Martin Chabičovský - Academia.edu (original) (raw)

Papers by Martin Chabičovský

DOAJ (DOAJ: Directory of Open Access Journals), Oct 1, 2014

The activities and performance of thirty major universities technology transfer offices (TTOs) se... more The activities and performance of thirty major universities technology transfer offices (TTOs) selected from major US universities are quantitatively assessed and compared. Six leading metrics, including TTOs' revenue, as well as quantity of invention disclosures, patent applications, patents granted, licenses signed, and startup companies launched, are used to develop a single overall performance metric (OPM) for representing the performance of the TTOs. The OPM are then evaluated for each of the thirty universities and their OPM scores are compared to each other to establish the reliability and effectiveness of a comprehensive OPM. A patenting control ratio (PCR) is also calculated to guide a TTO in setting its patenting strategy and procedures. These two metrics should be able to provide a comprehensive overview of how good is the TTO of a university as compare to those of its peers and, even more importantly, how the program fares globally.

Metals, Nov 22, 2020

Spray cooling of hot steel surfaces is an inherent part of continuous casting and heat treatment.... more 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.

Proceedings of the 4th International Conference of Fluid Flow, Heat and Mass Transfer, Jun 1, 2022

Steel production and processing are connected with the formation of an oxide layer on a hot surfa... more Steel production and processing are connected with the formation of an oxide layer on a hot surface of steel. The oxide layer influences cooling and the final quality of the steel. Spray cooling is mainly influenced by water impingement density and by surface temperature, but the influence of the oxide layer is not negligible. The oxide layer can be considerably porous. The porosity of the oxide layer significantly influences its thermal conductivity, because air pores have much lower thermal conductivity compared to pure oxides. In this paper, the influence of the oxide layer on water spray cooling is experimentally and numerically investigated. The heat transfer coefficient of an oxidized steel surface and a clean steel surface are compared and the effect of the oxide layer on the Leidenfrost temperature is studied. Also, the porosity of the oxide layer and the average thermal conductivity of the porous oxide layer are determined for different oxidation regimes.

Acta Metallurgica Slovaca, Sep 30, 2018

This paper describes the stages of applied research and development leading to a functional proto... more This paper describes the stages of applied research and development leading to a functional prototype of a quenching unit. It became a part of a closed facility of process equipment for thermal treatment by refining and other methods of annealing of seamless steel tubes for the OCTG industry (Oil Country Tubular Goods), power engineering and mechanical engineering in Třinecké Železárny. The development of the prototype has been divided into several stages: mapping of the current state and critical assessment of the technical and technological level of the existing equipment in the Tube Mill, laboratory testing of tube samples cooling, including numerical simulations with the prediction of the initial settings of the process parameters for the recommendation of the technological configuration of the quenching unit prototype and finally a comprehensive technical design of the prototype quenching unit. The design of the prototype technical solution served as the basis for the creation of the detailed engineering documentation with the subsequent construction of the prototype quenching unit. The paper summarizes the procedures and results of individual development stages, including the results of measured temperatures of tubes during actual operation of the prototype and the results of additional numerical simulations of its actual cooling capacity.

Advanced Materials Research, Jun 1, 2014

Stainless steel sheets are successively heated to a temperature of 1150°C and cooled until ambien... more Stainless steel sheets are successively heated to a temperature of 1150°C and cooled until ambient temperature during the production process. Requirements for high cooling rates of stainless steel sheets producers lead to use water as a cooling medium. The information about cooling intensity (heat transfer coefficient) of different nozzles configurations is necessary for designing cooling sections. Although many researchers deal with water spray cooling, actually a general correlation for predicting heat transfer coefficient for wide range of nozzles configurations does not exists. That is the reason why heat transfer coefficient for different nozzles configurations can be only obtained by laboratory measurements. Heat transfer coefficient is mostly influenced by water impingement density and impact velocity. However other factors e.g. water temperature and velocity of the sheet can influence the heat transfer coefficient. Optimized design of the cooling unit with high cooling intensity and low water consumption was achieved by appropriate choice of these parameters. The moving experimental sheet was cooled from a temperature of 900°C to a temperature of 50°C with various configurations of nozzles. The tests shown that heat transfer coefficient was increasing with water impingement density and impact velocity. Increasing water temperature from 20 °C to 80 °C caused a decrease of the heat transfer coefficient and Leidenfrost temperature. The effect of velocity is negligible when velocities are between 25 and 100 m/min. The cooling unit was designed according to laboratory measurements to fulfill the stainless steel producer&amp;#39;s requirements. The measurements which were done in an industrial plant confirmed the accuracy of heat transfer coefficient obtained in the laboratory. The maximum difference between laboratory and plant measurements was 15%.

International Journal of Heat and Mass Transfer, Sep 1, 2015

ABSTRACT Spray cooling is a common cooling method used in many high-temperature metal processes. ... more 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.

Materiali in Tehnologije, May 3, 2015

The cooling of vertically moving strips is used very often to obtain the required material proper... more The cooling of vertically moving strips is used very often to obtain the required material properties. Water spray cooling has to be used when a high cooling intensity is needed. Our Heat Transfer and Fluid Flow Laboratory is equipped with a testing device which allows vertical movement of a heated experimental plate (sheet). Two different sizes of flat-jet nozzles were tested with different water pressures and angles of the water impact (inclination angles of the spraying bar). The water-pressure range was between 2 bar and 9.3 bar and the angle of the water impact changed from 20°to 40°. The dependence of the heat-transfer coefficient on the surface temperature was evaluated for each experiment. Interesting results were obtained from the comparison of these experimental results, showing that the heat-transfer coefficient and the Leidenfrost temperature increase with the increasing water pressure. Very interesting results were obtained during the tests with different inclination angles. The highest heat-transfer coefficient was obtained for the angle of 20°and the lowest value of the heat-transfer coefficient was obtained for the angle of 40°at the surface temperatures of around 200°C.

Heat Transfer Engineering, Jun 29, 2018

A basic energy balance that includes phase change has been used to describe the boiling heat tran... more A basic energy balance that includes phase change has been used to describe the boiling heat transfer process. By using the differential form of this energy balance, the relative change in the heat transfer coefficient can be determined when the surface and coolant temperature change. This represents a general solution to the boiling heat transfer problem under high flux conditions where fully mixed thermal boundary layer exists, although the solution procedure is approximate. The results agree quite well with experimental data. Further work remains to prescribe the heat transfer process near the critical heat flux and Leidenfrost point. This approach vastly reduces the empiricism and data required for boiling heat transfer processes, and also existing data can be used to generalize to a wide range of conditions.

Journal of flow control, measurement & visualization, 2016

We present a new Nusselt number correlation for spray cooling at large Reynolds numbers and high ... more We present a new Nusselt number correlation for spray cooling at large Reynolds numbers and high surface temperatures for water sprays impinging perpendicularly onto a flat plate. A large set of experimental data on spray cooling of hot surfaces with water has been analyzed, including the water temperature effects. For large-scale cooling, such as in industrial processes, large number of injection parameters such as number, type, pressure, and angle of the spray injection has led to a multitude of correlations that are difficult for general and practical applications. However, by synthesizing a set of experimental data where all of the above parameters have been varied, we find that the Nusselt number and therefore the heat transfer coefficient can be cast accurately as a function of the Reynolds number. Water is widely used as the coolant during spray cooling, and has a specific phase change characteristic. At large Reynolds number (Re > 100,000) and surface temperature (Ts > 600˚C) ranges, which are of interest in large-scale spray cooling, the effect of water temperature is quite significant as it affects the film boiling close to the surface. This effect also has been parameterized using experimental data.

Materials today communications, Sep 1, 2021

Engineering Mechanics ..., May 13, 2019

Steel production and processing are connected with high temperatures. Due to a reaction between h... more Steel production and processing are connected with high temperatures. Due to a reaction between hot surface of the steel and oxygen contained in surrounding atmosphere, oxides are formed on the surface of the steel. Created layer of oxides is called scales and has influence on cooling and quality of steel. Thickness and structure of scale layer are influenced by chemical composition of the steel, temperature and atmosphere during oxidation. Scale layer can be considerably porous which has a significant influence on thermal conductivity of this layer, because air pores have much lower thermal conductivity compared to scales. Steel samples were prepared and porosity of scale layer was studied. Further, the average thermal conductivity of porous scale layer was determined for different regimes of oxidation by FEM modelling. It was found that the average thermal conductivity of porous scale layer is influenced not only by porosity of scale layer, but also by distribution of air pores, which can has a significant effect.

Metals, Sep 21, 2020

This study considers spray cooling starting at surface temperatures of about 1200 • C and finishi... more 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.

Revue De Metallurgie-cahiers D Informations Techniques, 2020

This paper describes experimental stages of a cooling system designing procedure in laboratory co... more This paper describes experimental stages of a cooling system designing procedure in laboratory conditions of vertically and horizontally moving surfaces. First stage of the experimental research is focused on a study of a water flow distribution and impact pressure using laboratory equipment and software. Water distribution and impact measurement tests are used for verification of catalogue data provided by nozzle producer so thus an input information to the theoretical water distribution visualization software. Second stage of the experimental research are dynamic tests to describe an influence of several parameters (water flow rate, pressure, nozzle position etc.) on the cooling capability and mainly on the cooling homogeneity. Heat transfer coefficient dependence on a surface temperature and position obtained from these results and used as a boundary condition for simulating real cooling process with real material and thickness. Verification and characterization of the final cool...

Procedia Manufacturing, 2018

Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.

Advanced Materials Research, 2014

To achieve the required mechanical properties in the heat treatment of steel, it is necessary to ... more To achieve the required mechanical properties in the heat treatment of steel, it is necessary to have an adequate cooling rate and to achieve the desired final temperature of the product. This should be achieved with one cooling unit for different product sizes. In order to provide high variability of the cooling system, different types of nozzles are used in modern cooling systems. Designers often use simplified, inaccurate correlations to predict the heat transfer coefficient, resulting in oversizing of the designed cooling or failure to provide the required cooling regime. This typically results in longer commissioning times and higher manufacturing costs of the new cooling system. Accurate information about the required cooling regime and the heat transfer coefficient of the designed cooling is critical. This paper presents a design approach based on laboratory measurements. Firstly, the way to find or validate the required cooling regime is presented. The paper then focuses on ...

An in-line heat treatment of rolled materials is becoming frequently used by hot rolling plants. ... more An in-line heat treatment of rolled materials is becoming frequently used by hot rolling plants. This method achieves the required material structure without the necessity of reheating. This paper describes a design procedure of cooling sections for obtaining the demanded structure and mechanical properties. Experimental stands, applied for the cooling study of steel samples, were built at the Brno University of Technology. The first experimental stand enables to simulate a variety of cooling regimes and evaluate the final structure of the tested samples which are instrumented by set of thermocouples indicating the temperature history of the tested material. The second experimental stand is a tool for the design of the cooling sections which can ensure obtaining demanded heat treatment procedure and demanded final structure. The heat transfer coefficient history at the surface is gained as an output of the inverse task. Mathematical model and its implementation into the software tool for computer simulation of heat treatment processes (quenching and tempering) of steel is presented. Heat transfer boundary conditions obtained from test on experimental stand are used for calculation of cooling curves followed by prediction of microstructure after austenite transformation and final mechanical properties as hardness, tensile strength and yield stress. The software QTSteel used for computer simulation of heat treatment of long products has been developed by ITA Ltd. Verification and practical examples of metallurgical predictions for long products, especially tubes and bars, are presented. PREDICTION OF HARDNESS AND MICROSTRUCTURE The MetaCool is the library of functions that enables prediction of mechanical properties and microstructure of heat treated steel. The data interface contains pure physical quantities on the input (chemistry, temperatures, times, strains, cooling curve) and microstructure fractions and final mechanical properties of the steel (hardness, yield stress, ultimate tensile strength) as output [2]. MetaCool is divided internally into 17 steel groups and covers carbon and structural steels with amount of carbon from 0.08% to 0.6% and with the total sum of alloying additions up to 10%. Assigning of the steel with specified chemical composition into particular group is performed automatically and metallurgical algorithms differ from one steel group to another. The CCT diagram model The model of the CCT (continuous cooling transformation) diagram consists of the set of lines (significant temperatures: Ac 3-Temperature at which ferrite completes its transformation

Applied Thermal Engineering

Spray cooling is a common cooling method used in many high-temperature metallurgical processes. H... more Spray cooling is a common cooling method used in many high-temperature metallurgical processes. Heat transfer in the spray cooling of hot surfaces depends on many parameters, and one of them is cooling water temperature. Especially in the steel industry, the cooling water temperature is influenced by the season, the location in the world and also by the intensity of the manufacturing process. Using an experimental approach, the influence of water temperature on the Leidenfrost temperature and film boiling heat transfer coefficient in spray cooling is investigated. Extensive measurements, taken for two types of nozzles, different water flow rates and different water temperatures (12 °C to 78 °C), are presented. It is shown that the film boiling heat transfer coefficient and the Leidenfrost temperature decrease linearly as the water temperature increases. The obtained results are generalised into correlations and transformation functions, allowing extension of existing correlations, which are mostly valid only for water temperatures around 20 °C, to arbitrary water temperatures. All existing papers, which deal with the influence of the water temperature on spray cooling, only present the measured data and do not provide a generalisation of the results. This is a research gap, and this paper tries to fill it.

Stochastic convergence, law of large numbers and central limit theorem is an important part of pr... more Stochastic convergence, law of large numbers and central limit theorem is an important part of probability theory, which is often used in mathematical statistics. The aim of this work is to describe this theory and demonstrate it with examples and graphical simulation. In addition simulation of stochastic convergence, law of large numbers and central limit theorem for some discrete and continuous probability distribution the work contains several interesting simulations for example simulation of Galton's box, Buffon's needle problem and Bertrand's paradox. To create a graphic simulation were used programming language matlab