Miroslav Raudenský

Combined Inverse Heat Conduction Method For Highly Transient Processes

Combined inverse heat conduction task was developed. The task uses classical minimisation method in combination with optimisation method. The method was developed for the very steep changes of the measured temperature and the demand on precise results. Typical industrial applications are in descaling (removing oxides from steel surface by high energetic spray). The minimisation method is used as a basic method. The precision of this method is improved in the area of big temperature gradients by combination with optimisation method. The peaks of HTC of heat flux are computed precisely afterwards.

Hiding Power of Aluminum Metal Pigments Development in the Ball Mill Grinding Process

Aluminum powders are used in porous concrete constructional elements production, in coating compositions and varnish media industry, introduction of printing inks and finally but not less in chemical and pyrotechnical production. The purpose of atypical grinding processes is to obtain fine metal powders of extremely high specific surface which should be evaluated by the parameter of hiding power ability of pigment materials. This paper shows the development of this basic parameter of metal pigment products under the wet process of milling using a pilot-plant ball mill, as a function of milling time and turns of mill drum as one of the basic parameters.

Uzajamna kolizija vodenih mlazova iz susjednih mlaznica s plosnatim mlazom visokog tlaka na ravnoj površini tijekom hidrauličnog skidanja kamenca

Original scientific paper High energetic water jets sprayed from nozzles are used for scale removal. Special nozzles with flat and very narrow jets for high feed pressure are used. This process, called descaling, is used in hot rolling, for example. A number of jets must be used to cover the total width of a rolled strip. High quality and homogeneity of the descaling process is required. A row of high pressure descaling nozzles is often used. This paper focuses on the area where water streams from adjacent nozzles interact. Water impact measurements were taken for several nozzle configurations and the measuring technique with the results obtained is presented. The water impact pressure for multiple nozzles was computed and the results were compared to the measurements.

Fatigue Testing of Polymeric Hollow Fibre Heat Transfer Surfaces by Pulsating Pressure Loads

This article deals with fatigue tests of polymeric hollow fibre heat transfer surfaces. The hollow fibres have an outer diameter between 0.5-0.8 mm and wall thickness 10 % of the outer diameter. These plastic heat transfer surfaces have some limitations but also many benefits. One of the limitations is the durability of plastic under fatigue loading. The heat transfer surfaces were subjected to pulsating pressure loads under different conditions (level of pressure, ambient temperature, number of cycles). Firstly, only an internal hydraulic pulsating load was applied and the behaviour of the hollow fibres was observed, focusing especially on the presence of leaks, ruptures, etc.Then, other conditions of operations were added. The heat transfer surfaces were immersed in a hot bath and loaded by internal pulsating pressure and high temperature simultaneously. Testing under different temperatures is important because the temperature significantly affects the material properties. The presence of leaks, ruptures and other possible damage was monitored as with previous tests.

Spray Cooling Unit for Heat Treatment of Stainless Steel Sheets

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 producers 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%.