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Miroslav Raudensky - One of the best experts on this subject based on the ideXlab platform.
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effects of oxide layer on leidenfrost temperature during spray Cooling of steel at high temperatures
International Journal of Heat and Mass Transfer, 2015Co-Authors: Monika Chabicovsky, M. Hnízdil, Ampere A. Tseng, Miroslav RaudenskyAbstract:Abstract Spray Cooling is a common Cooling method used in many high-temperature metal processes. Using a combined numerical and experimental approach, the influence of the oxide layer on the Leidenfrost temperature during spray Cooling of surfaces at high temperatures was investigated. The heat transfer from a metal surface covered by an oxide layer is described using the concept of the effective heat transfer coefficient and this concept is extended to the Leidenfrost temperature. The effective Leidenfrost temperature is introduced. The prediction of the effective Leidenfrost temperature is compared with the numerical simulation and with the experiment, which was conducted on an austenitic stainless steel plate with varied oxide layer thicknesses. The test plate with the oxide layers was heated to 1000 °C and then cooled using flat jet nozzles. The present study confirms that the use of water in the spray Cooling of hot surfaces can create a situation where the oxide layer not only serves as insulation but can also increase the Cooling Intensity for short time period, mainly by a shift of the Leidenfrost temperature.
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Impact of the oxide scale on spray Cooling Intensity
2014Co-Authors: Jan Horsky, J. Hrabovsky, Miroslav RaudenskyAbstract:Heat treatment of steel is attended by oxide scales growth with various physical properties. The most common and most dominant impact of the oxide scale layers is on the surface quality and mechanical properties of steel. This paper is focused on study of influence of the oxide scale on Cooling Intensity. Spray Cooling is a typical technique used in heat treatment and other metallurgical processes where controlled temperature regimes are required. Cooling Intensity is primarily affected by spray parameters as pressure and coolant impingement density. It is not frequently reported but even thin layers of oxides can significantly modify the Cooling Intensity. This effect is dominant in the Cooling of steel surfaces at high surface temperatures. Study of the influence of the oxide scale layers on Cooling Intensity was carried out by experimental measurements and numerical analysis. Experimental measurements compare the Cooling of scale-free surfaces and oxidized surfaces. Experimental investigations show a difference in the Cooling Intensity. Numerical analyses were prepared to simulate Cooling of the samples with different oxide scale layers and different thermal conductivity of scales. Even a scale layer of several microns can significantly modify the Cooling Intensity. A low thermal conductivity of the oxides can make the Cooling more intensive. The paper provides experimental evidence of this fact and numerical study of the oxide scale layer thickness and thermal conductivity on the influence on the spray Cooling with boiling. The Leidenfrost phenomenon and change in surface temperature provides key to the explanation why the hot surface covered by the oxides is sometimes cooled more intensively than the clean surface.
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influence of the water temperature on the Cooling Intensity of mist nozzles in continuous casting vpliv temperature vode na intenziteto ohlajanja z megli nimi obami pri kontinuirnem ulivanju
2012Co-Authors: Miroslav Raudensky, M. Hnízdil, Jong Yeon Hwang, Sang Hyeon Lee, Seong Yeon KimAbstract:Small mist nozzles used in continuous casting were tested for heat-transfer Intensity. These nozzles are used in the secondary Cooling area of a steel slab casting machine. The impact pressure distribution was measured first. The laboratory measurements of the Cooling Intensity (the HTC distribution) were performed with a variable water temperature. A temperature range from 20 °C to 80 °C was used in the tests. Surprisingly, the water temperature was found to have a strong influence. The most noticeable effect is a shift in the Leidenfrost temperature to low temperatures. Changing the water temperature from 20 °C to 80 °C caused a change in the Leidenfrost temperature of 130 °C. This can be significant and can change the Cooling character of the continuous casting machine. It is interesting that with an increase in the Cooling Intensity, following an increase in the water temperature in a high-temperature region (above the Leidenfrost temperature), there is a small difference of about 30 W/(m 2 K). Surprisingly, high differences in the Leidenfrost temperature were found for an intensive Cooling, where a difference of only 20 °C in the coolant temperature makes a difference of about 100 °C in the Leidenfrost temperature. The results of the experiments performed with an elevated water temperature showed a high sensitivity of the Cooling Intensity to this parameter. The decreasing effect of the Cooling Intensity related to the water temperature is more important for the spray Cooling of high intensities.
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secondary Cooling in continuous casting and leidenfrost temperature effects
Ironmaking & Steelmaking, 2005Co-Authors: Miroslav Raudensky, Jan HorskyAbstract:AbstractThe present study was motivated by problems at continuous casting plants where a variety of thermally induced defects were observed. The paper outlines an experimental method for the measurement of Cooling Intensity in the secondary Cooling area where nozzles are applied. The precision of a variety of experimental methods is discussed. The nozzles have been investigated in terms of pressure setting, the influence of casting speed, and behaviour in the overlapping areas. The tests have provided information on heat transfer coefficient characteristics and heat flux distribution on the cooled steel surface. The paper presents new experimental findings regarding specification of the Leidenfrost temperature, which is the point between high and low surface temperature regions where a large difference in Cooling Intensity is observed. The paper also deals with the problems of homogeneity of Cooling along the nozzle spray angle and in the overlapping area where thermal 'stripes' occur. The sensitivity of ...
Hein A.m. Daanen - One of the best experts on this subject based on the ideXlab platform.
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The effect of pre-Cooling Intensity on Cooling efficiency and exercise performance
Journal of sports sciences, 2010Co-Authors: Nina Bogerd, Claudio Perret, Cornelis P. Bogerd, René M. Rossi, Hein A.m. DaanenAbstract:Although pre-Cooling is known to enhance exercise performance, the optimal Cooling Intensity is unknown. We hypothesized that mild Cooling opposed to strong Cooling circumvents skin vasoconstriction and thermogenesis, and thus improves Cooling efficiency reflected in improved time to exhaustion. Eight males undertook three randomized trials, consisting of a pre-Cooling and an exercise session. During the pre-Cooling, performed in a room of 24.6±0.4°C and 24±6% relative humidity, participants received either 45 min of mild Cooling using an evaporative Cooling shirt or strong Cooling using an ice-vest. A no-Cooling condition was added as a control. Subsequent cycling exercise was performed at 65% VO2peak in a climatic chamber of 29.3±0.2°C and 80±3% relative humidity. During the pre-Cooling session, mild and strong Cooling decreased the skin blood flow compared with the control. However, no differences were observed between mild and strong Cooling. No thermogenesis was observed in any conditions investigated. The reduction of body heat content after pre-Cooling was two times larger with strong Cooling (39.5±8.4 W · m-2) than mild Cooling (21.2±5.1 W · m-2). This resulted in the greatest improvement in time to exhaustion with strong Cooling. We conclude that the Cooling intensities investigated had a similar effect on Cooling efficiency (vasoconstriction and thermogenesis) and that the improved performance after strong Cooling is attributable to the greater decrease in body heat content. © 2010 Taylor & Francis.
Monika Chabicovsky - One of the best experts on this subject based on the ideXlab platform.
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effects of oxide layer on leidenfrost temperature during spray Cooling of steel at high temperatures
International Journal of Heat and Mass Transfer, 2015Co-Authors: Monika Chabicovsky, M. Hnízdil, Ampere A. Tseng, Miroslav RaudenskyAbstract:Abstract Spray Cooling is a common Cooling method used in many high-temperature metal processes. Using a combined numerical and experimental approach, the influence of the oxide layer on the Leidenfrost temperature during spray Cooling of surfaces at high temperatures was investigated. The heat transfer from a metal surface covered by an oxide layer is described using the concept of the effective heat transfer coefficient and this concept is extended to the Leidenfrost temperature. The effective Leidenfrost temperature is introduced. The prediction of the effective Leidenfrost temperature is compared with the numerical simulation and with the experiment, which was conducted on an austenitic stainless steel plate with varied oxide layer thicknesses. The test plate with the oxide layers was heated to 1000 °C and then cooled using flat jet nozzles. The present study confirms that the use of water in the spray Cooling of hot surfaces can create a situation where the oxide layer not only serves as insulation but can also increase the Cooling Intensity for short time period, mainly by a shift of the Leidenfrost temperature.
M. Hnízdil - One of the best experts on this subject based on the ideXlab platform.
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effects of oxide layer on leidenfrost temperature during spray Cooling of steel at high temperatures
International Journal of Heat and Mass Transfer, 2015Co-Authors: Monika Chabicovsky, M. Hnízdil, Ampere A. Tseng, Miroslav RaudenskyAbstract:Abstract Spray Cooling is a common Cooling method used in many high-temperature metal processes. Using a combined numerical and experimental approach, the influence of the oxide layer on the Leidenfrost temperature during spray Cooling of surfaces at high temperatures was investigated. The heat transfer from a metal surface covered by an oxide layer is described using the concept of the effective heat transfer coefficient and this concept is extended to the Leidenfrost temperature. The effective Leidenfrost temperature is introduced. The prediction of the effective Leidenfrost temperature is compared with the numerical simulation and with the experiment, which was conducted on an austenitic stainless steel plate with varied oxide layer thicknesses. The test plate with the oxide layers was heated to 1000 °C and then cooled using flat jet nozzles. The present study confirms that the use of water in the spray Cooling of hot surfaces can create a situation where the oxide layer not only serves as insulation but can also increase the Cooling Intensity for short time period, mainly by a shift of the Leidenfrost temperature.
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influence of the water temperature on the Cooling Intensity of mist nozzles in continuous casting vpliv temperature vode na intenziteto ohlajanja z megli nimi obami pri kontinuirnem ulivanju
2012Co-Authors: Miroslav Raudensky, M. Hnízdil, Jong Yeon Hwang, Sang Hyeon Lee, Seong Yeon KimAbstract:Small mist nozzles used in continuous casting were tested for heat-transfer Intensity. These nozzles are used in the secondary Cooling area of a steel slab casting machine. The impact pressure distribution was measured first. The laboratory measurements of the Cooling Intensity (the HTC distribution) were performed with a variable water temperature. A temperature range from 20 °C to 80 °C was used in the tests. Surprisingly, the water temperature was found to have a strong influence. The most noticeable effect is a shift in the Leidenfrost temperature to low temperatures. Changing the water temperature from 20 °C to 80 °C caused a change in the Leidenfrost temperature of 130 °C. This can be significant and can change the Cooling character of the continuous casting machine. It is interesting that with an increase in the Cooling Intensity, following an increase in the water temperature in a high-temperature region (above the Leidenfrost temperature), there is a small difference of about 30 W/(m 2 K). Surprisingly, high differences in the Leidenfrost temperature were found for an intensive Cooling, where a difference of only 20 °C in the coolant temperature makes a difference of about 100 °C in the Leidenfrost temperature. The results of the experiments performed with an elevated water temperature showed a high sensitivity of the Cooling Intensity to this parameter. The decreasing effect of the Cooling Intensity related to the water temperature is more important for the spray Cooling of high intensities.
Chabičovský Martin - One of the best experts on this subject based on the ideXlab platform.
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Prediction of Leidenfrost Temperature in Spray Cooling for Continuous Casting and Heat Treatment Processes
'MDPI AG', 2020Co-Authors: Hnízdil Milan, Komínek Jan, Lee Taewoo, Raudenský Miroslav, Čarnogurská Mária, Chabičovský MartinAbstract:Spray Cooling of hot steel surfaces is an inherent part of continuous casting and heat treatment. When we consider the temperature interval between room temperature and for instance 1000 C, different boiling regimes can be observed. Spray Cooling Intensity rapidly changes with the surface temperature. Secondary Cooling in continuous casting starts when the surface temperature is well above a thousand degrees Celsius and a film boiling regime can be observed. The cooled surface is protected from the direct impact of droplets by the vapour layer. As the surface temperature decreases, the vapour layer is less stable and for certain temperatures the vapour layer collapses, droplets reach the hot surface and heat flux suddenly jumps enormously. It is obvious that the described effect has a great effect on control of Cooling. The surface temperature which indicates the sudden change in the Cooling Intensity is the Leidenfrost temperature. The Leidenfrost temperature in spray Cooling can occur anywhere between 150 C and over 1000 C and depends on the character of the spray. This paper presents an experimental study and shows function for prediction of the Leidenfrost temperature based on spray parameters. Water impingement density was found to be the most important parameter. This parameter must be combined with information about droplet size and velocity to produce a good prediction of the Leidenfrost temperature
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Spray Cooling heat transfer above leidenfrost temperature
'MDPI AG', 2020Co-Authors: Chabičovský Martin, Komínek Jan, Kotrbáček Petr, Bellerová Hana, Raudenský MiroslavAbstract:This study considers spray Cooling starting at surface temperatures of about 1200 °C and finishing at the Leidenfrost temperature. Cooling is in the film boiling regime. The paper uses experimental techniques for the study of which spray parameters are necessary for good prediction of spray Cooling Intensity. The research is based on experiments with water and air-mist nozzles. The following spray parameters were measured together with a heat transfer coefficient: water flowrate, water impingement density, impact pressure, droplet size and velocity. Derived parameters as droplet kinetic energy, droplet momentum and droplet Reynolds number are used in the tested correlations as well. Ten combinations of spray parameters used for correlation functions for the heat transfer coefficient (HTC) are studied and discussed. Correlation functions for prediction of HTC are presented and it is shown which spray parameters are necessary for reliable computation of HTC. The best results were obtained when the parameters impact pressure and water impingement density were used together. It was proven that the correlations based only on water impingement density, which are the most frequent in literature, can not provide reliable results
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Experimental study of in-line heat treatment of 1.0577 structural steel
'Elsevier BV', 2018Co-Authors: Hnízdil Milan, Chabičovský MartinAbstract:In-line heat treatment is frequently used in rolling mills because it offers a significant improvement of rolled product mechanical properties with costs benefits. This method allows achieving required mechanical properties without necessity of additional alloying and rolled product reheating. Disadvantage of in-line heat treatment is fixed rolling velocity which is typically strong parameter in controlling of final Cooling regime. Water flow rate, pressure, type, size and position of nozzles, water temperature are examples of parameters influencing Cooling Intensity and the Leidenfrost temperature. Laboratory experimental study is needed to design well controllable Cooling system which allows keeping required Cooling regimes for various product steel grades and dimensions. This paper describes experimental stages of Cooling system designing procedure for improving structural steel 1.0577 mechanical properties. First experimental part began with building of Cooling intensities (heat transfer coefficients - HTC) database for tested several nozzles configurations. Then required Cooling regime was selected according to the continuous Cooling transformation diagram. The target was obtaining harder (quenched) material with good ratio between elongation and strength. The final equalization temperature was set to 600 °C in the whole body. Numerical simulations of Cooling followed based on the knowledge of heat transfer coefficients from database. Appropriate nozzle configuration was chosen and numerical results were experimentally validated using modified Jomminy test. A hardness was improved significantly up to thickness of 12 mm (275 HV under sprayed surface decreasing to 180 HV in 12 mm). When the required material structure and hardness verified appropriateness of Cooling regime by previous tests, the first design of Cooling section was done. Full scale sample was heat treated on a new experimental stand (Karusel) which was developed by HeatLab. It enabled to simulate real Cooling process in laboratory conditions. The sample was heated to rolling temperature and moved through the intensive spray (surface temperature drop to 300 °C) and then through the soft spray because of water savings. The Cooling stopped in required time and the sample tempered to the target equalization temperature of 600 °C in the whole body. Finally, the hardness was measured, tensile and Charpy pendulum tests were done to confirm design of Cooling unit. The hardness of the original material was constant along depth – 160 HV. It was improved by heat treatment – decreasing from the sprayed surface (265 HV) to the depth of 12 mm (175 HV). The minimal yield strength of the heat treated material increased from 355 MPa 400 MPa (maximal up to 750 MPa – closed to the sprayed surface). The sample was cooled to -20 °C for Charpy pendulum test. The pendulum energy of heat treated material rapidly increased from 50 J to 150 J