EÚ-odbor energetického inženýrství

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Development Boiling to Sprinkled Tube Bundle
(EDP Sciences, 2016-03-28) Kracík, Petr; Pospíšil, Jiří
This paper presents results of a studied heat transfer coefficient at the surface of a sprinkled tube bundle where boiling occurs. Research in the area of sprinkled exchangers can be divided into two major parts. The first part is research on heat transfer and determination of the heat transfer coefficient at sprinkled tube bundles for various liquids, whether boiling or not. The second part is testing of sprinkle modes for various tube diameters, tube pitches and tube materials and determination of individual modes' interface. All results published so far for water as the falling film liquid apply to one to three tubes for which the mentioned relations studied are determined in rigid laboratory conditions defined strictly in advance. The sprinkled tubes were not viewed from the operational perspective where there are more tubes and various modes may occur in different parts with various heat transfer values. The article focuses on these processes. The tube is located in a low-pressure chamber where vacuum is generated using an exhauster via ejector. The tube consists of smooth copper tubes of 12 mm diameter placed horizontally one above another.
Identification of Wind-Induced Particle Resuspension in Urban Environment Using CFD Modelling
(MDPI, 2023-01-01) Linda, Jakub; Pospíšil, Jiří; Köbölová, Klaudia
Air pollution caused by particulate matter (PM) is a current problem in many cities. With the introduction of strict emission limits and electric cars, lower particle production is expected in the future. However, there are sources of particles that cannot be easily influenced. These include resuspension, where particles deposited on surfaces re-enter the air, causing pollution multiple times. Resuspension can account for up to 18% of the total emissions in some cases. The present paper focuses on the use of the computational fluid dynamics (CFD) tools to describe the flow in a street canyon where resuspension by wind occurs. Based on the calculated flow, a resuspension model is applied to see where resuspension occurs and how far the particles can travel. The shear stresses on the surfaces and the character of the flow field in the boundary layer are evaluated. Different building configurations and flow parameters are tested using a simple 2D model. The model makes it possible to see in which parts of the street canyon resuspension can occur. It shows that the particles leave the street canyon only from the surfaces where the conditions are suitable for resuspension. These particles then enter the mainstream. However, most of the particles stay in the canyon, which can cause resuspension to pollute the air repeatedly. This effect can have a severe impact on human health. The total dispersion of particles in the urban environment is evaluated. The results may be useful for cities that clean the streets, as it is clear which areas will benefit most from the cleaning.
Ceramic filters for high-temperature flue gas filtration and their regeneration: A review of the current state of knowledge
(ELSEVIER, 2024-07-22) Gregorovičová, Eva; Pospíšil, Jiří
The combustion of solid fuels in combustion devices produces pollutants that have a negative impact on human health and the environment. One way to reduce the concentration of sub-micron particulate matter (PM) in the flue gas is to filter the flue gas using ceramic filters. Their main advantage, compared to other flue gas cleaning methods, is the possibility of using them at high flue gas temperatures (>400 degrees C). This review article presents an overview of research articles published mainly between 2020 and 2023 on flue gas filtration using ceramic filters (candles, membranes, foams, and discs) and on their regeneration. Ceramic filters are used in many flue gas cleaning applications where the cleanliness of hot flue gas is required. Their inclusion in the flue gas path is associated with increased energy consumption for forced exhaust and pressure pulse filter regeneration. The review also includes an introduction to the materials and methods used to manufacture the filters and to test their effectiveness. This review provides a comprehensive overview of the current state of knowledge on ceramic filters. Specifically, the focus is on the filtration efficiency, pressure drop, and regeneration of the ceramic filters under consideration.
Influence of temperature on the production and size distribution of fine particles released from beech wood samples
(2018-05-23) Poláčik, Ján; Pospíšil, Jiří; Šnajdárek, Ladislav; Sitek, Tomáš
This study deals with laboratory investigation of fine particulate matter production over controlled heating of beech wood samples in the atmosphere with 21% of oxygen. From carried out measurements follow that majority of emitted fine particles is in the range 40 nm to 500 nm. The peak number of particles is between 100 nm an 300 nm. The mass concentration of produced particulate matter increases proportionally with increasing size of the sample. The number of particles is increasing too, but not proportionally. In the second step, the samples in form of sawdust, bark and heartwood were analyzed from the view of particulate matter production. Obtained results are strongly influenced by actual combustion conditions that significantly differ between wood samples forms. It is not easy to find any clear trend between temperature and size distribution of produced particles. From the general view, the bark produces higher number concentration of ultrafine particles in comparison with heartwood and sawdust samp
Measurement of an electronic cigarette aerosol size distribution during a puff
(EDP SCIENCES, 2017-05-12) Bělka, Miloslav; Lízal, František; Jedelský, Jan; Jícha, Miroslav; Pospíšil, Jiří
Electronic cigarettes (e-cigarettes) have become very popular recently because they are marketed as a healthier alternative to tobacco smoking and as a useful tool to smoking cessation. E-cigarettes use a heating element to create an aerosol from a solution usually consisting of propylene glycol, glycerol, and nicotine. Despite the wide spread of e-cigarettes, information about aerosol size distributions is rather sparse. This can be caused by the relative newness of e-cigarettes and by the difficulty of the measurements, in which one has to deal with high concentration aerosol containing volatile compounds. Therefore, we assembled an experimental setup for size measurements of e-cigarette aerosol in conjunction with a piston based machine in order to simulate a typical puff. A TSI scanning mobility particle sizer 3936 was employed to provide information about particle concentrations and sizes. An e-cigarette commercially available on the Czech Republic market was tested and the results were compared with a conventional tobacco cigarette. The particles emitted from the e-cigarette were smaller than those of the conventional cigarette having a CMD of 150 and 200 nm. However, the total concentration of particles from e-cigarette was higher.

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