In the Republic of Serbia there are significant quantities of coffee and tire wastes that can be utilized as Solid Recovered Fuel (SRF) and used as an additional fuel for co?combustion with coal and biomass in energy production and cement industry sectors. Differences between SRF and base fuel are a cause of numerous problems in design of burners. The objective of this study was to determine the kinetic parameters for the thermochemical conversion of selected SRF using Simultaneous Thermal Analysis (STA). Samples of coffee and tire waste were used for the experimental tests. Thermal analysis was carried out in nitrogen atmosphere at three different heating rates 10, 15 and 20 K/min for each sample, while it was heated from room temperature up to 900?C. Two sample sizes x <0.25 mm and 0.25 < x <0.5 mm of each SRF were used in experiments, in order to obtain reliable Thermal Gravimetric Analysis (TGA) data for estimation of kinetic parameters for SRF pyrolysis. Experimental results were used for determination of pre-exponential factor and activation energy according to methods presented in the literature. Presented research provides valuable data of coffee and tire waste that can be used for the burners design.

Influence of local loads on the stress state of the shell appears as the consequence of pressure, external forces, and moment influence. Loads which act directly upon the shell surface or the parts (nozzles) connected to the shell appear in their proximity, especially in the welded joint influence zones.The influence of the torque moment affecting the free end of a slanted branch on the pressure vessel cylindrical shell is considered in this article. The stress on the cylindrical shell was analysed on 245 models of different geometrical characteristics. Stress calculated by applying the finite element method was classified by maximum stress criteria. For every considered model, maximum stress envelope has been prepared. The regressive analysis enabled the determination of correlation functions, which allow calculation of stress maximum values on the cylindrical shell according to which the shell dimensions may be determined. Result analysis shows that the percentual error is within limits as follows: from À13.4 per cent to þ12.7 per cent.

To ensure reliability of pressure vessels during service it is necessary to (1) know properties of materials used in their design and (2) evaluate vessels’ behaviour under different working conditions with satisfying accuracy. Due to various technical and/ or technological requirements, nozzles are usually welded on vessel’s shell producing geometrical discontinuities that reduce the safety factor. To evaluate their influence, vessels with two different nozzles were experimentally studied and critical areas for crack initiation have been identified by 3D Digital Image Correlation (DIC) method. After that, the numerical analysis of equivalent 3D finite element model was performed and obtained results were compared with experimental values. In the most critical area, next to the one of the nozzles, crack was initiated and then growth of the damage was simulated using extended finite element method (XFEM). In this paper evaluation of stress intensity factors (SIFs) along crack path is presented, as well as the most probable direction of the crack propagation on the shell. Based on SIFs values, critical length of the crack and number of pressure cycles to the final failure were estimated.

The detailed kinetic analysis of slow pyrolysis process of apricot (Prunus armeniaca L.) kernal shells has been estimated, under non-isothermal conditions, through thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG). Thermal decomposition was implemented using four different heating rates (5, 10, 15 and 20 ?C min-1), with consideration of how this parameter effects on the process kinetics. The higher heating rates provoke the shift of thermo-analytical curves towards more elevated temperatures. Using isoconversional differential method, the variation of activation energy (Ea) with conversion fraction (?) was detected, and pyrolysis reaction profile was discussed. After resolving the pyrolysis rate curves of individual biomass constituents, the temperature and conversion ranges of their thermal transformations were clearly identified. In the latter stage of analysis, every identified reaction step was considered through mechanistic description, which involves selection of the appropriate kinetic model function. The comparison of the results as well as discrepancies between them has been discussed. The corresponding rate-law equations related to thermal decomposition reactions of all biomass constituents present in the tested agricultural waste material have been identified.

Original scientific paper The subject of this paper is testing of complex geometrical structures, i.e. stress analysis of a pipe branch model of A6 third pipeline at Hydropower Plant Perućica, Nikšić. Analysis of pipe branch model stress distribution was carried out by using finite element method and experimental methods. Finite element method defined 3D pipe branch model. Numerical calculation defined critical locations on model, i.e. locations with the greatest stress concentration. Strain gauges were placed on identified critical locations. Measured stress values confirmed values obtained by using numerical calculation. Experimental measurements were also taken by using new digital image correlation (DIC) method. DIC method is an optical non-contact method that can provide full 3D stress field and enables better understanding of complex structures such as pipe branches. The aim of this paper was to determine stress concentration factor for the pipe branch model by using numerical and experimental analysis.Keywords: finite element method; pipe branch model; strain gauges; stress concentration factor; 3D DIC method Numeričko i eksperimentalno određivanje faktora koncentracije naprezanja na modelu cijevne račve Izvorni znanstveni članak Predmet ovog rada je ispitivanje struktura složene geometrije, odnosno analiza naprezanja modela cijevne račve A6 trećeg cjevovoda u hidroelektrani Perućica, Nikšić. Analiza stanja naprezanja modela cijevne račve provedena je numeričkom metodom konačnih elemenata i eksperimentalnim metodama. Metodom konačnih elemenata definiran je 3D model cijevne račve. Numeričkim putem određena su kritična mjesta na modelu, odnosno mjesta najveće koncentracije naprezanja. Mjerne trake su pozicionirane na identificirane kritične zone. Izmjerene vrijednosti naprezanja metodom mjernih traka potvrdile su vrijednosti dobivene metodom konačnih elemenata. Mjerenja su provedena i uporabom 3D optičke beskontaktne metode koja se bazira na digitalnoj korelaciji slika. Tom metodom se može dobiti cjelokupno 3D polje naprezanja, odnosno ona omogućava bolje razumijevanje kompleksnih struktura kao što su cijevne račve. Cilj ovog rada je bio određivanje faktora koncentracije narezanja na modelu cijevne račve uporabom numeričkog i eksperimentalnog pristupa.Ključne riječi: faktor koncentracije naprezanja; konačni elementi; mjerne trake; model cijevne račve; 3D DIC metoda