Temperature Time Plots Research Articles

Investigation of the Formation of Iron‐Rich Intermetallic Phases in Al–Si Alloys via Thermal Analysis Cooling Curves, Including a Real‐Time Detection for Filtration Process

The formation of iron (Fe)‐containing intermetallics during solidification is challenging due to the influences of cooling rate and chemical composition. Differential scanning calorimetry (DSC) is an accurate analysis method but merely replicates adjustable cooling conditions. Thereby, the solidification range is traversed several times before DSC measurement. For this purpose, thermal analysis cooling curves with double thermocouple are conducted to investigate the formation temperature of Fe‐rich intermetallics in different AlSi casting alloys. In addition, the influence of chemical composition is examined by increasing the initial contents of iron, manganese, and chromium to 0.8 wt% each. The double thermocouple setup allows determining feeding points and solid fractions of the alloy compounds. To evaluate the data sets, the statistical program R is used to improve data processing and smoothing. The signature of Fe‐rich intermetallics in the temperature–time plots corresponds to the detected phases in optical micrographs. In addition, scanning electron microscopy with energy‐dispersive spectroscopy and electron backscattering diffraction are used to measure the local chemical composition and identify the iron‐rich intermetallics. Real‐time evaluation (differential calculation, first derivative, incl. smoothing) for an applicable filtration process can be performed using thermocouples with analog‐to‐digital converter and Python programs with an interactive graphical interface.

Densification kinetics of P/M austenitic (316L) stainless steels processed by rapid microwave hybrid heating method at various conditions

ABSTRACT Microwave sintering of powder metals is recognised for better process advantages, namely, less process time, rapid densification, uniform volumetric and selective heating characteristics. There are certain theoretical analyses to explain the mass transport mechanisms during microwave sintering. The current study reports on an investigation of densification kinetics in austenitic (316 L) stainless steel powder compacts processed by microwave hybrid heating method at solidus and super-solidus temperatures. The analysis of densification kinetics and sintering mechanisms were studied using the grain growth exponential and time-temperature plots. The results revealed that the major densification is achieved through bulk diffusion (viscous mass flow) at a higher temperature (1250°C–1300°C) under the super-solidus region while grain boundary retardation is the mechanism for the reduced grain growth at a lower sintering temperature (1100°C–1200°C) under solidus region. The apparent activation energies are calculated using the Arrhenius plot and classical grain growth analysis simultaneously. The activation energies of 42 ± 3 kJ/mol and 24 ± 2 kJ/mol are observed for the samples sintered at a lower temperature. The higher activation energies of 219 ± 8 kJ/mol and 254 ± 7 kJ/mol are obtained for the samples sintered at 1250°C–1300°C for both analyses.

Molecular dynamics simulation of the effect of temperature and size on the mechanical behavior of Cu50Zr50 metallic glass

Abstract Amorphous materials such as metallic glasses have been a recent area of research because of their more or less defined position of atoms at the molecular level. Because of their superior strength and corrosion resistance properties, metallic glasses can be used as structural materials in applications such as in nuclear reactors, marine vessels, etc. This work presents a Molecular Dynamics (MD) simulation of the mechanical behavior of Copper-Zirconium (Cu-Zr) metallic glass under the application of temperature (at a constant quenching rate (1014 K/s) for all specimens) on different sizes. The volume-temperature and temperature–time plots were drawn and the results analyzed for various sizes to estimate their mechanical behavior.

Design-of-experiments application in the friction stir welding of aluminium alloy AA 8011-h14 for structural application

Purpose The demand for aluminium alloys has been increasing in almost all the fields. In this study, the friction stir welding (FSW) of similar aluminium alloy AA 8011-h14 has been presented using three levels of tool rotational speed (n), tool tilt angle (ϴ) and tool feed (f). The purpose of this paper is to study the effect of welding parameters on various properties and time-temperature plots. Design/methodology/approach FSW was carried out using the L-9 orthogonal array of welding parameters generated using the Taguchi approach. Visual inspection and radiography testing were conducted to detect the surface and volume defects, respectively. Taguchi analysis was carried out to get optimised welding parameters for tensile testing. The microstructural analysis was carried out for the specimen possessing maximum tensile strength and the obtained grain structures were compared with the microstructure results of the base material. The peak process temperatures were noted and time-temperature plots were analysed for the varying parameters. The maximum value of hardness was recorded and analysed. Findings Visual inspection and radiography testing confirmed defect-free joints. The maximum tensile strength achieved was 84.44 MPa with 64.95 per cent efficiency. The optimised parameters obtained using Taguchi analysis for tensile testing were 1,500 rpm, 1° and 50 mm/min. Microstructure analysis for the specimen possessing maximum tensile strength revealed fine and equiaxed grains in the nugget zone. Time-temperature plots suggested the maximum temperature of 389 °C on the advancing side. A maximum hardness value of 36.4 HV was obtained in the nugget zone. Originality/value As per the knowledge of the authors, this study is the first attempt for the detailed experimental analysis on the FSW of this particular aluminium alloy AA 8011-h14.

Designing an active phase change material package for thermal and qualitative protection of meat

Abstract The aim of this study is to design a phase change material (PCM) package prototype for maintaining meat cold temperature and quality during its exposure to room temperature, or during temperature fluctuations in refrigerated vehicles. Therefore, tetradecane was packed and placed on the top, bottom or both sides of meat in the package. Thereafter, the meat and tetradecane-containing packages were cooled down to 3 °C and then exposed to the two incubation temperatures of 12.5 and 30 °C while meat temperature was recorded using a K-type thermocouple. Hardness and drip loss were also examined as two important meat quality attributes. Temperature-time plots showed that where tetradecane was placed had a significant effect on maintaining meat temperature during incubation at 12.5 °C but that using the phase change material at a temperature of 30 °C had no effect on delaying the rise in meat temperature. This is while the placement of tetradecane at bottom of meat could significantly decrease weight loss during exposure to room temperature. Based on the results, designated package containing tetradecane can effectively prevents from meat temperature rise by about 2 h while maintaining meat quality.

Unified Ignition – Devolatilization model for fixed bed biomass Gasification/Combustion

Counter-current flame propagation through fixed packed beds serves as a canonical form for understanding biomass thermochemical conversion phenomenon – this is due to the ‘universal behavior’ of fuel consumption rate per unit area with superficial velocity variation. This behavior is directly related to the particle density scaled ignition time being independent of biomass type, varying only with superficial velocity. But when the devolatilization time exceeds ignition time for a particle, the predicted fuel consumption rates will be higher than the actual values due to overlap of ignition and devolatilization. This situation is relevant for larger particles (> 30 mm equivalent sphere) and thin wood chips, due to sharp edges aiding quick ignition. The current work aims at generalizing the ‘universal propagation model’ to account for this effect which is critical to designing grate furnaces. Towards this, packed bed experiments were performed in a 500 mm dia, 1 m height cylindrical reactor with groundnut shell briquettes (GSB; dia 100 mm, lengths varying from 40 to 110mm) and pellets (dia 8mm and length varying between 15 to 20mm) at a superficial velocity of 20 and 30 cm/s. The fuel mass flux is calculated by two methods 1) from the slope of time-mass curve 2) from time-Temperature plots measured at fixed thermocouple locations along the reactor. Fuel flux measured using the two methods match closely for pellets, but with GSB, the fuel flux from method 2 is higher than method 1 by about 15 %. This indicates that subsequent fresh layer of biomass ignites before complete devolatilization of the previous layer leading to oxygen starvation. This also indicates a transition from ignition controlled to devolatilization rate controlled flame propagation, consistent with the expectations based on variation of ignition and devolatilization time with particle size measured for single particles in an earlier study at our lab. These results are used to develop a unified ignition-devolatilization model for single particle combustion, which is used to modify the ‘universal propagation model’ to account for particle size and shape effects. The predictions from this model are shown to closely match with the observed results.

Thermal analysis of a non-homogeneous insulating panel

This article describes heat flow meter measurements and transient thermal modelling (using ANSYS) of a webbed, hollow-cored panel located between silicone sponge buffer materials chosen to provide boundary conditions comparable to standard surface coefficients. Panel surface temperatures were also measured at eight locations to record the thermal measurement as a temperature step function following isothermal stabilization. An uninsulated configuration was studied as well as cases with different levels of bulk insulation filling the panel cores. Measured and modelled temperature–time plots agreed well after corrections for web and airspace thermal conductivity. Modelled spatial variation in heat flow exceeded 200% for one insulated case but was only about 2% for the uninsulated panel. Modelled values for heat flux and overall thermal resistance agreed well with standard analytical calculations. However, heat flows indicated by the apparatus were consistently higher than the modelled and calculated values by up to 8%, expected to be due at least partially to specimen non-homogeneity. Nevertheless, results suggest a useful role for the apparatus in providing temperature measurement under controlled conditions, helping to validate thermal modelling as a potential alternative to hot box measurement for non-homogeneous assemblies.

ТЕРМОДИНАМІЧНІ ЦИКЛИ ТА ПРАВИЛА РЕГУЛЮВАННЯ СИСТЕМ ОБОРОТНОГО ВОДОПОСТАЧАННЯ З ВИПАРНИМИ ОХОЛОДЖУВАЧАМИ

The analysis of existing regulatory designing documents on chimney-type and mechanical-draft water cooling towers is carried out. It is shown the documents are out of date and to be improved. The efficiency criteria for water circulating systems (WCS), such as the mass transfer coefficient, efficiency factor of fill packing and cooling curves are lost their applied significance and no condition to solve appropriate problems. To analyse WCS with different coolers, the thermodynamic cycles in the Temperature-Time plot are introduced. The thermodynamic efficiency of WCS, which is equal to temperature difference to cooled water temperature ratio is proved as the integral efficiency index. Diagrammatical thermodynamic cycles for WCS with a cooling tower, sprinkling basin or cooling pond are adduced and comprehensive analysis of their specific operation features is carried out. Three rules for WCS control are formulated: 1) When putting into operation and removal from service of a heat exchanging equipment, it is necessary to observe the equation of a resulting water temperatures drop in both heaters and coolers; 2) The cooler hydraulic load variation without its efficiency decrease, is allowed only within the operation range of its individual performance; 3) The WCS thermodynamic efficiency drop under production and ambient conditions is an evidence necessity to fulfil required maintenance or to repair proper equipment. On the basis of the suggested thermodynamic cycles and their analysis a comparative estimation of cooling towers, the sprinkling basin and cooling ponds is carried out. The transpiration coolers disrepairings which influence the WCS operation efficiency require their timely elimination are indicated.

Evaluation of a buried power cable's thermal behavior using phase diagrams and calculation of the phase difference between temperature and power

As most of the studies about thermal behavior of cables perform the steady state thermal analysis, a dynamic analysis of these problems can be proved very interesting. In the current study, a dynamic thermal analysis of an underground cable which operates under a continuously changing load and thus continuously changing Joule losses is carried out. With the Joule losses as the input signal it is proved that the thermal time constants in the range up to several hours are possible. It is also observed that the dynamic analysis, presented in this work, indicates an increase on the peak value of the cable's temperature that can reach up to 81%. This increase proves the importance of a dynamic analysis. Furthermore, the comparison between the steady state and dynamic analysis resulted in the conclusion that it is practically impossible to achieve steady state condition for power losses other than the mean value, thus steady state analysis cannot determine the instantaneous temperature of the cable. The analysis is based on the Temperature–Power (T–P) phase diagrams which are proved to be a more suitable representation method of the results comparing to the Temperature–Time plots. Lastly, the phase difference between the power and the temperature vectors is calculated.

Thermal stability of surface-esterified cellulose and its composite with polyolefinic matrix

Thermal stability of hydrophobized cellulose powders was investigated from the perspective of potential use as filler in non-polar polyolefinic matrix. The hydrophobization was done by heterogeneous esterification with three carboxylic acids which differ in chain length (3, 10 and 18 carbons). Data measured by means of thermogravimetry (TG) were recalculated according to model-free isoconversional method to construct time–temperature plots. It was demonstrated that the esterification significantly decreases thermal stability of the material, which reduces feasible processing window. Under non-oxidative atmosphere, the single-step decomposition of materials is prevailing, while the process is more complex in air. In both cases the oleic acid esters showed the lowest stability and the original cellulose was the most stable. Finally, all powders were compounded with polyethylene or polypropylene. Obtained composites were then subjected to color measurement and TG. Even though the materials were partly degraded, which was indicated by the yellowish hue of the composites, virtually no impact of the filler pyrolysis on the polymer matrix decomposition was observed, particularly in case of decanoyl esters.

Corresponding states for mesostructure and dynamics of supercooled water

Water famously expands upon freezing, foreshadowed by a negative coefficient of expansion of the liquid at temperatures close to its freezing temperature. These behaviors, and many others, reflect the energetic preference for local tetrahedral arrangements of water molecules and entropic effects that oppose it. Here, we provide theoretical analysis of mesoscopic implications of this competition, both equilibrium and non-equilibrium, including mediation by interfaces. With general scaling arguments bolstered by simulation results, and with reduced units that elucidate corresponding states, we derive a phase diagram for bulk and confined water and water-like materials. For water itself, the corresponding states cover the temperature range of 150 K to 300 K and the pressure range of 1 bar to 2 kbar. In this regime, there are two reversible condensed phases - ice and liquid. Out of equilibrium, there is irreversible polyamorphism, i.e., more than one glass phase, reflecting dynamical arrest of coarsening ice. Temperature-time plots are derived to characterize time scales of the different phases and explain contrasting dynamical behaviors of different water-like systems.

Observable characteristics of flashover

Definitions of flashover are multifarious but may be categorized as three types: mathematical, visual and those relying on diction. There are at least two arguments to be had with regard to the definition of flashover:(i) Is rapidity of transition to a state of total surface involvement an essential criterion for flashover?(ii) Is instability in the heat balance an essential criterion of flashover?This article postulates a one-dimensional scale with three major types of compartment fire (that evolve beyond smoldering but rely on unpressurized contained fuel); and two of those fire types can be split into two sub-categories. In all, five sub-categories exist ranging from fuel-restricted pre-flashover fires at one extreme, to vent-restricted pre-flashover fires at the other, via post-flashover fires in the middle where there is neither fuel nor vent restriction sufficient to prevent flashover; and with borderline (or weak flashover) fires lying between them on the scale.Each sub-category has a tendency to produce its own particular pattern of fire growth (in the form of hot gas temperature rise), which is different from one another and for which some explanation can be offered. By examining the temperature–time plots of 53 fixed-vent, single-source scaled laboratory fires it is concluded that rapidity of fire growth is a common but not an essential characteristic of flashover. Furthermore, conditions considered to be post-flashover can be attained without much/any evidence of thermal instability.It is suggested that the most convenient definition of ‘flashover’ for experimentalists is a visual one, based on observation of flame projecting from the vent; and that any dictionary style definition should be based on this observation.

Thermokinetics: Iodide-Catalyzed Decomposition Kinetics of Hydrogen Perioxide. An Initial-Rate Approach

A temperature-based determination of the kinetics of the H2O2 decomposition using the method of initial rates is described. The reagents (total volume 5 mL) are added to a microcalorimeter and the temperature–time data are collected using a temperature sensor and a datalogger. The temperature–time plots are linear for a considerable length of time allowing for a straightforward and accurate determination of the initial rate, dT/dt. Changing from dT/dt to an initial rate in terms of H2O2 concentration (–d[H2O2]/2dt), requires the determination of the enthalpy of the reaction as well as the heat capacity of the microcalorimeter. In doing so, this lab combines thermochemistry and kinetics. The reaction is first order with respect to the catalyst, [I–], and first order with respect to [H2O2]. The average rate constant reported by students is 0.0108 ± 0.0003 L mol–1 s–1 at ~20 °C.

Fission track dates of Mandi granite and adjacent tectonic units in Kulu–Beas valley, NW Himalaya, India

We present zircon fission track (FT) ages from the lower parts of the Higher Himalayan crystalline (HHC) ranging from 3.9 to 4.3 Ma and apatite FT age as 1.9 ± 0.4 Ma . Combined with previous radiometric dates, these ages provide the low temperature data for the area and enable us to draw temperature–time plot which shows significant increase in cooling rates from 25 ∘ C / Ma in Oligocene and 4 ∘ C / Ma in Miocene to about 64 ∘ C / Ma during Pliocene. For the Mandi granite, the zircon FT ages range from 3.9 to 4.9 Ma while apatite FT obtained is 2.8 ± 0.5 Ma . The rapid Pliocene exhumation is characterized by a rapid increase in cooling rates from ∼ 3.4 ∘ C / Ma in Miocene to ∼ 77 ∘ C / Ma after 5.0 Ma. Our results confirm the rapid Pliocene to Pleistocene cooling of rocks of Kulu–Beas valley similar to that of the neighboring units from the frontal parts of HHC.

Surface roughness evaluation of marble by 3D laser profilometry and pulsed thermography

Three dimensional (3D) laser profilometry (LP) and pulsed thermography (PT) were used in the inspection of Pentelic marble. Quarry Pentelic marble samples, after processed with different roughness treatments (i.e. 60, 80, 100, 220, 400 and 600 mesh), were evaluated in the laboratory. Furthermore, different surface cleaning treatments were applied to a Pentelic marble surface in situ and then representative samples were collected and evaluated in the laboratory by the means of these two non-destructive techniques. Quantitative analysis of all samples was performed. The surface roughness parameter Rq at a specific length scale was estimated by the use of the LP scanning approach. Furthermore, 3D micro-topography plots from the laser scans were attained. PT, through the formation of temperature—time plots that display the intensity of pixels as a function of time on the obtained thermal images, was able to distinguish the influence of the applied roughness treatments. Results indicate that these two non-contact and non-destructive techniques can be used for the assessment of surface roughness.

The isochronous strain energy approach applied to the load–strain–time–temperature behaviour of geosynthetics

The load–strain–time–temperature behaviour of geosynthetics can be determined by a variety of strength-testing methodologies. However, to date it has not been possible to directly compare and correlate the data obtained from different testing regimes in a generally applicable manner. In this paper, a strain energy approach to the characterisation of the load–strain–time–temperature of geosynthetics is developed that is intended to deal with this problem. This approach takes account of the changes in the behaviour of geosynthetics that occur with time, and is called the isochronous strain energy (ISE) approach. The background to the ISE approach is set out and used to compare and correlate the data from various strength tests carried out on a wide range of geosynthetics. This shows that the isothermal load–strain–time behaviour of a geosynthetic can be represented in a generally applicable manner within an ISE–time plot and that temperature effects can be represented within ISE–time–temperature plots. It is shown that the ISE absorbed by a geosynthetic comprises two basic components, the immediately recoverable ISE and the locked-in ISE. Representation of the behaviour of geosynthetics using these two ISE components allows the prediction of their response to any loading regime applied over any time period.

Response of sub-surface fatigue damage under sonic load – a computational study

Graphite/epoxy composite samples with a center hole were subjected to fatigue loading, and were tested for damage using the sonic infrared (sonic IR) imaging technique. The technique revealed the presence of semi-elliptical delaminations near the circular notch. In the sonic IR technique, a short pulse of sound infuses into the material and results in frictional heating at the delamination surfaces. The heating at the damage locations reaches the surface of the sample by conduction, and is captured by an IR camera. In the present analysis, the finite element technique was employed to model a notched sample with two semi-elliptical delaminations. The delaminations were modeled using a surface-to-surface contact algorithm, and the frictional energy developed during the infusion of sound pulse was graphed. A separate finite element model was developed for transient heat transfer analysis by utilizing the calculated frictional energy as a heat source. Variation in surface temperature within the delamination regions was plotted with time, and was compared with the temperature–time plot obtained from the sonic IR technique.

Thermodynamics of thermal methods for rapid screening of combinatorial libraries

General equations are developed relating the dependence of temperature on time for a closed system undergoing chemical reaction. Equations are reported for thermally insulated systems and for systems where Newton's law of cooling describes the exchange of thermal energy between system and surroundings. These equations provide the basis for analysing and modelling thermal methods for screening combinatorial libraries. Key equations describe the impact of chemical reactions having different orders and molecularities. The potential of resulting differential equations is illustrated using numerical integration to yield temperature–time plots which highlight the roles of rate constants and enthalpies of reactions.

High-temperature erosion of titanium-carbide-particle-reinforced tungsten composites

High-temperature erosion of tungsten composites reinforced with 30 vol% titanium carbide particles (TiC p /W) was studied with the use of specially constructed oxyacetylene erosion equipment. Results revealed that the mass-erosion and linear-erosion rates of TiC p /W are much lower than those of traditional copper-infiltrated tungsten material. The erosion resistance of the composite was greatly increased by TiC p addition. Thermochemical oxidation of tungsten and TiC p particles was the main erosion mechanism of TiC p /W. Temperature-time plots of the eroded surfaces of the specimens were successfully measured in situ with a dynamic-response multi-wavelength pyrometer, which indicated that TiC p /W composite had good thermal shock resistance. The good physical properties and good high-temperature erosion resistance of TiC p /W composite makes it a good candidate for rudders of solid rocket motors.

Consolidation of copper powders with dispersed titanium carbonitride : Y.Ogino et al. (Himeji Inst. of Technology, Himeji, Japan.) J. Jpn Soc. Powder Powder Metall., vol 45, no 4, 1998, 379–384. (In Japanese.)

We present zircon fission track (FT) ages from the lower parts of the Higher Himalayan crystalline (HHC) ranging from 3.9 to 4.3 Ma and apatite FT age as 1.9±0.4Ma. Combined with previous radiometric dates, these ages provide the low temperature data for the area and enable us to draw temperature–time plot which shows significant increase in cooling rates from 25∘C/Ma in Oligocene and 4∘C/Ma in Miocene to about 64∘C/Ma during Pliocene. For the Mandi granite, the zircon FT ages range from 3.9 to 4.9 Ma while apatite FT obtained is 2.8±0.5Ma. The rapid Pliocene exhumation is characterized by a rapid increase in cooling rates from ∼3.4∘C/Ma in Miocene to ∼77∘C/Ma after 5.0 Ma. Our results confirm the rapid Pliocene to Pleistocene cooling of rocks of Kulu–Beas valley similar to that of the neighboring units from the frontal parts of HHC.