Energetický ústav

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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.
Transport and deposition of inhaled fibers in a realistic female airway model: A combined experimental and numerical study
(2025-08-01) Prinz, František; Kánská, Jana; Elcner, Jakub; Hájek, Ondřej; Jícha, Miroslav; Lízal, František
This study presents a combined experimental and numerical investigation of fiber transport and deposition in a realistic model of the female respiratory tract, extending to the seventh generation of branching. Numerical simulations were performed using the Euler-Lagrange Euler-Rotation (ELER) method, an efficient alternative to conventional Finite Volume Methods that benefits from explicit formulation and vast scalability, enabling fast parallelization on high-performance clusters. The ELER method was coupled with the Lattice Boltzmann Method (LBM) to simulate fiber dynamics under a realistic inspiratory flow profile. Experimental validation was conducted using an identical physical airway replica. The results demonstrated good agreement between simulations and experiments in the upper airways and trachea, with some discrepancies in the bifurcations, likely owing to the challenges of modeling complex turbulent flow with ELER. This method is more accurate than corresponding effective diameter simulations. Deposition patterns were analyzed as a function of fiber dimensions, revealing higher accuracy of the ELER method for smaller particles and confirming the tendency of higher aspect ratio fibers to penetrate deeper into the lungs. The orientation-dependent deposition mechanism was deployed, underscoring the importance of solving the actual orientations of the fibers. While advancing our understanding of fiber transport in female airways, the findings also reveal limitations in current numerical techniques, particularly in bifurcations. This study emphasizes the distinct behavior of fibrous versus spherical particles, with fibers exhibiting a greater propensity to reach deeper lung regions, which has significant implications for inhalation toxicology and drug delivery.
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.
Simulation of the acoustic wave propagation using a meshless method
(EDP Sciences, 2017-05-12) Bajko, Jaroslav; Niedoba, Pavel; Čermák, Libor; Jícha, Miroslav
This paper presents numerical simulations of the acoustic wave propagation phenomenon modelled via Linearized Euler equations. A meshless method based on collocation of the strong form of the equation system is adopted. Moreover, the Weighted least squares method is used for local approximation of derivatives as well as stabilization technique in a form of spatial fltering. The accuracy and robustness of the method is examined on several benchmark problems.

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