Influence Of Heating Rate Research Articles

Toughening of a dicyandiamide‐cured epoxy resin: Influence of cure conditions on different rubber modifications

AbstractCure kinetics of modified epoxy resins cured with dicyandiamide are studied. The influence of different heating rates in the curing process, such as curing behavior, morphology, and thermo‐mechanical properties, is studied. Additionally, three different post‐cure cycles at 180°C are employed. Two butadiene‐based toughening agents are used, a carboxyl‐terminated polybutadiene‐co‐acrylonitril (CTBN) prepolymer and a functionalized block copolymer of polytetrahydrofuran and hydroxyl‐terminated polybutadiene. The amphiphilic block copolymer enables investigations with a bimodal particle size morphology. All results are contrasted with those of the neat resin and butadiene‐free block polymer. Faster curing processes result in smaller average particle sizes and better fracture toughness of the modified epoxy resins. Further improvements are achieved with additional post‐cure cycles at 180°C. An increased interfacial adhesion between the particles and the epoxy matrix is considered to be the main mechanism. Optimized lengths of the post‐cure process can be determined with the butadiene‐based toughening agents indicating a competing thermal degradation. Longer post‐cures than 40 min lead to lower fracture toughness in the butadiene‐based modified materials. In general, similar influences of the curing and post‐curing process on the bimodal and unimodal distributed system can be observed differing in more intense dependencies of the bimodal system.

A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study

• Review of nitrogen migration and transformation based on quantum chemistry and experiment. • Summarized the mechanism and regulation of nitrogen migration and transformation. • Emphasized the importance of N 2 formation during pyrolysis. The emission of NO x during coal combustion contributes to the formation of acid rain and photochemical smog, which would seriously affect the quality of atmospheric environment. Therefore, the decrease of NO x is of great importance for improving the efficient utilization of coal. The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation. Firstly, in the process of pyrolysis: the occurrence state and transformation of nitrogen were concluded. The influence of temperature, atmosphere, heating rate and catalyst on formation of NO x precursor and nitrogen migration path at the molecular level were summarized; Secondly, during the process of combustion: the influence of temperature, ambient oxygen concentration, physical structure of coal char, catalyst on heterogeneous oxidation of char (N) were summarized; The effects of char surface properties, catalyst and ambient atmosphere on heterogeneous reduction of NO x were also concluded. Based on the quantum chemical calculation, the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NO x were described in detail. Current studies focus more on the generation of HCN and NH 3 , but in order to reduce the pollution of NO x from the source, it is necessary to further improve the process conditions and the optimal formula of producing more N 2 during pyrolysis, as well as clarify the path of the generation of N 2 . Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.

A Detailed Experimental Study on the Thermal Decomposition Behaviour of Wood Pellets Under Inert and Oxidative Conditions in a Fixed Bed Reactor

In this work, spruce wood pellets are pyrolysed in an electrically heated fixed bed reactor. Experimental campaigns have been conducted to investigate the influence of final pyrolysis temperature (600-800°C), heating rate (5-20 K/min) and purge gas composition (none, 100% N2 and 90/10% N2/O2). The instrumentation of the reactor includes transient temperature measurements in the reactor (3 locations in the vertical direction) and inside the pellets bed (3 locations in the radial direction) throughout the thermal decomposition process. Gas measurements are carried out for permanent gases (using a GC), condensables are condensed and collected and the remaining solids are also collected. Hence, the mass balance can be established. The detailed experimental results make them useful for validation of thermal decomposition modelling approaches. The experimental results show evidence of endothermal cellulose decomposition reactions as well as the exothermal char formation process. The occurrence of these two processes overlap at high heating rates and when oxygen is used in the purge gas. The two processes can be separated visually by decreasing the heating rate to 5 K/min. The separation shown in the temperature curves is confirmed by the gas analysis. The yields of CO and CH4 show a visible shoulder in the higher temperature region. The endothermic plateau visible on the temperature readings can be reduced by increasing the heating rate. Oxygen present in the purge gas will further reduce the visibility of the plateau. The amount of CO2 formed during experiments shows dependency on the oxygen in the purge gas but appears independent of the applied heating rate. The comprehensive experimental results provide both useful knowledge and a validation basis for further modelling work.

Controlling thermal-induced dewetting of As20Se80 thin films for integrated photonics applications

As the use of photonics circuits expands, the optical quality and performance of integrated components in the microscale become a major concern. Aiming to improve the performance while reducing the time processing, new microfabrication approaches are being investigated. The dewetting of glassy thin films have been recently proposed as an alternative for nano and microfabrication of chalcogenide optical components. Besides being the best materials for light transmission in the infrared region, chalcogenide glasses possess a flexible molecular structure that allows using a cheap and simple molding process. Here we investigate the thermal-induced dewetting of chalcogenide As20Se80 thin films, by studying the influence of temperature, atmosphere, and heating rate on the formation of self-assembled microstructures. We found that thin films between 150 and 700 nm dewet via structural relaxation, similarly to liquid agglomeration, and produce solid microstructures with the same composition and molecular structure as the initial film. By controlling the glass viscosity and the kinetics of the nucleation process it was possible to adjust the distribution and size of glassy microstructures. Additionally, we combine the dewetting process with standard photolithography and by avoiding the capillary instabilities, we are capable to obtain waveguides with the smooth and symmetric surfaces required for optical applications in the microscale size.

Estimating the levels of process parameters for tar and char production via fast pyrolysis of Hypericum perforatum and characterization of the products

The influence of pyrolysis temperature, pressure and heating rate was investigated on the tar and char yield from the fast pyrolysis of Hypericum perforatum (St. John's wort). The experiments were conducted using a fixed bed reactor. Response surface methodology (RSM), with a central composite design (CCD), was used for modeling and optimization of the process parameters. The optimum conditions were found to be at a temperature of 513.13 °C and 400 °C, pressure of 1 and 41 bar and heating rate of 489.39 °C/min and 150 °C/min for maximum tar and char yield, respectively. Maximum yields of tar and char were obtained as 32.98% and 41.23% under optimum process conditions, respectively. Scanning electron microscopy (SEM), ultimate analysis, and gas chromatography/mass spectrometry (GC/MS) were used to determine the physico-chemical properties of char, and the chemical properties of tar. The higher heating value of the chars produced at pressurized atmosphere were 29 MJ/kg. GC/MS analysis showed that the tar was rich in phenol, methyl and methoxy phenols, oxygenated benzenes and fatty acids. Furthermore, the formation of polycyclic aromatic hydrocarbons (PAHs) in the tar, obtained at pressurized pyrolysis in a nitrogen atmosphere, was investigated. Pressure increased the residence time of the volatile components in the reactor and this phenomenon led to the formation of PAHs. The derived tars were found to contain mainly 2-ring (naphthalene and its derivatives), 3-ring (acenaphthylene, Fluorene, Phenanthrene, 2-methyl anthracene), and 4-ring (Fluoranthene) PAHs.

Effect of heating rate on the pyrolysis of camel manure

Information on the pyrolysis degradation kinetics of feedstock is critical for the design and fabrication of pyrolysis reactors. In this study, the pyrolytic behaviour of a novel biomass, camel manure, has been studied in a non-isothermal thermogravimetric analyser. The thermal analyses were performed from room temperature to 950 °C at different heating rates (10, 20, and 50°C/min) in an N2 environment (100 ml/min). The kinetic parameters of the manure components are determined using an Arrhenius model equation, and the influence of heating rate on the pyrolytic characteristics and kinetic parameters of the manure components has been examined. The results indicated that the increase in heating rates increased the starting and ending temperatures (decomposition) of manure components. The increase in heating rates shifted the ignition, peak, and burnout temperatures to higher temperatures. At the same time, the increase in heating rates improved the char yield from 22.50 to 31.51%. However, the increase in heating rates showed an insignificant effect on the kinetic parameters of the camel manure components.

Influence of heating rate during microwave pasteurization of ground beef products: Experimental and numerical study

AbstractA finite element model coupling electromagnetism with standing‐wave propagation, heat transfer and microbial inactivation equations has been developed to study microwave food pasteurization with three heating rates (7, 10, and 13°C/min). Inactivation of a target microorganism was studied from a single temperature measurement at a given location. Electric fields, temperature distribution and inactivation kinetics were predicted as a function of time and space coordinates. Good agreement was found between experimental and predicted thermal and inactivation curves. The inactivation kinetics parameters (D and z‐value) identified under water bath heating remained valid during the microwave process. Thus, the E. coli inactivation is mainly due to the thermal effect under lethal conditions. The differences between logarithmic reductions between both heating processes was attributed to the non‐uniform temperature distribution.Practical ApplicationsFrom the industrial point of view, temperature heterogeneity is known to be the main barrier impeding the development of microwave food pasteurization technology. The use of a multiphysics model that takes into account the real geometry of the microwave cavity made it possible to optimize the process and achieve a more uniform temperature distribution within the product. Therefore, the simulation of the electric field distribution can provide relevant information on the amplitude and shape of the electromagnetic field. The degrees of freedom of the model led to the optimization of parameters, such as cavity size, microwave frequency shifting, product mass, the position of the sample in the cavity, and the optimization of the shape of the product containers and supports. The combination of microwaves (with or without modulated power input) with other energy sources (i.e., hot air injection, immersion of the product in water) also seemed promising for pasteurization applications.

Investigation of Hazelnut Husk Combustion by using A Novel Non-linear Kinetic Model through Thermogravimetric Analysis

Considering economic and environmental issues, boosting renewable energy source is the main subject to fulfill energy demand in these days. Biomass as natural and abundant energy source can be typically used to produce electricity, fuels and heat applying thermochemical conversion processes such as combustion, pyrolysis or gasification. Biomass combustion is the most common process to produce electricity and useful heat in Turkey and all over the world. The aim of this study is to investigate the considerable influence of heating rates on combustion characteristics and kinetics employing a new developed non-linear kinetic model for hazelnut husk samples through thermogravimetric analysis. Furthermore, this work comprehensively assesses the variations in the reactivity of hazelnut husk combustion, expressed from thermogravimetric curves. The non-linear kinetic model developed in this study integrates the various kinetic pathway to estimate the major controlling parameter of combustion reactivity, its activation energy, pre-exponential factor and reaction order. According to comparison of results from the non-linear kinetic model for volatile combustion and fixed carbon combustion, correlation coefficients (R2) for both models are higher than 0.9985. These results proved the non-linear regression model for kinetic pathways in combustion reactivity worked properly to estimate thermal decomposition behavior.

Liquid bio-fuels and carbon adsorbents production via pyrolysis of non-edible feedstock

The slow pyrolysis of milk thistle (Silybum marianum L.) seeds (MTS) in a lab-scale batch reactor to investigate the influence of heating rate, temperature, contact period, and particle size on the yields of bio-oil (BO) and bio-char (BC) was presented for the first time. The maximum yield of BO (49.55 ± 2.50 %) was obtained at a pyrolysis temperature of 475 °C for 60 min using a 0.25 mm MTS particle size at 20 °C/min heating rate. The chemical composition of BO from MTS was identified by FTIR, 1H NMR, and GC–MS techniques. Following the FTIR outcomes, aldehydes, alcohols, phenols, acids, and alkanes are present in the BO . Also, results from 1H NMR spectrum indicated that the percentage of the aliphatic compounds in the as-synthesized BO was greater than that of the aromatic compounds. The GC–MS analysis exhibited that the MTS derived BO is rich in higher acids (38.64 %), higher esters (21.30 %), and hydrocarbons (11.39 %). The elemental analysis consequences revealed that the attained BO possessed a higher carbon content and a lower oxygen content than its respective MTS with a chemical formula of CH1.67 N0.025O0.10. Additionally, the BO owned a calorific value of 39.47 MJ/kg, close to that established for petro based liquid fuels and comparable to those of BOsamples declared in the literature. Besides, the physic-chemical properties of the MTS derived BO were close to those specified for conventional fossil fuels. Proximate analysis, elemental composition, higher heating value, iodine number, surface area, and morphology of the attained biochar were determined. The ZnCl2 activation method was employed to synthesize activated carbon from the produced BC via the optimized procedure. An impregnation ratio of 1.5:1 ZnCl2:BC, 500 °C, 60 min activation period, and 0.21 mm particle size were the best conditions to yield an activated carbon with 638.66 mg/g iodine number and 677.22 m2/g surface area. The FESEM results affirmed the mesoporosity of the attained activated carbon compared to the macroporosity of the pristineBC .

Thermogravimetric and Kinetic Analysis of Co-Combustion of Waste Tires and Coal Blends.

The waste tire is a fuel with the potential to partially replace coal due to the high heat value. In the present study, the combustion characteristics of the tire powders, bituminous coal, and their blends were examined using the thermogravimetric analyzer. The influence of heating rate on tire powders combustion and the burnout characteristics of their blends were studied. The increase of the heating rate caused the combustion temperature of the tire powders to become high but reduced the maximum weight loss rate. The combustion characteristics of the blends of coal and tire powders approached the combination of those of the individual sample, suggesting that the interaction effects between coal and tire powders were slight. Furthermore, the influence of different ratios on ignition characteristics, burnout temperature, and combustion effect of the blends was studied at the optimal combustion rate. The addition of tire powders improved the ignition characteristics, reduced the burnout temperature and increased the burnout rate of coal to a certain extent. An increase in the proportion of tire powders led to a decrease in the activation energy in the temperature range of 349–465 °C, whereas it caused an increase from 465 °C to burnout, which could be attributed to the fact that the volatile matter was more combustible than fixed carbon within 349–465 °C, and the combustion effect of fixed carbon in the tire powders gradually manifested in the combustion from 465 °C to burnout when the tire powders content increased.

A ReaxFF molecular dynamics study on the hydropyrolysis process of Huadian oil shale kerogen

ABSTRACT The product distribution and reaction mechanism in the process of Huadian oil shale kerogen hydropyrolysis were investigated via reactive molecular dynamics (RMD) simulations with a reactive force field (ReaxFF). A large-scale reactive system based on 10 Huadian oil shale kerogen structural models was used to investigate the effect of heating rates on the product distribution. Reactive force field molecular dynamics was used to simulate the hydropyrolysis process of the 10 models at four different heating rates of 20, 40, 60 and 80 K/ps. The simulation results proved the influence of heating rate on the product distributions, intermolecular interactions and elementary reactions in the process of hydropyrolysis. A conclusion was made about the suitable heating rate for producing useful organic gases and the highest yield of shale oil. This work also analysed the distribution of hydropyrolytic gas product and the reaction mechanism of Huadian oil shale hydropyrolysis, which is an intensive study on the mechanism of hydropyrolysis and the different formation paths of the symmetrical isoformers of typical products at the atomic level. These conclusions will be of great significance for the development and utilisation of oil shale mineral resources.

Considering the influence of heating rate, complex hardening and dynamic strain aging in AISI 1045 machining: experiments and simulations

In the modelling of machining operations, constitutive models must consider the material behavior subject to high plastic strains, high strain rates, high temperatures and high heating rates. A new material model for AISI 1045, which captures time-dependent plastic response associated with interrupted austenite transformation under short (sub-second) heating times, is deployed to simulate orthogonal cutting experiments. High speed video and digital image correlation measurements are used to capture chip behavior. The new model, which also includes complex strain hardening and dynamic strain aging effects, show better agreement with experiments at high cutting speeds compared with a basic Johnson-Cook material model from the literature.

Flash sintering: A new frontier in defect physics and materials science

Interest in ultrafast sintering has been expanding from different directions that include not only electric and electromagnetic field driven accelerations, but also the influence of heating rates. Among them, the electrical method of flash sintering is most quantitative (and, therefore, most amenable to manufacturing). The electric field, the current density and temperature can be explicitly controlled and measured as a function of time, and related to the sintering behavior and microstructure evolution. In this article, we attempt to explain the greater generality of flash sintering, not just unto itself, but also to heating rate experiments carried out without electrical fields. The rise in electrical conductivity and electroluminescence are the principal features of flash; they are likely to be of general significance in accelerated sintering. Their occurrence in high heating rate experiments, highlighted in this article, is particularly salient, raising new fundamental issues in the science of flash sintering.

Study on reaction kinetics of single slime

The study of the combustion characteristics of single slime fuels is the basis for achieving clean combustion of solid fuels. This paper uses a combination of experimental and theoretical analysis, combined with the Coats-Redfen integration method, to study the influence of ash content and heating rate on the kinetic parameters of coal slime, and solve the combustion kinetic parameters. The results show that under the same heating rate, the activation energy gradually increases. As the ash content of coal slime increases, the activity of the coal slime sample decreases, and the reaction activation energy gradually increases.

Influence of heating rate on formation of nanostructured tungsten carbides during thermo-chemical processing

The structure, morphology and growth mechanism of nanostructured W-C phases during its synthesis by thermo-chemical processing at different heating rates was investigated. Higher heating rates of 8 and 4 K/min led to the formation of core–shell type nanoparticles via sequential formation of the trigonal ε-W2C (Space group:P3¯m1) followed by the hexagonal α-WC layer (Space group: P6¯m2). It appears that the formation of the core–shell possibly initiates by the nucleation of metastable W2C to form octahedral core, which subsequently act as the nucleation site for the growth of the lower order α-WC from the surface layer. The surface layer encapsulating the metastable phase possibly restricts the coarsening of the particles to a size less than 100 nm. Slow heating rate of 1 K/min, on the other hand, leads to the formation of single phase ε-W2C with abnormal particle size growth and epitaxial morphology along (001) crystallographic plane. This observation confirms that the anisotropic lattice volume expansion in the crystalline ε-W2C induced diffusion of carbon leading to abnormal particle coarsening.

Applications of Concentrating Photothermal Reactor in Coal Combustion Research

High temperature, rapid heating rate and application potential of special reaction conditions (high pressure, high humidity, corrosive atmosphere) made the concentrating photothermal reactor (CPR) become a hot spot in the thermal experimental research. By the 1930s, the concepts of radical reactions and thermal equilibrium concepts had contributed to the formation of theoretical basis of coal combustion. The application of concentrating photothermal reactor in coal combustion research had provided a new perspective for this traditional subject. This paper introduced the structure and characteristics of concentrating photothermal reactor, and summarized the latest research results on the influence of heating rate, oxygen concentration and biomass addition on coal combustion. A potential frontier research direction - pressurized combustion based on concentrating photothermal reactor was also proposed.

Pyrolysis and oxidation behaviour of dehydrogenation silicone foam containing Pt compounds

In this paper, effects of Pt compounds (C8H18OPtSi2) on pyrolysis and oxidation characteristics of silicone foam (SiFs), gas volatiles of SiFs during pyrolysis and oxidation process, influence of heating rate on pyrolysis and oxidation of SiFs, and the thermal reaction kinetics of SiFs were analysed. The residual mass of SiFs at 900.0 °C in N2 atmosphere increased from 59.7 to 74.1% as the content of Pt compounds changed from 0.3 to 1.2 mass%. Whereas, the residual mass of SiFs in air atmosphere was higher than in N2 atmosphere. CO2 and CO as new gas volatiles appeared in air atmosphere when compared in N2 atmosphere. The residual mass of SiFs rose with the increase of heating rate. Besides, the apparent activation energy in N2 atmosphere grew significantly with conversion rate, and the apparent activation energy in air atmosphere was significantly lower than that in N2 atmosphere.

Influence of heating rate, temperature, pressure on the structure, and phase transition of amorphous Ni material: A molecular dynamics study

The present article is aimed to investigate influence of the heating rate, temperature (T), pressure (P) on the structure and phase transition of amorphous Ni material with heating rate 2 × 105, 2 × 106 and 2 × 107 K/s at T = 300 K; T = 300, 400, 500, 600, 700, 800, 900 and 1000 K at heating rate 2 × 106 K/s; T = 300, 621 and 900 K at P = 1, 2, 3, 4 and 5 GPa by molecular dynamics simulation method with Sutton-Chen embedded potential and periodic boundary conditions. The structure of amorphous Ni material determined through the radial distribution function, the total energy, the size and the average coordination number. The phase transition and the glass transition temperature determined through the relationship between the total energy and temperature. The result shows that when the heating rate increases, the first peak's position for the radial distribution function is 2.45 Å and a constant, the first peak's height, the total energy and the size increase, the average coordination number decreases from 13 to 12. When temperature increases from 300 to 1000 K at P = 0 GPa, the position decreases from 2.45 Å to 2.40 Å, the average coordination number is 13 and a constant, glass transition temperature is 631 K, the total energy increases, the size increases and happens the phase transition from the amorphous state to the liquid state. When pressure increases from 0 GPa to 5 GPa at T = 300, 621 and 900 K, the position decreases, the height increases, the total energy increases, the size decreases, the average coordination number decreases from 13 to 12, that shows with amorphous Ni material when increasing heating rate, T, P lead to structural change, phase transition of materials is significant.

Effect of heating rate on the free expansion deformation of concrete during the heating process

Concrete will expand after being heated at high temperature, and the thermal stress generated will cause cracks inside the concrete, which seriously endangers the safety of concrete. The influence of heating rate on the free expansion deformation of concrete during heating process was studied. Three heating rates were used to conduct high-temperature deformation test. The concrete specimens were heated from room temperature to the target temperature. The temperature in the furnace was maintained at the target temperature until the temperature in the center of the concrete specimen also reached the target temperature. The influences of heating rate on the linear expansion rate (LER) and thermal expansion coefficient (TEC) of concrete at different temperatures were analyzed. The results showed that in the range of 100–800 °C, the LER of concrete increased gradually with the increase of temperature, and the maximum value reached 1.336%. In the range of 100–400 °C, the deformation of concrete was slightly affected by the heating rate. In the range of 500–800 °C, the greater the heating rate, the greater the LER and TEC of concrete.

CFD-DEM Simulation of Biomass Pyrolysis in Fluidized-Bed Reactor with a Multistep Kinetic Scheme

The pyrolysis of biomass in a fluidized-bed reactor is studied by a combination of a CFD-DEM algorithm and a multistep kinetic scheme, where fluid dynamics, heat and mass transfer, particle collisions, and the detailed thermochemical conversion of biomass are all resolved. The integrated method is validated by experimental results available in literature and a considerable improvement in predicting the pyrolysis product yields is obtained as compared to previous works using a two-fluid model, especially the relative error in the predicted tar yield is reduced by more than 50%. Furthermore, the evolution of light gas, char and tar, as well as the particle conversion, which cannot easily be measured in experiments, are also revealed. Based on the proposed model, the influences of pyrolysis temperature and biomass particle size on the pyrolysis behavior in a fluidized-bed reactor are comprehensively studied. Numerical results show that the new algorithm clearly captures the dependence of char yield on pyrolysis temperature and the influence of heating rate on light gas and tar yields, which is not possible in simulations based on a simplified global pyrolysis model. It is found that, as the temperature rises from 500 to 700 °C, the light gas yield increases from 17% to 25% and char yield decreases from 22% to 14%. In addition, within the tested range of particle sizes (<1 mm), the impact on pyrolysis products from particle size is relatively small compared with that of the operating temperature. The simulations demonstrate the ability of a combined Lagrangian description of biomass particles and a multistep kinetic scheme to improve the prediction accuracy of fluidized-bed pyrolysis.