Non-equilibrium Model Research Articles

Condensation mechanism and pressure fluctuation of a steam centrifugal compressor based on a non-equilibrium condensation model

In this paper, the condensation mechanism and pressure fluctuation of a steam centrifugal compressor are deeply studied based on a non-equilibrium condensation model. The wet steam model is generated to predict the flow characteristics and the condensation of the steam centrifugal compressor. The effect of different inlet temperatures on the steam condensation characteristics is deeply explored. Numerical results show that the steam condensation phenomenon on the high span surface is increasingly obvious, and the mass fraction of liquid steam first increases and then decreases with the increase in temperature. The droplet particle diameter and the droplet number gradually increase with the increase in temperature. It is also found that the blade loading on the impeller blade also becomes more unstable with the increase in inlet temperature. The amplitude spectrum of pressure fluctuation on the both sides of impeller blade and diffuser blade is analyzed through the fast Fourier transform. The pressure fluctuation in the flow channel becomes severe first and then becomes stable with the increase in temperature, which is well consistent with the variation trend of liquid mass fraction. The quantitative relationship between condensation strength and operating temperature is established to explore the variation trend essence of surface-average wetness fraction of different span surfaces at different inlet temperatures, which further reveals the condensation sensitivity to temperature at different blade heights. It is further found that the condensation strength on the low span surface and the average wetness fraction of steam condensation in the flow field increasingly decrease with the increase in inlet temperature.

A thermochemical nonequilibrium model of CO2 plasma for studying flow-field properties of the spacecraft Mars Pathfinder

A thermochemical nonequilibrium model of CO2 plasma for studying flow-field properties of the spacecraft Mars Pathfinder

A three-dimensional thermochemical nonequilibrium model for simulating air plasma flows around an inflatable membrane reentry vehicle

A three-dimensional thermochemical nonequilibrium model for simulating air plasma flows around an inflatable membrane reentry vehicle

Unusual nanoscale amorphization of metallic chromium interfacing with SiC under high energy irradiation

Layered metal/silicon carbide (SiC) materials systems are becoming increasingly relevant to solve materials challenges in advanced fission and fusion nuclear energy systems, necessitating a deeper understanding of how interfaces between dissimilar materials behave under high energy irradiation. In this work, we use a Cr-SiC bilayer system as a model to study the behavior of such interfaces under high energy ion irradiation (80 MeV Xe26+ ions) at elevated temperatures (∼350 °C). Through high resolution characterization of the interface, we observed the formation of a nanoscale Cr-rich amorphous layer adjacent to crystalline SiC. We explain this phenomenon through a multi-scale computational approach incorporating ballistic mixing simulations, density functional theory calculations, and CALPHAD-based non-equilibrium modeling that shows the localized amorphization of Cr to be driven by the synergistic action of irradiation-induced point defects within Cr and transport of Si and C atoms across the interface. In particular, the accumulation of radiation damage results in the thermodynamic destabilization of the point-defect containing, metastable Cr-Si-C solid solution with respect to an amorphous phase of identical composition. This study advances the understanding of how metal/SiC interfaces behave under irradiation and establishes a modeling framework that can be applied to interfacial systems to understand irradiation-induced amorphization.

Effects of non-equilibrium phase behavior in nanopores on multi-component transport during CO2 injection into shale oil reservoir

Injecting CO2 into shale oil reservoirs is one of the most effective methods for enhancing oil recovery (EOR) while simultaneously facilitating CO2 capture, utilization, and storage (CCUS). However, it is not always that gas dissolution or condensate evaporation reaches equilibrium instantaneously during the CO2 injection process. In cases where equilibrium is not attained instantaneously, conventional vapor-liquid equilibrium models will have certain limitations in characterizing phase transition hysteresis. These limitations will affect the accuracy of simulating multi-component transport in porous media. In this paper, a robust and generic vapor-liquid non-equilibrium thermodynamic model considering nano-confinement effects (NC) was established by introducing component mass transfer rates proportional to the chemical potential difference. The established model was then used to modify the fully-compositional, projection-based embedded discrete fracture model (pEDFM). Furthermore, C++ hybrid programming and the Graphics Processing Unit (GPU) parallel method were both used to accelerate both the nonlinear and linear solvers. By comparing with results from MATLAB Reservoir Simulation Tools (MRST), Eclipse, and tNavigator, the accuracy and advantages of our solver were demonstrated. The results show that if the underground fluid undergoes a phase transition from a vapor-liquid two-phase state to a single-phase state, non-equilibrium thermodynamic effects need to be considered, and the simulation results show a larger two-phase zone, higher bottom hole pressure, and lower cumulative liquid production. But the nano-confinement effects will weaken the non-equilibrium thermodynamic effects.

Transient absorption of warm dense matter created by an X-ray free-electron laser

Warm dense matter is at the boundary between a plasma and a condensed phase and plays a role in astrophysics, planetary science and inertial confinement fusion research. However, its electronic structure and ionic structure upon irradiation with strong laser pulses remain poorly understood. Here, we use an intense and ultrafast X-ray free-electron laser pulse to simultaneously create and characterize warm dense copper using L-edge X-ray absorption spectroscopy over a large irradiation intensity range. Below a pulse intensity of 1015 W cm−2, an absorption peak below the L edge appears, originating from transient depletion of the 3d band. This peak shifts to lower energy with increasing intensity, indicating the movement of the 3d band upon strong X-ray excitation. At higher intensities, substantial ionization and collisions lead to the transition from reverse saturable absorption to saturable absorption of the X-ray free-electron laser pulse, two nonlinear effects that hold promise for X-ray pulse-shaping. We employ theoretical calculations that combine a model based on kinetic Boltzmann equations with finite-temperature real-space density-functional theory to interpret these observations. The results can be used to benchmark non-equilibrium models of electronic structure in warm dense matter.

Numerical investigation of methane steam reforming in the packed bed installed with the fin-metal foam

Methane steam reforming via packed bed reactors currently is the primary method for industrial hydrogen produce worldwide. Optimizing the structure of packed bed reactors is an effective approach to enhance the hydrogen yield. This study introduces an innovative structure, the fin-metal foam, combined into a packed bed reactor. A numerical investigation was conducted by the new coupling simulation way, which consists of the equivalent medium model, the Darcy extended Forchheimer flow model and the local thermal non-equilibrium model. A conventional reactor, a reactor installed with a metal foam and a reactor installed with the fin-metal foam were compared. It was found that the fin-metal foam structure improves the performance of flow, heat transfer and hydrogen production. By comparing with the conventional reactor, the fin-metal foam structure reduces the energy dissipation by 35.13 %, increases the fluid temperature by 23 K and improves the overall heat transfer coefficient by 28.59 %. The hydrogen mass flow per catalyst mass per energy dissipation was employed to evaluate the comprehensive hydrogen production performance. The fin-metal foam structure leads to a notable improvement of 113.36 %. These findings suggest a promising way for improving the industrial hydrogen produce, with benefits including reduced energy consumption and catalyst usage.

Reconciliation of wire woven mesh porous media in controlling the desired heat transfer and pressure drop

Purpose Despite the reputation of the metal-based porous media for their ability to augment heat transfer as widely witnessed in the literature and practically operating heat exchanging applications, the coexisting penalty of the increased pressure drop demanding increased pumping power poses a major concern that invites the need for an alternate solution to handle this unsought outcome. Therefore, this study aims at providing a better solution to the existing cost and benefit scenarios to benefit a plethora of engineering applications including energy transfer, energy storage and energy conversion. Design/methodology/approach This work highlights on the property of stacked woven wire mesh porous media such as their stacking types, porous conditions and thickness scenarios that can potentially result in distinct trade-off scenarios. A vertical channel is numerical modelled by using REV scaled modelling technique using Darcy-Forchheimer and local thermal non-equilibrium models to illustrate the possibilities of this variety of trade off scenarios between the desirable heat transfer and the unsought flow resistance. Findings This work illustrates the advantages of wire mesh-based porous medium and its distinct potential in controlling the existing trade-offs between the cost and benefit aspects. It is found that by varying the features of wire mesh porous media, the interplay between the conflictingly existing characteristics can be much easily handled specific to distinct requirements associated with variety of engineering applications. Originality/value The study emphasizes on a new solution or methodology to handle the penalty of pressure drop associated with metal-based porous media. Through this study, a novel approach to control the ultimately costing pumping power at the benefit of increased heat transfer is provided considering various requirements that could be associated with any thermal management systems. Various possibilities and potentials of wire mesh porous media are illustrated highlighting on their benefit of ease with which the mentioned goals can be achieved.

Analyses of nonequilibrium transport in atmospheric-pressure direct-current argon discharge under different modes

Abstract The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow, arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current (DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath (P c) was used as a key parameter for judging different discharge modes, and the range of (0.28–1.2) × 1012 W m−3 was determined as a critical window of P c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.

Ferrihydrite colloid-mediated transport of sulfamerazine in saturated porous media: Combined roles of rhamnolipid and solution pH

To date, there is still very little knowledge about the combined effects of typical biosurfactants and solution pH values on iron oxide colloid-mediated transport of sulfamerazine (SMZ, a typical sulfonamide antibiotic) in saturated porous media. Herein, the influences of rhamnolipid (a common biosurfactant in the environment) on SMZ mobility in the absence or presence of ferrihydrite (a model iron oxide) colloids in saturated quartz sand were explored. Generally, the rhamnolipid suppressed the transport of SMZ without ferrihydrite colloids owing to the bridging effect of this biosurfactant (i.e., rhamnolipid served as a bridging agent between SMZ and sand). Moreover, ferrihydrite colloids also inhibited SMZ mobility due to the deposition of colloid-associated SMZ. Surprisingly, the presence of rhamnolipid significantly influenced ferrihydrite colloid-mediated transport of SMZ, and this effect was highly dependent on the solution pH. Concretely, rhamnolipid enhanced the inhibitory effects of ferrihydrite colloids on SMZ transport at pH 5.0 because of the increased SMZ retention on the deposited colloids via the bridging effect of biosurfactant. At pH 7.0, the transport-inhibition effects of colloids were weakened by adding rhamnolipid, which was due to the colloid-associated SMZ transport and the promoting electrostatic repulsion between the free SMZ and sand/ the deposited colloids. Surprisingly, ferrihydrite colloids facilitated SMZ transport in the addition of rhamnolipid at pH 9.0. This phenomenon stemmed from the enhanced free SMZ mobility, the colloid-assisted mobility of SMZ, and the competitive deposition between SMZ– species and negatively charged colloids. Moreover, the two-site non-equilibrium model was performed to help interpret the controlling mechanisms for the synergistic effects of rhamnolipid and solution pH on colloid-mediated transport of SMZ. The outcomes of this study offer valuable knowledge about the functions of widespread biosurfactants in the environmental consequences of antibiotics in subsurface systems with iron oxide colloids.

Numerical modeling of heat transfer behavior for two-phase flow in a nozzle considering phase change

The heat transfer and phase change of alumina particles in the gas-particle flow of the nozzle plays an important role in solid rocket motors (SRM) due to the coupling between the heat transfer and two-phase flow. However, it lacks precise modeling of the heat transfer behaviors of condensed particles in the nozzle, especially the phase change effect. In this article, we determine that the Drake model has the highest accuracy in calculating the convective heat flux between two phases, and propose a correlation to obtain radiative heat flux between the particle and walls. Then, a one-dimensional two-phase non-equilibrium model is established to consider the effects of heat transfer and solidification of particles on the two-phase flow in the nozzle. The results show that considering the phase change of particle improves the outlet thrust of the nozzle, but such increment decreases with the gas inlet temperature. When the supercooling phenomenon is considered, the nozzle thrust is reduced by 1.14% compared with that considering no supercooling. As the particle size increases, the outlet temperature of the particle phase rises and can even surpass the solidification temperature of particles and the velocity of the particle phase decreases significantly.

CFD simulation of the influence of swirl intensity on entropy production for wet steam flow in supersonic dehydration

The energy loss within a supersonic separator is highly dependent on the cyclonic intensity. In this paper, an entropy production analysis model and a nonequilibrium condensation model are developed to study the liquefaction performance of the supersonic nozzle and the energy loss under different swirl intensities. With an increase in swirl intensity from 0 to 0.94, the nucleation starting point and Wilson point at the centerline move forward by 45.05 mm and 69.17 mm, respectively. The mass-average liquid fraction at the nozzle outlet increases by 28.81 %, but the flow rate decreases by 43.02 %, and the total entropy production experiences a 19.66 % increase. Indirect (or turbulent) dissipation dominates the total entropy production of wet steam flow resulting from the large gradient of velocity at the boundary layer, whereas phase change entropy production ranks second and mainly occurs in the nucleation region. Overall, the swirl intensity should be kept below 0.30 to achieve a balance between gas handling capacity, liquefaction performance, and energy loss for the supersonic nozzle.

The impact of grazing on biodiversity and forest succession in the Brazilian dry forest region is constrained by non-equilibrium dynamics

The impacts of grazing on rangelands have historically been studied within the framework of the equilibrium model, which predicts significant impacts of grazing on ecosystems. However, in recent decades, studies have observed a non-equilibrium pattern, suggesting that abiotic factors play a primary role compared to grazing. These studies are primarily focused on rangelands, despite animal husbandry occurring in other biomes, such as seasonally dry tropical forests. Our study examines the influence of goat grazing on biodiversity and forest succession in the Brazilian dry forest (Caatinga). Considering its high interannual precipitation variability, we hypothesize a response that aligns with the non-equilibrium paradigm. We established a gradient of grazing intensity and history in areas at different stages of vegetation succession. A survey of tree - shrub and herbaceous species was conducted at each site and the biomass of both strata was quantified. Linear mixed models and Permanova were employed to assess differences in richness, composition, structure, and biomass among the areas. Our results suggest that grazing (history and intensity) and forest fallow age did not affect species richness, but only species composition. Low and high grazing intensity drive ecosystems toward similar compositions, which align with the non-equilibrium model predictions. Biomass in the herbaceous layer remained unaffected by grazing history, intensity, or forest fallow age, whereas woody biomass was influenced by grazing intensity in older forest fallows. Although trees in low-intensity grazing sites were significantly taller compared to those in other levels, overall, grazing did not disrupt the natural succession process. Older forest fallows exhibited greater diversity and higher basal area compared to new forest fallows, irrespective of grazing intensity. Our findings suggest that: a) grazing has minimal effects on biodiversity and biomass due to non-equilibrium dynamics, and b) with appropriate management, grazing can coexist with the conservation of the Caatinga.

On thermal non-equilibrium (TNE) model for heat transfer in ternary ferro-nanofluid with rectangular porous fin

The heat transmission in a rectangular porous fin affected by a thermal non-equilibrium model with radiation and magnetic field influences is studied in this study. A ferrofluid containing ferroparticles (Fe3O, CoFe2O4, and Cu) and a mixture of 50 % water and 50 % ethylene glycol coats the fin. Dimensionless form is later achieved by formulating the governing equations for both the solid and ferrofluid phases. In order to get the answer, the Runge–Kutta–Fehlberg (RK-45) scheme is used. Visual and tabular representations are used to investigate the effect on heat transmission of the Biot and Rayleigh numbers as well as the porous and convective parameters. The results show that the solid phase temperature profile is inferior for lower Hartmann numbers (H) and Rayleigh numbers (Ra). The disparity in temperature between the solid and ferrofluid phases decreases in proportion to the Ra. Applications for this type of device include heat exchangers, air conditioners, and cooling towers.

Exploring spin photovoltaics in defective armchair phosphorene nanoribbons

This study explores the spin photovoltaic potential within armchair phosphorene nanoribbons (APNRs) that feature a periodic distribution of monovacancies (MVs) under the influence of light radiation. We investigate spin-semiconducting behavior induced by MV defects by utilizing both the mean-field Hubbard approximation and the self-consistent non-equilibrium Green's function model. This behavior is characterized by localized and anisotropic band structures around the Fermi energy, particularly within the antiferromagnetic phase. The existence of spin-splitting band gaps in defective APNRs not only enables the crafting of spin-optoelectronic nanodevices but also allows for the manipulation of electronic structure behavior with applied electric fields in both the vertical and transverse directions. Notably, the implementation of electric fields, offering tunability in electronic structure, results in varied spin photovoltaic responses encompassing a broad spectrum of photon energies from visible to ultraviolet. This research reveals promising avenues for advancing the field of spin-optoelectronic devices by MVs in APNRs.

Statistical mechanics of active vesicles and the size distribution paradox

Vesicles are the primary modes of communication and transport in cell biology. Conventional wisdom based on thermodynamic equilibrium says that vesicles should have a certain minimum size and size distribution dictated by their thermal fluctuations. However, there is compelling experimental evidence that vesicles exhibit a vast variety of size distributions depending on their formation process and function which cannot be explained by equilibrium statistical mechanics alone. We investigate a non-equilibrium statistical mechanics-based model to understand the role of active membranes on the size distribution of vesicles. Active membranes contain proteins that use external energy sources, such as adenosine triphosphate hydrolysis, and are known to exert forces on the membrane during their activity to carry out different biological functions. The central idea behind our model is that activity, attributed to different sources, impacts vesicle fluctuations in two opposing ways — by active noise which enhances fluctuations, and membrane tension which decreases fluctuations. The interplay of active fluctuations and active tension endows the vesicles with the ability to achieve size distributions that are deemed improbable by equilibrium statistical mechanics. We show that our model for active vesicles, based on linearized curvature elasticity, can reproduce different experimental data for vesicle size distributions available in the literature by varying the activity. Elucidating how these vesicles achieve such diverse size distributions can open avenues for a deeper understanding of physiological and pathological processes and help design vesicles for diagnostics and drug delivery applications.

Deciphering the dynamical chromosome structural reorganizations in human neural development

Understanding the mechanisms of cell-fate determination in neural development is pivotal for advancing regenerative medicine and addressing neurodegenerative diseases. Cell-fate determination is controlled by the underlying gene expression networks, which are further regulated by the three-dimensional chromosome structures. During neural development, chromosomes progressively adapt their structures to accommodate the requisite gene expressions. However, elucidating the pathways of chromosome structural dynamics during these transitions remains a grand challenge. In this study, we employed the data-driven coarse-grained molecular dynamics simulations, coupled with the nonequilibrium landscape-switching model, to quantify the chromosome structural dynamics during human neural development. We focused on a simplified human neural developmental system, comprising of cell differentiation, reprogramming, and transdifferentiation among the neural progenitor cell (NPC), the glia cell, and the neuron cell. We identified significant large-scale chromosome structural reorganizations during cell-state transitions. From the chromosome structural perspective, the transdifferentiation processes between the glia and neuron cells exhibited nonmonotonic behaviors characterized by an initial increase followed by a subsequent decrease in cell stemness. The transdifferentiation appeared to share the same routes of differentiation after passing through the NPC. Additionally, our findings revealed that the chromosome structural dynamical pathways at the scale of topologically associating domains exhibited little overlap, in contrast to the ones at the long-range regions. This suggests that the active, ATP-driven molecular processes play dominant roles in modulating topologically associating domain (TAD) structures, while the compartmental segregation in chromosomes is primarily governed by the passive phase separation. Our study offers a theoretical exploration of neural cell-fate determination from the chromosome structural perspective, paving a way for potential applications in neuroregeneration. Published by the American Physical Society 2024

Numerical and thermal resistance analysis on the cryogenic porous medium heat exchanger with liquid channel

The porous medium heat exchanger has been increasingly utilized in cryogenic applications, especially in the milli-Kelvin region. This study focuses on the porous medium heat exchanger with liquid channel commonly used in the dilution refrigerator and proposes a numerical model, which applies the local thermal non-equilibrium (LTNE) model coupled with N–S equations and Brinkman-Forchheimer model. Comparing with literature results validates the numerical model. By analyzing the heat transfer characteristics of the heat exchanger, a thermal resistance network model is developed to capture the heat transfer mechanism. The results show that the total thermal resistance mainly depends on the fluid conductive thermal resistance and Kapitza thermal resistance inside the porous medium. The fluid conductive thermal resistance dominates at higher temperature while the Kapitza thermal resistance dominates at lower temperature. The expression of critical temperature is derived to determine the priority of reducing thermal resistance. At cryogenic temperatures, the porous medium serves to bypass the significant Kapitza thermal resistance by introducing much lower thermal resistances, while at normal temperatures, the porous medium reduces the overall thermal resistance by incorporating a parallel thermal resistance but without magnitude difference.

Pyrolytic urban mining of waste printed circuit boards: an enviro-economic analysis.

E-waste, a global environmental concern resulting from supply chain inefficiency, also offers the opportunity to recover valuable materials, including general and rare earth metals. Waste printed circuit boards (WPCBs) are integral components of e-waste that contains substantial amounts of precious metals, making them a valuable waste category. Pyrolysis has emerged as a promising method for material recovery from WPCBs. Hence, pyrolytic urban mining of WPCBs offers an excellent avenue for resource recovery, redirecting valuable materials back into the supply chain. Under the current study, experimental investigation has been conducted to explore the recovery of materials from WPCBs through pyrolysis followed by process simulation, economic analysis, and life cycle assessment (LCA). An Aspen Plus simulation was conducted to model the pyrolysis of WPCBs and subsequent product recovery using a non-equilibrium kinetic model, which represents a unique approach in this study. Another distinct aspect is the comprehensive assessment of environmental and economic sustainability. The economic analysis has been carried out using Aspen economic analyzer whereas the LCA of WPCB pyrolysis has been conducted using the SimaPro software. The experimental investigation reveals yield of solid residues are about 75-84 wt.%, liquid yields of 6-13 wt.%, and gas yields of 4-21 wt.%, which is in well agreement with the Aspen Plus simulation results. The economic analysis for an e-waste pyrolysis plant with an annual feed rate of 2000 t reveals that the total capital cost of a pyrolysis plant is nearly $51.3 million, whereas the total equipment cost is nearly $2.7 million and the total operating cost is nearly $25.6 million. The desired rate of return is 20% per year and the payback period is 6years with a profitability index of 1.25. From the LCA, the major impact categories are global warming, fossil resource scarcity, ozone formation in human health, ozone formation in terrestrial ecosystems, fine particulate matter formation, and water consumption. The findings of this study can serve as a guideline for e-waste recyclers, researchers, and decision-makers in establishing circular economy.

Numerical assessment of thermomagnetic convection of ferrofluid in a porous cavity employing a local thermal nonequilibrium model

Utilizing a two-temperature model, this study investigates the thermomagnetic convection of a ferrofluid within a porous cavity. The cavity is heated from the bottom and cooled from the sides to establish thermo-gravitational convection, whereas the thermomagnetic convection is induced by permanent magnets. The equations that govern flow and heat transfer are discretized using the finite volume method and the SIMPLE algorithm. The first part of the study evaluates the impact of the permanent magnet’s position on the flow pattern and ferrofluid and solid temperature fields. The results showed that positioning the magnet at the bottom of the cavity enhances heat transfer rate. The second part investigates the impact of the distance between two magnets at different magnetic, Rayleigh, and Darcy numbers, as well as the conduction ratio. The numerical findings exhibit that the heat transfer rate attains a peak at a certain distance between the magnets, depending on the Rayleigh number. With increasing Rayleigh number and conduction ratio, or decreasing Darcy number, the role of the magnetic field in improving heat transfer becomes less important. It is observed that thermomagnetic convection is replaced by thermo-gravitational one at high conduction ratios. The study emphasizes the need to use a local thermal non-equilibrium model in porous media with high magnetic and Darcy numbers, as well as large conduction ratios, to accurately capture the heat transfer phenomenon. It is observed that by placing two magnets at an appropriate distance, the heat transfer rate could be augmented by more than 136 %.