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In this research the 3-D transient non-linear thermal analysis of the hard-facing process was performed by using the experimental testing and finite element method. Testing was done at three different carbon steels and the obtained results were compared to one obtained by empirical formulas and welding recommendations. Experimental testing was done on hard faced specimens (plates) with different thickness. Temperatures and temperature cycles was measured by using thermocouples in order to determine maximal temperature and cooling time between 800 degrees C and 500 degrees C. After experimental testing the finite element method analysis was done. The simulations were executed on the open source platform Salome using the open source finite element solver Code Aster. The Gaussian double ellipsoid was selected in order to enable greater possibilities for the calculation of the moving heat source. The numerical results were compared with available experimental and mathematical results.

The utilization of modern paraboloidal concentrators for conversion of solar radiation into heat energy requires the development and implementation of compact and efficient heat absorbers. This research is directed toward innovative design solution that involves the development of heat absorber made of spirally coiled tubes with transverse circular corrugations. The main advantage of the considered design solution is a coupling effect of the two passive methods for heat transfer enhancement - coiling of the flow channel and changes in surface roughness. Investigation of the influence of hydraulic, physical and thermal conditions, as well as the geometry of the spirally coiled corrugated heat absorber, on the local intensity of heat transfer and pressure drop was conducted using modern experimental and numerical methods. Laboratory model of heat absorber was instrumented and mounted in the radiation field. Test section instrumentation included inlet fluid flow rate, pressure drop, inlet and exit fluid temperature and 35 type K thermocouples welded to the surface of the coil. The thermal analysis of experimentally obtained data included consideration of the externally applied radiation field, convective and radiative heat losses, conduction through the tube wall and convection to the internal fluid. The experimental results showed significant enhancement of the heat transfer compared to spirally coilled smooth tubes, up to 240% in the turbulent flow regime. The influence of radiant field intensity and geometrical parameters of corrugations outside the experimental range were investigated using computational fluid dynamics techniques in terms of heat transfer and pressure drop. Finally, the reliable correlations for determining the intensity of convective heat transfer coefficient and pressure drop were obtained for different flow regimes, which are applicable in engineering practice.

Determination of reliability indicators of steam turbine system in the thermal power plant 'Nikola Tesla, Block A4'during useful life period is based on a ten-year operational database. By implementation of mathematical theory of reliability to exploitation research data and using simple and complex two-parameter Weibull distribution, the theoretical reliability functions of the considered system are determined. The graphical method is applied to quantitatively determine reliability indicators. Obtained probabilistic laws of failure density and failure rate, according to which the random variable behaves, do not coincide completely with empirical distributions, regardless of whether the theoretical functions are obtained by simple or complex Weibull distribution.

Representation of probabilistic technique for evaluation of thermal power system reliability is the main subject of this paper. The system of thermal power plant under study consists of three subsystems and the reliability assessment is based on a sixteen-year failure database. By applying the mathematical theory of reliability to exploitation research data and using complex two-parameter Weibull distribution, the theoretical reliability functions of specified system have been determined. Obtained probabilistic laws of failure occurrence have confirmed a hypothesis that the distribution of the observed random variable fully describes behaviour of such a system in terms of reliability. Shown results make possible to acquire a better knowledge of current state of the system, as well as a more accurate estimation of its behavior during future exploitation. Final benefit is opportunity for potential improvement of complex system maintenance policies aimed at the reduction of unexpected failure occurrences.

The main subject of this paper is the representation of the probabilistic technique for thermal power system reliability assessment. Exploitation research of the reliability of the fossil fuel power plant system has defined the function, or the probabilistic law, according to which the random variable behaves (occurrence of complete unplanned standstill). Based on these data, and by applying the reliability theory to this particular system, using simple and complex Weibull distribution, a hypothesis has been confirmed that the distribution of the observed random variable fully describes the behaviour of such a system in terms of reliability. Establishing a comprehensive insight in the field of probabilistic power system reliability assessment technique could serve as an input for further research and development in the area of power system planning and operation.

As a result of a very limited number of geometric and other input data, the temperature modeling of the river Ibar downstream of the lake Gazivode was started by analyzing one river reach between Pridvorica, secondary dam in the system Gazivode, and the city Kosovska Mitrovica. River reach was selected so that the numerical results can be compared with available measured temperature data. Water quality component of HEC-RAS one-dimensional hydraulic river model was used for temperature calculations.

Procesi elektrootpornog zavarivanja i lemljenja delova izrađenih od legura PbSbSn u industriji akumulatora tipa olovo-kiselina, u energetici, elektronici i hemijskoj industriji zahtevaju detaljna istraživanja termomehaničkih osobina ovih legura, koje zavise od temperature. Eksperimentalni rezultati koeficijenta provođenja toplote, dobijeni su upotrebom metode laserskog impulsa, zasnovanoj na matematičkoj analizi nestacionarnog jednodimenzijskog provođenja toplote kroz beskonačan ravan adijabatski zid. Rezultati toplotne provodljivosti dobijeni su iz merenja brzine porasta temperature na jednoj strani epruvete. Temperatura topljenja, latentna toplota i specifični toplotni kapacitet određeni su korišćenjem kalorimetra. Koeficijent linearnog širenja je određen korišćenjem visoko temperaturnog dilatometra. Data je temperaturska zavisnost ispitivanih mehaničkih osobina. Eksperimentalni rezultati su predstavljeni za date PbSbSn legure, u kojima je sadržaj Sb ograničen do 3,5 %, a sadržaj Sn do 0,5 %. Svi dobijeni rezultati temperaturske zavisnosti termomehaničkih osobina su predstavljeni grafički i tabelarno., Resistance welding and soldering processes of parts made of PbSbSn alloys in the industry of lead-acid batteries, power engineering, electronics and chemical industry require a detailed research of thermomechanical properties of these alloys that depend on temperature. Data on thermal conductivity are acquired from experiments with a laser pulse method, and based on mathematical analysis of non-stationary one-dimensional heat conduction through an infinite flat adiabatic wall. Data on thermal conductance are determined from measurements of the temperature increase rate on one side of a sample. The melting temperature, latent heat and specific heat capacity are determined by calorimeter. The coefficient of linear expansion is determined by using a high-temperature dilatometer. Temperature dependence of tensile testing mechanical properties is also given. The experimental results are presented for the chosen PbSbSn alloys in which the Sb content is limited to 3.5 % and the content of Sn to 0.5 %. All results of temperature dependence of thermomechanical properties are given in graphical and tabular form.

The analytical modelling of the PbSb alloy resistance spot welding process has been developed on the basis of mathematical analysis of thermomechanical conservation laws. The numerical solution of partial differential equations, obtained by such modelling, has been achieved by the finite element method. Thermomechanical equilibrium equations are derived, including specific properties, typical for PbSb alloys. The paper utilizes the basic experimentally proven assumption, that the temperature fields govern all processes during welding. Full agreement is evident between the experimental and analytical data.