Energetický ústav

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Hydrogen Safety in Energy Infrastructure: A Review
(2025-10-17) Gregorovičová, Eva; Pospíšil, Jiří
For the transition to emission-free or low-emission energy, hydrogen is a promising energy carrier and fuel of the future with the possibility of long-term storage. Due to its specific properties, it poses certain safety risks; therefore, it is necessary to have a comprehensive understanding of hydrogen. This review article contains ten main chapters and provides, by synthesizing current findings primarily from standards and scientific studies (predominantly from 2023 to 2024), the theoretical basis for further research directed toward safe hydrogen infrastructure.
Effect of shear-thinning on pressure-swirl atomization
(2026-02-01) Jedelský, Jan; Cejpek, Ondřej; Malý, Milan; Kadlec, Martin; Smilek, Jiří; Strmiska, Pavel; Hájek, Ondřej
Atomization of non-Newtonian liquids is an underexplored topic despite their numerous spray applications. Key spray characteristics in such processes are mean droplet size and size distribution. Several studies demonstrate that non-Newtonian shear-thinning liquids can narrow the droplet size distribution compared to Newtonian liquids, reducing the number of excessively small or large droplets. Various spray applications benefit from minimized occurrence of droplets outside the desired size range. This applies to atomizers in spray towers or agricultural sprays where too-small droplets are blown away while those too large are ineffectively used. In this study, several non-Newtonian dilute aqueous solutions with different degrees of shear-thinning were prepared by mixing Xanthan Gum or Sodium carboxymethyl cellulose with deionized water. Their performance was compared with Newtonian sprays (water and water-glycerol solution) of comparable shear viscosity at defined shear rates. A common pressure-swirl atomizer was used, and a range of operational pressures along with varying viscosities allowed for examining the spraying process across a wide spectrum of Reynolds and Weber numbers. Velocity and size of droplets in the spray were measured simultaneously using a 1D phase Doppler anemometer. High-speed visualization was employed to track spray morphology and the breakup process. Calculations of the flow parameters inside the atomizer complemented these outcomes. Results show that varying viscosity and shear-thinning behaviour influence the flow dynamics from the liquid entry into the atomizer to the fully developed spray. Viscoelasticity complicates these processes further. The discharge occurs near the infinite-shear rate viscosity plateau, and its character depends, primarily on the flow conditions near the exit orifice. The shear-thinning and elasticity slightly affects liquid breakup, with production of more frequent and longer-lasting ligaments. Droplet size reduces with increasing pressure as expected, and this effect is more pronounced for non-Newtonians, the impact on the Relative span factor is inconsistent. Downstream droplet size increases for all liquids due to coalescive droplet collisions, with the secondary breakup and evaporation being ineffective.
Numerical Study on Microdroplets Interaction with Solid Surfaces
(EDP Sciences, 2025-09-05) Mlkvik, Marek; Vach, Matej; Hájek, Jiří; Jedelský, Jan
The presented study addresses the issue of deposition and splashing of microscopic droplets upon impact with a solid surface. It presents the results of numerical simulations using the commercial code ANSYS Fluent 2025R accelerated using a newly implemented multiphase VOF GPU solver. The simulations allowed us to study the whole process with both spatial and temporal resolution, which is currently on the edge of the experimental capabilities. The simulation results were in qualitative agreement with published experimental data and captured in detail the droplet deposition or formation of micro ligaments, and the subsequent separation of secondary microdroplets that propagate upon splashing into the surroundings. An important finding is the effect of high surface roughness on droplet impact. If the value of roughness is comparable to the droplet diameter, the dissipation of kinetic energy occurs, which shifts the limit of the transition to the splash regime to higher impact velocities compared to smooth surfaces. Another effect observed was the thickness of the liquid film on the rough surface. It was found that a liquid film with a thickness comparable to the surface roughness promotes splash formation, whereas a thicker film does not show this effect.
Implementation of the equivalent temperature measurement system as a part of the vehicle Heating, ventilation and Air-conditioning unit
(BioMed Central, 2015-06-29) Fišer, Jan; Povalač, Aleš; Urbanec, Tomáš; Pokorný, Jan; Fojtlín, Miloš
Thermal comfort evaluation based on the Comfort zone diagram is relatively new and promising method [1] developed by Hkan O. Nilsson [2]. The method was developed mainly for non uniform indoor environments [3] such as vehicle cabins [4]. Mean thermal vote (MTV) is correlated with equivalent temperature, which is typically measured by a thermal manikin with clothing or by a sensor with heated surface. This fact is the advantage of this method because prediction of thermal comfort is based on a measurable physical phenomenon which is called dry heat loss. The essence of this method inspired us to develop a measurement system that will be based on miniaturised and cost effective equivalent temperature sensors. Such sensors could be easily integrated into the surroundings of seated human and could provide data about local thermal comfort as feedback information for HVAC control unit. Our project, which started last year, is called Innovative control for Heating, Ventilation and Air Conditioning systems, iHVAC.
Technical and economic optimization of cogeneration technology using combustion and gasification
(Czech Technical University in Prague, 2014-02-28) Lisý, Martin; Baláš, Marek; Špiláček, Michal; Skála, Zdeněk
This paper presents the technical and economic optimization of new microcogeneration technology with biomass combustion or biomass gasification used for cogeneration of electrical energy and heat for a 200 kW unit. During the development phase, six possible connection solutions were investigated, elaborated and optimized. This paper presents a basic description of the technology, a description of the technological solutions, and especially the results of balance and financial calculations, ending with a comparison and evaluation of the results.

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