Flux Profiles Research Articles

OBurnett Equations: Thermodynamically Consistent Continuum Theory Beyond the Navier–Stokes Regime

Abstract Rarefied gas flows are highly nonequilibrium flows whose flow physics cannot be discerned accurately within the framework of the Navier–Stokes equations. The Burnett equations and the Grad moment equations, which form a super-set of the Navier–Stokes equations, have been proposed in the literature to model such flows but not much success has been achieved because of some inherent limitations of these equations. In this review article, we mainly focus on the recently proposed Onsager-Burnett equations (Singh et al., 2017, “Derivation of stable Burnett equations for rarefied gas flows,” Phys. Rev. E 96, p. 013106) for rarefied gas flows, and the progress achieved so far by solving these equations for some benchmark flow problems. Like Burnett and Grad equations, the OBurnett equations form a super-set of the Navier–Stokes equations and belong to the class of higher order continuum transport equations. However, there are two fundamental aspects where the significance of the OBurnett equations is clearly visible. First, the OBurnett equations are unconditionally stable as well as thermodynamically consistent unlike the conventional Burnett and Grad moment equations. Second, the OBurnett constitutive relations for the stress tensor and the heat flux vector do not have any higher order derivatives of velocity, pressure, or temperature. This is quite significant since now the equations need the same number of boundary conditions as that of the Navier–Stokes equations. As such, the OBurnett equations form a complete theory, which cannot be said for the conventional Burnett equations. These two important aspects help to set the OBurnett equations apart from the rest of the higher order continuum theories. The results of the OBurnett equations are compiled for two benchmark rarefied flow problems: force-driven compressible Poiseuille flow and the normal shock wave flow problem. For force-driven compressible Poiseuille flow, the OBurnett equations successfully capture the nonequilibrium effects such as nonuniform pressure profile and presence of normal stresses and tangential heat flux in the flow. The accurate description of highly nonequilibrium internal structure of normal shocks has always been the stringent test for the higher order continuum theories. The results of the OBurnett equations for normal shocks show that there is no theoretical upper Mach number limit for the equations. Further, the equations predict smooth shock structures at all Mach numbers, existence of heteroclinic trajectory, positive entropy generation throughout the shock, and significant improvement over the results of the Navier–Stokes equations. Finally, the recently proposed Grad's second problem, which has the potential to become a benchmark problem, is discussed. The solution of Grad's second problem for different interaction potentials (Maxwell and hard-sphere molecules) within the Burnett hydrodynamics is also presented at length and some important remarks are made in this context.

A hybrid ultrafiltration membrane process using a low-cost laterite based adsorbent for efficient arsenic removal

Adsorption has proven to be most effective for arsenic removal. But standalone adsorption cannot cater to the need for large-scale treatment in centralized water supply systems. Combining adsorption with other low-pressure membrane processes may aid in scaling up and intensifying the overall arsenic removal. In the present pilot study, a low-cost laterite-derived adsorbent (LDA) has been used in combination with cross-flow ultrafiltration (Ads-UF) to develop a strategy suitable for remediation of arsenic-contaminated water. Effect of adsorbent particles on permeate flux has been assessed at different transmembrane pressure (0.2–0.6 MPa). Two different hybrid configurations, with and without intermediate sand filtration (SF), i.e. Ads–SF–UF and Ads-UF, were considered. Resistance-in-series and combined complete pore block-cake layer models have been used to understand the flux profiles. In the case of arsenic-spiked groundwater, it was observed that flux decline, at 0.6 MPa, was 28% higher with Ads-UF during a 12 h run compared to Ads–SF–UF. Spent LDA retrieved from the sand column was found to retain the elemental composition as that of the unused LDA (as per FT-IR and EDX) and was considered safe for disposal based on Toxicity Characteristic Leaching Procedure (TCLP). Cost estimation for a facility with 200 m3/day treatment capacity has also been presented.

A Comparison of Industrial-Scale Radiometer Heat Flux Measurements Between Pulverized-Coal and Coal/Biomass Co-Firing Combustion

Abstract This work evaluates and compares radiative heat transfer measurements conducted at the 471−MWE Hunter Power Plant Unit 3 utility boiler in Utah, United States, during standard operation with coal and also co-firing with biomass. The coal used was a Utah-sourced bituminous coal, which was mixed with torrefied wood (15% by weight) for the co-firing test. Radiation from the flame was measured using radiometers of three different designs. Data were gathered at three elevations along the boiler wall. Overall, the measured heat fluxes and corresponding temporal variations decreased with increasing boiler elevation. While the variation in the replicates of the heat flux data is notable, a statistical analysis indicates that the heat flux profile at the elevations investigated is not significantly affected by the change in fuel.

Design and fabrication of an axial neutron flux profile measurement assembly for the Advanced Test Reactor Critical Facility

Design and fabrication of an axial neutron flux profile measurement assembly for the Advanced Test Reactor Critical Facility

On modelling conjugated heat transfer in the thin slab CC mold and solid shell formation under the applied EMBr

Continuous casting (CC) became one of the dominant steel production technologies throughout last decades. Better quality, energy savings and high production rates are the main aims of the research especially in the field of the thin slab casting (TSC). The electromagnetic brake (EMBr) is applied to control the highly turbulent flow after the fresh melt is fed through the ports of a submerged entry nozzle (SEN). The numerical modelling is a perfect tool to investigate the multiphase phenomena of the turbulent flow in the CC mold, heat transfer and solidification coupled with the effects of the magnetohydrodynamics (MHD). Traditionally the heat transfer in the CC mold during the numerical simulations is predefined by the heat flux profile which could be taken from the plant measurements, published data, or is described by the semi-empirical formulas. In all these cases the heat extraction in the CC mold cavity is strictly predefined and is not significantly influenced by the transient flow behavior. Moreover, the heat flux, used in a simulation, is frequently measured for the different flow pattern inside the mold. That is especially important when the EMBr effects on the solid shell formation are investigated. Thereby, the presented study considers the coupled heat transfer in the water-cooled copper mold, including the averaged thermal resistance between the slab and mold, implemented using OpenFOAM® open-source CFD software. The melt flow, the temperature field, and the induced electric current density are compared between the traditional approach (the applied heat flux) and the modelled heat transfer in the TSC mold. Different scenarios are studied without and with the applied magnetic field.

Sensorless DTC-SVM applied to an induction motor controlled by a three-level inverter using SMSFO

PurposeThe direct torque control (DTC) of induction motor (IM) drive is featured by high ripples in the electromagnetic torque and stator flux profiles because they are controlled by two hysteresis regulators. Furthermore, the machine flux is not directly measurable. Hence, it is better to reconstitute it from the instantaneous electrical equations of the machine. Once the stator flux is estimated, we can guarantee a reliable sensorless DTC control. Thus, the purpose of this research work is to ensure fast response and full reference tracking of the IM under sensorless DTC strategy with desired dynamic behavior and low ripple levels.Design/methodology/approachIn this work, an improved DTC strategy, which is DTC_SVM_3L, is suggested. The first step of the designed approach is to substitute the conventional inverter feeding the motor with a three-level inverter because it guarantees reduced switching losses, improved quality of voltage waveform and low-current total harmonic distortion rate. The second aim of this paper is to make the IM operate at a constant switching frequency by using the nearest three vectors-based space vector modulation (SVM) technique rather than hysteresis controllers. The third objective of this study is to conceive a sliding-mode stator flux observer, which can improve the control performances by using a sensorless algorithm to get an accurate estimation, and consequently, increase the reliability of the system and decrease the cost of using sensors. The stability of the proposed observer is demonstrated based on the Lyapunov theory. To overcome the load change disturbance in the proposed DTC control strategy, this paper exhibits a comparative assessment of four speed regulation methods: classical proportional and integral (PI) regulator, fuzzy logic PI controller, particle swarm optimization PI controller and backstepping regulator. The entire control algorithm was tested under different disturbances such as stator resistance and load torque variations.FindingsIt was ascertained that the IM, controlled with three-level inverter, exhibits good performances under the proposed DTC-SVM strategy based on a sliding-mode observer. The robustness of the suggested approach against parameter variations is also proved.Originality/valueThe theoretical development of the proposed control strategy is thoroughly described. Then, simulations using Matlab/Simulink software are launched to investigate the merits of the sensorless DTC-SVM command of three-level inverter-fed IM drive with different speed regulators.

Dynamic CFD modeling coupled with heterogeneous boiling for deep two phase closed thermosyphons in artificial ground freezing

Super-long thermosyphons exceeding 100 m are being employed more frequently in artificial ground freezing (AGF) applications. In this study, we develop a fully-conjugate computational-fluid-dynamics (CFD) model to fundamentally analyze the heat extraction capacity and profile of super-long thermosyphons in AGF. The CFD model couples a heterogeneous condensation/evaporation mass transfer model inside the thermosyphon with thermosyphon-pool hydrostatic pressure distribution and heat diffusion from the ground. The heterogeneous model also considers the kinetic energy required for bubble nucleation and has been validated against experimental studies from the literature. Three main parameters have been investigated: 1) the filling ratio, 2) the charge pressure inside the thermosyphon, and 3) the wind temperature. The results reveal a no-boiling-zone below 10–25 m of pool surface. Further, the charge pressure significantly affect the start-up of the thermosyphon. Lastly, lower wind temperature extracts more heat from the ground in a qualitatively similar manner (similar heat flux profile along thermosyphon wall) to that of higher wind temperature. Overall, the results of this study provide fundamental understanding of the performance of super-long thermosyphons in AGF.

Investigation of a temperature-sensitive ferrofluid to predict heat transfer and irreversibilities in LS-3 solar collector under line dipole magnetic field and a rotary twisted tape

This article numerically studies the performance of the LS-3 parabolic trough collector. The parabolic trough solar system is equipped with an innovative rotary twisted tape. The absorber tube and twisted tape have the same length. Moreover, line dipole magnetic field is applied to improve the performance of solar collector. In addition, the characteristics of the irreversibilities are investigated. Commercial temperature-sensitive ferrofluid is selected for working fluid, and the nanoparticles along with the base fluid assumed to be uniform. The effect of rotational speed, twisted ratio, and line dipole magnetic field are compared with plain tube. The heat flux profile on absorber tube is ascertained by the Monte Carlo Ray Tracing method. Curve fitting method is used to obtain the mathematical function of the heat flux profile. To solve the equations including continuity, momentum, energy, and SST κ−ω model, the finite volume procedure is selected. The more convective heat transfer coefficient occurs by dipole magnetic field, the maximum enhancement reaches over 97% at B = 100 G. In addition, the twisted tape can increase heat transfer by 305% at twisted ratio = 2.5 and rotational speed = 200 rpm. Furthermore, if the twisted tape has rotational speed, the thermal entropy generation decreases.

Design of selective and self-cleaning iron aminoclay thin film nanocomposite membranes

Selective separation using efficient high-performance nanofiltration membranes has the potential for widespread application in multiple fields, including dye desalination, industrial wastewater treatment, and resource recovery from different feed streams. This study focused on the design of selective and self-cleaning nanofiltration membranes by incorporating iron aminoclay nanoparticles in a piperazine-based polyamide active layer supported on an ultrafiltration PAN substrate. Fe-AC nanoparticles and thin film nanocomposites (TFNC) were characterized for their morphology, surface chemistry, roughness, and surface area. In terms of wettability/hydrophilicity, TFNC membranes with Fe-AC incorporated had the lowest contact angle of 33.5°, while that of the pristine TFNC0 membrane was 60.5°. They also had a higher surface negative zeta potential and smoother surface morphology. The TFNC membranes also exhibited higher water fluxes and enhanced selectivity towards molecular separation compared to the control membranes. The water flux of the optimized AC polyamide membrane, TFNC3, was 19.70 ± 0.5 LMH (L.m−2.h−1), while that of the pristine TFNC0 membrane was 4.85 ± 0.6 LMH at 4 bar. 98.0–99.0 % rejection of model organic moieties was achieved at a constant flux (Congo red, Eriochrome Black T, methylene blue, Rhodamine 6G, and Crystal violet). When simulated wastewater was purified, the Fe-AC TFNC showed 98.0 % rejection of dyes and 20.0 % rejection of inorganic salts. In long-term filtration studies (>210 h) using simulated wastewater spiked with multiple foulants, >98.0 % rejection of organic matter and foulants was recorded with a stable long-term flux profile. A leaching study confirmed that the membranes were structurally stable, even after the self-cleaning process and at elevated temperatures, without any significant reduction in flux or rejection. Comparing the fouling performance between TFNC3 membranes and commercial reverse osmosis (RO) membranes, the FDR and Flux Recovery Ratio (FRR) values of commercial RO membranes were 58.0 % and 73.0 %, while those of TFNC3 were 47.0 % and 97.0 %, respectively. The results show that the membranes have lower fouling values and higher FRR values when iron clay is present. These results demonstrate the potential of the membranes for effective pre-treatment of various industrial wastewaters and selective separation.

A first wind tunnel study on the aeolian sand transport of coral sands

Although wind-blown sand activity may be crucial for the landform and stability of coral islands in the ocean, the characteristics of coral sand movement remain largely unknown. This study is the first to quantify coral sand flux by wind tunnel measurement with various wind speeds using coral samples collected from an island and a sand cay from Yongle Atoll, Xisha Island in the South China Sea. The particle morphology, grain size, chemical and mineral composition, as well as threshold wind speed, transport rate, and transport flux profile of blowing coral sands, were investigated and compared to those of quartz sands from an inland desert. The basic features of coral sand movement, including an increase in threshold wind speed with grain size and density, an increase in total rate with wind speed, and an exponential decrease in transported sand concentration with height, have been determined. Cay sands with a grain size of about 1.24 mm behave similarly to coarse quartz sands, whereas island sands with a grain size of 0.49 mm perform similarly to medium and medium coarse quartz sands. Contrary to normal desert and beach sands, the decay trend of the flux profile of coarse coral sand increases with wind speed, just as it does for coarse desert sand. Due to their irregular morphology, coral sands are difficult to entrain by wind, with a threshold wind speed of about 11.64 m s−1 for island sand and 16.98 m s−1 for cay sand, which are much greater than the 4.32 m s−1 for fine and 12.67 m s−1 for coarse desert sands in the wind tunnel. The results can be incorporated into existing sand transportation models and used to evaluate the influence of aeolian processes on the landform of coral islands.

A Case Study for 50 kVA Toroidal Core Partially Superconducting Transformer

We report some numerical results obtained for 50kVA single phase partially superconducting toroidal and core power transformers. Transformers are calculated using the Comsol Multiphysics software with ac/dc and heat transfer modules. They are modeled in such a way that their primary parts (medium voltage) consist of copper windings and secondary parts (low voltage) are formed by superconducting MgB2 windings which are immersed into the liquid helium. Magnetic flux density profile on the iron core, primary and secondary currents, transformer power, and AC losses in superconducting windings are explored for one full cycle of AC voltage. Short-term temperature investigation for quenching showed that AC losses act as a heat source. We think that these numerical results are very important in terms of industrial-scale superconducting transformer applications because there are very few studies on MgB2 transformers. Our results will enable the design of toroidal-type power transformers that may be operable in practice. According to the numerical simulation results, it seems that a compact low cost superconducting MgB2 toroidal transformer can be realized with advances in cryostat systems and reducing AC losses. We suggest that the present study will contribute to the literature according to both the models applied and the results obtained.

Combined Thermal Performance Enhancement of Parabolic Trough Collectors Using Alumina Nanoparticles and Internal Fins

Parabolic trough collectors are the currently dominant technology for concentrated solar power systems, employed to produce thermal energy at low to medium temperatures (up to 400°C). Extensive research has been carried out to enhance the thermal efficiency and reduce the power production costs of these concentrators. However, there is a lack of studies on combined passive performance enhancement using alternative fluids and absorber designs. In this study, the thermal performance of a full-sized parabolic trough collector is analyzed with the presence of internal longitudinal fins in combination with the use of oil-based nanofluid (Al2O3-Syltherm 800) of different volume fractions. The governing equations are numerically solved using ANSYS FLUENT 17.1 software and the Monte-Carlo ray-tracing (MCRT) model was used to apply the non-uniform heat flux profile over the external surface of the solar receiver. The results show that both techniques enhance thermal energy utilization and reduce radiative and convective thermal losses, resulting in higher thermal efficiency, but also larger pressure losses. The thermal performance is enhanced by 0.1-1.16 % with nanofluid, up to 6.8 % with internal fins, and by up to 7.25 % when both techniques are adopted. These enhancements are attributed to the reduced mean circumferential temperature of the absorber tube.

Flame characteristics and heat flux profile of a tank surface caused by horizontal gas leak jet fire impingement

Jet fire accidents caused by leaks in gas pipelines or gas tanks often occur, which may trigger a domino effect. The present work experimentally investigated the characteristics and heat flux profile of flames on a tank surface, with different leak hole-tank spacing and fuel initial velocity. The results show that, for any given leak hole diameter, the height and width of the impingement flame increase with an increasing heat release rate, whereas they decrease with an increase in the leak hole-tank spacing. The impingement flame height correlated well with the characteristic length Lm, which was used in free jet fires. Based on the balance of the momentum flux to the buoyancy flux of the horizontal jet fire, a new characteristic length scale and a dimensionless heat release rate was proposed. Meanwhile, some of the numerical results were also analyzed and the non-dimensional functional correlation for the flame width of the impinging area was proposed with the fire heat release rate and flame Froude number Frf. Finally, considering the effect of the unburned portion of the fuel with jet fire impinging the tank, a new correlation was proposed to describe the heat flux and temperature profile of the tank surface.

Bayesian inference of axisymmetric plasma equilibrium

We present a Bayesian method for inferring axisymmetric plasma equilibria from the magnetic field and plasma pressure measurements. The method calculates all possible solutions for plasma current and pressure distributions consistent with the measurements and magnetohydrodynamic (MHD) force balance. Toroidal plasma current and magnetic field coils are modelled as a set of axisymmetric current-carrying solid beams. The other parameters such as plasma pressure and poloidal current flux are given as a function of poloidal magnetic flux, which is determined given a 2D current distribution. Plasma pressure and poloidal current flux profiles are modelled as Gaussian processes whose smoothness is optimally chosen based on the principle of Occam’s razor. To find equilibrium solutions, we introduce an MHD force balance constraint at every plasma current beam as a part of the prior knowledge. Given all these physical quantities, predictions calculated by the predictive (forward) models for diagnostics are compared to the observations. The high dimensional complex posterior probability distribution is explored by a new algorithm based on the Gibbs sampling scheme.

STRIKE Heat Flux Reconstruction by Using Neural Networks: Application to the Experimental Results

To characterize the SPIDER negative ion beam in terms of beam uniformity and divergence during short pulse operations, an instrumented calorimeter named short-time retractable instrumented kalorimeter experiment (STRIKE) has been designed and operated. STRIKE is made of 16 1D carbon fiber-carbon composite (CFC) tiles, intercepting the whole beam and observed on the rear side by two infrared (IR) cameras. To know the energy flux profile hitting the front surface and then the beam parameters, it is necessary to solve an inverse non-linear problem, mathematically ill-posed, upon knowing the non-linear characteristics of the tiles and the 2-D temperature pattern measured on the rear side of the tiles themselves. Most of the conventional methods used to solve this inverse problem are unbearably time-consuming; when fully operative STRIKE receives 1280 beamlets, each one characterized by at least five features, a ready-to-go tool to determine the beam condition is highly recommended. In this work, the inverse problem in stationary conditions is faced by using a neural network (NN) model, pursuing different training approaches. The NN is trained by associating features extracted from the 2-D temperature profile, obtained by a fitting process to the heat flux profile parameters. The proposed method is then applied to experimental STRIKE data from the beam campaigns.

A three-dimensional model to describe complete human corneal oxygenation during contact lens wear.

We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species.

Experimental study and physical modeling of ceiling temperature and heat flux profiles by wall-attached fires in inclined tunnels

In this work, the longitudinal heat flux, temperature distribution and flame spread length, beneath a sloping tunnel ceiling caused by fire sources attached to the sidewall were experimentally investigated. The effect of heat release rate (HRR) and tunnel slope on the flame spread length, temperature and heat flux profile were comprehensively considered. The present results show that, in the longitudinal direction, the temperature and heat fluxes under ceiling decrease with increasing distance in the downstream and upstream directions from the flame stagnation point. Thermal and flame buoyancy will change the forces on the ceiling jet caused by a wall-attached fire, resulting in differences in the mass flow rate of fire plumes in upstream and downstream directions. A correlation is developed for the flame extent in the longitudinal upward and downward directions. The temperature and heat flux under ceiling increase in the upstream direction for a given distance in the longitudinal direction compared with the downstream direction and with increasing slopes of the tunnel inclination. This is due to the fact that the upstream thermal flow increases, and the flame extension length becomes larger, while the downstream thermal flow decreases exacerbating the difference of heat flux between upstream and downstream. In addition, the correlation between the dimensionless heat flux and the temperature profile under inclined ceiling in the upstream and downstream directions was further analyzed as a function of the flame length variation. These correlations are well described by physically based models for all the experimental results, including the heat flux under the tunnel ceiling at stagnation point and along the longitudinal flame extension.

Modeling and Optimization of Mass and Heat Flux Profiles in a Multifunctional Reactor for CO2 and H2 Valorization to Dimethyl Ether

Dimethyl ether is one of the future synthetic fuels in the 2025–2050 energy mix. This work presents a detailed numerical optimization approach for a multifunctional reactor for the direct synthesis of dimethyl ether from CO2 and H2, with a specific focus on the methodological aspect that can be used as a guide to help or evaluate the development of innovative technological strategies. An innovative approach based on the dynamic optimization of the mass and heat flux profiles is applied for the intensified configuration, coupling simultaneously the reaction, heat exchange, and membrane separation (R–E–M). Several degrees of freedom and optimization strategies (mono- and multi-objective/deterministic and stochastic) are addressed. The energetic criterion is evaluated, namely, the total heat power exchanged. Optimization results highlight the performance improvement potentialities offered through the optimal exploitation of the synergy between these elementary functions. Simulation results show that the kinetic inhibition caused by water can be overcome and that a water-free process output is achievable, enabling an economic gain due the removal of a postreaction separation (water/methanol). The heat flux optimization provides more flexibility for mass transfer. Up to 95 and 98% in DME yield and CO2 conversion have been obtained per single pass for optimal theoretical heat- and mass-transfer flux profiles, respectively, within a multifunctional reactor. The results are obtained for the reactor inlet temperature and pressure of 518.15 K and 70 bar, respectively.

Radon Flux Density In Conditions Of Permafrost Thawing: Simulation Experiment

This paper describes a five-month experiment (February – July 2021) measuring the gradual thaw diffusion of radon-222 (further in the article – radon) from a frozen environment in NW Russia (i.e. Arhangelsk region). Red clay substrate containting a high content of 226Ra filled the bottom insides of 200-liter barrel holding the source of radon and buried at 1.6 m depth (e.g., the radium source zone), then covered with native soil, filled with water and frozen under in-situ conditions. Radon measurements were carried out from soil surface above the container (disturbed soil layer) and at background location (undisturbed soil layer). Several periods of increased radon flux density were observed, which was related to radium source zone thawing. It was shown that in 1-2 days after thawing of the radium source zone and drying of the upper soil layer, the radon flux increases sharply – more than 8 times compared to background values. These results show a strong relationship between radon flux density and soil temperature profiles at different depths. The calculations of radon sourced from frozen and thawed zones show how temperature phase of substrate (e.g. clays) control the barrier influence of radon migration. It reduced them by 10-20 times (according to the results of a theoretical calculation), depending on the characteristics of frozen rocks (density, porosity). Thus, the barrier function of permafrost is related to the physical properties of ice and frozen rocks. These temperture phases controls radon emanation coefficients and significantly influences the migration of radon to the earth’s surface.

Tracer diffusion under a concentration gradient: A pathway for a consistent development of mobility databases in multicomponent alloys

Diffusion in the CoCrFeMnNi high-entropy alloy is investigated using an augmented tracer / interdiffusion couple approach. The tracer diffusion coefficients are measured along the diffusion path developed between the Co17Cr20Fe20Mn20Ni23 and Co23Cr20Fe20Mn20Ni17 end-members allowing an elaboration of a consistent composition-dependent diffusion database. Both tracer and chemical concentration profiles are successfully reproduced to a tolerable level using a pair-diffusion model avoiding the reference element concept. Up-hill diffusion of Co in the experimental profile is not reproduced by the existing kinetic and thermodynamic databases. The reasons for this mismatch are discussed. The calculation of intrinsic and interdiffusion coefficients from the estimated tracer diffusion coefficients utilizing the thermodynamic parameters is demonstrated. The calculated values of the interdiffusion coefficients produced a reasonable match with the interdiffusion flux profiles developed in the multicomponent diffusion couple. The calculation of the vacancy wind effect indicates its strong influence on several intrinsic cross diffusion coefficients.