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This paper reports the temperature-dependence of methanol generation and the tensile index under ageing conditions for two paper/oil systems: one consisting of a standard wood Kraft paper and the other of a thermally-upgraded Kraft paper (TUK). A linear correlation between methanol and the tensile index for these paper/oil systems was observed in a previous study at 170 °C. In the current study, the correlation was extended to a large range of temperatures (150-190 °C). The experimental data were fitted with a modified Calvini's kinetic model, while the Arrhenius equation was used to model the kinetic of changes of the paper's mechanical properties during ageing. Good agreement with the temperature ( lnk vs. 1/ T) was observed for the rate constants of the chain-end group production, methanol formation, and the decrease of mechanical properties. The Arrhenius equation applied to this data grouping showed activation energy of 130 ± 29 kJ/mol for the decrease in mechanical strength of the standard Kraft paper, while the value was 118 ± 55 kJ/mol for the TUK paper. These values are of the same order of magnitude as those obtained in this study and in the literature for the depolymerization of cellulose and the generation of methanol that was reported. This confirmed the close relationship between cellulose depolymerization, methanol generation and the reduction of the paper's mechanical strength during ageing, dominated by the acid hydrolysis mechanism. The results, which can be seen as a benchmark and pave the way to further research, provide an opportunity for applying the proposed correlations to estimate the insulation condition in operating transformers. [ABSTRACT FROM AUTHOR]

Due to rapid temperature rise and insulation moisture, bubbles can generate in the oil-paper insulation of oil-immersed power transformers, which can reduce the dielectric strength of oil-paper insulation and even bring about the risk of insulation breakdown. In order to accurately evaluate the conditions of bubble formation, the physical process of bubble formation in oil-paper insulation is studied in this article. Considering the effects of water vaporization, gas dissolution in oil, and moisture migration on bubble formation, a bubble formation prediction model is constructed. Based on Henry’s law, the dissolution equilibrium of gas in oil is taken into consideration and the upper boundary of the initial temperature of bubble effect (ITBE) envelope is obtained in this model. Based on the moisture equilibrium in oil-paper insulation, the bubble formation process caused by the emergence and rapid evaporation of free water is analyzed, and then, the lower boundary of the ITBE envelope is obtained in this model. The model results show that the moisture content of the pressboard and the presence of free water have a great impact on ITBE. Specifically, the higher the moisture content, the lower the ITBE value. In addition, with the further increase of moisture content, the upper and lower boundaries of the ITBE envelope gradually tend to be the same. However, once free water is present on the surface of cellulose, ITBE decreases rapidly to below 120 °C. The model built in this article is of great significance to study the temperature limit of the power transformer. Hence the ITBE envelope can provide an important theoretical reference for reducing the risk of bubble formation during power transformer operation. [ABSTRACT FROM AUTHOR]

A substantial quantity of testing has been performed on the degradation of paper insulation over the decades. The aim being to better educate the electrical industry on how to best operate expensive assets, such as transformers. The longevity of paper insulation is frequently tested using accelerated ageing experiments, where the effects of temperature and the chemical environment on paper lifespan can be studied. Such research has resulted in paper life expectancy curves being published by the IEEE and the IEC. The investigations tend to use sealed vessels. However, the disadvantage of using this method is that the water content of the paper changes during the ageing process which then changes the ageing rate. In these ageing experiments the water and oxygen content was controlled using a special test rig to compare the ageing rate to previous work and to determine the ageing effect of paper by combining temperature, water content of paper and oxygen content of the oil. We found that the rate of paper ageing can be more accurately determined by controlling the water and oxygen during the experiment which then produced noticeable changes in predicting life expectancy. [ABSTRACT FROM PUBLISHER]

To model advanced 3-D forming strategies for paper materials, the effects of environmental conditions on the mechanical behavior must be quantitatively and qualitatively understood. A tensile test method has been created, verified, and implemented to test paper at various moisture content and temperature levels. Testing results for one type of paper for moisture contents from 6.9 to 13.8 percent and temperatures from 23 to 168 degrees Celsius are presented and discussed. Coupled moisture and temperature effects have been discovered for maximum stress. Uncoupled effects have been discovered for elastic modulus, tangent modulus, hardening modulus, strain at break, tensile energy absorption (TEA), and approximate plastic strain. A hyperbolic tangent function is also utilized which captures the entire one-dimensional stress-strain response of paper. The effects of moisture and temperature on the three coefficients in the hyperbolic tangent function may be assumed to be uncoupled, which may simplify the development of moisture- and temperature-dependent constitutive models. All parameters were affected by both moisture and temperature with the exception of TEA, which was found to only be significantly dependent on temperature. [ABSTRACT FROM AUTHOR]

Abstract: We developed a new meat product referred to as meat paper, which is edible paper made from beef, and the purpose of this study was to establish optimal conditions for making meat paper. Response surface methodology was used to model and optimize responses (folding test, springiness and cohesiveness). Dehydration conditions, such as drying temperature (46.6–63.4 °C) and drying time (78.0–138.0 min), and sample cutting time (13.2–46.8 s) were selected as the main processing conditions in the making of meat paper. Optimal conditions for the minimum folding test (cm), maximum springiness (%) and cohesiveness (%) of the meat paper were established. We found four solutions with the following conditions: 17.2–19.2 s of sample cutting time, 52.6 °C of drying temperature and 123.0–125.0 min of drying time. We then successfully made meat paper under these conditions and confirmed various desirable properties of this product. [Copyright &y& Elsevier]

Abstract: A wide range of mathematical models for multiple effect evaporators in process industry including paper industry are well reported in the literature but not so extensive work on the dynamic behavior of MEE system is available in the literature. In the present study dynamic behavior of multi-effect evaporator system of a paper industry is obtained by disturbing the feed flow rate, feed concentration, live steam temperature and feed temperature. For this purpose an unsteady-state model for the multi-effect evaporator system is developed. Each effect in the process is represented by a number of variables which are related by the energy and material balance equations for the feed, product and vapor flow. A generalized mathematical model which could be applied to any number of effects and all kinds of feeding arrangements like forward feed, backward feed, mixed feed and spilt feed in the MEE system with simple modifications was finally obtained. Finally model for mixed feed sextuple effect falling film evaporators system was solved using MATLAB. For the steady state and dynamic simulation the ‘fsolve’ and ‘ode45’ solvers in MATLAB source code is used respectively. [Copyright &y& Elsevier]

This paper refers to the bubble effect in transformer bushings. The bubble effect consists in releasing water from moistened cellulose insulation after exceeding a critical temperature. The most dangerous result is a pressure increase that leads to an explosion and fire. Research was conducted using laboratory models of OIP (Oil- Impregnated Paper) and RBP (Resin-Bonded Paper) types of bushings immersed in mineral oil and synthetic ester. For all of the investigated systems we determined the dynamics of water adsorption upon contact of the insulating material with air and the temperature characteristics of bubble effect initiation depending on water content in cellulose. In the experiment we investigated the dynamics of changes of water content in dielectric liquid, water content in air over the surface of the dielectric liquid, and air pressure over the surface of the dielectric liquid. In the future, the technical possibilities will be analyzed of using the dynamic changes of the three quantities investigated here to detect the bubble effect in bushings. [ABSTRACT FROM AUTHOR]

Abstract: Zanotti et al. recently reported on the thermal diffusivity of NiTi shape memory alloys. In the experimental part of their work, they measured the temperature in the cylindrical sample, and they found that this temperature is significantly influenced by the latent heat. The mathematical model used for the determination of the thermal diffusivity was based on the 1D unsteady heat diffusion equation. They found a drastic decrease and then increase of the thermal diffusivity in the transformation temperature range. This negative peak, however, has no physical meaning because the general heat conduction equation was derived and solved with boundary conditions that require that no phase transformations occur in the material. The latent heat changes the temperature distribution in the sample, so selected model cannot be applied in the transient temperature range. [Copyright &y& Elsevier]

We use a soil carbon (C) model (RothC), driven by a range of climate models for a range of climate scenarios to examine the impacts of future climate on global soil organic carbon (SOC) stocks. The results suggest an overall global increase in global SOC stocks by 2100 under all scenarios, but with a different extent of increase among the climate model and emissions scenarios. Projected land use changes are also simulated, but have relatively small impacts at the global scale. Whether soils gain or lose SOC depends upon the balance between C inputs and decomposition. Changes in net primary production (NPP) change C inputs to the soil, whilst decomposition usu ally increases under warmer temperatures, but can also be slowed by decreased soil moisture. Underlying the global trend of increasing SOC under future climate is a complex pattern of regional SOC change. SOC losses are projected to occur in northern latitudes where higher SOC decomposition rates due to higher temperatures are not balanced by increased NPP, whereas in tropical regions, NPP increases override losses due to higher SOC decomposition. The spatial heterogeneity in the response of SOC to changing climate shows how delicately balanced the competing gain and loss processes are, with subtle changes in temperature, moisture, soil type and land use, interacting to determine whether SOC increases or decreases in the future. Our results suggest that we should stop asking the general question of whether SOC stocks will increase or decrease under future climate since there is no single answer. Instead, we should focus on improving our prediction of the factors that determine the size and direction of change, and the land management practices that can be implemented to protect and enhance SOC stocks. [ABSTRACT FROM AUTHOR]

This paper proposed a temperature-dependent iron loss model and corresponding dynamic hysteresis model, where temperature coefficient k is introduced to consider the thermal effect on eddy-current loss. The iron loss model is validated by massive experimental measurement of test samples, 1174 combinations of various temperatures, magnetic inductions, and frequencies for nonoriented silicon steel specimen. The relative error of the model is $\sim 11$ % in a wide range of 50–400 Hz, 26 °C–200 °C, and 0–2 T. The proposed method can be applicable to other types of magnetic materials as long as whose resistivity rate exhibits approximately linear thermal dependence within a temperature range of 26 °C–200 °C. [ABSTRACT FROM AUTHOR]

Modeling of dielectric relaxation function ϕ(t) by a distribution of exponential decay functions is advantageous due to its monotonically decreasing property which ensures that ϕ(t) is integrable over any period of time. Several equivalent circuits based on simple combination of energy storing and dissipating elements are available in literature which are capable of modeling ϕ(t). One of the widely used two-parameter equivalent circuit for dielectric response modeling of various polymeric dielectric as well as oil-paper insulation is the Maxwell ladder structure. In this paper it is shown that for more accurate modeling and better understanding of the dielectric response of complex insulation system like oil-paper insulation of high voltage equipments operating under temperature gradient, modification of Maxwell model is necessary. The proposed model, similar to the classic Maxwell circuit, is also composed of a number of parallel branches, but unlike the former, the proposed model considers each of the parallel branches to be composed of not just one but a number of exponential functions. [ABSTRACT FROM PUBLISHER]

In this paper, we show a validation of our compact model for negative capacitance FET (NCFET) presented in Part I. The model is thoroughly validated with the TCAD simulations with respect to ferroelectric thickness scaling and temperature effects. Interestingly, we find that an NCFET with PZT ferroelectric of a large thickness provides a negative output differential resistance in addition to an expected high ON current and a sub-60 mV/decade subthreshold swing. The model is also tested for the Gummel symmetry and its transient capabilities are highlighted through a ring oscillator circuit simulation. [ABSTRACT FROM PUBLISHER]

Abstract: A multivariate data analysis of cavitation indicators and parameters was carried out to improve the quantitative characterization of cavitation processes used in manufacturing and medical applications. The indicators were obtained from four model measurement methods applied to a 45kHz cleaning vessel. Together with experimental data such as temperature and electrical input power they form the data basis of a factor analysis. The loadings of three factors were calculated and the indicators, the parameters, and finally the data were depicted in factor space. The factors show relations between the variables and several overlapping indicators and parameters were identified. The coordinates of the data (data scores) indicate tendencies within the data and the assessment of the factors allows the finding of hidden relations. Using the factor analysis three representing indicators or parameters specific to the application case are identified which can be used for a complete description of the process. This characterization method can favourably be applied in quality management systems. [Copyright &y& Elsevier]

This paper takes a different look at the mathematical modeling of the effective thermal conductivity of nanofluids. Most related published experimental-based mathematical models have been analyzed statistically. The sensitivity analysis showed that in the most published models, the role of nanofluids bulk temperature may be ignored. Then, we extracted a lot of data from the models in the valid ranges of variables. The next step was performing statistical analysis of the variances and means of different datasets (data populations). The results showed that changing considerably the nanofluids temperature doesn't affect considerably the nanofluids thermal conductivity. We introduced a comprehensive, simpler and more accurate correlation neglecting the nanofluids temperature to predict the effective thermal conductivity of nanofluids. Results indicated that the predicted values using the proposed correlation are in a good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The mechanical properties of multi-layer corrugated sandwich structure are investigated in this paper. The mathematical model in which the structure factors and temperature and relative humidity are concerned is developed through the cooperation of theories and experiments. Then the model is normalized by the elastic modulus of the medium under controlled condition, thus this model can be used to predict the effect of various temperature and relative humidities on the plateau stress of multi-layer corrugated sandwich structure under flatwise compression. Comparisons of the predictions and experiments are made in order to examine the accuracy of the model, and a good correlation is obtained in view of the experimental error. The proposed model can be applied to the practical material selection and optimal design of corrugated sandwiches. Meanwhile, the proposed model might provide valuable information for the investigation of different materials with corrugated sandwich structure. [ABSTRACT FROM AUTHOR]

In this paper, optical power of high-power white-light-emitting diode (LED) devices is evaluated and characterized. A theoretical model for optical power is proposed. The measurements reveal that optical power decreases exponentially with junction temperature and increases linearly with current. The model considers conjunct effect of current and junction temperature on emitted optical power. The proposed theoretical model of optical power will facilitate the optical and thermal performance evaluation of LED devices and will be helpful to device design. With the presented optical power model, heat power can be estimated, because they are complementary to each other. Then, junction temperature of LED device can be predicted with known heat power. In addition, the optical power model can be applied to eliminate chromaticity shift phenomenon of trichromatic-based white-LED devices, simply by monitoring junction temperature and injection current of each chip. Validity of the optical power model has been verified by experimental measurements on two types of commercial LED devices. [ABSTRACT FROM AUTHOR]

In order to study the thermal safety of cylindrical battery and solve the three-dimensional cylindrical battery thermal explosion problem, a common thermal explosion physical model of cylindrical battery and three-dimensional thermal explosion mathematical model of cylindrical fireworks with non-uniform heat dissipation of the lateral surface were established for the first time. By applying the theory of heat transfer, the boundary conditions of cylindrical battery were simplified reasonably. The seven-point difference method was introduced to disperse the model. The three-dimensional numerical program was written by homotopy continuation method and Newton iteration method based on Matlab. Comparison of two-dimensional numerical solutions obtained by taking ϕ = 0 and classical solutions proved the accuracy of model. A common kind of fireworks was calculated in this paper. When this single cylinder firework stored individually, the criterion of thermal explosion is 1.796, and critical ambient temperature is 450.484 K. When stored in combination form (that is battery), the criterion of thermal explosion is 1.363 and critical ambient temperature is 447.964 K. The results show that the cylindrical fireworks stored in combination form is more dangerous than this single cylinder firework stored individually, so the cylindrical battery is the focus of safety prevention of fireworks. [ABSTRACT FROM AUTHOR]

This paper presents a method of automatically constructing and parameterizing accurate lumped parameter thermal equivalent circuits (TECs) with nodes arranged in a regular mesh pattern. The approach exhibits a number of advantages over conventional lumped parameter TECs including superior thermal field resolution, reduced model construction and setup times and more accurate identification of hot-spot temperatures and their location. The method serves as a desirable compromise between the fine detail and high computational cost of a full finite element analysis and the coarse detail and short solution times afforded by lumped parameter TECs. The benefits of the method are demonstrated by the analysis and experimental test of a demonstration linear actuator. [ABSTRACT FROM AUTHOR]

This paper deals with the temperature estimation of interior permanent magnet synchronous motor (IPMSM). A thermal equivalent circuit of IPMSM is proposed with considering eddy current loss of PM as well as core losses of rotor. Heat sources, which are core loss of stator/rotor core and eddy current loss of PM, are calculated by numerical method to enhance the accuracy of thermal estimation. The thermal equivalent model is represented by the thermal resistances and thermal capacitances, which are determined by motor configuration. Meanwhile, a temperature test is performed using prototype to determine the heat transfer. Finally, this thermal equivalent model is verified by a temperature test in a 25 kW 12-pole/18-slot IPMSM. [ABSTRACT FROM PUBLISHER]

Reliability and variability have become big design challenges facing submicrometer high-speed applications and microprocessors designers. A low area overhead adaptive body bias (ABB) circuit is proposed in this paper to compensate for negative-bias temperature instability (NBTI) aging and process variations to improve the system reliability and yield. The proposed ABB circuit consists of a threshold voltage-sensing circuit and an on-chip analog controller. In this paper, post-layout simulation results, referring to an industrial hardware-calibrated STMicroelectronics 65-nm CMOS technology transistor model, are presented. The transistor model contains process variations and NBTI aging model cards, which are declared by STMicroelectronics to be Silicon verified. Cadence RelXpert, Virtuoso Spectre, and Virtuoso UltraSim tools are used to estimate the NBTI aging and process variations impacts on a circuit block case study, extracted from a real microprocessor critical path. These results show that the proposed ABB compensates effectively for NBTI aging and process variations. For example, the proposed ABB improves the timing yield from 74.4% to 99.7% at zero aging time and from 36.6% to 97.1% at 10 years aging time. In addition, the proposed ABB increases the total yield from 67% to 99.5% at zero aging time and from 35.9% to 97.1% at 10 years aging time. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, four sensor types are presented for quantitative measurements in an ultrasonic cleaning vessel: (1) a hydrophone to measure spectral components of the sound field; (2) an aluminium foil technique as a model process for erosion; (3) a test tube filled with a solution of luminol to measure the emission of light; and (4) a test tube filled with potassium iodide solution to measure the oxidation of iodide. Thus a broad range of diverse cavitation effects is covered. The quantities were measured in dependence on three parameters: the electrical input power of the transducers, the temperature and the O2 concentration of the water. To ensure constant environmental conditions, a flow system was built up which continuously exchanges the water in the vessel. The comparability of the data measured in subsequent measurement cycles is discussed and the influence of the different sensor types on the cavitation field is considered. Dependences on the three parameters are shown. A quantitative analysis of correlations between the data is carried out in the second part of the study (Koch and Jüschke, 2012 ). [Copyright &y& Elsevier]

Thermodynamical considerations have largely been avoided in the modelling of complex fluids by invoking the assumption of incompressibility. This approximation allows pressure to be defined as a Lagrange multiplier, and therefore its natural connection with other thermodynamic variables such as density and temperature is irretrievably lost. Relaxing this condition to allow more realistic modelling involves much more than prescribing an equation of state. Even for a simple isothermal viscoelastic model, as explored in this paper, the transition to a compressible model is non-trivial. This paper shows that pressure enters the governing equations in a non-intuitive way. Furthermore, a fluid volume element, which is no longer constant, radically changes the way the basic element of the constitutive equations is viewed-stress is no longer the fundamental constitutive link between the momentum equations and velocity. The importance of geometry in fluid modelling is emphasised through the use of the Lie derivative, which is of a more fundamental character than the 'upper' and 'lower' convected derivatives prevalent in the literature and which are found to be almost redundant for a compressible fluid. There is now a strong body of non-equilibrium thermodynamics theory for flowing systems, which proves indispensible for this development. These fundamental principles are described herein using methodology and examples, that are sometimes conflicting, from the literature. The main conflict arises from the relationship between thermodynamic pressure and the trace of Cauchy stress, where the current preferred choice is (up to a constant) to set them equal-this is shown to be incorrect. Other issues such as the dependence of viscosity on density, bulk viscosity, integral modelling, the principle of objectivity and convected derivatives, are also clarified and resolved. [ABSTRACT FROM AUTHOR]

The acceptability of three transformer hottest-spot temperature (HST) models for use in dynamic loading are investigated and discussed in this paper. The hottest-spot models are the modified HST model, Swift's model, and Susa's model. The investigation fitted the models to measured field data obtained from utility transformers using numerical and statistical methods. Acceptability metrics to evaluate the models' accuracy, adequacy, and consistency in predicting HST were evaluated using results from the fitting procedures. These metrics serve as absolute measures to reveal any potential deficiencies in the models when they are used to build hottest-spot models for transformers using field data. The metrics also serve as relative measures to compare the performance of the models to one another. It is shown that the modified HST model and Susa's model are acceptable for implementing models from field data. And it is concluded that the Swift's model is not acceptable because it is structurally inaccurate. [ABSTRACT FROM PUBLISHER]

This paper describes the identification of a temperature dependent FitzHugh-Nagumo model directly from experimental observations with controlled inputs. By studying the steady states and the trajectory of the phase of the variables, the stability of the model is analyzed and a rule to generate oscillation waves is proposed. The dependence of the oscillation frequency and propagation speed on the model parameters is then investigated to seek the appropriate control variables, which then become functions of temperature in the identified model. The results show that the proposed approach can provide a good representation of the dynamics of the oscillatory behavior of a Belousov-Zhabotinskii reaction. [ABSTRACT FROM AUTHOR]

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This paper presents an improved semitheoretical fluorescent lamp model by including the effect of the lamp tube temperature on the lamp electrical parameters at different dimming levels. The experimental results have verified that the lamp tube temperature is a linear function of the lamp's input power and has significant influence on the lamp's electrical parameters during the dimming process. The comparison on the simulation and measurements shows that the improved lamp model can predict the lamp electrical characteristics accurately in a wide dimming range under both low- and high-frequency operations. [ABSTRACT FROM AUTHOR]

Aggressive transistor scaling affects the threshold voltage Vth in two ways: space and time. Transistors on the same die can have different Vth due to random dopant fluctuations (RDFs). On the other hand, Vth of a specific transistor can randomly shift in time due to random position of dangling bonds and random motion of atomic H or \H2 molecules in the oxide [negative bias temperature instability (NBTI)]. These two random effects are not totally independent because the dissociation rate of Si–H bonds at the silicon–oxide interface depends on the nonuniform electric field. In this paper, we describe the combined effect of RDF and NBTI on Vth using stochastic differential equation. In this paper, we are able to examine the effect of RDF on critical NBTI parameters such as kf, kr, and temperature and the correlation among these parameters. The efficacy of the proposed model is evaluated by performing Monte Carlo simulations on various transistors under different direct-current stress and obtained distributions for NIT and Vth. [ABSTRACT FROM PUBLISHER]

In this paper, the plasma arc welding is studied and stainless steel temperature field is gained in this process. An adaptive model of the heat source in numerical simulation of the keyhole plasma arc welding (PAW) requires that the model take into consideration the larger aspect ratio of welds and the volumetric distribution characteristic of heat intensity along the direction of the plate thickness. The available heat source models, either planar one like Gaussian or body ones like double-ellipsoidal and rotary Gaussian modes, are unable to describe the keyhole PAW process accurately. This paper reports the determination of optimum welding conditions (welding intensity and travel speed) for butt joints of α-phase stainless steel sheets using plasma-arc welding (PAW). Minimum net energy input for proper operative and metallurgical weldabilities is studied using two different welding modes: the melt-in or conduction mode and the keyhole mode. The influence of the welding parameter for each mode on the dimensions and shape of the welds and on their ferrite contents is investigated. [ABSTRACT FROM AUTHOR]

The topic of this paper is a building process of a real fuel cell mathematical model, based on the mixed logarithmic and polynomial approximation, focused on the 3-D load characteristics. The model's input is the values of load resistance and temperature (independent variables), whereas the output is the value of voltage. The coordinates of the operating point are determined analytically, using the double approximation (both transverse and longitudinal). The resulting 3-D model is then implemented in the MATLAB (text source code) and Simulink (block model) system environments. The core of the model is a system of optimal logarithmic approximation functions. The mathematical principle of the method and a numerical example are then presented. The main idea of the paper is to offer an accurate fuel cell model for more extensive computer experiments and to verify the presented original approximation methods. [ABSTRACT FROM AUTHOR]

In this paper, the problems of two-dimensional temperature distribution for the microwave heating process are analyzed and discussed. Different from the traditional models in previous literature, the paper proposes several two-dimensional global temperature models which consist of explicit dissipation powers. By analyzing microwave propagation characteristics and spatial distribution of dominant modes into the rectangular medium, the different dissipation powers in different microwave applications are derived, such as the short waveguide, long waveguide and resonant cavity. Then, substituting the proposed dissipation powers into heat transport equation, the simplified temperature models are obtained. For further validation, traditional finite element models in COSMOL Multiphysics are used to compare the proposed temperature models in the same parameters. The comparative results show that the mathematical models can approximately predict the global temperature variation and hot spot distribution in two-dimensional rectangular medium. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to investigate the effect of rotation and a magnetic field on the wave propagation in a generalized thermoelastic problem for a medium with an internal heat source that is moving with a constant speed. Design/methodology/approach – The formulation is applied to a generalized thermoelastic problem based on the three-phase-lag model and Green-Naghdi theory without energy dissipation. The medium is a homogeneous isotropic thermoelastic in the half-space. Findings – The exact expressions of the displacement components, temperature, and stress components are obtained by using normal mode analysis. Originality/value – Comparisons are made with the results predicted by the two models in the absence and presence of a magnetic field as well as a rotation. A comparison also is made with the results predicted by the two models for two different values of an internal heat source. [ABSTRACT FROM AUTHOR]

Arundo donax L. is an energy crop with the potential use as a renewable fuel. This study focused on the drying process of the canes in field and laboratory conditions to determine the effect of the harvest conditioning on the kinetics parameters of whole and slashed canes. The lab drying test was conducted in a thin layer dryer at temperatures between 30 and 80 °C and a 0.5 m•s-1 air velocity. The whole and slashed canes showed faster water evaporation rates as the temperature increased, but the slashed canes achieved a lower final moisture content in a shorter time. The effective diffusion coefficient varied between 3.67 x 10-12 and 1.28 x 10-11 m²•s-1 and showed a significant effect of the temperature, but not between samples; its temperature dependence was determined by the Arrhenius equation giving activation energies of 24.4 and 20.2 kJ•mol-1 for the whole and slashed canes respectively, not significantly different. The modelling of the experimental drying data to six thin layer drying models achieved good performance (R² > 95.9%), although the Logarithmic model showed the best fit for both samples (R² > 99.4%). In addition, a temperature dependent equation for the drying constant was included in the Logarithmic model for the whole and slashed canes which predicted with good performance (R² > 97%) the moisture loss. The developed tools constitute an adequate model for the simulation of the drying process of Arundo donax L. that could be useful for the design of various equipment and systems. [ABSTRACT FROM AUTHOR]

An improved model of medium voltage (1200 V) silicon carbide (SiC) MOSFET based on PSpice is proposed in this paper, which is suitable for wide temperature range applications especially at low temperature. The static characteristics of SiC MOSFET are described by introducing temperature-dependent voltage source and current source. The effect of negative turn-off gate drive voltage is also taken into account in the modeling. In order to reflect the low-temperature characteristics of SiC MOSFET accurately, low temperature (-25 °C) measurements are carried out, which provide the modeling basis. The determinations of key parameters in the model are analyzed in detail, including the on-state resistor, internal gate resistor, temperature dependent sources, and some capacitors. The proposed model is verified by the experimental tests on a buck converter prototype at different input voltages, input currents, and temperatures. Simulation results on the proposed model coincide well with the experimental test results, in terms of switching waveforms and power losses even at low temperature (-25 °C). These results demonstrate that the proposed model exhibits high accuracy within wide temperature range. [ABSTRACT FROM AUTHOR]

In order to investigate the heat transfer characteristics of transformer oil containing nanoparticles, an electric-thermal-fluidic analysis using the FEM is carried out in this paper. The temperature and velocity distribution of oil and density of nanoparticles in a nanofluid filled transformer under natural and forced convections are obtained. The results show that generally the heat transfer efficiency is better under the forced convection. In addition, the distribution of nanoparticles in the oil depends on the temperature and velocity of the oil. This indicates that the local density and electrophoresis of nanoparticles must be considered for nanofluid application in transformers because of their potential influence on the temperature and velocity of the oil. Therefore, improvement of the simulation model taking into account of the local density of nanoparticles using the effective thermal conductivity had been carried out. Furthermore, electrophoretic force term had been implemented in Navier–Stokes equation, whereas the effective dielectric permeability was obtained by a homogenization technique using FEM. [ABSTRACT FROM AUTHOR]

An extremely important oil crop in the world, Helianthus annuus L. is one of the world's most significant members of the Asteraceae family. The rate and extent of seed germination and agronomic features are consistently affecting by temperature (T) and changes in water potential (ψ). A broad hydrothermal time model with T and ψ components could explain sunflower responses over suboptimal T and ψ. A lab experiment was performed using the HTT model to discover both T and ψ and their interactive effects on sunflower germination and also to figure out the cardinal Ts values. The sunflower seeds were germinated at temperatures (15 °C, 20 °C, 25 °C and 30 °C); each Ts had five constant ψs of 0, 0.3, 0.6, 0.9, and 1.2 MPa via PEG 6000 as osmotic stress inducer. The results revealed that highest germination index was found in seed grown at 20 °C in distilled water (0 MPa) and the lowest at 30 °C with osmotic stress of (− 1.2 MPa). The highest value of germination rate index was found in seed grown at 20 °C in distilled water (0 MPa) and the lowest at 15 °C with an osmotic stress of (− 1.2 MPa). In conclusion, water potential, temperature, and their interactions have a considerable impact on seed germination rate, and other metrics (GI, SVI-I, GRI, GE, SVI-II, and MGT). Seeds sown at 20 °C with zero water potential showed high germination metrics such as GE, GP, GRI, and T50%. The maximum value to TTsub noted at 30 °C in − 0.9 MPa osmotic stress and the minimum value was calculated at 15 °C in − 1.2 MPa osmotic stress. The result of TTsupra recorded highest at 15 °C in controlled group (0 MPa). Moreover, θH was highest at 30 °C in controlled condition (0 MPa) and minimum value was observed at 20 °C under − 1.2 MPa osmotic stress. The value of θHTT were maximum at 30 °C in controlled group (0 MPa) and minimum value was recorded at 15 °C under − 1.2 MPa osmotic potential. The base, optimum and ceiling temperatures for sunflower germination metrics in this experiment were noted 6.8, 20 and 30 °C respectively. [ABSTRACT FROM AUTHOR]

The development of precision machine tools requires an accurate understanding of the thermal behaviour of the tools. Therefore, by developing highly accurate machine tool thermal behaviour simulations, it can accurately forecast the functional performance of a machine tool at the prototype design stage and provide guidance on its design and performance optimization. To improve the accuracy of the thermal simulation of machine tools, it proposed whole-machine temperature field and thermal deformation modeling and a simulation method for vertical machining centers. Based on the studies of thermal-structure coupling finite-element data flow and its critical conditions, it also proposed design and computational methods for obtaining the heat-source power, when various rotational speeds, the forced convection heat transfer coefficient between a rotating surface and the air, the combined heat transfer coefficient between a stationary surface and the air/environment, and key contact surface thermal resistances were considered. Furthermore, this paper performed finite-element simulation analysis based on the constructed whole-machine thermal model, and the temperature characteristics and heat deformation mechanism/state were obtained. After comparing the simulation and experimental results, it verified the effectiveness of the finite-element simulation model and the relevant methods and confirmed that the simulation accuracy for both the temperature characteristics and the thermal deformation had been improved significantly, with a simulation error less than 10 %. [ABSTRACT FROM AUTHOR]

This paper presents an accurate and robust compact model for high-voltage MOS (HV-MOS) transistors for high-voltage IC simulation. This model describes the extended-drain MOS and lateral double-diffused HV-MOS effects such as quasi-saturation, gm reduction, self-heating, impact ionization, output conductance, and charge/capacitance effects accurately. In addition, the quasi-saturation effects are, for the first time, illustrated with a simple mathematic formulation. This model is developed with BSIM4 as the base and validated extensively with technology computer-aided design and measurement for wide ranges of power supplies and operating temperatures. [ABSTRACT FROM PUBLISHER]

The phase structures of one-dimensional quantum sine-Gordon-Thirring model with N-impurities coupling are studied in this paper. The effective actions at finite temperature are derived by means of the perturbation and non-perturbation functional integrals method. The stability of coexistence phase is analyzed respectively in the weak and strong coupling case. It is shown that the coexistence phase is not stable when fermions have an attractive potential g < 0, and the stable coexistence phase can form when fermions have an exclude potential g > 0. [ABSTRACT FROM AUTHOR]

The hot spot temperature (HST) plays a most important role in the insulation life of the transformer. Ambient temperature and environmental variable factors involved in the top oil temperature (TOT) computations in all transformer thermal models affects insulation lifetime either directly or indirectly. The importance of the ambient temperature in transformer's insulation life, a new semi-physically-based model for the estimation of TOT in transformers has been proposed in this paper. The winding hot-spot temperature can be calculated as function of the TOT that can be estimated by using the ambient temperature, wind velocity and solar heat radiation effect and transformer loading measured data. The estimated TOT is compared with measured data of a distribution transformer in operation. The proposed model has been validated using real data gathered from a 100 MVA power transformer. For a semi-physically-based model to be acceptable, it must have the qualities of: adequacy, accuracy and consistency. We assess model adequacy using the scale: prediction R2, and plot of residuals against fitted values. To assess model consistency, we use: variance inflation factor (VIF) (which measure multicollinearity), condition number. To assess model accuracy we use mean square error, maximum and minimum error values of semi-physically-based model parameters to the existing model parameters. [ABSTRACT FROM AUTHOR]

Modelling and optimisation of the under-floor heating system (UFHS) with Pex pipes are studied in this paper. For modelling the system, two regions were considered. The first one was the over-floor region which included room air and walls. This region was considered as one control volume and the system of non-linear energy equations for room air and walls were solved using Newton–Raphson method. The second or under-floor region included heating pipes, concrete and floor finish. This region was modelled using finite volume method. For optimising the UFHS, an objective function (sum of investment and operating costs of UFHS) was proposed and type and thickness of the floor finish, velocity of hot water passing through the pipe, concrete thickness and pipe diameter, were considered as the decision variables (design parameters). The sensitivity analysis showed 19.8%, 10.5%, 2.8% and 0.3% increase in the objective function with the deviation of the four above-mentioned design parameters from their optimum values (floor finish from tile to marble, water velocity from 1.5 to 2.5 m/s, concrete thickness from 6 to 8 cm and pipe diameter from ½ to ¾ in.). Finally, with the decrease in external temperature from −10°C to −20°C, the objective function increased by 21.7% and the required floor heat flux increased by 33.1%. Increasing the insulation thickness from 2.5 to 7 cm also decreased the objective function by 20.5% and decreased the required floor heat flux by 38.5%.Practical application: A new and fast combined numerical and analytical procedure for thermal modelling of UFHS was proposed in this paper. By applying the proposed modelling procedure, the optimum values of UHFS design parameters for reaching the system lowest cost were obtained. The variation of total cost with deviation of design parameters from their optimum values was investigated. The effects of change in atmospheric temperature and wall insulation thickness on building thermal load and the total cost were studied. [ABSTRACT FROM AUTHOR]

Since Adrian Brown and Victor Henri's work, the simplest enzyme kinetics model, which contains only three rate constants k, k and k in 1902, has been thoroughly explored in many directions. By using the Michaelis-Menten equation, K and k can be measured quickly. All the three rate constants can be derived by temperature jump method or transient state kinetics, but both methods need more complicated techniques and equipments. In our previous paper (Li et al. in J Math Chem 46:290-301, ), we gave a method to measure all the rate constants which does not require any additional equipment other than those needed for measuring K and k. Here, we propose a new one which needs no additional equipment either. This method is based on a study of inflection points of integral curves. Numerical results show that the new one is much better than the previous one in two aspects: near the end of the reaction, the new one gives more accurate estimation; during the quasi-steady state of the reaction, it also gives good estimations while the previous one can not. Hence, this method not only advances the estimation accuracy, but also has more choices for measuring. [ABSTRACT FROM AUTHOR]

In this paper we have developed a semi-analytical model to study the temperature distributions in infra red (IR) optical materials heated by laser pulses. Our model takes into account two-photon absorption and calculations arc based on a three-dimensional model of heat diffusion in solids using the integral transform method. We found out that the rigorous semi-analytical expression of the thermal field when one considers both one and two-photon absorption. The model is valid for any laser-solid system whose interaction can be described by the generalized Beer-Lambert law. Specific results are presented for an application of the model to GaAs sample. We discovered that two-photon absorption can produce detectable temperature variation. The main goal of the present paper was to correlate the thermal field with the two-photon absorption anisotropy. [ABSTRACT FROM AUTHOR]

In this paper an experimental study was carried out on forced draft cooing tower with expanded wire mesh (EWMP) packing. Air quality and performance of the tower was studied over the packing height. Due to complicated configuration of packing surface, it is not possible to measure the air temperature at the intermediate points of the packing height. In the present experimental study a new concept of psychrometric gun technique is used to measure dry/wet bulb temperature of air at intermediate points of tower packing. The paper elaborates the effect of L/G ratio on the thermodynamics properties of moist air inside the cooling tower and performance characteristics over the packing height. It has been concluded from this work that the minimum cold water temperature was attained at lower L/G ratio and the tower performance decreases with an increase in the L/G ratio. Experimental values were compared with the mathematical model. [ABSTRACT FROM AUTHOR]