Characteristics Temperatures Research Articles

COMPUTER SIMULATION OF THERMAL AND HYDRAULIC PROCESSES IN NPP STEAM GENERATOR CHANNELS ON THE BASIS OF INTERVAL-ITERATIVE METHOD

The designing of NPP steam generators, which are complex technical systems, requires a large number of variant calculations, as result of which must be obtained both optimal integral characteristics of steam generators (total heat transfer surface, metal capacity, hydraulic circuits, etc.) and many of their local characteristics (distributions heat flux densities and temperatures, possible amplitudes of their pulsations and others). The complexity of NPP steam generators as technical systems is determined by their multi-parameter, the presence of a complex logical and functional relationship between the parameters, the presence of various restrictions on the change of parameters, the stochastic change of parameters during exploitation. The article presents methods of mathematical modeling of thermal and hydraulic processes in NPP steam generators and modular programs of their calculations in one-dimensional formulation on the example of a steam generator with countercurrent (direct current) mutual motion of the coolant and the working substance. Logical and structural schemes of computer programs of thermal and hydraulic calculations of NPP steam generators are presented.

Industrial scale gasification of T-grade coal via fixed bed technology

The gasification of solid fuel is known technology suitable for many purposes which has found quite limited applications worldwide. The one of the major reasons is deficiency of practical operation experience of industrial scale units. The paper reports the data on T-grade coal gasification by air via 4 ton per hour pilot scale VTI gasifier situated in Tomsk polytechnic university (Tomsk, Russia). The tests were carried out for bituminous coal of Kuznetsk basin. The results presented were obtained in nonstationary regime for single 4 t load of fuel. The characteristics temperatures into gasifier as well as generator gas composition were determined. Obtained results allowed to conclude that T-grade coal is suitable fuel for VTI gasification technology.

Curing and thermal properties of tannin-based epoxy and its blends with commercial epoxy resin

In order to find partial substitution for bisphenol A-based commercial epoxy resin (CE), a bio-based epoxy resin was prepared from eucalyptus tannins through a typical glycidylation reaction with epichlorohydrin. The structure of tannin-based epoxy resin (TE) was confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. Herein, mixtures of TE and CE (TE–CE) were prepared using varying loading amounts (20, 40 and 60) wt/wt%of TE. Tannins used here are produced by solid–liquid extraction from the outer bark of eucalyptus tree, mainly consisting of condensed tannins. Through the use of differential scanning calorimetry (DSC) and FTIR techniques, the reactivity of tannin epoxy with and without commercial epoxy resin to form cross-linking network was investigated. TE was successfully cured with amine-based curing agent. Furthermore, compared to commercial epoxy resin (CE), TE exhibited broad low exothermic peak, insignificant cross-linking properties and low curing enthalpy at different levels of curing agent. Moreover, to study the influence of TE substitution on the curing properties of CE, curing behavior of TE–CE mixtures was investigated by DSC. It was found that TE at high loading levels such as 40 and 60 wt/wt% increases slightly the reactivity of CE by decreasing curing characteristics temperatures such as the initial of curing, peak exotherm and completion of curing temperatures. TE can serve as curing accelerator and has a non-desirable impact on the curing performance of CE resin such as curing enthalpy. And up to 20 wt/wt% of CE could be replaced by TE without any significant reduction in the curing behavior of CE.

Concentration dependence of the elastic moduli, thermal properties, and non-isothermal kinetic parameters of Yb3+ doped multicomponent tellurite glass system

The thermal properties and the kinetic parameters of TeO2–Li2O–ZnO–Nb2O5–Yb2O3 glass series have been evaluated as a function of increasing Yb2O3 content. The theoretical elastic properties and the quantitative analysis (the link between the elastic features and the changed chemical composition of the glass) have been determined by the use of bond compression and Makishima–Mackenzie models. The thermal analysis Differential Scanning Calorimetry (DSC) test was used for estimating the glass characteristics temperatures, thermal stability, and non-isothermal kinetic parameters at the heating rates (β) 10, 15, 20 and 25 K/min. The activation energies of the glass transition 〈Eg〉 and crystallization 〈Ec〉, as well as the order of the crystallization reaction (n), have been computed by different models with clear consistency and harmony between them. It was found that the characteristics temperatures of transition (Tg), softening (Ts), the onset of the crystallization (Tx) and the crystallization (Tc) increased with increasing the heating rate. Also, the results showed the higher thermal stability values (>100 K) for the understudied glass which is confirmed by KSP and ((Tc–Tg)/Tg) parameters values. Calculating of (n) showed that the crystallization started with surface nucleation and finished with bulk volume nucleation with rising Yb2O3 (mol %). The computed elastic moduli were linked with the interpretation of the thermal parameters to give a comprehensive image of the studied glass system.

Effect of Mn doping on the acoustic and vibrational behaviors of lead-free piezoelectric (Na1/2Bi1/2)TiO3-xBaTiO3 single crystals

The acoustic and vibrational properties of Mn-doped (Na1/2Bi1/2)TiO3-xBaTiO3 with x = 0.05 were investigated by using Brillouin and Raman spectroscopies and compared with those of undoped crystals. The mode frequency and the half width of the Brillouin doublet of the longitudinal acoustic mode showed more drastic changes near the dielectric maximum temperature compared to the broad and diffused changes of the undoped crystals, which indicates that Mn-doping induces polar domains larger than the typical polar nanoregions formed in undoped counterpart. The acoustic anomalies were most pronounced along the <100> direction suggesting that the polarization fluctuations are anisotropic and largest along this direction. Temperature dependence of Raman spectra showed that there are two characteristics temperatures where mode splitting occurs due to local symmetry changes. The high-temperature anomaly was associated with the changes in the acoustic properties, while the low-temperature mode splitting was related to the dielectric anomaly near depolarization temperature.

Environmental Determinants of Choice of Sustainability Strategies Adopted by Group Ranches in Samburu County, Kenya

The group ranch system is one of the best land ownership and livestock production strategies in the dry lands of the world where the potential for rain-fed agriculture is limited. Its sustainability relies greately on choice of sustainability strategies adopted by group ranches. Numerous studies on the establishment of group ranches, their dissolution and coping strategies have been conducted but with less focus on the sustainability of the group ranches.This study attempts to fill the gap. It is against this background that this study investigated environmental characteristics influencing choice of sustainability strategies adopted by group ranches in Samburu County, Kenya. The investigation adopted a descriptive survey research design employing use of Questionnaires, Key Informant Interviews, Focus Group Discussions and observation as primary data collection methods.The target population for the study was the 16,611 registered members in 38 group ranches spread out in the County. The study sampled 12 group ranches with approximately 5,643 members from which 374 respondents were systematically sampled. Purposive sampling was used to select Key Informants and the participants in the Focus Group Discussions.The study employed Multi-linear Regression to analyse environmental characteristics determining choice of sustainability strategies. The Analysis of Variance (ANOVA) was used to test the hypothesis and p-value of 0.00 was obtained, indicating that environmental characteristics (rainfall patterns, droughts, temperatures, diseases and floods) significantly influenced choice of sustainability strategies adopted by group ranches in the County. Overall, rainfall patterns were the predominating environmental characteristic with a regression coefficient of 0.317 while diseases had the least influence on choice of sustainability strategies adopted by group ranches in Samburu County, with a regression coefficient of 0.029. The study recommended integration of environmental characteristics in formulating policies for sustainability of group ranches.

Phy-chemical Attributes of Nano-scale V2O5/TiO2 Catalyst and Its’ Effect on Soot Oxidation

The V2O5 catalysts which supported on nano-scale TiO2 with variation of vanadium contents (5%, 10%, 20% and 40%) were prepared by an incipient-wetness impregnation method. The phase structures of nano-scale V2O5/TiO2 catalysts with different loading rates were characterized by Scanning electron microscope (SEM), X-Ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra. The oxidation activities of catalysts over diesel soot were performed in a themogravimetric analysis (TGA) system. The kinetics of the catalytic oxidation process were analyzed based on Flynn-Wall-Ozawa method. The characterization results showed that the phase structure of V2O5 supported on TiO2 depends heavily on the vanadium contents, which will put great effects on the catalytic performances for soot oxidation. At a low vanadium loading rates (V5-V20), active species exist as monomers and polymeric states. At a high loading rate (V40), the crystalline bulk V2O5 covers the surface of TiO2. The formed crystal structure occupied the active sites and led a decreasing in the catalytic effect. By comparing the characteristics temperatures of soot oxidation over V2O5 catalysts, the catalytic activities of catalysts with different loading rates for soot oxidation can be ranked as: V5 &lt; V10 &lt; V40 &lt; V20. Via pyrolysis kinetics analysis, it is revealed that the activation energy of soot oxidation is minimum when the vanadium loading rates is 20%, which is fit well with the TG experimental results. The consistency of pyrolysis kinetics and TG experimental results confirm that the best activity catalyst is V20 in discussed catalysts of this paper, which is nearest to the monolayer dispersion saturated state of V2O5/TiO2 catalyst. Moreover, it convincingly demonstrate the obvious threshold effect in V2O5 catalysts.

Heating Rate and Composition Dependence of Crystallization Temperature of Cu-Based Metallic Glasses

The variation of onset of crystallization temperature (Tx) and peak crystallization temperature (Tp) with heating rate (q) is studied. Tx and Tp vary in a power law behavior with heating rate (q) for Cu60 Zr20Ti20 metallic glass and these parameters show a linear variation for Cu60Zr40 metallic glass. The power law variation is expressed as Tx (or Tp) = T0 [q]y; where, q is the normalized heating rate, T0 is the Tx (or Tp) at a heating rate of 10Cmin-1. Further, the calculated values of Tx (or Tp) are found to be in good agreement with the experimental results. Hence, the power law relation is found to be an appropriate theoretical expression for the variation of crystallization temperature (Tx or Tp) with heating rate (q) for Cu60 Zr20Ti20 metallic glass. In addition to heating rate, the composition of a metallic glass also affects its crystallization temperature. It is observed that the characteristics temperatures shift towards higher values with increase in number of components.

Fusion characterization of biomass ash

The ash fusion characteristics are important parameters for thermochemical utilization of biomass. In this research, a method for measuring the fusion characteristics of biomass ash by Thermo-mechanical Analyzer, TMA, is described. The typical TMA shrinking ratio curve can be divided into two stages, which are closely related to ash melting behaviors. Several characteristics temperatures based on the TMA curves are used to assess the ash fusion characteristics. A new characteristics temperature, Tm, is proposed to represent the severe melting temperature of biomass ash. The fusion characteristics of six types of biomass ash have been measured by TMA. Compared with standard ash fusibility temperatures (AFT) test, TMA is more suitable for measuring the fusion characteristics of biomass ash. The glassy molten areas of the ash samples are sticky and mainly consist of K-Ca-silicates.

Electron energetics in the expanding solar wind via Helios observations

AbstractWe present an observational analysis of electron cooling/heating rates in the fast and slow solar wind between 0.3 and 1 AU. We fit electron velocity distribution functions acquired in situ by Helios 1 and 2 spacecraft by a three‐component (core‐halo‐strahl) analytical model. The resulting radial profiles of macroscopic characteristics (density, temperatures, and heat fluxes) are employed to examine properties of theoretical energy balance equations and to estimate external cooling/heating terms. Our analysis indicates that in contrast to solar wind protons the electrons do not require important heating mechanisms to explain the observed temperature gradients. The electron heating rates are actually found to be negative for both the slow and fast solar wind, namely, due to the significant degradation of the electron heat flux with increasing radial distance from the Sun. Cooling mechanisms acting on electrons are found to be significantly stronger in the slow wind than in the fast wind streams.

Phase Evaluation of Pure Mg, Mg-1Ca and Mg-1Ca-3Zn ‎Alloys by Thermal Analysis Used in ‎Medical Applications

In this research paper phase identification was conducted based on the thermal and microstructural analysis of pure Mg, binary ‎Mg-Ca and ternary Mg-Ca-Zn alloys which have been received significant attention to be used as biodegradable implants. ‎Thermal analysis results show that nucleation temperature of primary Mg decreased and solidification range expanded with ‎adding Ca and Zn to the Mg melt. Moreover, characteristics temperatures of intermetallic phase assess for Mg-1Ca and Mg-‎‎1Ca-3Zn alloys. Microstructural evolutions of specimens were characterized by optical microscopy, scanning electron ‎microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The result revealed that the identification of Mg2Ca and Ca2Mg6Zn3‎intermetallic phases by thermal analysis which were also detected by EDS. Furthermore with addition of Ca and Zn elements, the ‎coherency time increased while, the fraction of primary α-Mg at dendrite coherency point (fαDCP) decreased.‎

Theoretical study of the effect of the size of a high-energy proton beam of the Large Hadron Collider on the formation and propagation of shock waves in copper irradiated by 450-GeV proton beams

The interaction of 450-GeV protons with copper, which is the material of the collimators of the Large Hadron Collider, has been theoretically studied. A theoretical model for the formation and propagation of shock waves has been proposed on the basis of the analysis of the energy released by a proton beam in the electronic subsystem of the material owing to the deceleration of secondary particles appearing in nuclear reactions induced by this beam on the electronic subsystem of the material. The subsequent transfer of the energy from the excited electronic subsystem to the crystal lattice through the electron-phonon interaction has been described within the thermal spike model [I.M. Lifshitz, M.I. Kaganov, and L.V. Tanatarov, Sov. Phys. JETP 4, 173 (1957); I.M. Lifshitz, M.I. Kaganov, and L.V. Tanatarov, At. Energ. 6, 391 (1959); K. Yasui, Nucl. Instrum. Methods Phys. Res., Sect. B 90, 409 (1994)]. The model of the formation of shock waves involves energy exchange processes between excited electronic and ionic subsystems of the irradiated material and is based on the hydrodynamic approximation proposed by Zel’dovich [Ya.B. Zel’dovich and Yu.P. Raizer, Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena (Nauka, Moscow, 1966; Dover, New York, 2002)]. This model makes it possible to obtain the space-time distributions of the main physical characteristics (temperatures of the ionic and electronic subsystems, density, pressure, etc.) in materials irradiated by high-energy proton beams and to analyze the formation and propagation of shock waves in them. The nonlinear differential equations describing the conservation laws of mass, energy, and momentum of electrons and ions in the Euler variables in the case of the propagation of shock waves has been solved with the Godunov scheme [S. K. Godunov, A.V. Zabrodin, M.Ya. Ivanov, A.N. Kraiko, and G.P. Prokopov, Numerical Solution of Multidimensional Problems in Gas Dynamics (Nauka, Moscow, 1976) [in Russian]]. The temperature, pressure, and specific internal energy have been calculated independently and separately for the ionic and electronic subsystems of the irradiated material. The formation of shock waves in copper has been simulated in the cylindrical geometry for various sizes and various types of the beam: for a needle beam (the distribution of protons in the beam is described by the Dirac delta function) and beams with a finite radius (0.3, 3, and 5 mm) with a Gaussian distribution of protons near the axis of the beam. The effect of the size and geometry of the proton beam, as well as of the form of the chosen boundary conditions, on the intensity of shock waves formed in copper and on change in their physicomechanical properties in the space and time has been revealed in the numerical simulation results.

Sintering of Rye Straw Ash and Effect of Additives

The effects of kaolin and calcite additives on the rye straw ash sintering behaviors were investigated. The rye straw ash has a high sintering tendency, with observation of severe fusion during combustion. The formation and melting of potassium silicates play key roles in sintering of the rye straw ash at elevated temperatures. Fusion characteristics temperatures of the rye straw ash were significantly increased upon kaolin and calcite addition. Kaolin addition led to formation of high temperature melting potassium aluminum silicates, which were revealed by XRD analyses. Due to formation of high temperature melting species due to kaolin addition, the severe sintering of the rye straw ash was significantly reduced. Addition of calcite provided CaO to react with silica in the rye straw ash, causing generation of high temperature melting calcium rich silicates. In addition, the dilution effect from calcite is a main reason for improved rye straw sintering behaviors.

Annealing time dependent up-conversion luminescence enhancement in magnesium–tellurite glass

Silver nanoparticles (NPs) embedded Er3+ ions doped magnesium–tellurite glasses are prepared using melt quenching technique. Heat treatment with different time intervals above the glass transition temperature is applied in order to reduce the silver ions (Ag+) to silver NPs (Ago). The transmission electron microscopy (TEM), differential thermal analyses (DTA), UV–vis-NIR absorption spectroscopy and photoluminescence (PL) spectroscopy are used to examine annealing time dependent structural and optical properties. The characteristics temperatures such as glass transition temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm) obtained from DTA for an as prepared sample are 322°C, 450°C and 580°C, respectively. TEM image clearly shows the homogeneous distribution of silver NPs with an average diameter ∼12nm. The observed localized surface plasmon resonance (LSPR) band is evidenced at 534nm. Furthermore, the infrared to visible frequency up-conversion (UC) emission under 786nm excitation exhibits three emission bands centered at 532nm, 554nm and 634nm corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+, respectively. Intensity of all the bands is found to enhance by increasing the annealing time up to 24h. However, further increase in the annealing time duration (∼40h) reduces the intensity. Enhancement in the luminescence intensity is understood in terms of the local field effect of the silver NPs whereas the quenching is attributed to the energy transfer from Er3+ ions to silver NPs.

Study of Amorphous-Crystalline Phase Transformations by DSC and Dilatometer in the Case of Al-Based Amorphous Alloys

The amorphous-crystalline transformation is studied by DSC and dilatometer. From the DSC signal the characteristic temperatures and the heat evolved during each transformation step can be determined. The dilatometer depicts the thermal contractions accompanying the changes in topological short range order. Although the characteristics temperatures determined by DSC and dilatometer, two methods are slightly different their dependences on the heating rate are very similar, where from the activation energies of each transformation steps can be determined using the Kissinger plots. As an example, two aluminum-based amorphous ribbon samples (Al88Mm5Ni5Co2 and Al85Y8Ni5Co2) will be measured and compared.

Sensitivity of Arctic ozone loss to polar stratospheric cloud volume and chlorine and bromine loading in a chemistry and transport model

The sensitivity of Arctic ozone loss to polar stratospheric cloud volume (VPSC) and chlorine and bromine loading is explored using chemistry and transport models (CTMs). One simulation uses multi‐decadal winds and temperatures from a general circulation model (GCM). Winter polar ozone loss depends on both equivalent effective stratospheric chlorine (EESC) and polar vortex characteristics (temperatures, descent, isolation, polar stratospheric cloud amount). The simulation reproduces a linear relationship between ozone loss and VPSC in agreement with that derived from observations for 1992–2003. The relationship holds for EESC within ∼85% of its maximum (∼1990–2020). For lower EESC the ozone loss varies linearly with EESC unless VPSC ∼ 0. A second simulation recycles a single year's winds and temperatures from the GCM so that polar ozone loss depends only on changes in EESC. This simulation shows that ozone loss varies linearly with EESC for the entire EESC range for constant, high VPSC.

Determination of the intragrain irreversible temperature Tgirr of Bi(2223) superconductor by ESR measurement

We consider our Bi(2223) polycrystalline sample to be made up to superconducting grains which are separated by Josephson junctions. Two characteristics temperatures, i.e. the irreversible temperature T g irr and T J irr of the grains and Josephson junctions should appear as a natural consequence of the electromagnetic theory and irreversible magnetization [1,2]. Macroscopically T J irr and T g irr correspond to the temperature, at which the diamagnetic hysteresis loop and the paramagnetic hysteresis loop disappear respectively [3]. It has been proposed that microwave absorption results from decoupling of grains (Dulcic's model). Extending this model to include temperature dependence of the resistivity ϱ( T) and the critical current I c( H, T), we have deduced an expression for microwave absorption. This expression includes a term which is non-zero even after the microwave absorption at low field disappears. We have therefore carried out ESR absorption measurement of our sample from 96 K to 110 K and have found that a broad weak absorption peak does occur in the temperature range T c > T ≥ 108 K, giving T g irr = 108 K. When T > T c, such a weak peak disappears. Apart from this finding, the result of low field microwave absorption is qualitatively similar to the results of others.

Improving the performance of porous radiant burners through use of sub-micron size fibers

An analysis has been carried out to determine the performance of porous radiant burners (PRB) as a function of fiber size. PRB made with silica or alumina fibers are considered. The radiative properties of the fibers are determined using the electromagnetic wave scattering theory for two different characteristics temperatures— 1000 and 1500°C. The properties are used in a combined-mode heat transfer model to calculate the amount of energy radiated by the PRB. It is found that fibers smaller than the order of 1 μm in diameter produce significantly higher radiant output. For a characteristic temperature of 1000°C, in some cases, the increase in output is as high as 63 and 109% for silica and alumina fibers, respectively. For a characteristic temperature of 1500°C, the corresponding increases are 72 and 150%, respectively.