Eksperimentalno i numeričko istraživanje termo-strujnih procesa u spiralnom naboranom toplotnom apsorberu koncentrisanog zračenja

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

Determining the theoretical reliability function of thermal power system using simple and complex weibull distribution

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

Determining the theoretical reliability function of thermal power system using simple and complex weibull distribution

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

Eksperimentalno i numeričko istraživanje termo-strujnih procesa u spiralnom naboranom toplotnom apsorberu koncentrisanog zračenja

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

Eksperimentalno i numeričko istraživanje termo-strujnih procesa u spiralnom naboranom toplotnom apsorberu koncentrisanog zračenja

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

Determining the reliability function of the thermal power system in power plant "Nikola Tesla, Block B1"

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

Numerical investigation on the convective heat transfer in a spiral coil with radiant heating

The objective of this study was to numerically investigate the heat transfer in spiral coil tube in the laminar, transitional, and turbulent flow regimes. The Archimedean spiral coil was exposed to radiant heating and should represent heat absorber of parabolic dish solar concentrator. Specific boundary conditions represent the uniqueness of this study, since the heat flux upon the tube external surfaces varies not only in the circumferential direction, but also in the axial direction. The curvature ratio of spiral coil varies from 0.029 at the flow inlet to 0.234 at the flow outlet, while the heat transfer fluid is water. The 3-D steady-state transport equations were solved using the Reynolds stress turbulence model. Results showed that secondary flows strongly affect the flow and that the heat transfer is strongly asymmetric, with higher values near the outer wall of spiral. Although overall turbulence levels were lower than in a straight pipe, heat transfer rates were larger due to the curvature-induced modifications of the mean flow and temperature fields. [Projekat Ministarstva nauke Republike Srbije, br. 42006

Determining the theoretical reliability function of thermal power system using simple and complex Weibull distribution

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

Ravnoteža para-tečnost OPLS, optimizovanje potencijala za tečnu simulaciju, modela binarnih sistema alkana i alkana + alkohola

The NpT - Gibbs ensemble Monte Carlo computer simulation method was applied to predict the vapour-liquid equilibrium (VLE) behavior of the binary systems ethane + pentane at 277.55 K and 310.95 K, ethane + hexane at 298.15 K, propane + methanol at 313.15 K and propane + ethanol at 325.15 K and 425.15 K. The optimized potentials for the liquid simulating (OPLS) model were used to describe the interactions of alkanes and alcohols. The simulated VLE predictions are compared with experimental data available for the pressure and phase composition of the analyzed binary systems. The agreement between the experimental data and the simulation results is found to be generally good, although slightly better for system in which both components were nonpolar.Metod NpT-Gibbs-ovih ansambla i Monte Carlo molekulska simulacija su primenjeni na predskazivanje ravnoteža para-tečnost (VLE) binarnih sistema etan + pentan na 277.55 K i 310.95 K, etan + heksan na 298.15 K, propan + metanol na 313.15 K i propan + etanol na 325.15 K i 425.15 K. Optimizovani parametri za tečnu simulaciju (OPLS) su korišćeni da opišu interakciju alkana i alkohola. Dobijeni rezultati simulacije ravnoteže para-tečnost su upoređeni sa dostupnim eksperimentalnim podacima za odgovarajuće pritiske i sastave ispitivanih binarnih sistema. Može se reći da je dobijeno dobro slaganje sa eksperimentalnim podacima, mada nešto bolje kod sistema u kojima su obe komponente nepolarne

Denture stomatitis: Ethiopathogenesis and therapeutic approach

Introduction: Denture stomatitis is the most common inflammatory reaction that occurs in people who wear dentures, localized mostly in the palatal mucosa. Etiophatogenesis of inflammation is multifactorial and complex. Infection by yeast of the genus Candida, mainly Candida albicans, poor oral hygiene and long-term wearing of dentures are the most important etiological factors. Factors that may contribute to the development of inflammatory reactions are some general factors, such as smoking, use of different drugs, and systemic diseases such as diabetes mellitus. As the inflammation usually goes without any symptoms and has high prevalence among denture wearers, it is desirable for patients to schedule regular examinations to obtain diagnosis early and to receive adequate therapy. Conclusion. The manuscript presents the etiopathogenesis of denture stomatitis and usual therapeutic procedures that are carried out during treatment