Initial Heating Rate Research Articles

Heterogeneous austenite grain growth in martensitic 9cr steel: coupled influence of initial metallurgical state and heating rate

The coupled influence of the initial metallurgical state and the heating rate to austenite on the occurrence of heterogeneous grain growth during austenitisation of an ASTM A213–T91 steel has been studied. To that aim, two-step thermal cycles were designed. In the first step, different starting metallurgical conditions were obtained by treating the as received material at 780°C for increasing times up to 6 h. In the second step, in situ austenitisation was performed by heating to austenite at rates of 1, 30 and 50°C s−1 and then holding at 1050°C for 30’. Two types of austenite grain structures were obtained after austenitisation, namely, homogeneous and heterogeneous. The homogeneous structure was characterised by a smooth size distribution of approximately equiaxed, normally grown grains. The heterogeneous structure, instead, exhibited the exaggerated growth of a few austenite grains embedded in a small to medium sized matrix. For the 1°C s−1 heating rate and all of the initial metallurgical states, only homogeneous grain growth was observed, whereas for the 50°C s−1 heating rate only heterogeneous grain growth was observed regardless the starting metallurgical condition. Instead, the occurrence of homogeneous or heterogeneous grain growth after heating at 30°C s−1 was observed to be a function of the time of previous tempering. Some explanations of the phenomenon are advanced taking into account the precipitation state of second phases.

Interaction between recrystallization and phase transformation during intercritical annealing in a cold-rolled dual-phase steel: A cellular automaton model

The concurrent ferrite recrystallization and austenitic transformation during intercritical annealing of cold-rolled DP steels is investigated by cellular automaton (CA) modeling. The simulations provide insight into the microstructural phenomena that result from the interaction of primary recrystallization and phase transformation. We find that the interaction between ferrite recrystallization and austenite formation affects not only the transformation kinetics but also the morphology and spatial distribution of the austenite. From this we can interpret experimental data of the observed temperature-dependent hardness and its dependence on the two metallurgical processes. The influence of the initial heating rate on subsequent isothermal transformation kinetics and the microstructure evolution is also obtained by the model.

Selecting the initial steam temperatures in starting combined-cycle plants in compliance with the conditions of heating the high-pressure steam superheater outlet headers

Results from an analysis of permissible initial steam temperatures and heating rates of the outlet headers of high-pressure steam superheaters and the steam lines of combined-cycle plants at which their cyclic strength is ensured are presented. A procedure is proposed using which startup assignment schedules for different thermal states can be constructed proceeding from the heating rates and initial steam temperatures selected depending on the initial temperature state of the high-pressure steam superheaters’ outlet headers.

Studying exothermic reactions in the Ni-Al system at rapid heating rates using a nanocalorimeter

Heats of reaction and heat capacity changes were measured using scanning nanocalorimetry for a nickel and aluminum bilayer where initial heating rates of 104 K/s were achieved. Multiple exotherms were observed on the initial heating, but the number of intermediate exotherms decreased with increasing heating rate. The final phase was the B2 NiAl intermetallic. Results from the nanocalorimeter were compared with a conventional differential scanning calorimeter (operating at 0.7 K/s) to understand the effect of significant (10 000×) increases in heating rate on the phase transformation sequence. The high heating rate in the nanocalorimeter delays reaction initiation, causes the exothermic peaks to shift to higher temperatures, and appears to suppress the formation of intermediate, metastable phases. Potential explanations for this apparent suppression are discussed.

4:02 PM Abstract No. 172 - Tungsten and nitinol braided endovascular catheters: an evaluation of heating in 1.5 t

Purpose Interventional MRI offers the ability to provide soft tissue contrast and functional information in the absence of ionizing radiation. However, performing endovascular procedures in MRI raises safety concerns due to heating from the metallic braid incorporated into catheters. Heating in tungsten and nitinol braided catheters was assessed in an in vitro model simulating a patient undergoing a scan at specific absorption rate (SAR) level of 4 W/kg. Materials and Methods Heating adjacent to the catheters was assessed with fluoroptic temperature probes placed at the device tip, 5cm, 10cm, and 20cm proximal to the tip in a polyacrylamide gel in the head portion of a phantom. A 2.8F tungsten braided catheter (Terumo Progreat, Somerset, NJ) and a 1.9F nitinol braided catheter (eV3 Echelon, Irvine, CA) were serially embedded in a laterally offset conformation. A 5F stainless steel braided catheter (Cook Beacon Tip Torcon Advantage, Bloomington, IN) was used as a positive control and a temperature sensor was placed in background gel, well away from devices. Endovascular devices were immersed at 98cm and exposed to 2-min of scanning followed by 8-min without scanning. The immersed length was shortened by 5cm and this cycle was repeated until the immersed length was 63cm. MR scanning was based on modified fast spin echo imaging on a 1.5T scanner. Results The tungsten braided catheter did not show heating. The maximal heating for the nitinol braided catheter occurred at 20cm proximal to the tip at an immersed length of 93cm. The maximal initial rate of heating was 4.00°C/min and the maximal temperature rise during a 2-min scan was 2.32°C. Heating varied along the catheter, with the most heating at 10cm and 20cm proximal to the tip. The maximal temperature rise during a 2-min scan was 0.33°C for the background and 2.65°C for the positive control. Conclusion The study provides information on the magnitude of focal heating induced in a head simulating a “worst-case” scenario of a patient undergoing a neurovascular procedure. Nitinol displayed substantial heating when compared to the tungsten device. This tungsten braided catheter showed potential safe use in interventional MRI without substantial SAR restrictions.

Martensitic–Austenitic phase transformation of Ni–Ti SMAs: Thermal properties

The main scope of this work concerns the definition of the thermal conductivity temperature dependence of fully dense NiTi SMAs in the temperature range where the Martensitic–Austenitic phase transformation occurs. The methodology used to evaluate this thermal property is based on an experimental-numerical approach that requires the definition of the heat capacity temperature dependence and the knowledge of the latent heat of transformation. The experimental work is based on the capability to heat the cylindrical NiTi samples uniformly on one side and to impose a variety of initial heating rates ranging from 0.1 to 5K/s. Laser radiant energy was used as the heating source and the temperature history of the top and bottom NiTi sample surfaces were recorded using thermocouples.The numerical code considered the sample as a solid with a constant density and with thermal properties that were dependent on temperature. The heat capacity and latent heat of transformation were defined on the basis of the thermal analysis data, while the convection heat exchange coefficient was estimated from knowledge of the experimental configuration, lateral sample surface and the temperature field of the gas surrounding the sample. The results indicated that the thermal conductivity generally increased with temperature, but a minimum in the temperature range defining the Martensitic–Austenitic transformation has been pointed out. The higher thermal conductivity value of the Austenite phase is correlated with its electronic structure.

Numerical Model of Thermal Processes in Domain of Thin Film Subjected to a Cyclic External Heat Flux

Thermal processes in a thin metal film subjected to a cyclic external short-pulse heating are considered (axially-symmetrical 3D problem). The heat transfer proceeding in domain analyzed is here described by the dual phase lag model (DPLM). According to the newest opinions the DPLM constitutes a very good description of real heat transfer processes proceeding in the micro-scale domains subjected to the strong external heat flux. The base of DPLM formulation is a generalized form of Fourier law (GFL) in which two times τq, τT appear (the relaxation time and thermalization one, respectively). The acceptation of GFL leads to DPLM equation [1, 2]. Thermal processes proceeding in a thin metal film subjected to a cyclic external short-pulse heating are considered (axially symmetrical 3D problem). In the paper the thermal interactions between cyclic external heat source qb and cylindrical micro-domain are analyzed. The external heat source is the function dependent on spatial co-ordinates and time. On the remaining parts of the boundary the no-flux conditions are assumed. It should be pointed out that the DPL model requires the adequate transformation of boundary conditions which appear in the typical macro heat conduction models. The initial conditions are also known (initial temperature of domain and initial heating rate). Numerical model of the process discussed bases on a certain variant of finite differences method and in the final part of the paper the examples of computations are shown.

Experimental study of fundamental mechanisms in inductive heating of ferromagnetic nanoparticles suspension (Fe3O4 Iron Oxide Ferrofluid)

An experimental investigation of the initial heating rate of 50 nm ferromagnetic nanoparticles (Fe3O4) suspended in water and incorporated in an agar gel was conducted to study the thermal heating effects resulting from Brownian motion and hysteresis losses. Particles were placed in an alternating current magnetic field with intensities of 28.6, 35.8, 38.9, and 43.0 kA m−1, at frequencies ranging from 161 to 284 kHz. The specific absorption rate based on the heating rate was calculated and the contributions from the Brownian motion and hysteresis losses are compared and analyzed.

The temperature response to stratospheric water vapour changes

AbstractThis study uses an analytical model, based on the cooling‐to‐space approximation, and a fixed dynamical heating model to investigate the structure of the stratospheric cooling that occurs in response to a uniform increase in stratospheric water vapour (SWV). At all latitudes, the largest cooling occurs in the lower stratosphere and decreases in magnitude with height. The cooling is strongly enhanced in the Extratropics compared to the Tropics. This is markedly different to the case of an increase in CO2, which causes maximum cooling near the stratopause and a small warming in the tropical lower stratosphere. The qualitative differences in the structure of the cooling can be explained by the smaller opacity of water vapour bands in the stratosphere compared to CO2. The small opacity means that the magnitude of the initial heating rate perturbation only decreases by a factor of four between the upper and lower stratosphere for a SWV perturbation. Therefore, to balance the heating rate perturbation, the largest temperature change is required in the lower stratosphere. Increasing the background concentration of SWV causes the water vapour bands to become more opaque. For a SWV perturbation applied to a background SWV concentration ≥30 ppmv, the heating rate perturbation and temperature change structurally resemble those from an increase in CO2. In the Extratropics, the lower height of the tropopause is found to cause the enhancement in the cooling at those latitudes. By controlling the depth of atmosphere which adjusts to the SWV perturbation, the tropopause height affects the net exchange of radiation between the layers in the stratosphere as they cool. The latitudinal gradient in upwelling infrared radiation at the tropopause and variations in the background temperature are found to have only a minor effect on the structure of the stratospheric temperature response to a change in SWV. Copyright © 2011 Royal Meteorological Society

Induction Hardening 5150 Steel: Effects of Initial Microstructure and Heating Rate

Induction heating has permitted great progress in the surface hardening of a wide variety of steels, but results in a wide range of local thermal cycles. The metallurgical changes during rapid heating and cooling have not been sufficiently studied with respect to heating rate and prior microstructure. In the present investigation, induction dilatometry was performed on 5150 steel with ferrite-pearlite and tempered martensite initial microstructures to assess effects of experimentally controlled prior microstructure and heating rate on austenitization kinetics. Heating rates were varied from 0.3 to 300 °C/s to simulate industrial processes, and post-hardening metallography and hardness testing were performed. Results show that the transformation kinetics for prior ferrite-pearlite microstructures are significantly slower than for prior tempered martensite microstructures, although hardness is equivalent for a given thermal cycle. Metallographic evidence suggests significant remnant segregation of chromium in regions of pearlitic cementite (enriched); evidence of segregation was not observed metallographically for prior tempered martensite. Diffusion-based transformation simulations support observed ferrite-pearlite alloy segregation, suggest residual alloy segregation is possible for prior tempered martensite, and can be used to tailor austenitization thermal cycles to process requirements. Detailed time and temperature-dependent local microstructure development results from this study are directly applicable to practical induction hardening simulations.

A COMPARISON STUDY ON DISTRICT HEATING AND COOLING IN TOKYO, BEIJING, AND SEOUL

This paper presents the study of DHC (district heating and cooling) business in 3 northeast Asian cities-Tokyo, Beijing and Seoul, in which, projects like initial background, annual fluctuation, current status and heat rate system were investigated. The difference and the feature of DHC use in the city in a country different through the comparison of three cities are analyzed, As a result, this paper may propose a material for DHC business progressing and a new way about the environmental policy in the future. During the period of 2006, DHC annual sales showed big differences in 3 cities. It can be seen that sales for houses and Commercial buildings were also different. The differences of the heat rate unit price by the heat service area of the DHC were large in Tokyo, while small in Beijing and Seoul. Additionally, by use of the building thermal model and comparing individual heat source system, the difference between DHC heat rates in 3 cities is confirmed.

Morphologically controlled synthesis of colloidal upconversion nanophosphors and their shape-directed self-assembly

We report a one-pot chemical approach for the synthesis of highly monodisperse colloidal nanophosphors displaying bright upconversion luminescence under 980 nm excitation. This general method optimizes the synthesis with initial heating rates up to 100 °C/minute generating a rich family of nanoscale building blocks with distinct morphologies (spheres, rods, hexagonal prisms, and plates) and upconversion emission tunable through the choice of rare earth dopants. Furthermore, we employ an interfacial assembly strategy to organize these nanocrystals (NCs) into superlattices over multiple length scales facilitating the NC characterization and enabling systematic studies of shape-directed assembly. The global and local ordering of these superstructures is programmed by the precise engineering of individual NC's size and shape. This dramatically improved nanophosphor synthesis together with insights from shape-directed assembly will advance the investigation of an array of emerging biological and energy-related nanophosphor applications.

Effects of rapid calcination on properties of calcium-based sorbents

The calcination process may influence subsequent fragmentation, sintering and swelling when CaO derived from limestone acts as a CO 2 or SO 2-sorbent in combustion, gasification and reforming. Sorbent properties are affected by CO 2 partial pressure, total pressure, temperature, heating rate, impurities and sample size. In this study, the effect of calcination heating rate was investigated based on an electrically heated platinum foil. The effects of heating rate (up to 800 °C/s), calcination temperature (700–950 °C), particle size (90–180 μm) and sweep gas velocity were investigated. Higher initial heating rates led to lower extents of limestone calcination, but the extents of carbonation of the resulting CaO were similar to each other. Calcium utilization declined markedly during carbonation or sulphation of CaO after calcination by rapid heating. Experimental results show that carbonation and calcium utilization were most effective for carbonation temperatures between 503 and 607 °C. Increasing the extent of calcination is not the best way to improve overall calcium utilization due to the vast increase in energy consumption.

Performance of hydrogen trapping and phase transformation in hydrogenated duplex stainless steels

Duplex stainless steels (DSS) (SAF 2507) have outstanding mechanical properties and high levels of corrosion resistance (especially to SCC in chloride-containing environments). However in spite of this they are susceptible to hydrogen embrittlement.The interaction of hydrogen with the microstructure and defects in DSS (SAF 2507) was investigated in order to gain an in-depth understanding of the behaviour of hydrogen in this material. Hydrogen was introduced into the metal by means of electrochemical cathodic charging in acid solution.Using X-ray diffraction and SEM microscopy, the phase transformation was studied. γ→γ* was the major hydrogen-induced phase transformation in duplex steel. The pseudo hydride phase of γ* was unstable—disappearing during ageing, over a period of 24h at room temperature, and after thermal desorption (20–450°C). This is as a result of hydrogen evolution. A negligible amount of ɛ-martensite was further observed immediately after charging. Hydrogen desorption induced surface tensile stress provoking the phase transformation γ→ɛ→αM.A linear model was used to analyze thermal desorption of hydrogen, through the TDS spectrum, and resulted in the identification of trapping types in DSS. These include: the strain regions around the dislocations with activation energy of about 20kJ/mol; grain boundaries (22.5–28.5kJ/mol); the dislocations core (34.8–40.3kJ/mol), vacancies and austenite–ferrite interfaces (50.2–57.4kJ/mol).The relation of initial hydrogen concentration and heating rate to the thermal desorption process is discussed.

Pure rotational CARS thermometry studies of low-temperature oxidation kinetics in air and ethene–air nanosecond pulse discharge plasmas

Pure rotational CARS thermometry is used to study low-temperature plasma assisted fuel oxidation kinetics in a repetitive nanosecond pulse discharge in ethene–air at stoichiometric and fuel lean conditions at 40 Torr pressure. Air and fuel–air mixtures are excited by a burst of high-voltage nanosecond pulses (peak voltage, 20 kV; pulse duration, ∼ 25 ns) at a 40 kHz pulse repetition rate and a burst repetition rate of 10 Hz. The number of pulses in the burst is varied from a few pulses to a few hundred pulses. The results are compared with the previously developed hydrocarbon–air plasma chemistry model, modified to incorporate non-empirical scaling of the nanosecond discharge pulse energy coupled to the plasma with number density, as well as one-dimensional conduction heat transfer. Experimental time-resolved temperature, determined as a function of the number of pulses in the burst, is found to agree well with the model predictions. The results demonstrate that the heating rate in fuel–air plasmas is much faster compared with air plasmas, primarily due to energy release in exothermic reactions of fuel with O atoms generated by the plasma. It is found that the initial heating rate in fuel–air plasmas is controlled by the rate of radical (primarily O atoms) generation and is nearly independent of the equivalence ratio. At long burst durations, the heating rate in lean fuel air–mixtures is significantly reduced when all fuel is oxidized.

First Line Ash Transformations of Coal and Biomass Fuels during PF Combustion

During a combustion process, fuel undergoes various physical and chemical transformations. First-line physical transformations such as char oxidation, devolatilization, and fragmentation are the most important aspects of the ash formation process in the radiant zone. These transformations will be the same for all fuels but the extent to which they occur will be different due to varying mineral matter contents in the carbon matrix and size distribution. At typical pulverized fuel firing conditions, characterized by the high initial heating rates (105 °C/s) and temperature (1450−1600 °C) the overall, reaction rate is initially controlled by the rate of volatiles diffusion through the pores of a char particle along with chemical reactions. A transition to a kinetically controlled regime is generally observed in the later stages of the combustion process. The extent of the fragmentation will be different in both regimes. In this paper an attempt is made to shed light on the first-line ash transformations of different coal and biomass fuels, by carrying out a thorough experimental study in an advanced lab-scale facility under typical PF-firing conditions, including air-staging. Ash release, conversion, size reduction, and distribution, alongside with the change in inorganic chemical compositions, are derived at different char burnout levels in the reactor at 20, 90, 210, and 1300 ms residence times. Results indicate that at typical PF firing conditions, char combustion will mainly be in a kinetic-diffusion controlled regime, even with extended residence times. Char oxidation and devolatilization are found to depend to a large extent on the fuel mineral matter and its association inside the char matrix under these conditions. However, fragmentation of the fuel particles depends on char devolatilization and oxidation. During the initial heating and devolatilization, smaller particles of coal and biomass were found to be converted faster than larger particles. After a certain conversion, larger-sized particles fragment more than smaller particles, likely due to the high temperature gradient. Attrition, breakage, and percolative fragmentation were observed throughout under the kinetic-diffusion controlled regime. On the basis of the results at hand, a qualitative predictive tool is also suggested to gauge the extent of first-line physical transformations.

Optimizing the TLD-100 readout system for various radiotherapy beam doses using the Taguchi methodology

The TLD-100 readout system was optimized for various radiotherapy beam doses using the Taguchi method. The radiotherapy beam was produced by a Varian 21EX linear accelerator (LINAC) at 6MV. The beam doses were 50, 100 and 150cGy, and the measured data in each group were averaged from three TLD-100 chips. A total of nine combinations of four parameters were arranged, in the manner suggested by Taguchi. The four parameters were defined as initial temperature, heating rate, preheat time and maximum set temperature of the readout system during TLD reading. The loss function eta adopted herein was specifically defined to satisfy the requirements of both sharp linearity and good reproducibility of the TLD reading at various radiotherapy beam doses. The optimized values were: (1) 50( composite function)C for initial temperature, (2) 3 (degrees C)/s for heating rate, (3) 5 min for the TLD preheat time and (4) 250 degrees C for the maximum temperature for TLD reading. Additionally, the parameters that dominated the TLD readout were: (1) initial temperature, (2) heating rate and (4) maximum temperature setting for TLD reading; and the minor parameter was (3) TLD preheat time before reading. The interactions among the dominant parameters were also studied: no significant cross interaction occurred between initial temperature and heating rate or between initial temperature and maximum temperature. However, a complex cross-interaction existed between optimal heating rate and maximum temperature.

Rapid Catalyst-Free Flame Synthesis of Dense, Aligned α-Fe2O3 Nanoflake and CuO Nanoneedle Arrays

This paper describes a simple and yet rapid flame synthesis method to produce one-dimensional metal oxide nanostructures by directly oxidizing metals in the postflame region of a flat flame. Single and bicrystal alpha-Fe(2)O(3) nanoflakes and CuO nanoneedles were grown in the postflame region by a solid diffusion mechanism and were aligned perpendicularly to the substrate with a surface coverage density of 10 nanostructures per square micrometer. The alpha-Fe(2)O(3) nanoflakes reached lengths exceeding 20 microm after only 20 min of growth. This rapid growth rate is attributed to a large initial heating rate of the metal substrate in the flame and to the presence of water vapor and carbon dioxide in the gas phase that together generate thin and porous oxide layers that greatly enhance the diffusion of the deficient metal to the nanostructure growth site and enable growth at higher temperatures than previously demonstrated.

Influence of heating rate on thermoluminescence of Mg2SiO4 : Tb dosimeter

In this paper the influence of different heating rates on thermoluminescence (TL) kinetics, glow-peak temperatures, heights and integrated TL intensities of the main glow peak of recently produced Mg2SiO4 : Tb dosimeters are reported. The TL properties of the phosphor were investigated after β-irradiation at room temperature. Glow curve shape, peak shape, repeated initial rise and variable heating rate methods were used to analyse the TL kinetics of the main glow peak at 473 K. Results show that the TL glow peak of Mg2SiO4 : Tb phosphor obeys second-order kinetics. Analysis of the main dosimetric peak by using the methods mentioned above revealed that activation energy (E) is about 1 eV and the pre-exponential factor (s) is in the range 1010–1011 s−1. In addition it is ascertained that the glow-peak temperature increases with heating rate. The glow-peak height showed two maxima in the heating rate range investigated. The behaviour of the integrated TL intensities and the maximum glow-peak temperatures related to the heating rate have been discussed in terms of thermal quenching and clustering formation.

Blistering of Moisture Saturated Graphite/Polyimide Composites Due to Rapid Heating

Polyimide matrices extend the role of composite materials to applications in extreme temperature environments. However, composites can be susceptible to damage under extreme hygrothermal environments such as rapid heating of moisture saturated materials. Here, rapid is defined as reaching high temperature in less than the drying time at that temperature. A new method to predict initiation of steam-pressure induced damage for rapidly heated neat resin and graphite/polyimide composites is proposed. This method entails comparing the calculated, available steam pressure within the laminate to an experimentally determined critical pressure—temperature envelope. Through experiments performed in a thermal mechanical analyzer it is shown that the onset of steam-induced damage can be detected by measuring the expansion of moisture-saturated specimens subjected to a rapid temperature ramp. Optical microscopy of damaged samples shows that the process of initiation and evolution of damage in neat resin and laminates begins with void growth and coalescence in the polyimide resin matrix. Data from tests performed over a range of heating rates and initial moisture saturations are used to develop a critical pressure—temperature envelope. With this envelope we show the dependence of damage on initial moisture content and heating rate and propose an application of this envelope to failure prediction and design of laminated structures subjected to rapid heating.