Papers by Author: Pavel Koštial

Abstract: The paper deals with the influence of microstructural changes of the nickel superalloy (NiS) on heat transport changes in MAR-M247. The dissolving annealing within the temperature interval of 900 – 1240°C and cooling in water has been applied to enhance structural changes. It has been shown that the narrow connection between the γ’ phase morphology changes, as well as values of density, thermal conductivity and specific heat capacity. In the dissolving annealing process, the γ’ particles change in certain cycles from fine to rough and back to fine one. Obtained results of changes of thermal conductivity, density and specific heat capacity correlate with image analysis and electron microscopy observation.

Abstract: This paper aims to study the cooling of a solid body. An analytical analysis of a solid body cooling in different regimes is presented, such as a simple first order exponential model, a modified exponential model, a generalized exponential model and the so-called regular temperature regime. The analysis also includes the influence of the dynamically changing relaxation time and we also present the solution of the nonlinear heat equation.

Abstract: In this paper, we present some distinguished methods of the digital thermograms software treatment which allows the visualization of hidden defects in glass fabric laminates, which are not usually visible in standard raw thermograms. The results of the software treatment are tested on artificial defects in glass laminate plates.

Abstract: Measuring of thermal distribution in certain material was done in Matlab. Obtained data are processed and displayed in fully 3D environment (virtual reality) using X3D. Paper deals with data processing and conversion from Matlab into X3D. Further development of visualization is discussed too – visualization of thermal gradient, Integration of measured a visualized data into real object or technological process visualization. The aim of this topic is to present information about discontinuities in solid materials.

Abstract: Contribution of the work consists in creation of a mathematical model (algorithm) for prediction of technological parameters of the two-high rolling stand DUO 210 Sva and Q110 at change of the absolute reduction Δh, for example for a deep-drawing steel and of the brand KOHAL grade 697 and low carbon steel, as well as generally speaking for any rolled material. It is possible to identify and predict on the basis of this algorithm an instant state of surface topography in respect to variable technological conditions. On this basis it is then possible to calculate and plot individual main technological parameters.

Abstract: The presented work is devoted to the investigation of the influence of single wall carbon nanotubes (SWCNT) on the thermal and mechanical properties of rubber blends. The materials under investigation were rubber blends filled by carbon black (CB-labelled as standard or S) or a mixture of CB with single wall carbon nanotubes (0.6 wt.% of SWCNT). The thermal parameters of the rubber samples were measured on the basis of an exponential model of a cooling body (developed in a lumped capacity model). From the measured cooling curve of the sample after its deformation, the specific heat capacity c_p [J/kg/, thermal diffusivity α [m²/ and thermal conductivity k [W/m/K] were measured. The increase of α and k was observed for rubber blends filled with a mixture of CB and SWCNT. The complex thermo mechanical analyzer (CTMA) was used for determination of thermal and mechanical parameters. The static Youngs modulus shows an immense increase after SWCNT addition. The dynamic Youngs modulus also shows an increase after SWCNT introduction. A simultaneous tgδ decrease caused by SWCNT presence is observed in this case.

Abstract: In addition to emission level reduction, combustion process optimization by modifications of pyrolysis boilers is aimed at fuel cost decrease. Knowledge of fuel composition and fuel combustion properties is important to the optimum and economical combustion process. The levels of emissions caused by the process can be reduced by several designs and operational modifications. This paper deals with modifications of combustion equipment in order to reduce harmful flue gas emissions in a boiler MA 23. The hot water boiler MA 23 belongs to gasification boilers for dry lump wood combustion; it is intended primarily for the heating of family houses, cottages, small office buildings and other small buildings and has the maximum required heat output of 23 kW. The boiler was tested in several modes, based on the requirements of the standard EN 303-5 dealing with emission limits. A basic requirement was the implementation of technical measures described in the paper and a proposal of method of regulation of flue gas volumetric flow rate and of installation in order to keep emission levels below the required limit.

Abstract: Nowadays, plastics have become one of the most demanded materials, replacing the traditional ones such as metals. Therefore, many companies are concerned with the production of plastics, with their distribution and innovation development. Plastics have found utility in a wide range of applications, we use them every day. Measurement of surface roughness of plastic moldings produced by the injection molding process was carried out by a contact profilometer Mitutoyo Surftest SJ401. A reason for this measurement is to obtain information about surface roughness. For further technical adjustment is required to have higher surface roughness what helps to increase electrical conductivity of plastic moldings. This involves determination of a ratio between Ra/Rz (the ratio between the arithmetic average of the roughness profile Ra and the average maximum height of the profile Rz) in order to satisfy customer demand for achieving better surface characteristics leading to an increase in electrical conductivity.

Abstract: Laser - cut quality is mainly characterized by a degree of accuracy in shape, size and also by surface layer conditions after cutting associated with surface roughness. An experimental determination of surface tension (or tensor components) of clean metal surfaces is very difficult and there is no direct method for its measurement. Attention was paid to numerical derivation of surface tensions according to the surface topographical features in laser cutting technology. The surface tensions and temperature dependencies of several metallic materials have been determined and confirmed by data obtained from the literature. It was found to be in very good agreement between our results and data from different sources in the literature.

Abstract: The paper deals with the electrical and mechanical properties of rubber blends filled by single wall carbon nanotubes (SWCNT-0,6 weight %). We have investigated the alternating current resistivity (ACR), real and imaginary part of dielectric constant,and loss factor .The addition of (SWCNT) to a rubber blend decreases ACR and increases constants ,and loss factor .