Self-heating Behavior Research Articles

Study on thermal decomposition characteristics of AIBN

It is found that the results such as observed in the differential scanning calorimeter (DSC), which show the major thermal decomposition (TD) of a self-reactive material, lack the detail to reveal what happens at the initial stage of a reaction. The reaction at this stage is corresponding to the handling condition of storage or transportation, often possibly having the potential to be developed to a runaway reaction. This paper examined and compared the thermal behaviors of AIBN at various working conditions in calorimeters and Dewar vessels. The mechanism that affects the initial reaction and self-heating behavior of the given material was clarified. Near its onset decomposition temperature, physical processes, such as sublimation or melting interfered the initial reaction of AIBN. The mutuality of the physical effect and the chemical reaction made AIBN behave differently under different measuring conditions, and as the result, quasi-autocatalysis or TD possibly occurs in the same sample at the handling temperature range. The heat accumulation storage tests in two Dewar vessels presented completely different self-heating behaviors due to this mechanism and heat transfer capability of the vessels.

Electrothermal model for an SOI-based LIGBT

Several vertical insulated gate bipolar transistor (IGBT) electrothermal models are currently available on circuit simulators. However, no reliable electrothermal models have been proposed for the lateral IGBT (LIGBT). In this paper, for the first time, an electrothermal model for an LIGBT structure based on a novel concept recently reported by Udrea (IEDM, p. 451, 2004), and here termed silicon-on-membrane, is presented. The model relies on a systematic study of both the isothermal and self-heating behaviors of the device. The model is further implemented in the SPICE circuit simulator language and validated against extensive Medici numerical simulations and experimental data

Nonlinear conductive properties and scaling behavior of conductive particle filled high-density polyethylene composites

The blends prepared by incorporation of carbon black (CB) or graphite powder (GP) into high-density polyethylene (HDPE) matrix have been novel and extensively applied polymeric positive temperature coefficient (PTC) composites. A phenomenological model was proposed on the basis of the GEM equation and the dilution effect of filler volume fraction due to the thermal volume expansion of the polymer matrix. Accordingly, the contribution of the thermal expansion of the matrix to the jump-like PTC transition of the composites was quantitatively estimated and a mechanical explanation was given. It was proved that the contribution of the volume expansion to PTC effect decreased for HDPE/CB composites crosslinked through electron-beam irradiation. Furthermore, the influences of the filler content, temperature and crosslinking on the self-heating behavior as well as the nonlinear conduction characteristics at electrical-thermal equilibrium state were examined. Based on the electric-field and initial resistivity dependence of the self-heating temperature and resistance dependence of the critical field, the mechanisms of the self-heating of the polymeric PTC materials were evaluated. The intrinsic relations between macroscopic electrical properties and microscopic percolation network at electrical-thermal equilibrium state were discussed according to the scaling relationship between the self-heating critical parameter and the conductivity of materials.

A novel temperature-dependent large-signal model of heterojunction bipolar transistor with a unified approach for self-heating and ambient temperature effects

A large-signal modeling of power heterojunction bipolar transistor (HBT) is demonstrated for an accurate simulation of self-heating and ambient temperature effects and nonlinear behaviors such as output power, gain expansion, intermodulation distortion (IMD), and adjacent channel power ratio (ACPR). The physical relationship between the device current and the rate of change in the built-in potential with respect to the device temperature has been utilized for a fully electrothermal modeling. To enable an immediate use for a circuit design, the model extraction was done for in-situ output-stage device from two-stage power amplifier (PA) circuit. In each parameter extraction step, measurement data obtained under a consistent environment, which are current-voltage (I-V) at various temperatures and small-signal S-parameters under various bias conditions, have been carefully examined and utilized to relate the meaning of each parameter to the physical principle of the device. Measurements and simulations are compared for the verification of the model under dc condition at various temperatures.

Assessing the self-heating behaviour of Callide coal using a 2-metre column

A 2-m, adiabatic column has been successfully refurbished and recommissioned for coal self-heating research at The University of Queensland. Subbituminous coal from the Callide Coalfields reached thermal runaway in just under 19 days from a starting temperature of 20-22 degreesC. The coal was loaded as two layers, with an R-70 index of 2.73 degreesC h(-1) and 5.90 degreesC h(-1) for the upper layer and lower layer respectively. Initially, a hotspot developed in the upper layer between 120 and 140 cm from the air inlet due to moisture adsorption. After 7 days, self-heating in the lower half of the column began to take over, consistent with the higher R-70 index of this coal. The location of the final hotspot was approximately 60 cm from the air inlet. Further tests on Australian coals, with the column, will enable a better understanding of coal self-heating under conditions closely resembling mining, transport and storage of coal. The results from the column will also provide industry with the information needed to manage the coal self-heating hazard. (C) 2002 Elsevier Science Ltd. All rights reserved.

A numerical study of partial-SOI LDMOSFETs

The high-voltage and self-heating behavior of partial-SOI (silicon-on-insulator) LDMOSFETs were studied numerically. Different locations of the silicon window were considered to investigate the electrical and thermal effects. It is found that the potential distribution of the partial-SOI LDMOSFET with the silicon window under the drain is similar to that of standard junction isolation devices. With the silicon window under the source the potential distribution is similar to that of the conventional SOI LDMOSFET. Using the two-dimensional numerical simulator MINIMOS-NT, we confirm that the breakdown voltage of partial-SOI LDMOSFETs with a silicon window under the source is higher than that of partial-SOI LDMOSFET with a silicon window under the drain.

Self-heating behaviour of low moisture content particles—modelling the basket-heating of solid particles and some aspects of the cross over behaviour using milk powder as an example

AbstractSelf-heating in packed paniculate that is exothermically reactive is a major cause of fire and explosion in the powder industry. This study is focused on part of the Auckland development of a mathematical model dealing with this hazardous process in industry using milk powder as an example. Milk powder is a primary powdered food product around the world.An update of the detailed mathematical model is given here, and predictions are made using the model to simulate the basket-heating behaviour of a milk powder in the laboratory (so the model can thus be validated). Basket heating in an oven is a standard laboratory technique for measuring the exothermic reactivity of a solid material.After a favorable comparison with the laboratory results, several aspects of basket-heating were investigated with a view to further improving the technique. Firstly, the model was used to explore the effect of elevated ambient humidity and initial sample water content upon the heating process in the basket. Secondly, the model was used to explore the cross over phenomenon which is related to a novel procedure for measuring activation energy and exothermicity (that is, the Crossing-Point-Temperature (CPT) method, which is a new version of the basket heating technique). The predictions together with the experimental evidence show that the reaction kinetics obtained using the Heat Release (HR) method (another version of the basket heating technique well published in the literature) may not be correct, especially for those measured at elevated oven temperatures and for larger basket sizes. Thirdly, simulations were performed to illustrate that the CPT phenomenon does not just occur at the center of the basket but also occurs everywhere else in the sample. This can become a significant advantage for further development of the CPT method in terms of reducing experimental duration and improving reproducibility.

Mathematical Modeling Of The Self-heating Behaviour Of Dusts Around A Power Cable

This paper has established mathematical models which describe the steady-state heat transfer in the seK-heating process of dusts around a working power cable. The self-heating behaviour of the dusts was discussed by the numerical solutions of the established models associated with the tested self-heating parameters. Critical spontaneous igniting conditions for the dusts with and without inner heat sources were compared using typical coal dusts. The results show that the self-heating dusts around the power cable are very easy to ignite spontaneously. The small working power cable acted as a weak intier heat source of the dusts around the cable plays an important role in the self-heating of the dusts. Inversely, the spontaneous ignition of the dusts around the cable may cause a power cable fire. MEWORDS: spontaneous ignition, dusts self-heating, mathematical model, numerical solutions, critical spontaneous ignition temperature/radius NOMENCLATURE A pre-exponential factor, mol/m3.s r* charactelistic dimension of sample, mm E activation energy (Jlmol) Tc ufform temperature within the power Gr Grashof number, G1=pgATd~/v,2 cable metal, K Pr Prantl number, P F C , , ~ ~ ~ /ha T dust temperature, K Q coal combustion heat, 3 ~ 1 0 ~ ~ / m o 1 0 ~ T characteristic temperature of air fihn, K Qd natural convection heat exchange, W Tk critical self-ignition temperature, K 90 heat generation per volume, w/m3 Ts temperature on the dust d a c e , K F H E SAFETY SCIENCE-PROCEECIYGS OF THE SIXTH INTERNATIONAL SYMPOSIUM, pp 603-610 Copyright © International Association for Fire Safety Science Q, heat generated by cable and dusts, W T, ambient air temperature, K r the radius of dust, m a heat transfer coefficient, w / m 2 ~ r,' critical ignition radius by F-K model, m h t h e m 1 conductivity, 0.116 W/mK ro the radius of power cable metal m Ljc critical F-K number, 2.0 for a cylinder 0.69x10.~m for the XV power cable p density of coal sample, 760 kgim3

The electric self-heating behavior of carbon black loaded high density polyethylene composites

The electric self-heating behavior of carbon black loaded high density polyethylene composites

The electric self-heating behavior of graphite-filled high-density polyethylene composites

The electric self-heating behavior of graphite-powder-filled high-density polyethylene is studied. Two equations are proposed to describe the electric-field dependence of the self-heating temperature and resistance dependence of the critical field. Based on Ohmic and non-Ohmic approximations and the heat-dissipation model, the self-heating equations are also derived theoretically. The equations show that self-heating is determined by the initial resistance and true positive temperature coefficient (PTC) effect under fields. Design and application principles for polymer PTC heaters are suggested on the basis of the experimental results and proposed equations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1756–1763, 2000

Use of infrared thermography for the evaluation of heat losses during coal storage

The exothermic processes during coal storage reduce the calorific value of the coal which in turn results in financial losses. An accurate and easy calculation of the losses may be an efficient tool to evaluate the effectiveness of the measures taken to reduce the spontaneous heating of coal and to predict the appearance of hot spots. This study was carried out with `Mezcla' coal used at Endesa power station in Andorra–Teruel (Spain). For this purpose, laboratory measurements relating to spontaneous heating properties and field measurements were carried out. Three experimental coal piles were built, a high porosity pile, a periodically compacted pile and a pile with a low angle slope in the prevailing wind direction. A method to determine the coefficient of total losses was developed and the coefficients of calorific losses and total losses were also found. Temperatures were measured by infrared thermography and by thermocouples and a good agreement between them was found. The use of a mathematical model, developed by ASINEL, allowed to calculate the heat fluxes due to spontaneous heating and a new coefficient of calorific losses, the similarity of this coefficient with the experimentally found revealed the effectiveness of this method to quantify heat emissions. The self-heating behaviour of the pile was also followed by an infrared thermographic camera which allowed the detection of heat fluxes.

The effect of exchangeable cations on low-temperature oxidation and self-heating of a Victorian brown coal

The effect of inorganic additives, when applied into a coal by ion-exchange, on low-temperature oxidation and self-heating of a Victorian brown coal is studied in this article. Acid-washed coal, and acid-washed coal ion-exchanged separately with seven additives, were prepared. Each of the samples was then tested in a wire-mesh reactor to obtain its critical ambient temperature, above which thermal runaway occurs. The relative effectiveness of the additives is determined by comparing their critical ambient temperatures with that of the acid-washed coal. Magnesium acetate (Mg(Ac) 2), calcium chloride (CaCl 2), and sodium chloride (NaCl) were found to inhibit low-temperature oxidation, while copper acetate (Cu(Ac) 2), potassium acetate (KAc), and sodium acetate(NaAc), promote the reaction. The effect of additive loading was also investigated for NaAc and Ca(Ac) 2. The effectiveness of NaAc to promote low-temperature oxidation is enhanced with an increase in its loading, while that of Ca(Ac) 2 remains unchanged with varying additive loading. Low-temperature oxidation kinetics were estimated by a transient energy balance and compared with the low-temperature oxidation and self-heating behaviour of the samples.

The self-accelerating decomposition temperature (SADT) of solids of the quasi-autocatalytic decomposition type

Self-heating or thermally explosible chemicals are divided into two large groups, the thermal decomposition or TD type and the autocatalytic decomposition or AC type. The TD type is further divided into liquids, for each of which the critical temperature for thermal explosion or T c is calculated by applying the Semenov equation, and, solids, for each of which the T c is calculated by applying the Frank–Kamenetskii or F–K equation. On the other hand, the AC type is further divided into solids of the quasi-AC type, in each of which the exothermic decomposition reaction occurs almost simultaneously with the endothermic melting, and, liquid or solid high explosives of the true AC type, in each of which the self-accelerating exothermic decomposition reaction begins after an autocatalyst has appeared and accumulated. Neither of the two critical conditions for thermal explosion, i.e., the Semenov equation or the F–K equation, is applicable to the self-heating behaviour of each individual chemical of the AC type for the calculation of the T c. Instead, the respective self-heating behaviour of them is in accord with the concept of the self-accelerating decomposition temperature (SADT) in principle. The SADT of each individual solid of the quasi-AC type discussed in this paper as well as the critical temperature for self-heating or T cs of each individual high explosive of the true AC type is determined by the isothermal storage test. In this study, the respective SADTs of five solids of the quasi-AC type were determined using a simple and safe isothermal storage testing device. The SADT thus determined ranged from 28.4°C for 95% 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) to 86.5°C for 98% 1,1′-azobis(cyclohexanecarbonitrile). These temperature values are in fair agreement with a few corresponding values of the SADT measured by other researchers for them of large quantities.

Using the crossing point method to assess the self-heating behavior of indonesian coals

Indonesian coal, although generally low in sulfur and ash content, is a lower rank coal with a relatively high moisture content (5–18%). Consequently, it has a greater propensity to self-heating behavior, and the aim of this paper is to assess the hazard for three typical coals that are used both domestically and for export. Experimental tests are reported using a new technique (the crossing point method) to determine the activation energy and reactivity of the low-temperature slow oxidation reaction. This uses the transient temperature profiles to deduce the activation energy and reactivity of the sample. The method relies on finding the center temperature at the point when a flat profile is observed (Called the crossing temperature) and has been used successfully to ascertain the kinetic parameters of three Indonesian coal samples. It is found that the method is valid as long as the coal experiment is not greatly supercritical when it is then difficult to determine an appropriate crossing temperature. The method has the distinct advantage over the traditional Frank-Kamanetskii approach, in that only one oven experiment is needed for any one point on the kinetic plot, and that the results are not heavily dependent on the fan setting of the oven, or on sample size. A comparable experiment using the Frank-Kamanetskii approach of finding the critical temperature for different sample sizes showed good agreement for estimating activation energy.

96/03588 Retardation of the spontaneous ignition of bituminous coal

Differential thermal analysis (DTA) has been used as a method to study the self-heating behaviour of fresh and oxidized coals. Oxidation was performed in air at 200°C for periods of up to 72 h. Six coals ranging from a High A Bituminous coal to a semi-anthracite were used. As the rank of the coal increases, both the self-heating and the end of combustion temperatures also increase. The total heat loss (area under the DTA curve) increases with the rank of the coal. An increase in the self-heating temperature, a decrease in the temperature of the end of combustion and a decrease in total heat flow were observed as a consequence of coal oxidation. A relationship between the total heat loss and the calorific value as determined using the ASTM standard method is pointed out.

A study of the self-heating of fresh and oxidized coals by differential thermal analysis

Differential thermal analysis (DTA) has been used as a method to study the self-heating behaviour of fresh and oxidized coals. Oxidation was performed in air at 200°C for periods of up to 72 h. Six coals ranging from a High A Bituminous coal to a semi-anthracite were used. As the rank of the coal increases, both the self-heating and the end of combustion temperatures also increase. The total heat loss (area under the DTA curve) increases with the rank of the coal. An increase in the self-heating temperature, a decrease in the temperature of the end of combustion and a decrease in total heat flow were observed as a consequence of coal oxidation. A relationship between the total heat loss and the calorific value as determined using the ASTM standard method is pointed out.

A study of the self-heating of fresh and oxidized coals by differential thermal analysis

Differential thermal analysis (DTA) has been used as a method to study the self-heating behaviour of fresh and oxidized coals. Oxidation was performed in air at 200°C for periods of up to 72 h. Six coals ranging from a High A Bituminous coal to a semi-anthracite were used. As the rank of the coal increases, both the self-heating and the end of combustion temperatures also increase. The total heat loss (area under the DTA curve) increases with the rank of the coal. An increase in the self-heating temperature, a decrease in the temperature of the end of combustion and a decrease in total heat flow were observed as a consequence of coal oxidation. A relationship between the total heat loss and the calorific value as determined using the ASTM standard method is pointed out.

Constitutive Equation of NiTi Superelastic Wire

ABSTRACTDuring the superelastic deformation process, because of the involvement of the austenite-martensite phase transformation, a superelastic wire will experience a self-heating or self-cooling process due primarily to the latent heat of the material. As the strain rate increases, and conditions become more adiabatic, the self-heating and self-cooling will cause a temperature rise upon loading and will drop upon unloading. As a consequence, an apparent effect of the strain rate on the superelastic behavior in the shape-memory alloys with a large diameter or more adiabatic conditions will be noticed. In the present paper, a constitutive stress-strain-strain rate equation is proposed to describe the self-heating behavior. In order to verify the model, a series of experiments have been conducted to study the effect of the strain rate, wire diameter, and adiabatic condition on the superelastic behavior of the shape-memory alloy wire. As will be shown later, the proposed equation can predict the behavior of the superelastic wire accurately, and the prediction is in good agreement with the experimental data.

Critical ignition temperatures of chemical substances

Abstract Critical ignition temperatures have been found for eight self-heating or thermally unstable chemical substances, using an adiabatic self-heating test. From the experiments, the self-heating behaviour of the substances has been classified into two groups. The first group has been termed ‘T-C’ (thermal combustion) type and the second termed ‘A-C’ (autocatalytic combustion) type. Five substances were classified as ‘T-C’ type, and the critical ignition temperatures ranged from 329 K for α, α'-azobisisobutyronitrile to 351 K for dinitrosopentamethylenetetramine. Ignition of the ‘A-C’ type substances ultimately occurred after 60 days at 314 K for nitrocellulose, 315 K for lauroyl peroxide, and 351 K for p-toluenesulphonylhydrazide. Such values agree with those of previous workers.

Thermal explosion of benzoyl peroxide

The thermal explosion of benzoyl peroxide, in the form of the commercially pure solid and as a paste with plasticizer, has been studied experimentally with the object of determining the extent to which small-scale explosion trials are likely to provide a useful guide to the behaviour of unstable compounds in storage or during transport. It has been found that the self-heating and explosion behaviour is broadly consistent with expectation on the basis of the generalized stationary-state thermal explosion model of Frank-Kamenetskii. In detail, however, the behaviour is complicated by melting of the peroxide during decomposition and by mixing due to gas evolution. It has been concluded that a simple graphical treatment of small-scale critical explosion data, based on the model, can give a useful guide to the practical hazard.