One-dimensional Temperature Profiles Research Articles

NO measurements in high temperature hydrogen flames: The crucial role of the hydrogen oxidation chemistry for accurate NO predictions

The current work investigates the formation of Nitric Oxide (NO) in hydrogen–air flames, over a wide range of flame temperatures. The use of hydrogen allows improved focus on the thermal-NO pathway by removing the complexity introduced by the prompt-NO pathway, which has been shown to be an important contributor to inaccurate predictions of absolute post-flame NO concentrations in hydrocarbon flames. This experimental study is conducted at atmospheric pressure using stoichiometric, premixed, laminar stagnation flames. Adiabatic flame temperatures ranging from 1600K to 2300K are achieved by varying the argon concentration in air. One-dimensional velocity, temperature, and NO concentration profiles are measured using non-intrusive laser diagnostics: Particle Tracking Velocimetry (PTV), NO multiline thermometry, and NO Laser Induced Fluorescence (NO-LIF), respectively. Results show that the experimental velocity profiles are incorrectly captured by the studied mechanisms, especially at low and high temperatures. This suggests that major inaccuracies are present in the hydrogen oxidation chemistry of the thermochemical models, regardless of their optimisation methodology. Furthermore, NO-LIF profiles show major discrepancies between all the studied mechanisms and the experiments, especially at elevated temperatures. The disagreement stems from an inaccurate description of the base chemistry of the models. These inaccuracies arise specifically from the description of the radical pool driving the flame behaviour and NO formation. This study demonstrates the need for model optimisation on experimental measurements using pure hydrogen 1D flames to obtain an accurate description of the hydrogen oxidation chemistry at play. This would lead to an improved description of the NOx sub-chemistry of any hydrogen, or hydrocarbon, combustion system.

Extension of the functionality of the software for MD-simulation of the SH-synthesis of intermetallides in Ni-Al and Ti-Al nanosystems

The subject of research: the methodological and functional capabilities of specialized software packages of free access LAMMPS and OVITO and author's programs used for simulation of SHS-microkinetics in heterogeneous systems.
 Purpose of research: to increase information content, 3D-visualization, and adequate interpretation of the processes of structural-phase transformations at interfaces of the layered, layered-block nanoscale Ni-Al and Ti-Al systems.
 Methods and objects of redearch: the molecular dynamics simulation method implemented in the basis of the LAMMPS software package simulates the process of initiation and propagation of the SHS combustion wave in the systems under study, and using the OVITO package, 3D-visualization of the processes of dissolution, diffusion, and motion of the SHS combustion wave front is carried out.
 Main results of research: it is shown that the development by the author of software modules for calculating one-dimensional temperature and density profiles of the synthesized material along the direction of combustion wave motion, as well as for calculating and visualizing the 3D-structure of the distribution of synthesized intermetallic interlayers at the interface in nanoparticles with the Ni-Al "core-shell" structure (and similarly for Ti-Al) allows, in contrast to the OVITO package, to detect heterophase intermetallic structures in such systems. As a result of a large series of computational experiments on simulation of microkinetics in the studied nanoscale Ni-Al and Ti-Al systems, it has been established that the software package created by the author with support for parallel computing, which, in addition to the licensed packages LAMMPS and OVITO, integrates author's software modules, has new broader functionality in the methodological aspect of the study of the problems of physical chemistry of the SHS process and is a vivid example of the created software engineering tools in this area of research.

How well do we know thermal-NO?An investigation of NO formation in flames over a wide temperature range

This study investigates the large variability and uncertainty in the thermal-initiation reaction rates found in the literature. An experimental study is conducted at atmospheric pressure in lean, premixed, laminar methane-air stagnation flames. Flame temperatures ranging from 1900K to 2500K are achieved by varying the argon concentration, in 21% and 40% oxygen mixtures balanced with nitrogen. The conditions are selected to promote the thermal route in the overall post-flame NO formation. One-dimensional velocity, temperature, and NO concentration profiles are measured with Particle Tracking Velocimetry (PTV), NO multi-line thermometry, and NO Laser-Induced Fluorescence (NO-LIF), respectively. While velocity and temperature measurements are accurately predicted by different thermochemical models, the simulated NO-LIF signal profiles show significant disagreement and large variability, relative to the measurements. Results show that, across all conditions, none of the studied mechanisms are able to capture accurately both the NO concentration, and formation rate in the post-flame region, suggesting that the fundamental chemistry remains inaccurate. The discrepancy in the predictions appears to be linked to the chosen parameters of the Arrhenius rate, specifically the pre-exponential factor, and the activation energy. Sensitivity and Reaction Pathway Analyses suggest that the differences in the Arrhenius parameters could originate from different consideration of the base radical chemistry, as well as different relative contributions of the four NO-formation routes. As a result, some models can predict similar NO concentrations but using significantly different underlying base and NOx chemistry. This implies that the models could diverge significantly in conditions where other non-thermal routes are more important. This study demonstrates the need for spatially-resolved experimental data across a broad range of experimental conditions, promoting and considering a variety of routes, in order to optimize NOx chemistry models with reduced uncertainty.

Deep learning for defect characterization in composite laminates inspected by step-heating thermography

This paper presents a complete procedure for the non-destructive analysis of composite laminates, taking advantage of the step-heating infrared thermography and the latest developments of deep neural networks. One-dimensional temperature profiles of the target surface are collected in response to long heat pulses and individually feed a compact network made of convolutional filters, self-tuned to represent the signals in an equivalent feature space of improved discrimination. The resulting features are then classified to obtain the complete three-dimensional characterization of the properties of possible subsurface defects. Experimental validation is proposed to investigate a laminate of glass-fiber-reinforced polymer with several flat-bottom holes by changing the duration of the input heat pulses. This test produces surprisingly good results in the characterization of three classes of defects of increasing depth, including the most challenging at a depth of 6.38 mm, i.e. at the limit of applicability of the step-heating thermography. In the case of an excitation length of 180 s, the average balanced accuracy, precision, and recall are equal to 84.03%, 87.62%, and 82.43%, respectively. Moreover, a threshold operation on the classification scores further boosts the recall values of the class of the deepest defects from 53.87% to 82.41%. This enhancement of sensitivity suggests the applicability of the proposed procedure for the automatic inspection of composites structures in all application fields where safety is mandatory.

Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster

Abstract We present new, deep observations of the Phoenix cluster from Chandra, the Hubble Space Telescope, and the Karl Jansky Very Large Array. These data provide an order-of-magnitude improvement in depth and/or angular resolution over previous observations at X-ray, optical, and radio wavelengths. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling models. In particular, the entropy profile is well fit by a single power law at all radii, with no evidence for excess entropy in the core. In the inner ∼10 kpc, the cooling time is shorter than any other known cluster by an order of magnitude, while the ratio of the cooling time to freefall time (t cool/t ff) approaches unity, signaling that the intracluster medium is unable to resist multiphase condensation on kpc scales. The bulk of the cooling in the inner ∼20 kpc is confined to a low-entropy filament extending northward from the central galaxy, with t cool/t ff ∼ 1 over the length of the filament. In this filament, we find evidence for ∼1010 M ⊙ in cool (∼104 K) gas (as traced by the [O ii]λλ3726,3729 doublet), which is coincident with the low-entropy filament and absorbing soft X-rays. The bulk of this cool gas is draped around and behind a pair of X-ray cavities, presumably bubbles that have been inflated by radio jets. These data support a picture in which active galactic nucleus feedback is promoting the formation of a multiphase medium via uplift of low-entropy gas, either via ordered or chaotic (turbulent) motions.

Regional stratification at the top of Earth's core due to core–mantle boundary heat flux variations

Earth’s magnetic field is generated by turbulent motion in its fluid outer core. Although the bulk of the outer core is vigorously convecting and well mixed, some seismic, geomagnetic and geodynamic evidence suggests that a global stably stratified layer exists at the top of Earth’s core. Such a layer would strongly influence thermal, chemical and momentum exchange across the core–mantle boundary and thus have important implications for the dynamics and evolution of the core. Here we argue that the relevant scenario is not global stratification, but rather regional stratification arising solely from the lateral variations in heat flux at the core–mantle boundary. Using our extensive suite of numerical simulations of the dynamics of the fluid core with heterogeneous core–mantle boundary heat flux, we predict that thermal regional inversion layers extend hundreds of kilometres into the core under anomalously hot regions of the lowermost mantle. Although the majority of the outermost core remains actively convecting, sufficiently large and strong regional inversion layers produce a one-dimensional temperature profile that mimics a globally stratified layer below the core–mantle boundary—an apparent thermal stratification despite the average heat flux across the core–mantle boundary being strongly superadiabatic.

Lidar thermometry using two-line atomic fluorescence.

In this work, Scheimpflug lidar has been combined with the thermometric technique two-line atomic fluorescence, to carry out stand-off, spatially resolved temperature measurements. Indium atoms were seeded into a modified Perkin-Elmer-burner and two tunable single-mode diode lasers with their wavelengths tuned to 410.17 and 451.12 nm were used to excite the seeded atoms. The fluorescence signal was collected using both a line-scan detector and a two-dimensional intensified CCD camera. One-dimensional flame temperature profiles were measured at different heights above a porous-plug burner, located at a distance of 1.5 m from the lidar system. The technique was also used to demonstrate two-dimensional temperature measurements in the same flame. The accuracy of the measured temperature was found to be limited mainly by uncertainty in the spectral overlap between the laser emission and the indium atom absorption spectrum as well as uncertainty in laser power measurements. With the constraint that indium can be introduced into the measurement volume, it is anticipated that the developed measurement concept could constitute a valuable tool, allowing in situ spatially resolved thermometry in intractable industrial applications, sufferings from limited optical access, thus requiring remote single-optical-port sensing.

A Lumped Thermodynamic Model of Gas Turbine Blade Cooling: Prediction of First-Stage Blades Temperature and Cooling Flow Rates

Turbine inlet temperatures (TIT) of 1500–2000 K have become a sort of standard for most modern advanced applications. First-stage blades are obviously the most exposed components to such hot gases, and thus they need proper cooling. In the preliminary design of the blades and their cooling system, designers must rely on simple models that can be further refined at a later stage, in order to have an approximate but valuable set of guidelines and to reach a feasible first-order configuration. In this paper, a simple lumped thermodynamic model of blade cooling is proposed. It is based on mass/energy balances and heat transfer correlations, and it predicts a one-dimensional temperature profile on the blade external surface along the chord for a given gas temperature profile, as well as the required cooling air flow rates to prevent blade material from creep. The greatest advantage of the model is that it can be easily adapted to any operating condition, process parameter, and blade geometry, which makes it well suited to the last technological trends, namely, the investigation of new cooling methods and alternative coolants instead of air. Therefore, the proposed model is expected to be a useful tool in the field of innovative gas turbine cycle analysis, replacing more computationally intensive and very time-consuming models.

Tokamak two-fluid ignition conditions

This work focuses on modeling the properties needed by a plasma to reach ignition, where ignition is the condition in which fusion power is produced at the steady state without any external input power. We extend the classic work by Lawson giving the ptotτE (product between density, temperature, and energy confinement time) needed for ignition [J. D. Lawson, Proc. Phys. Soc. London, Sect. B 70, 6 (1957)] by improving the original zero-dimensional, single fluid model. The effect of multi-fluid physics is included, by distinguishing ions, electrons, and α particles. The effects of one-dimensional density and temperature profiles are also considered. It is found that the multi-fluid model predicts a larger Lawson product required for ignition than the single-fluid one. A detailed analysis of the energy confinement times for each species and energy equilibration times between species shows that the electron energy confinement time is the parameter more strongly affecting the Lawson product needed for ignition. It is also found that peaked profiles (of either temperature or density) require a smaller Lawson product for ignition than flat profiles.

High Resolution Temperature Measurement of Liquid Stainless Steel Using Hyperspectral Imaging.

A contactless temperature measurement system is presented based on a hyperspectral line camera that captures the spectra in the visible and near infrared (VNIR) region of a large set of closely spaced points. The measured spectra are used in a nonlinear least squares optimization routine to calculate a one-dimensional temperature profile with high spatial resolution. Measurements of a liquid melt pool of AISI 316L stainless steel show that the system is able to determine the absolute temperatures with an accuracy of 10%. The measurements are made with a spatial resolution of 12 µm/pixel, justifying its use in applications where high temperature measurements with high spatial detail are desired, such as in the laser material processing and additive manufacturing fields.

Large eddy simulations of complex multicomponent diesel fuels in high temperature and pressure turbulent flows

A multicomponent droplet evaporation model, which discretizes the one-dimensional species and temperature profiles inside a droplet with a finite volume method and treats the liquid phase as thermodynamically real, has been developed and used for large-eddy simulations of high speed diesel sprays in high temperature and pressure closed chambers. Single drop evaporation results obtained by the variable property multicomponent model are shown to match with the constant property model in the limiting conditions. The multicomponent liquid model used together with the Kelvin–Helmholtz – Rayleigh–Taylor droplet breakup model is found to reasonably well predict the experimentally observed non-linear behavior of spray penetration with changing ambient conditions for n-hexadecane and 4 different multicomponent surrogate diesel fuels with 2–8 components. The effects of various modeling assumptions and gas and liquid parameters on the drop and spray evolution and evaporation are investigated in details.

Molten thermoplastic dripping behavior induced by flame spread over wire insulation under overload currents

The dripping behavior of the molten thermoplastic insulation of copper wire, induced by flame spread under overload currents, was investigated for a better understanding of energized electrical wire fires. Three types of sample wire, with the same polyethylene insulation thickness and different core diameters, were used in this study. First, overload current effects on the transient one-dimensional wire temperature profile were predicted using simplified theoretical analysis; the heating process and equilibrium temperature were obtained. Second, experiments on the melting characteristics were conducted in a laboratory environment, including drop formation and frequency, falling speed, and combustion on the steel base. Third, a relationship between molten mass loss and volume variation was proposed to evaluate the dripping time and frequency. A strong current was a prerequisite for the wire dripping behavior and the averaged dripping frequency was found to be proportional to the square of the current based on the theoretical and experimental results. Finally, the influence of dripping behavior on the flame propagation along the energized electrical wire was discussed. The flame width, bright flame height and flame spreading velocity presented different behaviors.

Modeling and Simulation of Thermal Runaway in Cylindrical 18650 Lithium-Ion Batteries

The thermal runaway of a single Li-ion battery (LIB) in larger battery package is the worst case scenario which must be avoided under all circumstances. In this work the electrochemical-thermal model for a LIB based on porous electrode theory is extended with contribution coming from exothermic side reactions to model the abuse mechanisms in Li-ion batteries with respect to the temperature which could lead to a thermal runaway. The electrochemical-thermal model is extended with several new contributions which occur in several temperature regimes. In detail the heat source in the corresponding heat equation is extended with the heat generated by various exothermic reactions, for example at the surface-electrolyte interface at temperatures in the interval T=[T1, T2], reactions between anode resp. cathode and the electrolyte between temperatures in the interval T=[T3, T4] and the destruction of the electrolyte above the temperature T>T5, where T1<T2 ≤T3<T4 ≤T5. These extensions will be modeled with a solid fuel or a constant fuel model as simplification coming from combustion theory. For this extended model simulations are performed for specified current profiles and exterior temperature profiles to simulate an oven trial and cell cycling. In the simulations a cylindrical 18650 LIB is investigated with a LiCoO2 cathode. The purpose of the simulations is to compute the temperature-field during the time evolution of a thermal runaway, therefore the cross section in horizontal and vertical direction are considered as well as the one-dimensional temperature profiles along these directions. Finally the time evolution of the overall mean cell temperature T is used to classify the different stages of a thermal runaway in a T-dT/dt-plot. The results will be compared with experimental ARC-measurements in pure oven experiments and cycling experiments.

1DTempPro V2: New Features for Inferring Groundwater/Surface‐Water Exchange

A new version of the computer program 1DTempPro extends the original code to include new capabilities for (1) automated parameter estimation, (2) layer heterogeneity, and (3) time-varying specific discharge. The code serves as an interface to the U.S. Geological Survey model VS2DH and supports analysis of vertical one-dimensional temperature profiles under saturated flow conditions to assess groundwater/surface-water exchange and estimate hydraulic conductivity for cases where hydraulic head is known.

ANALYSIS OF THERMALLY DEVELOPING LAMINAR CONVECTION IN THE FINNED DOUBLE-PIPE HEAT EXCHANGER

In this work we have carried out the study of convective heat transfer of hydrodynamically fully developed but thermally developing laminar flow in the entrance region of a finned double-pipe heat exchanger. We have taken one-dimensional temperature profile in the radial direction of the fins under the thin fin assumption. It is shown that the heat transfer rate in the thermal entrance region is much higher than in the fully developed region, and the assumption of infinite fin conductivity loses validity in the entrance region.

1DTempPro: Analyzing Temperature Profiles for Groundwater/Surface‐water Exchange

A new computer program, 1DTempPro, is presented for the analysis of vertical one-dimensional (1D) temperature profiles under saturated flow conditions. 1DTempPro is a graphical user interface to the U.S. Geological Survey code Variably Saturated 2-Dimensional Heat Transport (VS2DH), which numerically solves the flow and heat-transport equations. Pre- and postprocessor features allow the user to calibrate VS2DH models to estimate vertical groundwater/surface-water exchange and also hydraulic conductivity for cases where hydraulic head is known.

Transient Heat Transfer Model of Machine Gun Barrels

The desire to significantly reduce the weight of machine gun barrels while simultaneously increasing their operational life has led to the need to develop a transient heat transfer model that accurately addresses the thermal management problem while simultaneously supporting the execution of rapid trade studies of barrel geometry and material. To address this need, National Technical Systems Ordnance Sciences Division has created a detailed finite-difference based numerical model using the Mathematica software, developed and marketed by Wolfram Research, as the solution platform. This model solves the one-dimensional temperature profile through the thickness of the barrel at a specified axial location.

Simplified account of Rayleigh streaming for the description of nonlinear processes leading to steady state sound in thermoacoustic engines

This paper focuses on the transient regime of wave amplitude growth and stabilization occuring in a standing wave thermoacoustic engine. Experiments are performed on a simple apparatus consisting of an open ended thermoacoustic oscillator with atmospheric air as working fluid. The results show that, even in that simple device, the transient regime leading to steady state sound exhibits complicated dynamics, like the systematic overshoot of wave amplitude before its final stabilization, and the spontaneous and periodic switch on/off of the thermoacoustic instability at constant heat power supply. A simplified model is then presented which describes wave amplitude growth from the coupled equations describing thermoacoustic amplification and unsteady heat transfer. In this model, the assumption of a one-dimensional and exponential temperature profile is retained and the equations describing heat transfer through the thermoacoustic core are substantially simplified into a set of ordinary differential equations. These equations include the description of two processes saturating wave amplitude growth, i.e. thermoacoustic heat pumping and heat convection by acoustic streaming. It is notably shown that accounting for the effect of acoustic streaming allows to reproduce qualitatively the overshoot process.

One-dimensional temperature profile prediction in multi-layered rigid pavement systems using a separation of variables method

This paper presents an analytical solution for prediction of the one-dimensional (1D) time-dependent temperature profile in a multi-layered rigid pavement system. Temperature at any depth in a rigid pavement system can be estimated by using the proposed solution with limited input data, such as pavement layer thicknesses, material thermal properties, measured air temperatures and solar radiation intensities. This temperature prediction problem is modelled as a boundary value problem governed by the classic heat conduction equations, and the air temperatures and solar radiation intensities are considered in the surface boundary condition. Interpolatory trigonometric polynomials, based on the discrete least squares approximation method, are used to fit the measured air temperatures and solar radiation intensities during the time period of interest. The solution technique employs the complex variable approach along with the separation of variables method. A FORTRAN program was coded to implement the proposed 1D analytical solution. Field model validation demonstrates that the proposed solution generates reasonable temperature profile in the concrete slab for a four-layered rigid pavement system during two different time periods of the year.

One-Dimensional Rigid Pavement Temperature Prediction Using Laplace Transformation

AbstractThis paper presents an analytical solution for the prediction of the time-dependent one-dimensional temperature profile in an N-layered rigid pavement system using Laplace transformation. Temperature at any depth in a rigid pavement system can be estimated by using the proposed solution with input data such as pavement layer thicknesses, material thermal properties, and the measured air temperature and solar radiation intensities. The associated initial boundary value problem is governed by the classic heat conduction equation with the air temperature and solar radiation considered in the surface boundary condition. Interpolatory trigonometric polynomials, based on the method of discrete least-squares approximation, are used to fit the measured air temperature and solar radiation intensities during a user-defined time period. The relationship between the constants of integration for the ith layer and the first layer are deduced, which simplifies the solution process. Model validation with the meas...