Papers by Miroslav Příhoda
The article deals with the possibilities to remove scale from a slab surface by means of a hydrau... more The article deals with the possibilities to remove scale from a slab surface by means of a hydraulic spray using pressurized water as well as with an analysis of the influence of the employed removal method on the thermal field of flat rolled products. The effect of spray descaling on the temperature field of the rolled material was established experimentally in a real mill in semi-operational conditions during the process of secondary spray descaling. The experiment was carried out with two sample slabs. The dimensions of a slab were 400 mm × 400 mm × 30 mm and the chemical composition was 0.20 % C, max. 1.4 % Mn, 0.045 % P, 0.045 % S and 0.009 % N. The temperature data for different depths below the surface of the slab being sprayed, obtained during the experiment, were processed using IHCP1D, a software developed on the basis of the Beck minimization-principle algorithm. The obtained values of the heat transfer coefficient represent the boundary condition for a numerical model of the spraying process. Its mean value established in the experiment was 18460 W/(m 2 K).
The article deals with the determination of the basic indicators of heat transfer in the continuo... more The article deals with the determination of the basic indicators of heat transfer in the continuous casting of steel, which can be described as an unsteady process with complicated boundary conditions for the solution. An analytical solution of this problem is practically impossible and, therefore, mathematical modelling is applied with a certain simplification of the real conditions and with a description of those criteria that influence the most the process of solidification and cooling. Using a simulation program and the knowledge of input parameters, it was possible to predict the distribution of the thermal field of a continuously cast blank in the course of its casting. Simulations also allowed us to deal with the issues of the inner structure, surface quality, mechanical properties of a continuously cast blank, metallurgical length, change in the thickness of a strand shell and overheating of steel. Some results obtained with numerical simulations are documented for concrete examples. Keywords: continuous casting of steel, modelling, heat transfer, shell, mould lanek obravnava dolo~anje osnovnih pokazateljev prenosa toplote pri kontinuirnem ulivanju jekla, ki se lahko opi{ejo kot nestabilen proces s kompliciranimi robnimi pogoji za re{itev. Analitska re{itev tega problema je prakti~no nemogo~a, zato je bilo uporabljeno matemati~no modeliranje z nekaterimi poenostavitvami realnih pogojev in z opisom tistih meril, ki najbolj vplivajo na proces strjevanja in ohlajanja. S programom za simulacijo in poznanjem vhodnih parametrov je bilo mogo~e predvideti razporeditev temperaturnega polja kontinuirno ulite gredice med njenim ulivanjem. Uporaba simulacije je omogo~ila opis notranje strukture, kvalitete povr{ine, mehanskih lastnosti kontinuirno ulite gredice, metalur{ke dol`ine, spreminjanja debeline strjene skorje in pregretja jekla. Nekateri rezultati, dobljeni z numeri~no simulacijo, so prikazani za konkretne primere. Klju~ne besede: kontinuirno ulivanje jekla, modeliranje, prenos toplote, skorja, kokila
Zenodo (CERN European Organization for Nuclear Research), Jun 30, 2022
This article deals with the effects of different structural arrangements inside a heat exchanger ... more This article deals with the effects of different structural arrangements inside a heat exchanger made of polypropylene tubes on the overall heat transfer coefficient. The experiments indicated that overall heat transfer coefficient k with stretched tubes was lower than the value observed when the tubes were slightly loosened. Tubes should not be loosened by more than 5 % of their length. If this value is exceeded, tubes may accumulate near the wall and their contact with water is insufficient; this results in reduced heat transfer. Equally important is to prevent tubes from attaching to each other. This may be achieved with a variety of turbulators. A turbulator may be any small object, metal or plastic, which is inserted among the tubes. Laboratory investigation indicated that turbulators can increase overall heat transfer coefficient by as much as 54 %compared to heat exchangers without turbulators, in identical operating conditions.
In the paper, the original methodology of the sediment thickness on the inner heat exchange area ... more In the paper, the original methodology of the sediment thickness on the inner heat exchange area of natural gas (NG) cooler's pipes is presented. This methodology enabled to create diagrams for the direct determination of sediment thickness in dependence on the degree of the gas cooling for coolers in NG Compressor Stations. Temperature range for the plotted diagrams is valid for the natural gas inlet temperature from 55 ° C to 40 ° C. At the same time, the diagrams for determination of the heat transfer coefficient, that is necessary to determinate the cooling performance of the NG cooler, were plotted.
Polish Journal of Environmental Studies, 2016
Our work presents the original mathematical model, which can be determined on the basis of the ac... more Our work presents the original mathematical model, which can be determined on the basis of the actual profits from electricity production in pumped storage hydropower plants (PSHP). The derived relationship was obtained by the dimensional analysis of the relevant physical parameters describing the production of energy. The main purpose of this paper is to prove whether a dimensional analysis can be a useful tool to describe the economic aspect of the phenomenon, as proved by its worth when examining technical phenomena. The mathematical model has been derived for PSHP Ružín in Slovakia, but its validity, based on the similarity theory, can be extended to any pumping power plant that works with the influx of water into the upper storage reservoir, and/or without the feed, respectively. The article discusses the effects of various parameters on the operating profit for the turbine operations and the costs associated with the pumping operation.
Nucleation and Atmospheric Aerosols, 2023
Manufacturing Technology, Nov 1, 2015
The paper experimentally and theoretically analyses the velocity profile of air in laboratory sta... more The paper experimentally and theoretically analyses the velocity profile of air in laboratory stand pipework. Flow velocities measured using a hot-wire anemometer and a vane anemometer were compared with the results of numerical simulation. The k-ε turbulence model was used in the numerical solution of flow rates and for determining the velocity profile using the ANSYS_CFX program. Using power law, this profile was described via an analytical function. Velocities determined by measuring with both instruments in the investigated place in the pipework showed lower values in comparison with the numerical solution. The cause of the difference in velocities was probably inaccurate stating of the volume flow of air through the ultrasonic anemometer. Measurements and simulation showed slight asymmetry in velocity which is related to an insufficiently large volume of the equalisation chamber and the mutual position of the input and output openings.
The article deals with the determination of the basic indicators of heat transfer in the continuo... more The article deals with the determination of the basic indicators of heat transfer in the continuous casting of steel, which can be described as an unsteady process with complicated boundary conditions for the solution. An analytical solution of this problem is practically impossible and, therefore, mathematical modelling is applied with a certain simplification of the real conditions and with a description of those criteria that influence the most the process of solidification and cooling. Using a simulation program and the knowledge of input parameters, it was possible to predict the distribution of the thermal field of a continuously cast blank in the course of its casting. Simulations also allowed us to deal with the issues of the inner structure, surface quality, mechanical properties of a continuously cast blank, metallurgical length, change in the thickness of a strand shell and overheating of steel. Some results obtained with numerical simulations are documented for concrete examples. Keywords: continuous casting of steel, modelling, heat transfer, shell, mould lanek obravnava dolo~anje osnovnih pokazateljev prenosa toplote pri kontinuirnem ulivanju jekla, ki se lahko opi{ejo kot nestabilen proces s kompliciranimi robnimi pogoji za re{itev. Analitska re{itev tega problema je prakti~no nemogo~a, zato je bilo uporabljeno matemati~no modeliranje z nekaterimi poenostavitvami realnih pogojev in z opisom tistih meril, ki najbolj vplivajo na proces strjevanja in ohlajanja. S programom za simulacijo in poznanjem vhodnih parametrov je bilo mogo~e predvideti razporeditev temperaturnega polja kontinuirno ulite gredice med njenim ulivanjem. Uporaba simulacije je omogo~ila opis notranje strukture, kvalitete povr{ine, mehanskih lastnosti kontinuirno ulite gredice, metalur{ke dol`ine, spreminjanja debeline strjene skorje in pregretja jekla. Nekateri rezultati, dobljeni z numeri~no simulacijo, so prikazani za konkretne primere. Klju~ne besede: kontinuirno ulivanje jekla, modeliranje, prenos toplote, skorja, kokila
DOAJ (DOAJ: Directory of Open Access Journals), Oct 1, 2009
Ispitivanje prijenosa topline u kalupu za kontinuirano lijevanje~elika. Rad prikazuje istra`ivanj... more Ispitivanje prijenosa topline u kalupu za kontinuirano lijevanje~elika. Rad prikazuje istra`ivanje temperaturnih profila i odre|ivanje toplinskih tijekova unutar kalupa u primarnoj zoni hla|enja. Jednolikost stvaranja ljeva~ke kore u kalupu ovisi o njegovom toplinskom radu, koji je uvjetovan raspodjelom temperature po visini stijenki konkretnog kalupa, {to temeljno utje~e na aktivnost cijele opreme za kontinuirano lijevanje. Idealan temperaturni profil du`visine stijenke kalupa jam~i jednoliko odvo|enje topline s povr{ine i nu`an je preduvjet kvalitatne proizvodnje. Posebno poglavlje rada obra|uje prevencije povr{inskog kidanja materijala koriste}i kine-ti~ku simulaciju u temperaturnom polju kalupa. Neki rezultati prikazani su na konkretnim primjerima.
Zenodo (CERN European Organization for Nuclear Research), Feb 28, 2023
The mathematical model of nitrogen oxides production described in the paper is developed on the b... more The mathematical model of nitrogen oxides production described in the paper is developed on the basis of dimensional analysis. The theory of dimensional analysis is used when a mathematical description of a phenomenon is lacking. The aim of using this method was to find out what is the relationship between the parameters of an operating hard coal combustion plant (boiler output, fuel calorific value, quantity and temperature of combustion air, negative pressure in the boiler and flue gas temperature) and the nitrogen oxides produced. The results obtained from the developed model are compared with the values measured on a real device.
MM Science Journal, 2020
The article presents the results of a numerical analysis of the flow conditions in the air distri... more The article presents the results of a numerical analysis of the flow conditions in the air distribution element in a combined refrigerator and freezer. A numerical analysis was carried out using the boundary conditions identified through an experiment. The article includes an analysis of the impact of the mesh type and the used turbulence models on the profile of the air flow velocity in the outlet openings of the used distribution element. The required ratio of the volumetric flow rates of the air absorbed by the fan, for the smaller to the larger outlet openings, should be 1:2.2. This air distribution ratio was monitored using three turbulence models: the SST model, the k- model and the RNG model, and two types of elements: tetrahedron and hexahedron, or combinations thereof. The obtained results were used as the basis for a modification of the geometry of the distribution element itself, and a concurrent modification of the size of the gap between the impeller and the internal space of the device.
Communications - Scientific letters of the University of Zilina, 2012
The paper describes a procedure for obtaining similarity criteria for a real object-a tundish for... more The paper describes a procedure for obtaining similarity criteria for a real object-a tundish for continuous casting machine (CCM) and its reduced physical model. The procedure is demonstrated on the basis of Navier-Stockes differential equations and with the help of dimensional analysis. To obtain similarity criteria dimensional analysis makes use of dimensions of those physical quantities which significantly influence the mentioned phenomenon. From the above it results that when modeling a concrete phenomenon with the help of this method it is inevitable to thoroughly know the physical substance of the phenomenon to expressly ensure the choice of all relevant quantities. On the basis of elaborated model laws the basic characteristics of flow (rate, flow volume, time intervals) were designed for the reduced model of the real CCM. The obtained dependences of characteristics feature the universal validity for all the models of tundishes.
Applied Sciences
This article describes an innovative method for the determination of heat flow (specific heat los... more This article describes an innovative method for the determination of heat flow (specific heat loss; linear heat flow density) from a one-metre length of a twin pipe directly-buried heat network. Such heat losses are currently described by applying analytical procedures based on the heat transfer theory. It is rather complicated to accurately express the heat loss using such procedures, due to the necessity to determine the individual values of thermal resistance. A simpler method to express heat loss is the balance method, as it requires measuring a temperature gradient Δt between the starting point of the heat network and the end point of the heat collection. A suitable measuring device must provide high-accuracy measurements of the temperature. In the case of very well-insulated distribution pipelines and short pipes, the temperature measurements must be accurate to the hundredths of a degree Celsius. It is impossible to install such devices as fixed equipment on every heat distri...
MATEC Web of Conferences
This article describes a methodology for the identification of cooling performance of a natural g... more This article describes a methodology for the identification of cooling performance of a natural gas cooler relative to the shape of its heat-transfer surface and presents the outputs of numerical solutions for four different shapes of heat-transfer surfaces in coolers designated as C_A, C_B, C_C and C_D. Calculations were carried out for a cooler with a single row of tubes, and for coolers with two through six rows of tubes that were positioned above one another with an alternating arrangement. In all of the surface shapes, the boundary conditions were respected in order to facilitate the identification of the shape of the heat-transfer surface which is the most appropriate for achieving maximum cooling performance. Out of these four shapes, the best results were observed with the heat-transfer surface of the cooler designated as C_A. The cooling performance of a 1 m long tube with such a surface was 1,650 W.
CERN European Organization for Nuclear Research - Zenodo, May 31, 2022
This article deals with the effects of a temperature, pressure, gravity, pipe flanges and saddle ... more This article deals with the effects of a temperature, pressure, gravity, pipe flanges and saddle supports of a measurement section of the pipeline on changes in the pipe geometry. The investigation was aimed, in particular, at examining changes in diameters of two pipeline sections relative to changes in their internal pressure, which ranged from 0 MPa to 6.0 MPa, and to changes in temperature, which ranged from 0 °C to 25 °C. As indicated by the results of a numerical simulation carried out within this research, a change in a diameter can be expressed most accurately if the effects of gravity, saddle supports and flanges are neglected. Changes in pipe diameters were examined merely as a function of changes in pressure and temperature. Gravity, flanges and saddle supports cause irregular pipe deformities that occur along the pipe circumference and length. These effects prevented identification of real values of changes in the pipe diameter on the measurement sections of the pipeline.
This paper describes numerical modeling of round billets solidification process during continuous... more This paper describes numerical modeling of round billets solidification process during continuous steel casting. Emphasis is placed not only on the mathematical nature of transmission events that affect the casting billet (heat conduction, convection and radiation), but also the methods of solving thermal problems (analytical, numerical). The numerical methods are discussed in detail the finite element method and the method of networks that form the core of the most common commercially used simulation software for modeling the temperature fields at various technological processes. In the research was compiled its own sophisticated software - Tefis - solving the problems of temperature fields by using of an explicit (numerical) method of networks. The actual solution is implemented using Fourier-Kirchhoff equation in differential form of enthalpy, which includes the velocity of solidified billet. By software Tefis are carried out a series of computer simulations and sensitivity analy...
MATEC Web of Conferences, 2020
Although the heat losses of the outdoor piping are minimised by thermal insulation, the distribut... more Although the heat losses of the outdoor piping are minimised by thermal insulation, the distribution of heat from the heating plant to individual consumers of the technological heating media is always accompanied by losses. In the case of large transported volumes of the flowing media, the loss values are negligible. The mathematical and physical analysis of the heat loss of the outdoor heat distribution systems, insulated and non-insulated, has been carried out while using the parameters measured on the real piping system.
Transactions of the VSB : Technical University of Ostrava, 2010
Analysed is the effect of the deposits formed on the inside and outside heat transfer surfaces of... more Analysed is the effect of the deposits formed on the inside and outside heat transfer surfaces of the natural gas coolers on the pressure losses. Sediments on both sides of the heat transfer surface represent the hydraulic resistance, overcoming of which, for the given degree of gas cooling, requires to increase the compression power and to exploit the higher volume of the cooling air. Operation of the cooler with the clean surface enables to save not negligible amount of the electrical power.
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Papers by Miroslav Příhoda