Variable Heating Rate Research Articles

Theory of Deep Level Spectroscopy in Semi-Insulating CdTe

Numerical simulations of thermoelectric effect spectroscopy (TEES) and photo-induced transient current spectroscopy (PICTS) in CdTe were performed with the aim to interpret experimental results and to look for possibilities to obtain credible information about trap capture cross-sections. The TEES and PICTS spectra were calculated by solving kinetic equations. Trap energy and capture cross section were determined by variable heating rate and double gate methods and compared with input data. Deviation of the established capture cross-section from the input value was demonstrated for the strong retrapping. It was concluded that the trap capture cross-section, especially if obtained anomalously low, might be incorrect due to invalid premises of models, which neglect retrapping. The possibility to acquire an information about trap properties from the shape or magnitude of glow curves was checked. It was demonstrated that the magnitude of TEES signal corresponding to slow or fast retrapping depends unequally on the initial optical excitation.

Effects of excess tellurium and growth parameters on the band gap defect levels in CdxZn1−xTe

This research summarizes an effective way to understand compensation for use of CdZnTe as ambient temperature radiation detector. The indium doped CdZnTe passivates certain detrimental intrinsic defects and defect complexes in the band gap. This was achieved by using a combination of excess tellurium in the starting material (0% to 7.5% by weight) and the process variables during growth, including the imposed temperature gradient, growth rate, and cool-down process. These studies have shown that a combination of slight excess tellurium as well as the cool-down scheme could control certain intrinsic defect levels and defect level complexes in the band gap of CdZnTe by causing favorable carrier compensation. At a macroscopic level, these manipulations help to minimize thermal instabilities during growth and determine the final grain structure, integrity, and yield of the ingot. Also, these manipulations help to control the formation of certain intrinsic defect levels and defect level complexes in the band gap, which have a direct bearing on the ability of the CdZnTe crystals to function as room temperature radiation detectors. The band-gap defects in CdZnTe were studied using the thermally stimulated current (TSC) technique. The thermal ionization energy and capture cross-section for 8 prominent defect levels (current peaks in the TSC spectrum) were calculated using the variable heating rate method. These fitted values were compared to transition energy levels of possible defects in the band gap of CdTe and purity data of CdZnTe samples used in this study. The theoretical values of the transition energy levels of defects in the band gap of CdTe were determined by the first principle band gap structure studies as well as our earlier studies on defects and defect levels in the band gap of CdTe. We have tentatively associated some prominent current peaks to certain defect levels and defect level complexes in Cd1−xZnxTe. The improvement in the detector properties was correlated to the reduction of a proposed deep level defect complex (TeCd + VCd) (thermal ionization energy >0.8 eV and capture cross-section of 10−13 to 10−14 cm2), and the reduction of the ionized species corresponding to an acceptor defect level (thermal ionization energy ∼0.2[03] eV), associated with dislocations/dislocation complexes with Te clusters. The best crystals tested had an average μτe (electrons) of 1.8 × 10−3 cm2/V, a peak-to-valley ratio of 2.0 for the 122 keV x-ray peak using a Co-57 source and bulk resistivity the order of 3 × 1010 Ω cm. The best radiation detector crystals corresponded to those grown with an excess tellurium of 0.5% (by weight in the starting CdZnTe charge) grown at a rate of 0.5 to 0.86 mm/h with an imposed temperature gradient of > 50 °C/in. There was a high yield without any post-processing of the ingots.

Glass foam of macroporosity using glass waste and sodium hydroxide as the foaming agent

Glass foams using float glass waste and sodium hydroxide were produced. The influence of the sodium hydroxide amount in the foam formulation was studied. Titanium dioxide was used as a strengthening agent. The variations of temperature, heating rate and sintering time were investigated during the synthesis process. Open porosity was estimated using mercury porosimetry. The morphology of the glass foams was evaluated using scanning electron microscopy, phase formation was studied using X-ray diffraction, and chemical composition was estimated using X-ray fluorescence. As a result, glass foams with macroporosity were obtained. Since the glass foams used glass waste as reactant, the results suggest the development of an alternative route for glass recycling.

Dosimetric features and kinetic analysis of thermoluminescence from ultra-high molecular weight polyethylene

Thermoluminescence (TL) from beta irradiated ultra-high molecular weight polyethylene has been studied for measurements between 30 and 200 °C. An aliquot studied in this work produced TL glow curves consisting of two peaks, the main peak at 88 °C and a weaker intensity peak at 148 °C for heating at 1 °C s−1 following an excitation dose of 215 Gy. The position of the main peak is poorly reproducible for heating rates of 0.2 and 0.6 °C s−1 investigated with the peak position decreasing when the sample is freshly irradiated and the TL re-measured. The said change in peak position is however less of an effect for measurements made at 1 °C s−1 with the peak position being fairly reproducible in this case. Further measurements of the dosimetric properties of ultra-high molecular weight polyethylene showed that its dose response is linear from 26 Gy to about 161 Gy but exhibits slower growth in intensity with dose from about 860 Gy after regions of sub- and supra-linearity in between. If the TL is not measured immediately after irradiation, the signal fades with the delay approximately exponentially. In addition, a number of tests including phosphorescence analysis showed the possibility that the order of kinetics might not be unique but sensitive to several factors including measurement temperature. Thus for instance, the dependence of the peak position on the stop temperature in the partial heating procedure Tm − Tstop implied first-order kinetics but analysis of the geometrical factor μg for the same set of data gave μg = 0.46 ± 0.03 a value corresponding to characteristics somewhat intermediate between first and second order. In comparison, the results of analysis of the phosphorescence recorded at several temperatures on the rising edge of the main peak were only in agreement for measurements at 40 °C with general-order analysis suggesting second-order kinetics apply as did TL-like transformation of the monotonic phosphorescence decay. Both results were also consistent with an additional finding that the time dependence of the isothermal decay at 40 °C was consistent with second-order kinetics. Analysis of the TL for the activation energy using the initial rise method, variable heating rate procedure, TL-like transformation of phosphorescence and the peak shape estimates, produced a self-consistent set of values equal to 0.76 ±0.05 eV, 0.66±0.03 eV, 0.77±0.06 eV and values of the order of 0.8 eV, respectively. The kinetic parameters found in this study compare favourably with literature values.

A novel fitting method for evaluating the thermal quenching parameters of TL with an application to undoped CVD diamond

AbstractThere are a number of thermoluminescence (TL) phosphors (and CVD diamond among of them), for which the integrated TL response decreases with the increasing of the heating rate. This effect relates to the thermal quenching (TQ) of luminescence caused by the increasing the non‐radiative recombination with the temperature increasing. In this work we present a new fitting method of evaluation the TQ parameters from a series of experimental TL glow curves recorded with variable heating rates. The method is simple, fast and effective. It quite general and can be applied to any series of TL glow curves consisting of several overlapped peaks and does not assume a particular type of TL kinetics. The only limitation of the method is that the end temperature of heating must be enough to ensure full readout of the analyzed TL peaks for all heating rates. The proposed method was applied to a series of TL glow curves measured with the heating rates from 0.1 to 17 K/s for the undoped CVD diamond film. The evaluated TQ parameters were found to be: an activation energy of 0.37 eV and a dimensionless constant of 3.7 × 103.

Ignition of polypropylene/montmorillonite nanocomposites

This paper addresses the flaming ignition of polypropylene and polypropylene-based nanoclay composites, under irradiation in a cone calorimeter. The surface temperature as a function of time was measured using thermocouples on the surface and the chemical changes occurring in the polymer leading to evolution of volatiles were studied by means of spectroscopic analyses of the surface. Thermogravimetric analyses were also carried out to study thermal and thermoxidative volatilization at variable heating rates, which correlate to the production of the critical concentration of combustible volatiles for ignition.The effect of both microdispersed and intercalated nanoclays on ignition time and ignition temperature is addressed and analysed in details.

Athermal and thermal mechanisms of sintering at high heating rates in the presence and absence of an externally applied field

Abstract In order to establish the relative contributions of thermal and athermal mechanisms to densification in the absence of an extrinsic sintering pressure, nanometric powder compacts were sintered with and without applied fields using varied heating rates from 50 °C/min up to 800 °C/min. The relative contribution of the thermal and athermal mechanistic contributions to the densification behavior of two model dielectric ceramics, hydroxyapatite and zinc oxide, is evaluated in the context of the current leading theories of field-assisted sintering mechanisms. The effects of elevated heating rates in nanometric, dielectric ceramics are found to be minimal in the absence of a field. However, in the presence of an applied field there appears to be a synergistic effect with heating rate.

Effect on thermoluminescence parameters of biotite mineral due to thermal quenching

The Thermally Stimulated Luminescence (TSL) at room temperature X-ray irradiated natural biotite in form of micro-grain powder was studied under various heating rates. TSL peaks showed at temperatures 393K, 399.6K, 403.5K, 404.5K, 406.9K at their respective heating rates 2K/s, 4K/s, 6K/s, 8K/s and 10K/s. The effect of thermal quenching on thermoluminescence parameters such as peak maximum temperature, peak area, FWHM, geometrical symmetry factor, the activation energy were investigated. From the symmetry factor it is clear that the TL glow curve follows the first order kinetics for the lowest heating rate, but as the heating rate increases it defers from the first order. The activation energies for each heating rates were calculated by using Chen peak shape methods for general order kinetics and found to be decreased for higher heating rates. When activation energy is calculated by variable heating rate method it is observed that the method overestimated the value of activation energy and pre-exponential frequency factor significantly due to thermal quenching.

열중량 분석법을 이용한 Deasphalted Oil의 열분해 특성 분석

기존 경질 원유 자원의 매장량 고갈과 중국, 인도 등 개발도상국에서의 에너지 수요가 급증하면서 원유 자원의 공급이 수요를 감당하지 못하는 상황이 벌어지고 있고, 따라서 상대적으로 활용도가 낮았던 중질유를 효율적으로 이용하는 방안이 대두되고 있다. 중질유를 활용하기 위해서는 경질화 과정을 거쳐야하는데, 특히 공정이 단순하고 경제적인 열분해 기술이 적합하다고 할 수 있겠다. 본 연구에서는 중질유의 열분해 특성 분석의 기초 자료를 얻기 위해 중질유에서 아스팔텐이 제거된 deasphalted oil(DAO)의 열분해 실험을 수행하였다. DAO는 solvent deasphalting 공정을 통하여 얻어지며 주로 탄소수가 20~40인 물질들로 이루어져 있는데, DAO의 열분해 반응 속도론적 분석 결과와 비교 분석하기 위해 DAO의 평균 탄소수를 갖는 탄소수 30의 단일 물질들(<TEX>$C_{30}H_{62}$</TEX>, <TEX>$C_{30}H_{58}O_4S$</TEX>, <TEX>$C_{30}H_{63}O_3P$</TEX>)을 선택하여 추가적인 열분해 실험을 수행하였다. 열분해 실험에서는 열중량 분석기를 이용하여 비등온 열분해 방법(10, 50, <TEX>$100^{\circ}C$</TEX>/min)으로 실험을 진행하였고, 열분해 반응을 분석하는 방법으로는 가장 기초적인 Arrhenius 방법을 비롯하여 Ingraham and Marrier 방법, Coats and Redfern 방법, Ozawa-Flynn-Wall 방법을 이용하였다. Arrhenius, Ingraham and Marrier, Coats and Redfern 방법으로 계산된 DAO의 열분해 반응 평균 활성화에너지 값은 72~99 kJ/mol이었다. 그리고 Ozawa-Flynn-Wall 방법으로 분석된 활성화에너지에서는 전환율의 증가에 따라 DAO의 경우 그 상승 폭이 단일 물질들에 비해 크게 나타났다. The depletion of conventional oil reserves and the increasing energy need in developing countries such as China and India result in exceeding oil demand over supply. As a solution of the problem, the efficient utilization of heavy oil has been receiving more and more interest. In order to utilize heavy oil, upgrading processes are required. Among the upgrading processes, thermal decomposition is thought to be relatively simple and economical. In this study, to understand basic characteristics of thermal decomposition of heavy oil, we conducted pyrolysis experiments of deasphalted oil (DAO) produced by a solvent deasphalting process. DAO is a mixture of many components and consists mainly of materials of carbon number 20~40. For the comparison with results of DAO pyrolysis, additional pyrolysis experiments with single materials of carbon number 30 (<TEX>$C_{30}H_{62}$</TEX>, <TEX>$C_{30}H_{58}O_4S$</TEX>, <TEX>$C_{30}H_{63}O_3P$</TEX>) were conducted. Pyrolysis experiments were carried out non-isothermally with variation of heating rate (10, 50, <TEX>$100^{\circ}C$</TEX>/min) in a thermogravimetric analyzer. Average pyrolysis activation energy determined by using Arrhenius method, Ingraham and Marrier method, and Coats and Redfern method was 72~99 kJ/mol. In the activation energy calculated by Ozawa-Flynn-Wall method, DAO had wider variation than other single materials.

Modeling of Temperature-Programmed Desorption (TPD) Flow Experiments from Cu/ZnO/Al2O3 Catalysts

Different procedures to extract the kinetics of hydrogen desorption from a Cu/ZnO/Al2O3 catalyst for methanol synthesis were studied by performing temperature-programmed desorption experiments under atmospheric pressure. The four methods include (i) heating rate variation, (ii) analysis using a fixed pre-exponential factor, (iii) lineshape analysis and (iv) full analysis. Before extracting the parameters, transport limitations could be excluded for all experiments and a criterion for inner particle mass transfer limitations could be extended in the case of activated re-adsorption. All methods could be valid in the whole range of experiments, with only one exception for the lineshape analysis at full coverage of hydrogen. However, each method requires different input to extract physically meaningful parameters. The best modeling results were obtained when repulsive interactions of adsorbed species were accounted for. This led to a k (des) = 3.75 center dot 10(10) s(-1)center dot exp (-(75 kJ center dot mol(-1)-5.5 kJ center dot mol(-1)center dot I similar to (H) (2.6) )/RT) in good agreement with the literature. Moreover, it was found that there is no difference, when extracting the kinetic parameters from a fresh or deactivated catalyst at full coverage.

Predicting the thermal response of timber structures in natural fires using computational ‘heat of hydration’ principles

ABSTRACTThe thermo‐physical response of timber structures in fire is complex. For this reason, debate still exists today as to the best approaches for simulating thermal response in fire using tools such as finite element analysis (FEA) modelling. Much of the debate is concerned with the thermal properties of timber, for example, conductivity, specific heat and density, at elevated temperature and how such properties should be implemented or interpreted in numerical calculations. For practitioners intending to use modelling as a fire design tool for timber buildings, guidance exists on the thermal properties of softwood in Annex B of EN 1995‐1‐2. These properties are limited for use under standard fire exposure conditions because of the way in which they were derived from calibration against focussed test data. As a result, they cannot be applied to non‐standard fires, which are more representative of real fires due to a combination of varying heating rates and the decay phase of fire development.The limitations of the standard fire test (and associated curve) are widely understood. As a result, much recent structures in fire research has focussed on the ‘performance based design’ of buildings subject to increasingly realistic fire conditions. Such an approach allows engineers to quantify the level of safety that can be achieved in a building should a fire occur. In addition, the design of buildings to withstand fires proportionate to the risks foreseen and also the geometry present results in better value buildings that are inherently more robust. For the same approaches and associated benefits to be realised for timber buildings, then a number of barriers must be overcome. The most obvious of these is engineers' ability to determine timber structure temperatures as a result of fires other than the standard fire curve. This however presents a number of challenges.Upon heating, the moisture bound within begins to evaporate, volatiles begin to flow from the heated surface and char forms. The rate of which these behaviours occur and the nature of the char that forms depends on a number of factors, but most notably the rate of heating. Upon cooling, the timber member continues to generate heat energy as the surface oxidises. As a result, any models intended to simulate temperature development must consider the relationship not only between temperature and thermo‐physical characteristics but also between heating rate and the process of heat generation. Many models have been developed for this purpose; however, they are extremely complex and are some way from being ready for implementation as design tools. This paper proposes implementing ‘heat of hydration’ routines, intended for the curing of concrete structures, to simulate the heating and cooling process in timber structures. Such routines are available in many commercial FEA software packages. The adoption of the hydration routines allows the heat generation process, as a result of oxidation, to be considered in parallel with solid phase heat transfer using apparent thermal properties.The approach is shown to be very effective in simulating temperature development in timber members subject to parametric design fires. The models developed are benchmarked against experiments conducted in the 1990s by SP Trätek. Predictably, a number of the heat generation parameters adopted are shown to depend on the fire dynamics considered. However, recommended parameters are given that provide an acceptable level of accuracy for most design purposes. Copyright © 2012 John Wiley &amp; Sons, Ltd.

The analysis of thermoluminescent glow peaks of natural calcite after beta irradiation

In this study, the thermoluminescence properties of natural calcite samples were examined in detail. The glow curve of the sample irradiated with beta radiation shows two main peaks, P1 (at 115 °C) and P4 (at 254 °C). The additive dose, variable heating rate, computer glow curve deconvolution, peak shape and three point methods have been used to evaluate the trapping parameters, namely the order of kinetics (b), activation energy (E) and the frequency factor (s) associated with the dosimetric thermoluminescent glow peaks (P1 and P4) of natural calcite after different dose levels with beta irradiation.

Crystallization kinetics and characterization of nanosized Nd:YAG by a modified sol–gel combustion process

Nanosized neodymium doped yttrium aluminum garnet (Nd:YAG) powders have been synthesized by a modified sol–gel combustion method by using nitrate salts as starting materials. Phase evolution, morphology, and microstructure of the synthesized powders were investigated. Solvent plays an important role in the phase formation of the precursor. Crystallized Nd:YAG powders can be directly obtained at as low as 800°C without the formation of any intermediate phase. The crystallization kinetics of amorphous YAG precursor was studied by variable heating rate of DTA. The activation energy for crystallization of the YAG by modified sol–gel combustion is 361.7kJmol−1, which is much lower than 480.6kJmol−1 determined from that by general sol–gel combustion. The as-prepared powders are well crystallized and soft aggregated with average crystalline size about 60nm at 1200°C. Good luminescent property is observed in the Nd:YAG nanopowders and the emission intensity increased with increasing the calcination temperatures.

Two-stage thermal stimulation of thermoluminescence

A thermoluminescence (TL) model of two-stage stimulation of electrons into the conduction band is discussed. This release of the carriers is assumed to take place via an intermediate localized excited state. Electrons are thermally stimulated from the trap into an excited state and then thermally released into the conduction band from which they may either be retrapped or recombine with holes in centers. The model resembles the previous “semi localized” model, but we concentrate only on recombination of electrons that go through the conduction band. It also bears similarity to the effect of thermally-assisted optically stimulated luminescence (OSL) previously discussed in the literature. The model is studied by solving the set of the relevant four simultaneous differential equations which govern the process during heating or isothermal decay. Using different sets of parameters, we can get pseudo-first-order, pseudo-second-order as well as intermediate cases, which are identified by their symmetry coefficient. Once the effective order is established, different analytical methods are used to determine the effective activation energy and frequency factor. We used the peak-shape methods, the various heating rate (VHR) method and the method based on the change of phosphorescence decay with temperature. The results are compared to the parameters used in the simulation. In many cases, the effective activation energy is equal to E1 + E2 where E1 and E2 are, respectively, the activation energies for the first and second stage of thermal stimulation. The numerical simulation results are accompanied by an analytical treatment using the usual quasi-steady assumption. Unusual cases, in which the effective frequency factor and the effective retrapping probability coefficient are temperature dependent, are identified. Some cases in which the effective activation energy is close to E1 rather than E1 + E2 are identified and discussed. The relevance of this possible situation to the evaluation of the stability of TL signals is also considered, and a possible effect of anomalous stability is predicted.

Synthesis and characterisation of BaSo4:Eu thermoluminescence phosphor

Polycrystalline powder samples of BaSO(4) doped with Eu(2+) were prepared by solid-state reaction in different reducing atmospheres. Photoluminescence (PL), thermoluminescence (TL), TL kinetic and dosimetric studies have been carried out in this phosphor. The TL glow curve of BaSO(4):Eu(2+) showed only a single peak at 513 K unlike other phosphors and the TL intensity is about three to four times higher than that of CaSO(4):Dy, which is currently used as the radiation dosemeter for personnel monitoring in India. The TL dose response of the phosphor was found to be linear up to the dose range of 10(3) Gy beyond which saturation sets in. PL and TL spectra showed the characteristic emission of Eu(2+) ion. The TL parameters such as trap depth (E) or the energy required to release the electron or hole from the trap, frequency factor (s) and the order of kinetics (b) are determined by different methods such as isothermal decay, initial rise and variable heating rate.

Pyrolytic Behavior of Green Macro Algae and Evaluation of Its Activation Energy

 Abstract—In this research work, the pyrolytic and kinetic characteristics of a green macro algae, Codium Fragile (C. Fragile) as a model for marine biomass was studied using thermogravimetric analysis (TGA) method in the range of 313 K to 973 K at atmospheric pressure. Proximate analysis of the freeze dried macro algae showed 6.5% water content, 58% degradable products, 10.5% char, and 25% ash content. The influences of particle size, initial weight of the sample, and heating rate on decomposition of the algae have been investigated. Both particle size and initial weight of the sample do not have a significant effect on the TG profile of the algae pyrolysis. In addition, the TGA and DTG (differential thermogravimetric) curves of algae differed significantly for variation in heating rates. The DTG results showed that there are three zones to the pyrolysis; and mainly second zone was significantly affected with heating rates. The non-isothermic integral isoconventional methods were used to obtain the kinetic parameters from data of the pyrolysis reactions of C. Fragile in the second zone. The corresponding activation energies of pyrolysis and decomposition stage of C. Fragile were calculated based on the weight loos data obtained from DTG data using the most popular methods (Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Fredman, and Coast-Redfren methods).

Assessment of Heating Rate and Non-uniform Heating in Domestic Microwave Ovens

Due to the inherent nature of standing wave patterns of microwaves inside a domestic microwave oven cavity and varying dielectric properties of different food components, microwave heating produces non-uniform distribution of energy inside the food. Non-uniform heating is a major food safety concern in not-ready-to-eat (NRTE) microwaveable foods. In this study, we present a method for assessing heating rate and non-uniform heating in domestic microwave ovens. In this study a custom designed container was used to assess heating rate and non-uniform heating of a range of microwave ovens using a hedgehog of 30 T-type thermocouples. The mean and standard deviation of heating rate along the radial distance and sector of the container were measured and analyzed. The effect of the location of rings and sectors was analyzed using ANOVA to identify the best location for placing food on the turntable. The study suggested that the best location to place food in a microwave oven is not at the center but near the edge of the turntable assuming uniform heating is desired. The effect of rated power and cavity size on heating rate and non-uniform heating was also studied for a range of microwave ovens. As the rated power and cavity size increases, heating rate increases while non-uniform heating decreases. Sectors in the container also influenced heating rate (p < 0.0001), even though it did not have clear trend on heating rate. In general, sectors close to the magnetron tend to heat slightly faster than sectors away from the magnetron. However, the variation in heating rate among sectors was only 2 °C/min and considered not practically important. Overall heating performance such as mean heating rate and non-uniform heating did not significantly vary between the two replications that were performed 4 h apart. However, microwave ovens were inconsistent in producing the same heating patterns between the two replications that were performed 4 h apart.

Multi-site characterization of tropical aerosols: Implications for regional radiative forcing

A land campaign, as a part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP), has been organized using a suit of instruments like AERONET (Aerosol Robotic Network) Sun/Sky sunphotometer, Microtops-II (MICROprocessor-controlled Total Ozone Portable Spectrometer), short-wave pyranometer from December 1, 2006 to April 30, 2007, over five locations (Ahmedabad, Pune, Sinhgad, Trivandrum and Gadanki) representing different environments. The dominance of different aerosol types such as biomass burning, urban/industrial pollution, marine origin and desert-dust particles is expected at these five sites. In all locations, significant day-to-day variability in AOD and Ångström exponent is observed. The Ångström exponent exhibits its lowest values over semi-arid region (Ahmedabad) 0.4–0.7, while it is around 1.8 at rural site (Gadanki). The retrieved volume size distributions for Pune, Ahmedabad and Trivandrum are found to be bimodal with varying concentration of each mode. Interesting feature of this observation is, very low coarse-mode volume concentration observed at Trivandrum even though observations were made about 300 m from the coast. The synergy of results from these complementary measurements is reflected in the computed regional aerosol radiative forcing and heating rates. We have used a radiative transfer model (SBDART) to examine the variations of aerosol direct radiative effect (ADRE) and heating rates to give an overall estimation of the effect on climate. The ADRE, over different measurement sites, at short wavelength is found to be negative at the surface in the range of − 18 to − 59 W m − 2 , and TOA forcing values varied from + 0.9 to − 8 W m − 2 .

Modelling pyrolysis with dynamic heating

In literature, the reaction kinetic of pyrolysis process is often determined and modelled under constant heating rates. In reality, the heating rate of an industrial pyrolysis process is difficult or often not necessary to be kept constant. The variation of heating rate at different reaction stages, termed “dynamic heating”, governs the pyrolysis performance such as production rate, energy consumption, product quality, etc. In this work, pyrolysis progress with dynamic heating is being studied. The rate and reaction heat of tyre pyrolysis at different heating rates are obtained experimentally. A transient model considering the effect of dynamic heating was then developed and compared with the conventional static heating model. Results show that a higher heating rate favours the production of volatiles and shifts the overall pyrolysis heat flow to more endothermic. The significance of the dynamic heating model was observed for processes with large feed size and/or with high heating rate.

Constitutive Equations and Empirical Creep Law of Structural Steel S460 at High Temperatures

Although the constitutive equations at elevated temperatures given in Eurocode 3 Part 1-2 are valid for steel grades up to S460, the experimental data base concerning the mechanical behaviour of this particular high strength fine-grained structural steel is very small. Especially its short time creep behaviour at high temperatures has not yet been analysed. A current research project, predominantly consisting of transient testing of numerous commercial S460 steels, targets a more precise determination of the stresss-train relationships at high temperatures. Additionally, the time-dependent strain components are extracted from test results gained at varying heating rates, and an empirical creep law, based on the concept of temperature-compensated time, is derived. As a result, the constitutive equations can be formulated taking the heating rate into account. The differences in the high temperature load-carrying capacity of steel structures made of S460 according to the research results and under the terms of Eurocode 3 Part 1-2 are assessed.