Unified Thermodynamic Framework Research Articles

A crystal plasticity-based creep model considering the concurrent evolution of point defect, dislocation, grain boundary, and void

Creep poses a significant threat to the integrity and longevity of structural components at high-temperature. The most current understanding of creep mainly focuses on the coupled dynamics of point defects and dislocation, which may well describe the first and second stage of creep. However, the behavior of the three stages of creep is jointly controlled by point defect (vacancy) diffusion, dislocation glide, dislocation climb, grain boundary (GB) sliding, and void evolution. A critical knowledge gap still exists regarding how these different creep mechanisms are simultaneously coupled during the three stages of creep. In this work, a multi-physical mechanisms-based crystal plasticity model is proposed to consider the concurrent evolution of point defect, dislocation, GB, and void based on a unified thermodynamic framework. In-situ scanning electron microscope creep experiments and macroscopic creep experiments of Ti-6Al-4V were conducted to validate our model. The in-situ creep experiment directly revealed the GB sliding creep failure behavior of Ti-6Al-4V for the first time. The proposed model well predicts both the microscopic and macroscopic experimental behavior of creep. The contribution of different microstructure evolutions is discussed, and a phase diagram of the dominated creep mechanism is obtained. An in-depth analysis was conducted on the coupling effects and microstructure characteristics of different creep mechanisms. This work not only deepens our understanding of the micro creep mechanism but also offers valuable insights for designing materials with specific microstructures to enhance their creep resistance.

Insights of water-to-hydrogen conversion from thermodynamics

<p>Water-to-hydrogen can be achieved using a variety of driving energy sources, including thermal, electrical, or photo energy. While methods for hydrogen production in specific energy driving scenarios have been extensively studied, a comprehensive theory to explain the conversion of various energies into hydrogen is still lacking. This study provides a novel exergy-based perspective on hydrogen production methods, revealing that the thermodynamic infeasible water splitting process is derived from insufficient exergy input relative to the reaction exergy requirement. Enhancing the exergy input beyond the reaction exergy requirement can break through chemical equilibrium and enable the reaction to proceed. Providing high exergy-to-energy ratios of energy sources such as electrical, photo, and chemical energy for thermochemical water splitting reactions can reduce the thermal exergy demand for hydrogen production, thus facilitating water-to-hydrogen conversion at lower temperatures. By applying this new insight to coupled photochemical- and thermochemical water splitting reactions, equilibrium conversion rates corresponding to solar spectra with different wavelengths are obtained. The highest water-to-hydrogen conversion rate is achieved by the solar spectrum at a wavelength of about 451nm. The appropriate wavelength region for high water-to-hydrogen conversion is identified. This study also identifies the theoretical conversion limit of photochemical water splitting, providing insights into the potential improvements of current experiments. More importantly, our work offers a unified thermodynamic framework for understanding hydrogen production methods and presents a theoretical basis for reducing reaction temperature and enhancing conversion rate.</p>

A coupled crystal-plasticity and phase-field model for understanding fracture behaviors of single crystal tungsten

The brittle-ductile transition (BDT) of tungsten depends heavily on temperature-dependent dislocation mobility. To well understand the underlying mechanism of tungsten fracture behavior, the dislocation activities need to be well described, but the related model remains limited. In this work, a coupled crystal-plasticity and phase-field model (CP-PFM) is developed based on a unified thermodynamic framework, which considers the thermal activated kink-pair mechanism of screw dislocation motion, the evolution of dislocation density, and the coupling effects between the plasticity and the crack propagation. The developed model can well predict the experimental results and is used to study the BDT process of tungsten. Four typical fracture processes are disclosed depending on the temperature, including the brittle fracture, semi-brittle fracture, micro-ductile fracture and ductile fracture. They exhibit different micro-cleavage crack features, induced by the competition between the shielding effect of the plastic zone and the crack propagation near the crack tip zone. In addition, the fracture process of tungsten is found to be significantly influenced by non-Schmid effect in the low and medium temperature regimes.

Molecular level insights into the dynamic evolution of forward osmosis fouling via thermodynamic modeling and quantum chemistry calculation: Effect of protein/polysaccharide ratios

While forward osmosis (FO) shows broad application prospects in wastewater reuse and desalination, it is still hindered by membrane fouling issues. From the perspective of molecular structure and energy, this work investigated the effects of protein (PN)/polysaccharide (PS) ratios of organic foulants on the dynamic evolution of membrane fouling in FO. Fouling tests showed two interesting membrane fouling phenomena: Ⅰ) when PN content increased from 0.2 to 0.8 g/L with fixed PS content of 0.2 g/L, membrane fouling decreased for filtration of the same volume of foulants; Ⅱ) with the increase of filtration volume, the membrane fouling caused by 1:1 PN/PS foulants increased almost linearly, while the membrane fouling caused by 4:1 PN/PS foulants increased significantly at first, and then rapidly reached a stable fouling state. Thermodynamic analyses and quantum chemical calculations revealed that the attractive interaction energy between 1:1 PN/PS foulants and membrane was 1.90 times greater than that for 4:1 PN/PS foulants, and the protein and polysaccharide molecules with a ratio of 1:1 were more likely to form a tight cross-linked structure. Furthermore, the reverse solute diffusion significantly reduced the electrostatic repulsion energy among the polymer chains for 4:1 PN/PS foulants, which induced the transformation of foulant morphology from gel to floc and reduced the adhesion energy to membrane surface by 61%. As a result, in the later fouling stage, few 4:1 PN/PS foulants were newly attached to the membrane, leading to a pseudo-stable flux. Based on the aforementioned findings, this study reveals a unified thermodynamic framework for the effects of the PN/PS ratios of organic foulants on the dynamic evolution of FO membrane fouling. The proposed mechanism is beneficial in formulating “tailored” fouling mitigation strategies and elucidating the appropriate application fields for FO technology.

A unified thermodynamic framework to compute the hydrate formation conditions of acidic gas/water/alcohol/electrolyte mixtures up to 186.2 MPa

The coexistence of acid gas/water/alcohol/electrolyte mixtures is common during the gas production process. Traditional methods have difficulty accurately predicting hydrate formation temperatures and pressures because of complicated molecular and ionic interactions in such mixture components. Based on the electrolyte Cubic-Plus-Association (e-CPA) equation of state (EoS) and the Parrish-Prausnitz model, this paper proposed a unified thermodynamic model to describe the multiple interactions of acid gas/water/alcohol/electrolyte components on gas, liquid, and hydrate phases by using the advantages of the e-CPA EoS to characterize the hydrogen bond association, solvation, ion electrostatic interaction, and ionic solvation. This work has achieved an accurate and flexible way to compute the hydrate formation conditions with or without acid gases, alcohols, and electrolytes. A total of 281 groups of experimental data at pressures from 0.068 MPa to 186.2 MPa are applied to validate this model. The results show that the average relative deviations (ARDs) of predicted temperatures and pressures are 0.13% and 6.52%, respectively. For nonelectrolyte systems, the ARD between the experimental and calculated hydrate formation temperatures is 0.19%, which is reduced by 0.24% and 0.34% in comparison with traditional Soave–Redlich–Kwong and Peng–Robinson EoSs. For mixtures containing alcohol and/or electrolytes, the ARD of predicted hydrate temperatures is 0.12%. Particularly, for harsh systems with ultrahigh pressure (186.2 MPa), the sour gas content of 24.52 mol%, MeOH concentration of 50% by mass, and salinity of 31% by mass, the deviations are less than 2.2 K. More cases demonstrate the performance and synergistic effect of alcohol and electrolytes in inhibiting hydrate formation.

Thermodynamic restrictions on linear reversible and irreversible thermo-electro-magneto-mechanical processes.

A unified thermodynamic framework for the characterization of functional materials is developed. This framework encompasses linear reversible and irreversible processes with thermal, electrical, magnetic, and/or mechanical effects coupled. The comprehensive framework combines the principles of classical equilibrium and non-equilibrium thermodynamics with electrodynamics of continua in the infinitesimal strain regime.In the first part of this paper, linear Thermo-Electro-Magneto-Mechanical (TEMM) quasistatic processes are characterized. Thermodynamic stability conditions are further imposed on the linear constitutive model and restrictions on the corresponding material constants are derived. The framework is then extended to irreversible transport phenomena including thermoelectric, thermomagnetic and the state-of-the-art spintronic and spin caloritronic effects. Using Onsager's reciprocity relationships and the dissipation inequality, restrictions on the kinetic coefficients corresponding to charge, heat and spin transport processes are derived. All the constitutive models are accompanied by multiphysics interaction diagrams that highlight the various processes that can be characterized using this framework.

Continuous Molecular Targeting–Computer-Aided Molecular Design (CoMT–CAMD) for Simultaneous Process and Solvent Design for CO2 Capture

Solvent-based separation systems have a substantial potential for improvement when the solvent and the process conditions are optimized simultaneously. The fully integrated design problem, however, leads to an optimization problem of prohibitive size and complexity owing to the many discrete degrees of freedom in selecting a solvent and the nonlinear nature of the process models. We here implement and extend the method of continuous molecular targeting–computer-aided molecular design (CoMT–CAMD) for the solvent and process optimization of a precombustion CO2-capture system with physical absorption. CoMT–CAMD is a deterministic procedure that does not require a preselection of solvent molecules. The process topology considered in our study includes all major process operations of an existing CO2-capture system: multistage absorption, desorption (two flash desorption stages with gas recycle) and CO2 compression. We measure the process performance with a single economic objective function. The objective function captures the process trade-offs and evaluates the potential process-solvent on a common basis. The solvent is represented as the pure component parameters of the perturbed-chain statistical associating fluid theory (PC-SAFT). The optimization problem is formulated with the pure component parameters of the solvent (PC-SAFT parameters) and with the process variables as degrees of freedom. Necessary auxiliary properties of the optimized solvent such as the ideal gas heat capacity and the molar mass are predicted with quantitative structure property relationship models, based on the pure component PC-SAFT parameters. As a result, one gets a unified thermodynamic framework for fluid properties based on the PC-SAFT model. With CoMT–CAMD we obtain a list of the best performing physical solvents for the considered CO2-capture application. The resulting list of best performing solvents contains state-of-the-art solvents and new green solvent molecules.

A unified thermodynamic framework for LNG rapid phase transition on water

Rapid phase transition (RPT) is a phenomenon which frequently occurs after an LNG release on water. Its effects are potentially hazardous mainly because of the very fast rate of high energy release, in addition to fire and explosion. A significant case history and various experimental campaigns provide evidence which has allowed assessing different aspects of this event. This paper aims at offering a unified thermodynamic analysis of RPT. The thermodynamic and the kinetic limits of liquid superheat have been fully reviewed and specifically applied to LNG, within the homogeneous nucleation theory for multi-component liquids. Thermal and thermo-mechanical interface properties, such as interface temperature, evaporation rate, surface properties and liquid fragmentation have also been investigated. The importance of LNG composition has been analysed with respect to the experimental data. Finally, on the basis of the well known Shepherd and Sturtevart test, bubble growth rate has been modelled according to Mikic, Rohsenow and Griffith (MRG) equation and a new rigorous method has been set up to predict RPT overpressure, in line with Lighthill's acoustic theory, which removes the existing uncertainty and some subjectivities of the available models and possibly increases the thermo-fluid dynamic understanding of the phenomenon.

Comparing RNA Kissing Interactions at Single-Molecule and Ensemble Levels

Single-molecule and ensemble techniques are employed to take different perspectives to complex, heterogeneous systems. The challenge remains whether we can interpret results from the two different approaches using a unified thermodynamic framework, despite the differences in experimental procedures and conditions? In RNA mediated gene regulations, RNA kissing complexes, a type of loop-loop interaction, play a critical role in speeding RNA-RNA interactions. However, to form a kissing complex, a regulatory hairpin must compete with RNAs for various targets and non-targets. To probe such an interacting network, we use optical tweezers to determine thermodynamics of each type of kissing complexes one molecule at a time, and use mass spectrometry to take a snapshot of simultaneous equilibria of multiple kissing interactions by many molecules. Especially, we examine strength of relatively weak kissing interactions at single-molecule level and monitor their competition with formation of stronger kissing structures at ensemble level. To compare the two types of measurements, we take into account different experimental conditions, including salts, concentrations of RNAs, time vs. numerical averaging, equilibrium vs. non-equilibrium, and difference between intra- and intermolecular interactions. With these adjustments, we establish a quantitative correlation between two types of measurements, which can be used to accurately predict abundance of subpopulations, especially that of rare species, in a heterogeneous mixture. These results show that complementary information of an interacting network, generated by the two-pronged methodology, can be unified in a thermodynamic framework.

A unified thermodynamic framework for the modelling of diffusive and displacive phase transitions

A thermodynamically consistent framework able to model both diffusive and displacive phase transitions is proposed. The first law of thermodynamics, the balance of linear momentum equation (in the linearized strain approximation) and the Cahn–Hilliard equation for solute mass conservation are the governing equations of the model, which is complemented by a suitable choice of the Helmholtz free energy and consistent boundary and initial conditions. To highlight thermo-chemo-mechanical interactions, some numerical tests are performed in which the phase transition is triggered by setting the value of the initial temperature; a time–temperature–transformation diagram is determined.

A unified residual-based thermodynamic framework for strain gradient theories of plasticity

A unified thermodynamic framework for gradient plasticity theories in small deformations is provided, which is able to accommodate (almost) all existing strain gradient plasticity theories. The concept of energy residual (the long range power density transferred to the generic particle from the surrounding material and locally spent to sustain some extra plastic power) plays a crucial role. An energy balance principle for the extra plastic power leads to a representation formula of the energy residual in terms of a long range stress, typically of the third order, a macroscopic counterpart of the micro-forces acting on the GNDs (Geometrically Necessary Dislocations). The insulation condition (implying that no long range energy interactions are allowed between the body and the exterior environment) is used to derive the higher order boundary conditions, as well as to ascertain a principle of the plastic power redistribution in which the energy residual plays the role of redistributor and guarantees that the actual plastic dissipation satisfies the second thermodynamics principle. The (nonlocal) Clausius–Duhem inequality, into which the long range stress enters aside the Cauchy stress, is used to derive the thermodynamic restrictions on the constitutive equations, which include the state equations and the dissipation inequality. Consistent with the latter inequality, the evolution laws are formulated for rate-independent models. These are shown to exhibit multiple size effects, namely (energetic) size effects on the hardening rate, as well as combined (dissipative) size effects on both the yield strength (intrinsic resistance to the onset of plastic strain) and the flow strength (resistance exhibited during plastic flow). A friction analogy is proposed as an aid for a better understanding of these two kinds of strengthening effects. The relevant boundary-value rate problem is addressed, for which a solution uniqueness theorem and a minimum variational principle are provided. Comparisons with other existing gradient theories are presented. The dissipation redistribution mechanism is illustrated by means of a simple shear model.

Chemical and Biochemical Thermodynamics: From ATP Hydrolysis to a General Reassessment

The Legendre-transformed Gibbs energy change for a biochemical reaction, Delta(r)G', is shown to be equal to the nontransformed Gibbs energy change, Delta(r)G, of any single reaction involving selected chemical species of the biochemical system. These two Gibbs energies of reaction have hitherto been thought to have different values. The equality of the quantities means that a substantial part of biochemical and chemical thermodynamics, previously treated separately, can be treated within a unified thermodynamic framework. An important consequence of the equality of Delta(r)G and Delta(r)G' is that the Gibbs energy change of many enzyme reactions can be quantified without specifying which chemical species is the active substrate of the enzyme. Another consequence is that the transformed standard Gibbs energy change of a reaction, Delta(r)G'(0), can be calculated by a simple analytical expression, rather than the complex computational methods of the past. The equality of the quantities is restricted to Gibbs energy changes and does not apply to enthalpy or entropy changes.

A universal surface complexation framework for modeling proton binding onto bacterial surfaces in geologic settings

Adsorption onto bacterial cell walls can significantly affect the specia- tion and mobility of aqueous metal cations in many geologic settings. However, a unified thermodynamic framework for describing bacterial adsorption reactions does not exist. This problem originates from the numerous approaches that have been chosen for modeling bacterial surface protonation reactions. In this study, we compile all currently available potentiometric titration datasets for individual bacterial species, bacterial consortia, and bacterial cell wall components. Using a consistent, four discrete site, non-electrostatic surface complexation model, we determine total func- tional group site densities for all suitable datasets, and present an averaged set of 'universal' thermodynamic proton binding and site density parameters for modeling bacterial adsorption reactions in geologic systems. Modeling results demonstrate that the total concentrations of proton-active functional group sites for the 36 bacterial species and consortia tested are remarkably similar, averaging 3.2 1.0 (1) 10 4 moles/wet gram. Examination of the uncertainties involved in the development of proton-binding modeling parameters suggests that ignoring factors such as bacterial species, ionic strength, temperature, and growth conditions introduces relatively small error compared to the unavoidable uncertainty associated with the determination of cell abundances in realistic geologic systems. Hence, we propose that reasonable estimates of the extent of bacterial cell wall deprotonation can be made using averaged thermodynamic modeling parameters from all of the experiments that are considered in this study, regardless of bacterial species used, ionic strength, temperature, or growth condition of the experiment. The average site densities for the four discrete sites are 1.1 0.7 10 4 , 9.1 3.8 10 5 , 5.3 2.1 10 5 , and 6.6 3.0 10 5 moles/wet gram bacteria for the sites with pKa values of 3.1, 4.7, 6.6, and 9.0, respectively. It is our hope that this thermodynamic framework for modeling bacteria-proton binding reactions will also provide the basis for the development of an internally consistent set of bacteria-metal binding constants. 'Universal' constants for bacteria-metal binding reactions can then be used in conjunc- tion with equilibrium constants for other important metal adsorption and complex- ation reactions to calculate the overall distribution of metals in realistic geologic systems.

Thermodynamic renormalization group.

For a system with a first or second order phase transition at ${\mathit{T}}^{\mathrm{*}}$, we construct a type of renormalization group transformation that maps the reduced temperature t=(T-${\mathit{T}}^{\mathrm{*}}$)/${\mathit{T}}^{\mathrm{*}}$ and the external field h for a system of volume V to t\ensuremath{'} and h\ensuremath{'} for another system of volume V\ensuremath{'}. Our construction is purely thermodynamic without reference to effective Hamiltonians. Using the transformation, we derive the finite size scaling form for the singular part of the free energy, which leads to the scaling laws in the thermodynamic limit. We thus provide a unified thermodynamic framework for phase transitions. \textcopyright{} 1996 The American Physical Society.