Assumption Of Local Equilibrium Research Articles

Interpretation of temperature measurements by the Boltzmann plot method on spatially integrated plasma oxygen spectral lines

In thermal plasma spectroscopy, the Boltzmann plot method is particularly popular for measuring plasma temperature independently of pressure. In order to better understand the results of the Botzmann plot measurements performed with atomic oxygen lines on our thermal plasma, which has a non-negligible thickness, a Python code was developed based on the assumption of local thermodynamic equilibrium (LTE) and the calculated plasma composition and properties. This code allows us to simulate a measurement of the oxygen line intensity resulting from an integration over the plasma thickness in a chosen direction for a given temperature profile. From these a simulated Boltzmann plot gave us a simulated temperature. It resulted that this measurement is governed by the maximum of the temperature profile until the maximum temperature exceeds that of the maximum emissivity of the atomic oxygen lines. Above that temperature a limitation was observed, it is possible to measure higher temperatures but the interpretation of that measurement is difficult. Plasma pressure has a limited effect on this limitation. When no limitation is observed, the temperature measurement from the Boltzmann plot method that we simulated is always at least 90% of the maximum of the temperature profile.

Calculation of thermodynamic properties and transport coefficients of Ar-C-Si plasma

The compositions, thermodynamic properties and transport coefficients of the argon-carbon-silicon plasma at local thermodynamic equilibrium and local chemical equilibrium in temperatures range of 300－30000 K and pressure range of 0.1 to 10 atm and are different mixture ratios are investigated in this work. The condensed phases and Debye-Hückel corrections are both taken into account. The equilibrium component in gas phase is calculated by mass action law (Saha’s law and Gulberg-Waage’s law), Dalton’s partial pressure law, conservation of the elements and charge quasi-neutral equation, and at the same time the condensed species is calculated under the assumption of local phase equilibrium. Thermodynamic properties including density, enthalpy and specific heat are evaluated through a classical statistical mechanics approach. The transport coefficient calculations including viscosity, electrical conductivity, and thermal conductivity are carried out by using a third-order approximation (second-order for viscosity) of the Chapman-Enskog method. Collision integrals are obtained by using the relatively new data. The results show that the concentration and ratio of blend of C vapor and Si vapor can greatly affect the properties of the Ar plasma owing to the introduced C and Si vapor’ s own properties and their new reactions. While the pressure influences those properties through the shift of chemical equilibrium and the change of total number density. In addition, the introduction of condensed species leads the thermodynamic properties and transport coefficients of the lower temperature plasma to become almost the same as those of pure argon, and causes discontinuous points at phase-transition temperature. The final calculation results are in good agreement with those in the literature, and the slight difference in transport coefficient between them can be explained by the different selection of interaction potentials. The results are expected to provide reliable basic data for the numerical simulation of argon-carbon-silicon plasma.

Effect of rolling temperature on microstructure and mechanical properties of medium manganese steel

The effect of rolling temperature on the incomplete recrystallization behavior and the relationship to mechanical properties in 0.06C–4Mn-1.2Cr (wt.%) steel was investigated. Three plates of experimental steel were produced by hot rolling at different temperatures and intercritical annealing processes in this study. The microstructure of experimental steels was examined by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The mechanical properties of test steel were examined by impact test and tensile test. Austenite reversion and cementite precipitation-dissolution was numerically simulated under the assumption of local equilibrium. With the decrease of hot rolling temperature from 1000 °C to 800 °C, the uniform equiaxed prior austenite grains microstructures changed to heterogeneous microstructures of laminated and ultrafine prior austenite grains arranged alternatively. The tensile and impact tests revealed that the medium manganese steels rolling at 800 °C had an excellent combination of mechanical properties. Elongation had a great relationship with retained austenite fraction and stability. The fractography of impact specimens was examined to explore the toughening mechanism of the micro-laminated steels. The steel with uniform equiaxed grain structure exhibited a relatively low tensile strength of 750 MPa and low elongation of ∼20% and an extremely poor low-temperature toughness of ∼40 J at −40 °C. An enhanced low-temperature toughness (∼233 J at −40 °C), as well as an improved tensile strength (823 MPa) and higher elongation of ∼40%, was obtained in the steel with heterogeneous microstructures. The content of austenite in heterogeneous microstructure is twice that in uniform equiaxed grain structure. And cementite dissolved more thoroughly in the heterogeneous microstructure. The high austenite content of heterogeneous microstructures enabled the steel to be significantly stronger and ductile, which contributed to the high tensile strength and elongation to some extent. It is concluded that the effect of interface decohesion resulted in the occurrence of delamination. And the high austenite content and delamination greatly improved the low-temperature toughness of experimental steel.

Modeling evaluation of physiochemical processes controlling gas migration in shallow groundwater systems

Gases may be released into shallow groundwater systems during energy development and geological carbon storage (commonly referred to as gas migration, GM) and can result in greenhouse gas emissions, safety concerns, and the reduction of groundwater quality. The physiochemical processes occurring during GM, including gas release, movement, partitioning, and dissolved-phase transport in the saturated groundwater zone, are difficult to characterize and model; however, modeling is important to develop strategies for detecting and monitoring GM and formulate conceptual models to describe GM at impacted sites. In this study, a previously developed numerical model, which coupled macroscopic invasion percolation (macro-IP) and multicomponent mass transfer, was enhanced to simulate gas releases in the shallow subsurface. Evaluation of the effects of the coupled physiochemical processes was performed by comparing model simulations to previously conducted bench-scale gas injection experiments. Results show that gas flow is highly sensitive to the entry pressures assigned within the model domain and the critical gas saturation (Sg,crit) used to model gas-water flow based on macro-IP; however, mass transfer and the resulting domain-scale dissolved-gas transport were relatively insensitive to these parameters. Multicomponent mass transfer, considering not only the partitioning of the released gas, but also the dissolved background gases ubiquitous in shallow groundwater, was vitally important to simulate dissolution and the resulting free-phase gas distribution within the experimental systems. The use of the local equilibrium assumption for gas-water mass transfer could not consistently describe the experimental observations. Overall, the modeling evaluation performed in this study provides improved understanding of the key processes controlling GM in the shallow subsurface and will advance efforts including up-scaling and scenario testing to accurately quantify the environmental impacts of GM.

Structure-based simulation of mass transfer in turbulent fluidized beds without local equilibrium assumption

Traditional methods based on local equilibrium assumption are unsuitable to describe the non-linear and non-equilibrium mass transfer in turbulent fluidized beds (TFBs), especially for industrial-scale reactors. In this work, the structure-based mass balance equations are proposed to describe the transfer and reaction of component on the surface of particles. These equations are valid and reasonable whether mass transfer and chemical reaction are in local equilibrium or not. Since local equilibrium assumption is not used, the proposed method can directly describe the transfer-reaction systems in TFBs, which are not in local equilibrium. Moreover, the proposed mass balance equations have also considered the meso-scale flow of particles. This can better reflect the transfer of component caused by the convection of particles in TFBs than the traditional models. The accuracy of the present model prediction was confirmed by comparison of the predicted results and the experimentation being available in literatures.

A lumped parameter model of continuous/dispersed phases mass transfer for simulating in-vessel corium stratification transients

In the frame of in-vessel corium modelling, this paper proposes an enhanced integral model in order to simulate the liquid phases stratification transients associated with the miscibility gap in the O,U,Zr,steel system. An important feature of this model is that it explicitly takes into account mono-dispersed metal phases in the continuous oxide phase. These droplets can either come from a direct molten steel relocation or be detached by Rayleigh–Taylor instabilities at the interface between the heavy or light metal layers and the oxide layer of the stratified pool. At all interfaces between metal and oxide phases, a same consistent local equilibrium assumption (based on a same simplified thermodynamic representation of the liquid miscibility gap) is made.A limited parametric analysis is reported. It highlights the possible impact of direct molten steel relocation into the oxide phase in comparison with a relocation on the top of the pool. Indeed, the U,Zr enrichment of the metal droplets during their residence time in the oxide phase significantly affects the remainder of the stratification transients in all cases. The parameters that affect this mass transfer are shown to have a significant impact on the overall stratification kinetics. These results also highlight an important qualitative difference between the two kinds of stratification transients: heavy metal phase formation or stratification inversion. In the latter, the heavy metal phase average composition always stays close to its interface composition equilibrium with the oxide and, accordingly, when the density criterion associated with the Rayleigh–Taylor instability is met, the heavy metal layer is, in most cases, completely relocated at the top of the pool. During the heavy metal phase formation, the situation is drastically different as the light metal layer is not initially close to equilibrium with the oxide in such a way that several intermittent droplets detachment are predicted.These different trends are reported taking into account the model underlying hypotheses and the path to move forward and increase knowledge about stratification kinetics is discussed.

Evolution of Turbulence and Its Modification by Axial Casing Grooves in a Multi-Stage Axial Compressor

Abstract This experimental study examines the evolution of turbulence across an axial compressor and its modification by semicircular axial casing grooves (ACGs) at the pre-stall and near the best efficiency (BEP) flowrates. The turbulence is highly anisotropic and spatially inhomogeneous, with each normal Reynolds stress component evolving differently. Most of the observed trends can be explained by examining the dominant production rate terms. At the pre-stall flowrate, the turbulence increases significantly upon entering the rotor with peak RMS values of axial velocity fluctuations reaching as high as 71% of the mean axial velocity. The region with elevated turbulent kinetic energy (TKE) covers 30% of the outer span near the rotor leading edge, expanding to 50% near the trailing edge. While the TKE in the outer span decays rapidly in the stator, the local turbulence production persists in the stator blade boundary layer. By stabilizing and homogenizing the flow, the ACGs reduce the turbulence production, hence the TKE, in the rotor and the stator. The only exception is an increase in turbulence in the region dominated by groove–passage flow interactions. Near BEP, the TKE is much lower everywhere, except for the region influenced by the outflow from grooves. Downstream of the rotor and the stator, the turbulence level with or without ACGs are similar. The large variations in the magnitude and even the sign of the measured eddy viscosity highlight the extreme non-equilibrium conditions over the entire machine, questioning the fundamental assumptions of local equilibrium in eddy viscosity-based Reynolds stress models.

Influence of local thermal non-equilibrium on enhanced geothermal system

Effective development of hot dry rock depends on complex fracture network formed by the enhanced geothermal system. Different scales of mass and heat transfer environment are formed between tight matrix and different fractures, which leads to the complexity of mass and heat transfer process of porous media. In order to analyze the influence of local thermal non-equilibrium on the mass and heat transfer process of complex fracture system, a micro pore scale mass and heat transfer model considering local non-thermal equilibrium is established. The microscopic mechanism of the effect of local non-thermal equilibrium assumption on mass and heat transfer process in matrix-fracture system is revealed. An embedded discrete fracture model considering local thermal non-equilibrium assumption and the solution method are also established. The necessity of considering local thermal non-equilibrium is analyzed by studying the sensitivity of formation physical parameters. The results show that ignoring the local thermal non-equilibrium assumption will underestimate the rock temperature near the fracture zone and overestimate the fluid temperature in the heat transfer front zone. The effect of local thermal non-equilibrium on the enhanced geothermal system is mainly reflected in the early stage of injection. The higher the injection intensity, the lower the matrix fracture permeability, the greater the matrix fracture porosity difference, the greater the rock thermal diffusion coefficient, the smaller the convective heat transfer coefficient, the more it is necessary to consider the local thermal non-equilibrium assumption. The research results can provide reference for the collection and collation of field data.

Turbulent kinetic energy evolution in turbulent boundary layers during head-on interaction of premixed flames with inert walls for different thermal boundary conditions

The statistical behaviour of turbulent kinetic energy, and its transport in turbulent boundary layers during premixed flame-wall interaction for isothermal and adiabatic chemically inert walls have been analysed using a Direct Numerical Simulation (DNS) database. The terms due to the mean velocity gradient (commonly known as the production term) and viscous dissipation remain leading order contributors to the turbulent kinetic energy transport when the flame is away from the wall, similar to that in the corresponding non-reacting turbulent boundary layer, but in addition to these terms, the pressure dilatation and pressure transport contributions play leading order roles when the flame interacts with the wall. It has been found that the gradient hypothesis-based Reynolds stress closures in the context of the k−ε model may yield an inaccurate prediction of the mean velocity gradient term due to the counter-gradient behaviour of Reynolds stresses in the premixed flame cases considered in this analysis. The thermal boundary condition at the wall does not have a major influence apart from a higher wall friction velocity for adiabatic boundary condition than in the case of isothermal boundary condition. The assumption of local equilibrium of production and dissipation of turbulent kinetic energy has been found to be rendered invalid when the flame is either near to the wall or interacting with the wall. This invalidates the conventional log-law for mean streamwise velocity variation, and the wall functions derived based on production-dissipation balance equipped by the usual gradient hypothesis in the context of the standard k−ε model for premixed flame-wall interaction in turbulent boundary layers. Therefore, improved wall functions are necessary for Reynolds averaged Navier-Stokes simulations of premixed flame-wall interaction in turbulent boundary layers.

Millimetre-wave spectroscopy of 2-hydroxyprop-2-enal and an astronomical search with ALMA

Context. Several sugar-like molecules have been found in the interstellar medium (ISM). The molecule studied in this work, 2-hydroxyprop-2-enal, is among the candidates to be searched for, as it is a dehydration product of C3 sugars and contains structural motifs that are typical for some interstellar molecules. Furthermore, it has recently been predicted that it is more abundant in the ISM than its tentatively detected isomer 3-hydroxypropenal. Aims. So far, only low-frequency microwave data of 2-hydroxyprop-2-enal have been published. The aim of this work is to deepen our knowledge about the millimetre-wave spectrum of 2-hydroxyprop-2-enal, enabling its detailed search towards astronomical objects. In particular, we target the solar-type protostar IRAS 16293-2422 and the star-forming region Sagittarius (Sgr) B2(N). Methods. The rotational spectrum of 2-hydroxyprop-2-enal was measured and analysed in the frequency regions of 128-166 GHz and 285-329 GHz. The interstellar exploration towards IRAS 16293-2422 was based on the Atacama Large Millimeter/submillimeter Array (ALMA) data of the Protostellar Interferometric Line Survey (PILS). We also used the imaging spectral line survey ReMoCA performed with ALMA towards Sgr B2(N) to search for 2-hydroxyprop-2-enal in the ISM. We modelled the astronomical spectra under the assumption of local thermodynamic equilibrium (LTE). Results. We provide laboratory analysis of hundreds of rotational transitions of 2-hydroxyprop-2-enal in the ground state and the lowest lying excited vibrational state. We report its non-detection towards IRAS 16293 B. The 2-hydroxyprop-2-enal/3-hydroxypropenal abundance ratio is estimated to be ≲0.9–1.3, in agreement with the predicted value of ~1.4. We report the non-detection of 2-hydroxyprop-2-enal towards the hot molecular core Sgr B2(N1), and we did not detect the related aldehydes 2-hydroxypropanal and 3-hydroxypropenal either. We find that these three molecules are at least nine, four, and ten times less abundant than acetaldehyde in this source, respectively. Conclusions. Despite the non-detections of 2-hydroxyprop-2-enal, the results of this work represent a significant improvement on previous investigations in the microwave region and meet the requirements for further searches for this molecule in the ISM.

Real-time analysis of the fine particles in volcanic plumes: A pilot study of Laser Induced Breakdown Spectroscopy with Calibration-Free approach (CF-LIBS)

Volcanic plumes are rich in fine juvenile ash, representing magma fragments expelled from the crater during explosive eruptions. The composition of fine ash is of primary importance for volcano monitoring and hazard assessment, but not much effort has been put until now to build portable instrumentation allowing real-time measurements. In this paper, a laboratory experiment is carried out to build and test an apparatus based on Calibration-Free Laser Induced Breakdown Spectroscopy (CF-LIBS). This methodology is extremely promising because it does not require any standard calibration strategies and the elemental composition is directly obtained by the laser-induced breakdown optical emission. In the experiment, volcanic ash samples are suspended in the air by a laser-induced shockwave in a dedicated chamber, as to mimic the conditions of a volcanic plume, and contemporaneously the laser-induced plasma (LIP) spectrum is analyzed. After spectrum acquisition, the quantitative analysis is performed using the so-called Calibration-Free (CF) analytical method, which is based on the assumption of plasma local thermodynamic equilibrium (LTE). Results show that by such methodology it is possible to measure ash composition in real-time, during its dispersion, with good precision. Based on the result of this experiment, the construction of a portable instrument to be used in the field for the monitoring of active volcanoes could be possible in the future.

Gas Dynamics Processes above the Polymers Surface under Irradiation with Broadband High-Brightness Radiation in the Vacuum Ultraviolet Spectrum Region.

Obtaining new data on the gas-dynamic responses from the polymer samples (polytetrafluoroethylene, PTFE) irradiated by powerful VUV radiation from compressed plasma flows is in the focus of the present study. An erosion type magnetoplasma compressor (MPC), a type of plasma focus discharge, was used as a radiation source. The operating voltages of the MPC were between 15 and 25 kV, the maximum measured discharge current was 200 kA, and the radiation energy in the VUV range was ≈1–2 kJ. The VUV fluxes on the sample surface were high and equal to ≈1022–1024 photons cm−2·s−1. Double-exposure laser holographic interferometry and schlieren photography were used to diagnose and visualize the gas-dynamic structures. The spatial distribution of the parameters (temperature, pressure and concentrations of electrons and ions) was defined based on the assumption of local thermodynamic equilibrium. It has been demonstrated that the maximum temperature ranged from ≈ 10 to 15 kK in the plasma layer. The electron concentration was ≈ (0.7–1.6) × 1018 cm−3 in this region. The used techniques of optical diagnostics and procedures of result processing make it possible to obtain data on the dynamics of polymer ablation, which occurs when their surface is exposed to powerful energy fluxes (thermal, shock-wave, radiation, and other extreme loads).

A Non-Equilibrium multiphysics model for coal seam gas extraction

Current permeability models are normally derived on the assumption of local equilibrium between coal matrixes and fracture within the representative elementary volume (REV) during gas extraction/injection. Under this assumption, the gas pressure and its associated swelling strain will distribute uniformly throughout the entire REV irrespective of the equilibration process between coal matrixes and fracture. This uniform distribution has long been considered as the reason why current permeability models cannot explain permeability data as widely reported. Significant efforts have been made to resolve this issue for the last decade but all these efforts ignore the transient nature of local equilibration evolution from initial to ultimate equilibrium states. In this study, we developed a concept of local non-equilibrium index (LNEI) to define a complete permeability model under the influence of gas extraction/injection. The application of this concept transforms equilibrium permeability models to non-equilibrium ones. Equilibrium models represent only two end points (before gas extraction/injection and after the completion of gas extraction/injection) while our non-equilibrium one represents the complete evolution of coal permeability between two end points. Our non-equilibrium model is degenerated to replicate all equilibrium models as reported in the literature and used as a key cross-coupling relation to formulate the non-equilibrium multiphysics model. Our non-equilibrium multiphysics model is verified against two rare experimental data sets and applied to predict the effects of the local equilibration process on both the evolution of coal permeability and the gas production under field conditions.

Coupled flow and transport simulation involving rate-limited adsorption in highly heterogeneous unconfined aquifers using a local strong form meshless method

Adsorption plays a vital role in contaminant transport in groundwater. Generally, a local equilibrium assumption is used in which the retardation factor is derived from aquifer material and contaminant type. However, for problems involving faster seepage velocities, this assumption becomes invalid and the mass transfer between mobile and immobile or, sorbed phases of contaminant becomes rate-limited. Traditionally, finite difference method (FDM) models are employed for contaminant transport simulation with rate-limited adsorption (RLA). Nonetheless, due to the presence of a grid, these models show instabilities, especially for advection dominant problems. In the present study, a meshless Radial Point Collocation Method (RPCM-RLA) is proposed for contaminant transport simulation with rate-limited adsorption. The proposed model is verified with semi-analytical solutions and its efficacy is assessed with the popularly used FDM-based Reactive Transport in 3 Dimensions (RT3D) model. The RPCM-RLA model is observed to provide stable and accurate solutions even for advection dominant problems whereas RT3D model simulations show excessive numerical dispersion. Furthermore, the effectiveness of RPCM-RLA model is demonstrated in two case studies concerning heterogeneous unconfined aquifers by comparing it with RT3D. Both model simulations agree consistently with maximum values of normalized mean absolute error (NMAE) being 0.0055 and 0.031 for case studies 1 and 2 respectively, with better performance of RPCM-RLA model.

Resolving desorption of complex organic molecules in a hot core

Context. The presence of many interstellar complex organic molecules (COMs) in the gas phase in the vicinity of protostars has long been associated with their formation on icy dust grain surfaces before the onset of protostellar activity, and their subsequent thermal co-desorption with water, the main constituent of the grains’ ice mantles, as the protostar heats its environment to ~100 K. Aims. Using the high angular resolution provided by the Atacama Large Millimetre/submillimetre Array (ALMA), we want to resolve the COM emission in the hot molecular core Sagittarius B2 (N1) and thereby shed light on the desorption process of COMs in hot cores. Methods. We used data taken as part of the 3 mm spectral line survey Re-exploring Molecular Complexity with ALMA (ReMoCA) to investigate the morphology of COM emission in Sagittarius B2 (N1). We also used ALMA continuum data at 1 mm taken from the literature. Spectra of ten COMs (including one isotopologue) were modelled under the assumption of local thermodynamic equilibrium (LTE) and population diagrams were derived for these COMs for positions at various distances to the south and west from the continuum peak. Based on this analysis, we produced resolved COM rotation temperature and column density profiles. H2 column density profiles were derived from dust continuum emission and C18O 1–0 emission and used to derive COM abundance profiles as a function of distance and temperature. These profiles are compared to astrochemical models. Results. Based on the morphology, a rough separation into O- and N-bearing COMs can be done. The temperature profiles span a range of 80–300 K with power-law indices from −0.4 to −0.8, which is in agreement with expectations of protostellar heating of an envelope with optically thick dust. Column density and abundance profiles reflect a similar trend as seen in the morphology. While abundances of N-bearing COMs peak only at the highest temperatures, those of most O-bearing COMs peak at lower temperatures and remain constant or decrease towards higher temperatures. Many abundance profiles show a steep increase at ~100 K. To a great extent, the observed results agree with results of astrochemical models that, besides the co-desorption with water, predict that O-bearing COMs are mainly formed on dust-grain surfaces at low temperatures, while at least some N-bearing COMs and CH3CHO are substantially formed in the gas phase at higher temperatures. Conclusions. Our observational results, in comparison with model predictions, suggest that COMs that are exclusively or, to a great extent, formed on dust grains desorb thermally at ~100 K from the grain surface, likely alongside water. A dependence on the COM binding energy is not evident from our observations. Non-zero abundance values below ~100 K suggest that another desorption process of COMs is at work at these low temperatures: either non-thermal desorption or partial thermal desorption related to the lower binding energies experienced by COMs in the outer, water-poor ice layers. In either case, this is the first time that the transition between two regimes of COM desorption has been resolved in a hot core.

Numerical Simulation of Helium Arc at High Pressure and Low Current

A computational fluid dynamics (CFD) model has been developed to investigate the time evolution of a helium plasma discharge at high pressures (from 2 to 8 MPa) and low electric current (0.35 A), including the interaction between the plasma and the electromagnetic fields, under local thermodynamic equilibrium (LTE) assumption. To account for pressure dependence, novel thermodynamic and transport properties have been calculated in a wide pressure and temperature range. The model has been further improved by considering the effect of plasma–electrode interactions and the formation of the plasma sheath. High-performance computing (HPC) was used to solve the CFD simulation, focusing on reference cases at 8 MPa and 0.35 A. Numerical results have shown that the sheath model and updated transport and thermodynamic properties have a significant impact on the electric potential, resulting in very good agreement between the simulation and experimental values.

Plasma environmental effects in the atomic structure for simulating x-ray free-electron-laser-heated solid-density matter.

High energy density (HED) matter exists extensively in the Universe, and it can be created with extreme conditions in laboratory facilities such as x-ray free-electron lasers (XFEL). In HED matter, the electronic structure of individual atomic ions is influenced by a dense plasma environment, and one of the most significant phenomena is the ionization potential depression (IPD). Incorporation of the IPD effects is of great importance in accurate modeling of dense plasmas. All theoretical treatments of IPD so far have been based on the assumption of local thermodynamic equilibrium, but its validity is questionable in ultrafast formation dynamics of dense plasmas, particularly when interacting with intense XFEL pulses. A treatment of transient IPD, based on an electronic-structure calculation of an atom in the presence of a plasma environment described by classical particles, has recently been proposed [Phys. Rev. E 103, 023203 (2021)2470-004510.1103/PhysRevE.103.023203], but its application to and impact on plasma dynamics simulations have not been investigated yet. In this work, we extend XMDYN, a hybrid quantum-classical approach combining Monte Carlo and molecular dynamics, by incorporating the proposed IPD treatment into plasma dynamics simulations. We demonstrate the importance of the IPD effects in theoretical modeling of aluminum dense plasmas by comparing two XMDYN simulations: one with electronic-structure calculations of isolated atoms (without IPD) and the other with those of atoms embedded in a plasma (with IPD). At equilibrium, the mean charge obtained in the plasma simulation with IPD is in good agreement with the full quantum-mechanical average-atom model. The present approach promises to be a reliable tool to simulate the creation and nonequilibrium evolution of dense plasmas induced by ultraintense and ultrashort XFEL pulses.

Simulating Nanofluid Forced Convection Flow by Thermal Lattice Boltzmann Approach

Improving heat transfer using nanofluids has proven to be a promising option with many practical applications. However, the behavior of particles conveying energy for thermal transport depends closely on the dimensions of systems and channels where the flow evolves. Thereby, any fine thermal analysis should lean on a mesoscale approach applied at a microscale level. To this end, the multi-distribution functions–thermal lattice Boltzmann method has been taken to deal with convective heat flow and entropy generation in a channel with isothermal top–bottom walls and filled with a nanofluid (Cu/water). It was extended to simulate the flow governed by the Brinkman–Forchheimer Darcy model using the local thermal equilibrium assumption. The effects of nanoparticles’ volume fraction, Darcy number, porosity, heat capacity ratio and thermal conductivity ratio on heat transfer, entropy generation, average Nusselt number, and Bejan number are investigated. Among the salient results, it can be stated that the nanoparticles’ volume fraction increases heat transfer and entropy generation, but such a propensity can be affected by the porous medium permeability used. To sum up, the findings confirm the potential of the multi-distribution functions–lattice Boltzmann formalism to tackle forced nanofluid flows with heat transfer in porous media.

Interstellar detection and chemical modeling of iso-propanol and its normal isomer

Context.The detection of a branched alkyl molecule in the high-mass star forming protocluster Sagittarius (Sgr) B2(N) permitted by the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) revealed a new dimension of interstellar chemistry. Astrochemical simulations subsequently predicted that beyond a certain degree of molecular complexity, branched molecules could even dominate over their straight-chain isomers.Aims.More generally, we aim to probe further the presence in the interstellar medium of complex organic molecules with the capacity to exhibit both a normal and iso form, via the attachment of a functional group to either a primary or secondary carbon atom. Methods. We used the imaging spectral line survey ReMoCA performed with ALMA at high angular resolution and the results of a recent spectroscopic study of propanol to search for the iso and normal isomers of this molecule in the hot molecular core Sgr B2(N2). We analyzed the interferometric spectra under the assumption of local thermodynamical equilibrium. We expanded the network of the astrochemical model MAGICKAL to explore the formation routes of propanol and put the observational results in a broader astrochemical context.Results.We report the first interstellar detection of iso-propanol, ¿-C3H7OH, toward a position of Sgr B2(N2) that shows narrow linewidths. We also report the first secure detection of the normal isomer of propanol, n-C3H7OH, in a hot core. Iso-propanol is found to be nearly as abundant as normal-propanol, with an abundance ratio of 0.6 which is similar to the ratio of 0.4 that we obtained previously for iso- and normal-propyl cyanide in Sgr B2(N2) at lower angular resolution with our previous ALMA survey, EMoCA. The observational results are in good agreement with the outcomes of our astrochemical models, which indicate that the OH-radical addition to propylene in dust-grain ice mantles, driven by water photodissociation, can produce appropriate quantities of normal- and iso-propanol. The normal-to-iso ratio in Sgr B2(N2) may be a direct inheritance of the branching ratio of this reaction process.Conclusions.The detection of normal- and iso-propanol and their ratio indicate that the modest preference for the normal form of propyl cyanide determined previously may be a more general feature among similarly sized interstellar molecules. Detecting other pairs of interstellar organic molecules with a functional group attached either to a primary or secondary carbon may help in pinning down the processes that dominate in setting their normal-to-iso ratios. Butanol and its isomers would be the next obvious candidates in the alcohol family, but their detection in hot cores will be challenging.

Non-LTE modelling of the HC2NC and HNC3abundance in astrophysical environments

The isomers of HC3N, namely HC2NC and HNC3, are widely observed in the interstellar medium and in circumstellar envelopes. Their abundance has been determined under the assumption of local thermodynamic equilibrium (LTE) conditions or non-LTE radiative transfer models, but in considering the collisional excitation of HC3N as the same for all isomers. Chemical models for the prototypical cold cores, TMC-1 and L1544, reproduced the abundance of HC3N fairly well, but they tend to overestimate the abundances of HC2NC and HNC3with respect to the observations. It is therefore worth revisiting the interpretation of the observational spectra of these isomers using a rigorous non-LTE modelling. The abundance of HC2NC and HNC3were then determined using non-LTE radiative transfer calculations based on the proper rate coefficients for the first time in this work. Modelling the brightness temperature of HC2NC and HNC3when using their proper collision rate coefficients shows that models based on LTE or non-LTE with approximate collision data may lead to deviations of up to a factor of ~1.5. Reinterpreting the observational spectra led us to significant differences relative to the observed abundances previously determined. Our findings suggest quite similar abundance ratios for the TMC-1 and L1544 cold cores as well as the L483 protostar. This work will encourage further modelling with more robust non-LTE radiative transfer calculations and future studies to revisit the chemistry of HC3N and its isomers in cold molecular clouds.