EÚ-odbor energetického inženýrství

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Experimental Study on Spray Breakup in Turbulent Atomization Using a Spiral Nozzle
(MDPI, 2019-12-03) Krištof, Ondřej; Bulejko, Pavel; Svěrák, Tomáš
Spiral nozzles are widely used in wet scrubbers to form an appropriate spray pattern to capture the polluting gas/particulate matterwith the highest possible efficiency. Despite this fact, and a fact that it is a nozzle with a very atypical spray pattern (a full cone consisting of three concentric hollow cones), very limited amount of studies have been done so far on characterization of this type of nozzle. This work reports preliminary results on the spray characteristics of a spiral nozzle used for gas absorption processes. First, we experimentally measured the pressure impact footprint of the spray generated. Then effective spray angles were evaluated from the photographs of the spray and using the pressure impact footprint records via Archimedean spiral equation. Using the classical photography, areas of primary and secondary atomization were determined together with the droplet size distribution, which were further approximated using selected distribution functions. Radial and tangential spray velocity of droplets were assessed using the laser Doppler anemometry. The results show atypical behavior compared to different types of nozzles. In the investigated measurement range, the droplet-size distribution showed higher droplet diameters (about 1 mm) compared to, for example, air assisted atomizers. It was similar for the radial velocity, which was conversely lower (max velocity of about 8 m/s) compared to, for example, effervescent atomizers, which can produce droplets with a velocity of tens to hundreds m/s. On the contrary, spray angle ranged from 58 degrees and 111 degrees for the inner small and large cone, respectively, to 152 degrees for the upper cone, and in the measured range was independent of the inlet pressure of liquid at the nozzle orifice.
An overview of slagging and fouling indicators and their applicability to biomass fuels
(Elsevier, 2021-06-15) Lachman, Jakub; Baláš, Marek; Lisý, Martin; Lisá, Hana; Milčák, Pavel; Elbl, Patrik
Slagging and fouling are common problems associated with biomass firing. The different nature of the mineral and phase composition of biomass ash makes the vast experience with coal firing insufficient for its translation to biomass fuels, especially when it comes to slagging and fouling behavior. Biomass tends to have lower ash content than coals; however, it is often rich in volatile alkalis. The mineral deposits found on boiler walls and superheater tubes are often comprised of alkali compounds. Numerous studies on ash melting and particle sticking behavior have been conducted. Laboratory observed ash fusion temperatures are commonly used to evaluate the slagging and fouling propensity of fuels. The tests are often time consuming, therefore several predictive indices have been developed to estimate the propensity based on the ash composition alone. Thermodynamic models as well as neural networks have also been applied to this end. However, for practical in the field purposes, the ash fusion tests and predictive indices are preferred because of their convenience. An overview of these indices is presented in this work. A sizeable dataset has been collected in order to statistically evaluate the applicability of the indices and of several AFT prediction formulas. General trends in ash composition on this extensive dataset have also been illustrated. Finally, a more convenient graphical solution is presented for preliminary slagging and fouling predictions.
Conditions Affecting Wind-Induced PM10 Resuspension as a Persistent Source of Pollution for the Future City Environment
(MDPI, 2022-07-27) Linda, Jakub; Pospíšil, Jiří; Matušková, Klaudia; Ličbinský, Roman; Huzlík, Jiří; Karel, Jan
Air pollution by particulate matter (PM) in cities is an ongoing problem with increasing severity. The biggest PM contributors are traffic and domestic fire burning. With the shift towards electromobility and the use of low-emission fuels, attention should be shifted to less mentioned sources of pollution. Such sources of pollution include wind-induced resuspension. This study focuses on determining the threshold wind speed causing the resuspension of particulate matter (TWSR) with aerodynamic diameter smaller than 10 mu m. A methodology is introduced that examines how data could be treated to identify its characteristics (for locations where only PM10 data are available). The most significant monitored parameters are air humidity, wind direction, time of the day, and surface type. The characteristic wind speeds causing resuspension are identified in four locations for different times of day. It was proven that at times of intense human activity, particles are lifted by wind more easily. The mean threshold wind speed causing resuspension in the studied urban environment was identified as 1.58 m/s at a height of 2 m above the surface. The wind speeds were also compared with experimental studies of resuspension. The results proved correspondence between the identified wind speeds and the experimental results.
Heat transfer during condensation of water vapour in the presence of non-condensable gas in vertical tube of small diameter
(Elsevier, 2022-12-01) Toman, Filip; Kracík, Petr; Pospíšil, Jiří
The paper deals with a detailed analysis of published analytical relations for heat transfer during steam condensation in a vertical tube. The historical development of the approaches and the chronological development of the used analytical relations are presented. Attention is focused on the description of the processes at the gas phase-condensate film interface as well as on the inclusion of the influence of the presence of non-condensable gases. The analytical relations in 12 modifications are compared with each other for the same geometrical configuration of the vertical tube and identical boundary conditions. The authors performed comparative experimental measurements of the heat transfer coefficient during condensation of the vapour-gas mixture in vertical tubes of three diameters, namely 16, 20 and 26mm. Based on a comparison of the experimental results and analytical relations, recommendations are made on the validity interval of the tested relations.
A Heat Exchanger with Water Vapor Condensation on the External Surface of a Vertical Pipe
(MDPI, 2022-08-03) Kracík, Petr; Toman, Filip; Pospíšil, Jiří; Kraml, Stanislav
The paper is concerned with water vapor condensation on vertical pipes. The vertical position of pipes in a condenser is not discussed very often. Its application has a number of particularities in terms of the numerical determination of heat transfer. In the first stage of this paper, the authors focus on the experimental identification of heat transfer during vapor condensation on vertical pipes with a diameter of 14.0 × 1.0 mm. The pipes are placed in a narrow channel and the steam flows around them in a perpendicular direction. Two channel widths were tested, i.e., 20.0 and 24.0 mm. In the second stage, numerical modelling (CFD) is used for a detailed identification of the vapor velocity fields near the pipes. In the third stage, the results of the experimental measurements and numerical modelling are compared with data published by various authors. There are studies in the literature dealing with axial flow around vertical pipes; however, the associated results are based on conditions which are distinct from those applied in our study. The outcome of this paper is the specification of the heat transfer coefficient and the calculation formulas precisely describing the studied condenser configuration.

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