Local Equilibrium Temperature Research Articles

Flame characteristics and NO emission behaviors of methane/ammonia counterflow premixed flames with opposed N2 or air stream

Behaviors of methane/ammonia counterflow premixed flames and NO emission are numerically and experimentally investigated with opposed N2 or air stream by varying strain rate (ag) and equivalence ratio (ϕ). The premixed stream is 80% methane and 20% ammonia by volume mixed with air considering the utilization of ammonia by blending hydrocarbon fuels. The opposed stream is either N2 or air considering the potential application in gas turbines having single- or two-stage combustion. The simulations are conducted by increasing ag up to flame extinction for a specified ϕ and an experiment is conducted to evaluate various kinetic mechanisms. The extinction strain rate increases monotonically with ϕ with opposed air stream (AS), while increases and then decreases with opposed nitrogen stream (NS). The extinction mechanisms are explained by adopting the concepts of the local equilibrium temperature and heat loss ratio. For lean and rich mixtures with NS and lean mixtures with AS, the extinction occurs due to comparable effects of incomplete reaction and heat loss from the flame to the downstream burnt region. While for rich mixtures with AS, the extinction is attributed mainly to incomplete reaction. The contribution of thermal NO as compared with prompt NO in NO production is weak for all cases with NS and AS. The emission index (EINO) for lean and rich mixtures with NS and for lean mixtures with AS decreases monotonically with the increase of strain rate for all ϕ. Increasing equivalence ratio at a specified ag decreases NO production for lean and rich mixtures with NS and lean mixtures with AS. While for rich mixtures with AS, the EINO increases monotonically with ag. From the reaction pathway analysis, for lean mixtures, the effect of increasing ag on the reduction of NO production is attributed by weakening NH-related reaction paths, while NH2-related reaction paths change little. When ϕ increases for a specified ag with NS, NO production is reduced by weakening NH2-related reaction paths and strengthening NH-related reaction paths. For rich mixtures with AS, increasing ag increases NO production by strengthening NH2-related reaction paths.

Planar phonon anisotropy, and a way to detect local equilibrium temperature in graphene

The effect of inclusion of the planar phonon anisotropy on thermo-electrical behavior of graphene is analyzed. Charge transport is simulated by means of Direct Simulation Monte Carlo technique coupled with numerical solution of the phonon Boltzmann equations based on deterministic methods.The definition of the crystal lattice local equilibrium temperature is investigated as well and the results furnish possible alternative approaches to identify it starting from measurements of electric current density, with relevant experimental advantages, which could help to overcome the present difficulties regarding thermal investigation of graphene.Positive implications are expected for many applications, as the field of electronic devices, which needs a coherent tool for simulation of charge and hot phonon transport; the correct definition of the local equilibrium temperature is in turn fundamental for the study, design and prototyping of cooling mechanisms for graphene-based devices.

Effects of water vapor addition on downstream interaction in CO/O2 counterflow premixed flames

The effects of H2O addition on downstream interaction in counterflow premixed CO/O2 flames are investigated by varying the global strain rate (ag) and CO mole fractions (XCO,L, XCO,U) in the lower and upper nozzles, respectively. For interacting premixed CO/O2 flames, the flammable region is very narrow such that the flames cannot be sustained for ag > 11.75 s−1. When 1.0% vol H2O is added to O2/CO2 mixtures, the flammable region is appreciably extended. At low strain rate, the lean-lean and rich-rich extinction boundaries show strong and weak interactions similar to those observed previously in hydrocarbon fuels. The flammable lean-lean and rich-rich regions gradually shrink with the increase of ag. When XCO,U is small for asymmetric lean double flames at low strain rate, the extinction boundary exhibits weak interaction behavior, where the weaker flame is parasitic to the stronger flame by XCO,L. The stronger flame experiences heat loss to the weaker flame. As the strain increases, the reaction cannot be completed due to the reduction in the flow time. The thermal energy loss by incomplete reaction leads to the flame extinction. This effect changes the qualitative nature of extinction boundary as strain rate increases, resulting in the extinction boundary having only the strong interaction mode having near constant (XCO,L + XCO,U) and bending toward larger XCO,L, and eventually forming an island shape at higher strain rate. The local equilibrium temperature (LET) concept is introduced to explain these flame extinction mechanisms. Local temperature behaviors are well explained by investigating major reaction contributions to heat release rate. In all cases, LET decreases by the effect of preferential diffusion because of the Lewis number of deficient reactant being larger than unity. For asymmetric double flames, conductive heat transfer (CHT) from the stronger to weaker flame reduces the LET of the stronger flame. Flame extinction mechanism can be explained by introducing a loss ratio. For CO/O2 flames, the effects of incomplete reaction as well as preferential diffusion and CHT lead to flame extinction. For (CO/O2 + 1.0% H2O) flames with the increase of strain rate, thermal energy loss by incomplete reaction becomes appreciable, as compared with the effects of preferential diffusion and CHT.

Study of Heat Transfer and Leakage Characteristics of Brush Seals Based on Local Temperature Non-Equilibrium Model

In this study, to improve the accuracy of the brush seal heat transfer model, based on the finite volume method (FVM) coupled with the three-dimensional Reynold-averaged Naviers-Stokes equations (RANS) equations of the Local temperature non-equilibrium (LTNE) model, and a mathematical model of the heat transfer and leakage characteristics of the brush seal was established. The distribution of the pressure, flow and temperature fields of the brush seal are analyzed. User-defined function (UDF) programming was performed for the LTNE model. And the LTNE model is then compared with the local temperature equilibrium (LTE) model in terms of the factors influencing the heat transfer and leakage characteristics. The results show that the maximum brush filament temperature increases with an increases in the pressure ratio, interference, and speed for both models; the fluid flow rate increases with an increases in the pressure ratio, interference, and speed; and the leakage rate increases with an increases in the pressure ratio and decreases with an increases in interference and speed. The maximum temperature of the brush filament under the LTNE model was found to be higher than that under the LTE model, but the maximum temperature difference does not exceed 3.1%. Additionally, the fluid flow rate under the LTNE model was higher than that under the LTE model, and the flow rate difference does not exceed 3.4%. And the leakage rate under the LTNE model was lower than that under the LTE model, and the leakage rates differ by no more than 9.0%. Ultimately, numerical analysis of the brush seal under the LTNE model was found to be more effective and consistent with actual working conditions than alternative models.

Influences of variable porosity on CaO/Ca(OH)2 thermochemical energy storage characteristics in direct/indirect heated reactor

• Influence of variable porosity on CaO/Ca(OH) 2 TCES characteristics is investigated. • Variable porosity significantly influences permeability and heat conductivity. • Constant porosity over/underestimates DHR/IHR performance in dehydration by 9%. • Constant porosity underestimates DHR/IHR performance in hydration by 19%. In the present work, the influences of variable porosity of CaO/Ca(OH) 2 , which is normally regarded as constant, on the thermochemical energy storage characteristics in direct/indirect heated reactor (DHR/IHR), are comprehensively investigated by establishing a transient multi-physics coupled model. It is found that, unlike the traditional constant porosity assumption, the variable porosity shows significantly two-fold competitive impacts. On the one hand, increasing/decreasing porosity increases/decreases the permeability of reaction bed, which leads to the drop/rise in pressure field and further the local reaction equilibrium temperature drop/rise. Thus, the local reaction rate increases/decreases correspondingly. On the other hand, increasing/decreasing porosity also decreases/increases the heat conductivity of the reaction bed, which leads to the drop/rise in transient temperature field. Thus, the transient reaction rate decreases/increases instantaneously. The results indicate that the constant porosity assumption may over/underestimate the performance of DHR/IHR during the charging (dehydration) process by around 9%, while underestimate the performances of both DHR and IHR during discharging (hydration) process by up to around 19%. It is also found that the variable porosity demonstrates greater influence on the discharging (hydration) process in DHR and on the charging (dehydration) process in IHR.

Emissions in short-gated ns/ps/fs-LIBS for fuel-to-air ratio measurements in methane-air flames.

A study of short-gated 10 nanosecond (ns), 100 picosecond (ps), and 100 femtosecond (fs) laser induced breakdown spectroscopy (LIBS) was conducted for fuel-to-air ratio (FAR) measurements in an atmospheric Hencken flame. The intent of the work is to understand which emission lines are available near the optical range in each pulse width regime and which emission ratios may be favorable for generating equivalence ratio calibration curves. The emission spectra in the range of 550-800 nm for ns-LIBS and ps-LIBS are mostly similar with slightly elevated atomic oxygen lines by ps-LIBS. Spectra from fs-LIBS show the lowest continuum background and prominent individual atomic lines, though have significantly weaker ionic emission from nitrogen. A qualitative explanation based on assumed local thermodynamic equilibrium and electron temperatures calculated by the ${{\rm{N}}_{\rm{II}}}({{565}}\;{\rm{nm}})$ and ${{\rm{N}}_{\rm{II}}}({{594}}\;{\rm{nm}})$ emissions is presented. In studying line emission ratios for FAR calculation, it is found that ${{\rm{H}}_\alpha}({{656}}\;{\rm{nm}})/{{\rm{N}}_{\rm{II}}}({{568}}\;{\rm{nm}})$ is best for FAR measurements with ns-LIBS and remains viable for ps-LIBS, while ${{\rm{H}}_\alpha}({{656}}\;{\rm{nm}})/{{\rm{O}}_{\rm I}}({{777}}\;{\rm{nm}})$ is optimal for the ps-LIBS and fs-LIBS cases. Due to low continuum background and short time delay for spectra collection, fs-LIBS is very promising for high-speed FAR measurements using short-gated LIBS.

SN 2010kd: Photometric and Spectroscopic Analysis of a Slow-decaying Superluminous Supernova

Abstract This paper presents data and analysis of SN 2010kd, a low-redshift (z = 0.101) H-deficient superluminous supernova (SLSN), based on ultraviolet/optical photometry and optical spectroscopy spanning between −28 and +194 days relative to B-band maximum light. The B-band light-curve comparison of SN 2010kd with a subset of well-studied SLSNe I at comparable redshifts indicates that it is a slow-decaying PTF12dam-like SLSN. Analytical light-curve modeling using the Minim code suggests that the bolometric light curve of SN 2010kd favors circumstellar matter interaction for the powering mechanism. SYNAPPS modeling of the early-phase spectra does not identify broad H or He lines, whereas the photospheric-phase spectra are dominated by O i, O ii, C ii, C iv, and Si ii, in particular the presence of both low- and high-velocity components of O ii and Si ii lines. The nebular-phase spectra of SN 2010kd are dominated by O i and Ca ii emission lines similar to those seen in other SLSNe I. The line velocities in SN 2010kd exhibit flatter evolution curves similar to SN 2015bn but with comparatively higher values. SN 2010kd shows a higher single-zone local thermodynamic equilibrium temperature in comparison to PTF12dam and SN 2015bn, and it has an upper O i ejected mass limit of ∼10 M ⊙. The host of SN 2010kd is a dwarf galaxy with a high star formation rate (∼0.18 ± 0.04 M ⊙ yr−1) and extreme emission lines.

Infrared and sub-mm observations of outbursting young stars with Herschel and Spitzer

Context. Episodic accretion plays an important role in the evolution of young stars. Although it has been under investigation for a long time, the origin of such episodic accretion events is not yet understood. Aims. We investigate the dust and gas emission of a sample of young outbursting sources in the infrared to get a better understanding of their properties and circumstellar material, and we use the results in a further work to model the objects. Methods. We used Herschel data, from our PI program of 12 objects and complemented with archival observations to obtain the spectral energy distributions (SEDs) and spectra of our targets. We report here the main characteristics of our sample, focussing on the SED properties and on the gas emission lines detected in the PACS and SPIRE spectra. Results. The SEDs of our sample show the diversity of the outbursting sources, with several targets showing strong emission in the far-infrared from the embedded objects. Most of our targets reside in a complex environment, which we discuss in detail. We detected several atomic and molecular lines, in particular rotational CO emission from several transitions from J = 38−37 to J = 4−3. We constructed rotational diagrams for the CO lines, and derived in three domains of assumed local thermodynamic equilibrium (LTE) temperatures and column densities, ranging mainly between 0−100 K and 400−500 K. We confirm correlation in our sample between intense CO J = 16−15 emission and the column density of the warm domain of CO, N(warm). We notice a strong increase in luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the beginning of an outburst.

Methylamine and other simple N-bearing species in the hot cores NGC 6334I MM1–3

Context. In the search for the building blocks of life, nitrogen-bearing molecules are of particular interest since nitrogen-containing bonds are essential for the linking of amino acids and ultimately the formation of larger biological structures. The elusive molecule methylamine (CH3NH2) is thought to be a key pre-biotic species but has so far only been securely detected in the giant molecular cloud Sagittarius B2. Aims. We identify CH3NH2 and other simple nitrogen-bearing species involved in the synthesis of biologically relevant molecules towards three hot cores associated with the high-mass star-forming region NGC 6334I, located at a distance of 1.3 kpc. Column density ratios are derived in order to investigate the relevance of the individual species as precursors of biotic molecules. Methods. High sensitivity, high angular and spectral resolution observations obtained with the Atacama Large Millimeter/ submillimeter Array were used to study transitions of CH3NH2, CH2NH, NH2CHO, and the 13C- and 15N-methyl cyanide (CH3CN) isotopologues, detected towards NGC 6334I. Column densities are derived for each species assuming local thermodynamic equilibrium and excitation temperatures in the range 220–340 K for CH3NH2, 70–110 K for the CH3CN isotopologues and 120–215 K for NH2CHO and CH2NH. Results. We report the first detections of CH3NH2 towards NGC 6334I with column density ratios with respect to CH3OH of 5.9 × 10−3, 1.5 × 10−3 and 5.4 × 10−4 for the three hot cores MM1, MM2, and MM3, respectively. These values are slightly lower than the values derived for Sagittarius B2 but higher by more than an order of magnitude as compared with the values derived for the low-mass protostar IRAS 16293–2422B. The column density ratios of NH2CHO, 13CH3CN, and CH3C15N with respect to CH3OH are (1.5 – 1.9) × 10−4, (1.0 – 4.6) × 10−3 and (1.7 – 3.0) × 10−3 respectively. Lower limits of 5.2, 1.2, and 3.0 are reported for the CH3NH2 to CH2NH column density ratio for MM1, MM2, and MM3 respectively. These limits are largely consistent with the values derived for Sagittarius B2 and higher than those for IRAS 16293–2422B. Conclusions. The detections of CH3NH2 in the hot cores of NGC 6334I hint that CH3NH2 is generally common in the interstellar medium, albeit that high-sensitivity observations are essential forthe detection of the species. The good agreement between model predictions of CH3NH2 ratios and the observations towards NGC 6334I indicate a main formation pathway via radical recombination on grain surfaces. This process may be stimulated further by high grain temperatures allowing a lager degree of radical mobility. Further observations with ALMA will help evaluate the degree to which CH3NH2 chemistry depends on the temperature of the grains in high- and low-mass star-forming regions respectively.

Low levels of methanol deuteration in the high-mass star-forming region NGC 6334I

Context. The abundance of deuterated molecules in a star-forming region is sensitive to the environment in which they are formed. Deuteration fractions, in other words the ratio of a species containing D to its hydrogenated counterpart, therefore provide a powerful tool for studying the physical and chemical evolution of a star-forming system. While local low-mass star-forming regions show very high deuteration ratios, much lower fractions are observed towards Orion and the Galactic centre. Astration of deuterium has been suggested as a possible cause for low deuteration in the Galactic centre. Aims. We derive methanol deuteration fractions at a number of locations towards the high-mass star-forming region NGC 6334I, located at a mean distance of 1.3 kpc, and discuss how these can shed light on the conditions prevailing during its formation. Methods. We use high sensitivity, high spatial and spectral resolution observations obtained with the Atacama Large Millimeter/ submillimeter Array to study transitions of the less abundant, optically thin, methanol-isotopologues: 13CH3OH, CH318OH, CH2DOH and CH3OD, detected towards NGC 6334I. Assuming local thermodynamic equilibrium (LTE) and excitation temperatures of ~120–330 K, we derive column densities for each of the species and use these to infer CH2DOH/CH3OH and CH3OD/CH3OH fractions. Results. We derive column densities in a range of (0.8–8.3) × 1017 cm−2 for 13CH3OH, (0.13–3.4) × 1017 cm−2 for CH318OH, (0.03–1.63) × 1017 cm−2 for CH2DOH and (0.15–5.5) × 1017 cm−2 for CH3OD in a ~1″ beam. Interestingly, the column densities of CH3OD are consistently higher than those of CH2DOH throughout the region by factors of 2–15. We calculate the CH2DOH to CH3OH and CH3OD to CH3OH ratios for each of the sampled locations in NGC 6334I. These values range from 0.03% to 0.34% for CH2DOH and from 0.27% to 1.07% for CH3OD if we use the 13C isotope of methanol as a standard; using the 18 O-methanol as a standard, decreases the ratios by factors of between two and three. Conclusions. All regions studied in this work show CH2DOH/CH3OH as well as CH2DOH/CH3OD values that are considerably lower than those derived towards low-mass star-forming regions and slightly lower than those derived for the high-mass star-forming regions in Orion and the Galactic centre. The low ratios indicate a grain surface temperature during formation ~30 K, for which the efficiency of the formation of deuterated species is significantly reduced. Therefore, astration of deuterium in the Galactic centre cannot be the explanation for its low deuteration ratio but rather the high temperatures characterising the region.

Effect of thickness of insulation coating on temperature of electrically exploded tungsten wires in vacuum

This paper reports an interesting observation of great differences in the temperature of exploded wires with insulation coating of different thicknesses. Two kinds of polyimide-coated tungsten wires were used with the same conductive diameter 12.5 μm but a different thickness of coating, 0.75–2.25 μm and 2.25–4.25 μm, respectively. The specific energy reconstructed from the current and voltage signals was quite close for the tested wires. However, the exploding scenario, obtained from Mach-Zehnder interferograms, showed great differences: a neutral outer-layer was observed around the thick-coated wire, which was absent for the thin-coated wire; and the calculated electron density and local thermal equilibrium temperature were much higher for thick-coated wires. The heat-preserving neutral layer formed by the decomposition of the insulation was supposed to be the cause of this phenomenon.

Radiative heat transfer and nonequilibrium Casimir-Lifshitz force in many-body systems with planar geometry

A general theory of photon-mediated energy and momentum transfer in N-body planar systems out of thermal equilibrium is introduced. It is based on the combination of the scattering theory and the fluctuational-electrodynamics approach in many-body systems. By making a Landauer-like formulation of the heat transfer problem, explicit formulas for the energy transmission coefficients between two distinct slabs as well as the self-coupling coefficients are derived and expressed in terms of the reflection and transmission coefficients of the single bodies. We also show how to calculate local equilibrium temperatures in such systems. An analogous formulation is introduced to quantify momentum transfer coefficients describing Casimir-Lifshitz forces out of thermal equilibrium. Forces at thermal equilibrium are readily obtained as a particular case. As an illustration of this general theoretical framework, we show on three-body systems how the presence of a fourth slab can impact equilibrium temperatures in heat-transfer problems and equilibrium positions resulting from the forces acting on the system.

Selection of the optimal combination of water vapor absorption lines for detection of temperature in combustion zones of mixing supersonic gas flows by diode laser absorption spectrometry

Determination of a gas medium temperature by diode laser absorption spectrometry (DLAS) is based on the measurement of integral intensities of the absorption lines of a test molecule (generally water vapor molecule). In case of local thermodynamic equilibrium temperature is inferred from the ratio of the integral intensities of two lines with different low energy levels. For the total gas pressure above 1 atm the absorption lines are broadened and one cannot find isolated well resolved water vapor absorption lines within relatively narrow spectral interval of fast diode laser (DL) tuning range (about 3 cm −1 ). For diagnostics of a gas object in the case of high temperature and pressure DLAS technique can be realized with two diode lasers working in different spectral regions with strong absorption lines. In such situation the criteria of the optimal line selection differs significantly from the case of narrow lines. These criteria are discussed in our work. The software for selection the optimal spectral regions using the HITRAN-2012 and HITEMP data bases is developed. The program selects spectral regions of DL tuning, minimizing the error of temperature determination δТ/T , basing on the attainable experimental error of line intensity measurement δS . Two combinations of optimal spectral regions were selected – (1.392 & 1.343 μm) and (1.392 & 1.339 μm). Different algorithms of experimental data processing are discussed.

PREDICTIONS FOR OBSERVING PROTOSTELLAR OUTFLOWS WITH ALMA

Protostellar outflows provide a means to probe the accretion process of forming stars and their ability to inject energy into their surroundings. However, conclusions based on outflow observations depend upon the degree of accuracy with which their properties can be estimated. We examine the quality of Atacama Large Millimeter/submillimeter Array (ALMA) observations of protostellar outflows by producing synthetic 12CO(1-0) and 13CO(1-0) observations of numerical simulations. We use various ALMA configurations, observational parameters, and outflow inclinations to assess how accurately different assumptions and setups can recover underlying properties. We find that more compact arrays and longer observing times can improve the mass and momentum recovery by a factor of two. During the first ∼0.3 Myr of evolution, 12CO(1-0) is optically thick, even for velocities km s−1, and outflow mass is severely underestimated without an optical depth correction. Likewise, 13CO(1-0) is optically thick during the first Myr. However, underestimation due to shorter observing time, missing flux, and optical depth are partially offset by the assumption of local thermodynamic equilibrium and higher excitation temperatures. Overall, we expect that full ALMA 13CO(1-0) observations of protostellar sources within 500 pc with observing times hr and assumed excitation temperatures of K will reliably measure mass and line of sight momentum to within 20%.

Quantification of extinction mechanism in counterflow premixed flames

The extinction mechanisms of stretched premixed flames have been investigated numerically for the fuels of CH4, C3H8, H2, CO and for the mixture fuels of CH4+H2 and CO+H2 by adopting symmetric double premixed flames in a counterflow configuration. The local equilibrium temperature concept was used as a measure of energy loss or gain in order to quantify the extinction mechanism by preferential diffusion and/or incomplete reaction. The energy loss ratio from preferential diffusion arising from non-unity Lewis number and the loss ratio from incomplete reaction were calculated at various equivalence ratios near flame extinction. The results showed that the extinction of lean H2, CH4, CH4+H2, CO+H2, and rich C3H8 premixed flames was caused by incomplete reaction due to insufficient reaction time, indicating that the effective Lewis number was smaller than unity, while the effect of preferential diffusion resulted in energy gain. However, the extinction of rich H2, CH4, CH4+H2, CO+H2, and lean C3H8 premixed flames was affected by the combined effects of preferential diffusion and incomplete reaction indicating that the effective Lewis number was larger than unity. In CO premixed flames, incomplete reaction was dominant in both lean and rich cases due to the effective Lewis number close to unity. The effect of H2 mixing to CO is found to be quite significant as compared to CH4+H2 cases, which can alter the flame behavior of CO flames to that of H2.

A continuum constitutive model and computational method of explosive detonation

Some basic thermodynamic relationships are used to develop a theroretical framework for modeling the detonation in explosives, on the assumption that explosive and detonation product are in a local thermodynamic equilibrium state, i.e., their pressures and temperatures are identical. Using this framework, a continuum constitutive model for explosive detonation is composed of a group of ordinary differential equations including the state equations of explosive and its product, simple mixing law, reaction rate equation and energy conservation equation, which are easily solved by a mature computational method such as trapezoidal rule. A group of nonlinear constitutive equations in a generalized Maxwellian form describe the relationship among the time evolution rates of pressure and temperature, the strain rate, and the chemical reaction rate. Coefficients appearing in the constitutive equations are determined only by parameters of the explosive and the product through using simple mixing rule. The continuum constitutive model and the corresponding computational method are verified by simulating the detonation behaviour of PBX9404 impacted by high velocity Cu flyer, and in the simulation the JWL equation of state for unreacted explosive and detonation product and the two-term Lee-Tarver reaction rate equation are adopted.

Temperature in nonequilibrium states and non-Fourier heat conduction

Macroscopic models beyond Fourier's law for fast-transient heating and heat transport in nanosystems have been proposed. Consequently, some basic quantities such as entropy and temperature need to be modified. From the viewpoint of the thermomass theory, we show that in nonequilibrium systems where heat conduction occurs, the static pressure of thermomass is lower than the total pressure, corresponding to a nonequilibrium temperature lower than the local-equilibrium temperature. The definition of entropy is also modified since the phonon kinetic energy conserves the ability to do work. The nonequilibrium temperature based on the thermomass theory is close to that in the extended irreversible thermodynamics. The microscopic foundation is explored through a phonon Boltzmann derivation. The higher-order contributions to the distribution function are found to be responsible for such modification of temperature. Therefore, the thermomass model gives not only non-Fourier conduction law, but also a physical picture about modified state variables in nonequilibrium states.

Fully covariant radiation force on a polarizable particle

The electromagnetic force on a polarizable particle is calculated in a covariant framework. Local equilibrium temperatures for the electromagnetic field and the particle's dipole moment are assumed, using a relativistic formulation of the fluctuation–dissipation theorem. Two examples illustrate radiative friction forces: a particle moving through a homogeneous radiation background and above a planar interface. Previous results for arbitrary relative velocities are recovered in a compact way.

Phonon temperature and electron temperature in thermoelectric coupling

We develop a mesoscopic model of thermoelectric coupling in nanosystems, allowing for different phonon and electron temperatures, and mutual energy exchange. Its compatibility with the second law of thermodynamics is proved. By comparisons with other theoretical proposals, the different coefficients involved in the model are identified. We consider two illustrations: (a) for systems where the electron mean-free path is considerably shorter than the phonon mean-free path, the non-equilibrium phonon temperature may be different with respect to the local-equilibrium temperature of electrons; (b) for systems with large electron mean-free path, one may have the so-called “hot electrons,” namely, electrons having a higher temperature than that of the phonons.

Modeling and simulation of dendrite growth in solidification of Al-Si-Mg ternary alloys

Based on a previously cellular automaton (CA) model for Al-Si binary alloys, a modified cellular automaton (MCA) model is developed to numerically simulate the dendrite growth and microsegregation of Al-Si-Mg ternary alloys. By direct coupling PanEngine, the MCA model can obtain thermodynamic data for dendrite growth of ternary alloys in real time, such as equilibrium liquidus temperature, partition coefficient and liquidus slope of two solute elements. In the model, the normal velocity of the interface cell can not be derived only by solving the solute conservation equation, and must be simultaneously coupled with dimensionless solute supersaturation equation for each alloying element and local equilibrium temperature equation at the S/L interface. All the equations of the MCA model are solved by finite difference method on a uniform mesh. By considering local curvature and constitutional undercooling, solute diffusion and solute redistribution at the S/L interface, the MCA model can simulate the columnar dendrite growth and the solidification path of the equiaxed dendrite growth.