteristics, environmental conditions, individual parameters, and expected workload. The PTS tool was validated by means of the results from real tests in a climatic chamber. The PTS was shown to be an easy-to-use computational tool, which can be run on a regular PC, based on real data applicable for the estimation of the permissible work time limit with regard to thermal strain in PPE under various conditions.
Plug-in Hybrids vs Battery Powered Vehicles - Optimisation Model for Charging Infrastructure at a University Campus
(AIDIC S.r.l., 2022-09-01) Cabalka, Matouš; Charvát, Pavel; Fišer, Jan; Popela, Pavel; Pešek, Martin
University campuses, as well as other workplaces, provide great opportunity for electric vehicle (EV) charging. A simulation model was created in GAMS (General Algebraic Modeling System) for the optimization study concerning charging infrastructure at the Faculty of Mechanical Engineering at Brno University of Technology. The study was conducted for 20 plug-in hybrid electric vehicles (PHEVs) and 20 battery electric vehicles (BEVs). This assumption was based on the similar sales of PHEVs and BEVs in the EU in 2021. The PHEVs could only be charged at alternating current (AC) chargers (using the EV’s built-in chargers) while the BEVs could be charged at both the AC chargers and the high-power DC (direct current) chargers. The AC chargers are much cheaper to install but because of the relatively small power of the BEV’s built-in chargers the charging at AC chargers takes a long time. As the university employees have flexible working hours, varying arrival times of the EVs as well as the varying duration of their stay on the campus was considered. The state of charge (SOC) of the EV’s batteries at the time of arrival on the campus was also considered. For the considered sets of parameters 3 DC chargers and 6 AC chargers covered 96 % of the total demand. A replacement of one DC charger with two AC chargers led to the decrease of coverage to 95 % but with significant reduction of capital costs.

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