Search

Temperature uniformity is a critical parameter in solid oxide fuel cells (SOFCs) since it directly impacts thermal stress, material degradation and output performance. Effective thermal management typically aims to achieve a minimal temperature gradient, especially within a SOFC stack assembled by numerous single cells. In this study, numerical simulations of various boundary conditions and cell designs are performed to investigate thermal uniformity in methane-rich internal reforming SOFCs, which can be utilized as a guidance for design and operation in practical application. The results indicate that the fuel gas with a 5 % mole fraction of methane is more effective in enhancing thermal uniformity through reforming cooling effect at the electrolyte compared to only a 1 % mole fraction. It is strongly recommended in cell design to maintain the ratio of the cell's length to its width (R cell) greater than or equal to 1.0 considering its better thermal uniformity. However, both increasing the ratio of channel width to rib width (R c-r) and decreasing the ratio of channel height to channel width (R H-W) have been demonstrated to deteriorate temperature uniformity. Within this study, increasing the backpressure to 1.5 bar is found to result in a 16.7 % reduction in the maximum temperature difference across the electrolyte when compared to that at atmospheric pressure. It is also advisable to operate at the inlet temperature ranging from 973 K to 1023 K for a more uniform temperature distribution within the SOFC. [Display omitted] • The dry reforming of methane is considered in thermal equilibrium analysis. • Effects of flow filed structure and operating parameters are investigated. • Operating parameters affect system efficiency and thermal uniformity differently. • There is a sweet spot for the effects of inlet temperature on thermal uniformity. [ABSTRACT FROM AUTHOR]

Centrifugal Nuclear Thermal Propulsion is a second-generation propulsion concept currently being researched to succeed traditional solid core nuclear thermal propulsion. Current efforts across the space industry are focusing on development of technologies for enabling manned flight to Mars and scientific missions to the outer planets. To enable these types of mission's direct injection trajectories are needed to decrease exposure to astronauts and scientific payloads to the harsh environment of space. Current efforts in nuclear thermal propulsion have shown great promise in higher specific impulses ∼900 s, but even these levels of specific impulse fall short for manned Mars missions with durations less than two years or direct injection to orbit of the outer ice giants Uranus and Neptune without the use of gravity assists. High performance nuclear thermal propulsion has been proposed using bubble through nuclear reactors to reach specific impulses as high as 1800 s, however significant challenges exist to prove the feasibility of such a system. One of the major challenges is the fluid mechanics within the core of the engine since little is known about uranium in the liquid phase. An experimental study has been conducted to better understand the fluid dynamics to better inform the thermodynamic and nucleonic models. Using the data from the experiment, high-fidelity simulations have been developed to predict the fluid dynamics of the uranium fuel. This information can then be further fed into thermodynamics models in development to predict core temperatures and system behaviour. The validated models show that small bubbles reach thermal equilibrium, and high centrifugal forces and surface tension assist in confining the molten uranium within the reactor core. Injector methods suggest feasible configurations to encourage bubble flow while minimizing backflow of the propellant, motivating further study of Centrifugal Nuclear Thermal Propulsion based systems. • Galinstan (Ga67In20.5Sn12.5) was determined to be a suitable uranium simulant for bubble formation. • High Speed Radiography was used to determine bubble characteristics using machine learning algorithm. • Hydrogen bubbles in uranium rapidly reach local equilibrium with diameters of 0.266 mm and reaching velocities of 16 m/s. • To date all research indicates that a centrifugal nuclear thermal rocket is feasible. [ABSTRACT FROM AUTHOR]

The non-equilibrium spectra of shock-heated nitrogen in the UV-visible range are investigated in a detonation driven shock tube. Spectral identification indicates that the main contributors to the spectra are molecular radiation of N 2 (2+) and N 2 + (1-). Vibrational and rotational temperatures of N 2 (C) and N 2 + (B) are determined through spectral fitting. The post-shock spectra of pure nitrogen are obtained for shock velocities ranging from 6.82–9.00 km/s and P 0 = 30–200 Pa at the shock arrival time. Differences between vibrational and rotational temperatures of N 2 (C) and N 2 + (B) are observed, suggesting that nitrogen is in a non-equilibrium state at shock arrival moment. Time-resolved spectra are obtained within varying delay times of 0– 2. 0 μ s at P 0 = 200 Pa and shock velocity of V sw = 6.60 km/s. Time-resolved temperatures are determined to illustrate the time-resolved non-equilibrium characteristics of nitrogen at high temperature. It is observed that the non-equilibrium characteristics of nitrogen gradually weaken with increasing time and the thermal equilibrium was not obtained within 2. 0 μ s. Finally, the time-resolved temperatures are compared with CEA (Chemical Equilibrium with Applications) prediction, revealing that the difference in temperature between the experiment and the CEA equilibrium calculation decreases as time increases. • The radiative spectra of nitrogen are obtained in shock tube with shock velocity of 6.5–9.0 km/s. • The shock velocity-dependent non-equilibrium characteristics of nitrogen are revealed. • The time-resolved non-equilibrium characteristics in the post-shock region are studied. • The non-equilibrium effects of N 2 (C) and N 2 +(B) are obtained and analyzed. [ABSTRACT FROM AUTHOR]

Mullite fiber-based porous ceramics is one of the most commonly used high-temperature insulation materials. However, how to further reduce the thermal conductivity and improve the strength of such materials has been a challenge in the field of high-temperature insulation. In this paper, mullite micro/nano fiber-based porous ceramic was prepared by introducing mullite nanofibers into mullite microfiber-based porous ceramics and the effect of microfiber/nanofiber weight ratio on the samples properties were characterized and analyzed. Results showed that the compressive strength and high-temperature thermal insulation properties of the porous ceramics increased significantly with an increase in the nanofiber content. For the porous ceramics with similar density (about 0.50 g/cm3), the compressive strength of the sample with a microfibers/nanofibers weight ratio of 1:2 was 1.43 MPa, which was much higher than that of the porous ceramics prepared with only microfibers (0.26 MPa). Meanwhile, the backside thermal equilibrium temperature of the sample with a microfiber/nanofiber weight ratio of 1:2 at 900 °C environment was 355.8 °C, which was much lower than that of the porous ceramic prepared with only microfibers (476.5 °C). In addition, in order to investigate the temperature resistance of mullite micro/nano fiber-based porous ceramics, the sintering temperatures was increased from 1400 °C to 1500 °C. Results shows that the high-temperature thermal insulation performance of mullite micro/nano fiber-based porous ceramics with high mullite nanofiber content decays more seriously. The back-temperature test showed that the thermal equilibrium temperature of the samples with a mullite micron/nanofiber weight ratio of 1:1 in 900 °C environment increased rapidly from 386.3 °C to 454.2 °C when the sintering temperature was increased from 1400 °C to 1500 °C. The preparation of mullite micro/nanofiber-based porous ceramics provides a new strategy to improve the performance of fiber-based porous ceramics. [ABSTRACT FROM AUTHOR]

Mullite fiber-based porous ceramics is one of the most commonly used high-temperature insulation materials. However, how to further reduce the thermal conductivity and improve the strength of such materials has been a challenge in the field of high-temperature insulation. In this paper, mullite micro/nano fiber-based porous ceramic was prepared by introducing mullite nanofibers into mullite microfiber-based porous ceramics and the effect of microfiber/nanofiber weight ratio on the samples properties were characterized and analyzed. Results showed that the compressive strength and high-temperature thermal insulation properties of the porous ceramics increased significantly with an increase in the nanofiber content. For the porous ceramics with similar density (about 0.50 g/cm3), the compressive strength of the sample with a microfibers/nanofibers weight ratio of 1:2 was 1.43 MPa, which was much higher than that of the porous ceramics prepared with only microfibers (0.26 MPa). Meanwhile, the backside thermal equilibrium temperature of the sample with a microfiber/nanofiber weight ratio of 1:2 at 900 °C environment was 355.8 °C, which was much lower than that of the porous ceramic prepared with only microfibers (476.5 °C). In addition, in order to investigate the temperature resistance of mullite micro/nano fiber-based porous ceramics, the sintering temperatures was increased from 1400 °C to 1500 °C. Results shows that the high-temperature thermal insulation performance of mullite micro/nano fiber-based porous ceramics with high mullite nanofiber content decays more seriously. The back-temperature test showed that the thermal equilibrium temperature of the samples with a mullite micron/nanofiber weight ratio of 1:1 in 900 °C environment increased rapidly from 386.3 °C to 454.2 °C when the sintering temperature was increased from 1400 °C to 1500 °C. The preparation of mullite micro/nanofiber-based porous ceramics provides a new strategy to improve the performance of fiber-based porous ceramics. [ABSTRACT FROM AUTHOR]

Shock/shock interactions (SSIs) often lead to high thermal loads. To understand the influences of thermochemical non-equilibrium effects on the Type III SSI, four gas models based on the assumption of thermal perfect gas (TPG), thermal equilibrium chemical non-equilibrium gas (TECNG), thermal non-equilibrium chemical frozen gas (TNCFG), and thermochemical non-equilibrium gas (TCNEG) are employed to simulate the Type III SSI at Mach 10. The intersection of incident shock and bow shock is determined by dimensionless intercept of 0.05 and 0.1. It is found that the chemical non-equilibrium effects significantly lift up the impingement position of shear layer by reducing the standoff distance of bow shock. As a result, the peaks of wall pressure and heat flux calculated by TECNG and TCNEG model are higher than TPG and TNCFG model, respectively. Type IIIa SSI occur in the flows calculated by the TECNG and TCNEG model for the case with a dimensionless intercept of 0.1. The peaks of wall pressure and heat flux calculated by TECNG model are both over four times higher than those of TPG model. The thermal non-equilibrium effects slightly increase the standoff distance of bow shock and lower the impingement position of shear layer. In addition, the thermal non-equilibrium reduces the angle to the horizontal direction of shear layer by increasing the specific heat ratio. • Type III shock/shock interaction at Mach 10 are simulated by four gas models. • The influences of non-equilibrium effects on flow fields are analyzed. • The chemical non-equilibrium effects significantly increase the peak values of heat flux and pressure. • The mechanisms of non-equilibrium effects on peak heat flux and pressure are revealed. [ABSTRACT FROM AUTHOR]

To characterize the impact of thermal nonequilibrium conditions in shock-induced combustion in high Mach number scramjet engines, a comparative numerical investigation has been performed. The combustor configuration was based on the HyShot II scramjet while the total enthalpy is 3.3 MJ/kg which resembles Mach 8 flight condition. The improved delay detached eddy simulation with Park two-temperature approach in combination with the vibration-chemical coupling model was employed in the nonequilibrium simulations. It is shown that under thermal nonequilibrium inflow conditions, noticeable stratification in the thermal state exists in the circumferential direction both in the combustor section and exhaust nozzle. In the inner core where the fuel mixes with the mainstream, flow deceleration caused by the heat release leads to a sufficient transformation of energy between the vibrational and translational-rotational modes approaching the thermal equilibrium state. However, the τ v , m i x is quite large in the supersonic mainstream, whereby the thermal nonequilibrium dominates. For the case with higher T v in the inflow, the fuel jet's penetration height is lower while the local viscosity is higher which results in poor mixing between the fuel and air stream. Nevertheless, a 400 K increase in inflow T v gives a higher effective temperature, which promotes the dissociation reactions, shortens the ignition distance and yields an 8% increase in the overall combustion efficiency. With better combustion performance, an additional 6% deceleration in the supersonic mainstream and the energy exchange rate between vibrational and translational-rotational modes becomes almost four times faster at the combustor outlet, which promotes the restoration of the thermal equilibrium state. Furthermore, under higher inflow vibrational temperature, the shock-induced combustion in supersonic crossflow becomes less stable with noticeable fluctuations in combustion heat release and local static pressure. • Combustion dynamics for the Hyshot II scramjet engine under different thermal nonequilibrium inflow conditions were investigated numerically. • Noticeable stratification in thermal state in the circumferential direction was observed when vibrational nonequilibrium effect was considered. • Increase in vibrational temperature at combustor inlet by 400 K resulted in an 8% increase in the overall combustion efficiency. • The instability of shock-induced combustion was enhanced under higher inlet vibrational temperature. [ABSTRACT FROM AUTHOR]

Recently, nanoscale thermometry has attracted extensive attention. Here, we present an innovative approach to enhance the sensitivity of upconversion nanoparticles for thermometry through near-field manipulation. This method involves a composite structure consisting of photonic crystals and upconversion nanoparticles, with the near-field of the nanoparticles manipulated by tuning the absorption of the photonic crystals. The fluorescence intensity ratio (540nm/520 nm) of 4H 11/2 and4S 3/2 states of upconversion nanoparticles doped with Er3+ ions is sensitive to temperature change and employed as a temperature indicator that satisfies Boltzmann thermal equilibrium. The composite structure exhibited a relative thermometry sensitivity of 21.9 × 10−3 K−1 at 298 K, representing a significant improvement over pure core-shell upconversion nanoparticles with a 63.43% increase in relative sensitivity and a 675% increase in absolute sensitivity. This finding demonstrates the potential of our approach for advancing nanoscale thermometry. [ABSTRACT FROM AUTHOR]

Active matter, responsive ("smart") materials and materials under time-dependent load are systems out of thermal equilibrium. To construct coarse-grained models for such systems, one needs to integrate out a distribution of microstates that evolves in time. This is a challenging task. As a preparation to the topic, we recall equilibrium coarse-graining methods, both theoretical and numerical, such as projection operator formalisms, united atom simulations, numerical reconstruction of memory and Markov State Modelling. Then we review recent developments in theoretical approaches to the non-equilibrium coarse-graining problem, in particular, time-dependent projection operator formalisms, dynamic density functional theory and power functional theory, as well as numerical schemes to construct explicitly time-dependent memory kernels. [ABSTRACT FROM AUTHOR]

The effects of metal foams on Latent Heat Thermal Energy Storage System, LHTESS, based on a phase change material, PCM, is numerically investigated. The geometry of the system is a vertical shell and tube LHTESS made of two concentric tubes. A constant temperature above the melting temperature of the PCM on the internal surface of the hollow cylinder is assumed to simulate the heat transfer from a hot fluid. The external surfaces are adiabatic. The PCM is completely embedded in the volume between the two coaxial cylinders. An aluminum metal foam is chosen, and it partially fills the volume starting from the internal cylinder. The enthalpy-porosity theory and the Darcy-Brinkman-extended model are employed to simulate, respectively, the phase change of the PCM and the metal foam which is modelled in local thermal equilibrium. Ansys-Fluent code is adopted to solve the governing equations. The results are rendered in terms of melting time, liquid fraction, temperature, and stored thermal energy as a function of time and for different metal foam thickness values. The results indicate that the melting time reduces with increase in the thickness of the metal foam. The partially filled thermal storage system exhibits varying characteristics at the initiation and at the sustenance periods of the heating process. A scale analysis is performed to estimate the melting time and the values are in tandem with the numerical model evaluation. [ABSTRACT FROM AUTHOR]

Aero-thermal analysis of hypersonic vehicles is of fundamental interest for structural design and material selection. Therefore, we investigated the aerodynamic heating characteristics of a blunt cone made from stainless steel in a combustion-heated hypersonic wind tunnel with a free stream of Mach 6. During ground testing, the temperature rise of the model from room temperature to thermal equilibrium under the influence of hypersonic flow was measured with thermocouples, and the equilibrium temperature of the blunt section was 1130–1150 K. In addition, the transient thermal response of the model to the aerothermodynamic load was simulated by fluid-thermal coupled analysis and compared with the measurement data. The obtained results correspond well to typical thermocouple data, and the temperature predicts the measurement with an accuracy on the order of 8.8%. On this foundation, some factors affecting the radiation equilibrium temperature of the blunt cone are also discussed. The analysis indicates that emissivity has an important influence, while turbulence intensity at the nozzle inlet has minimal impact. • The effective experimental time reached 350 s, and the radiation equilibrium temperature of the cone section is obtained in 225 s. • Under the experimental conditions of Mach 6 and total temperature of 1712 K, the radiation equilibrium temperature of the cone section is 1130–1150 K. • The fluid-thermal coupling analysis method can effectively predict the thermal response process of the model. • The radiation equilibrium temperature in the blunt section is not sensitive to the change of the total temperature of the gas flow. • Surface emissivity has a great influence on the radiation equilibrium temperature, while the turbulence intensity gives the minimal impact. [ABSTRACT FROM AUTHOR]

Chilled water systems in large-scale central air conditioning consume more than 30 % of the total energy. To reduce this energy consumption, a model can be used to explore the optimal operating parameters of chilled water systems. The chilled water system is a multivariable highly coupled nonlinear system. The type and number of variables change with the hydraulic characteristics of the piping network and the operating data sparsity is high. For these reasons, data-driven methods are not suitable for modeling chilled water systems. Therefore, there is an urgent need to develop a model that is not constrained by the type and number of variables and can establish a complete data structure. According to the principles of differential pressure equilibrium, flow conservation, and thermal equilibrium, this study establishes a physical model of the hydraulic–thermal coupling of chilled water systems. The hydraulic–thermal characteristics of chilled water systems under multiple operating conditions were investigated, and the reliability of the model was verified through experiments. Furthermore, the difficulty of effective modeling owing to dynamic changes in the types of variables and lack of operating data were addressed. The study showed that the model has a wide range of applications, high reliability, and high computational efficiency. • Physical models are not affected by changes in the type and number of variables. • Enable model convergence and computational efficiency by building a database. • Model applications to big data simulation; sensitivity analysis; boundary problems, etc. • High reliability of the model verified by experiments. [ABSTRACT FROM AUTHOR]

• DUGKS is extended to moving boundary rarefied gas flows with heat transfer. • The complex advancing boundary condition is handled by the IB method. • Least square method is applied to the information construction at the ghost cell. • Six flow problems are performed to test the versatility of the method. Rarefied gas flows in complex geometries with heat transfer and moving boundaries have received remarkable attention due to the prevailing of micro/nano science and engineering applications. This study presents an immersed boundary (IB)-based discrete unified gas kinetic scheme (DUGKS) for the simulation of complex moving boundary thermal rarefied flows. The fluid and temperature fields are solved according to the DUGKS with Shakhov collision model (SDUGKS), which is capable of modeling non-unit Prandtl number problems in all Knudsen regimes. The IB approach, featured by its superior performance to incorporate complicated boundary constraints on Cartesian grids, is applied here to handling the interaction between the micro gas and curved boundaries. Specifically, for the IB adopted in this study, we use the least square method for the reconstruction of the distribution functions near the boundary. The accuracy of the IB-SDUGKS is explored comprehensively in six benchmark problems, including the micro lid-driven cavity flow, thermal equilibrium gas in a circular domain, thermal transpiration in an enclosure, moving shuttle in a rarefied gas, movement of a piston with pressure differences and particle free motion in a lid-driven cavity. The present results agree well with the corresponding analytical and direct simulation Monte Carlo (DSMC) solutions, illustrating the versatility of the present IB-SDUGKS complex thermal rarefied flows. [ABSTRACT FROM AUTHOR]

• The melting behaviors under four different strengthening structures are compared. • The finned metal foam tube under steady rotation realizes the best performance. • The effect of fin type, graded porosity, and rotational speed are further analyzed. • A maximum 46.68% melting time reduction is realized under the optimal structure. The latent heat thermal energy storage (LHTES) technology based on solid-liquid phase change material (PCM) is of great significance for the efficient utilization of thermal energy. To address the issues of slow thermal response and non-uniform melting of the LHTES technology, a hybrid heat transfer enhancement method combined with finned metal foam and steady rotation is proposed in this work. An enthalpy-porosity model considering non-Darcy porous effects and mechanical rotation is established based on the local thermal equilibrium assumption and the fixed grid system. Four different structures (uniform metal foam, graded metal foam, finned metal foam with uniform porosity, and finned metal foam with graded porosity) are investigated firstly to identify the optimal structural arrangement under the same volume of PCM. Numerical results demonstrate that the LHTES units strengthened by the finned metal foam with graded porosity achieve the shortest melting time and largest thermal energy storage rate (TESR). The graded porous structure reduces thermal resistance, rotation enhances flow and heat transfer inside the container, and the fins expand the heat source area. Moreover, the effect of different fin types, graded porosities, and rotational speeds are further considered. The findings suggest that the increase of these three parameters does not correspond to better thermal performance; instead, there is an optimal value. Compared with the base case, the optimal configuration (fin length of 20 mm, fin width of 1.5 mm, porosity gradient of 2%, and rotational speed of 0.5 rpm) can shorten the melting time by 46.68%, increase the TESR and Nu by 74.06% and 69.02%, respectively. This paper validates the feasibility of the hybrid heat transfer enhancement method with finned metal foam and steady rotation, which can offer new insights into the engineering practice of the LHTES technology. [ABSTRACT FROM AUTHOR]

Understanding the behavior of fluids in seismically active faults and their chemical-physical (dis)equilibrium with the host rock is important to understand the role of fluids upon seismicity and their possible potential for forecasting earthquakes. The small number of case studies where seismic and geochemical data are available and the lack of accessibility to fault zones at seismogenic depth for recent earthquakes limit our understanding of fluid circulation and its relationship to seismicity. The study of fault-fluid relationships in exhumed faults can broaden the number of case histories and improve our understanding of the role of fluids in the seismic cycle in different tectonic settings. Here we use new geochemical and thermal data and a review of published studies from the Apennines fold-and-thrust belt (Italy) to provide a model of fluid circulation during the seismic cycle related to either the local orogenic compressional or post-orogenic extensional tectonics. We also suggest a workflow based upon different methods to identify tectonic-related chemical-physical (isotopic and thermal) (dis)equilibria in fluid-rock systems during the seismic cycle. The proposed workflow involves multiscale structural and isotope geochemical analyses, radiometric dating, and burial-thermal modeling. It is applied to carbonate-hosted faults exhumed from a depth shallower than 4 km (temperature ≤ ∼130 °C and pressure ≤ ∼130 MPa). We show that in the Apennines, during syn-orogenic shortening, thrusting is mostly assisted by fluid circulation in an effectively closed system where fluid and host rock remain close to chemical and thermal equilibrium. In contrast, post-orogenic normal faulting occurs in association with upward and/or downward open fluid circulation systems leading to chemical-physical disequilibria between the host rock and the circulating fluids. Isotopic and thermal fluid-rock disequilibria are particularly evident during pre- and co-seismic extensional deformation. Mineralizing fluids, whose temperature can vary between 30 °C warmer and 16 °C colder than the host rock, result from the mixing of fluids derived from both the deforming host rock and external sources (meteoric or deep crustal). The proposed workflow offers the potential to track past seismic cycles and provide indications on actual fluid-earthquake relationships including the identification of potential seismic precursors and modes of triggered seismicity that might be different in extensional and compressional tectonic settings. • Fluid-rock chemical-physical (dis)equilibrium during faulting in the Apennines • Structural, isotopic, and thermal proxies for tectonic mineralizations • Fluid-rock systems and relationships to the seismic cycle [ABSTRACT FROM AUTHOR]

[Display omitted] • Current intensity, current density and resistance voltage under thermal equilibrium are considered. • Studied the influence of various electrode structural parameters on the performance of the electrolysis cell. • Compared multiple optimization algorithms to verify the reliability of the obtained Pareto frontier distribution. • Utilized NSGA-II for multi-objective optimization of the Multipolar electrolysis cell. • Reduced electrolysis cell resistance voltage, enhanced current density. In the operation of industrial multipolar magnesium electrolysis cell, cell voltage and current density are important indicators of the production performance of the cell, while thermal balance is a key factor for normal operation. This paper utilizes the finite element method to establish a three-dimensional full cell thermal-electric model, studying the thermal field distribution and current density distribution in a 165kA multipolar magnesium electrolysis cell. Based on the heat balance of the multipolar cell, the influence of structural parameters on current intensity, average current density at the anode surface and resistance voltage is assessed. Dimensionless analysis yielded optimization criteria, and the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was employed for multi-objective optimization problems. When stringent optimization is executed, significant performance improvements can be achieved in terms of the electrolysis cell's resistance voltage and current density. Moreover, under the optimization criteria, the relative error of the 265kA multipolar magnesium electrolysis cell model is less than 1 %. The results indicate that the workflow combining the finite element method with multi-objective optimization algorithms can be applied to the optimization and scale-up design of high-current multipolar magnesium electrolysis cell. [ABSTRACT FROM AUTHOR]

• Decreasing the production of CO 2 and tar in biomass gasification. • Effect of CaO carbonation heat release on biomass gasification to hydrogen. • Reducing O 2 consumption for biomass gasification in self-heating systems. • Obtaining hydrogen-rich syngas. In pine chips gasification experiment, at 700 °C and 15 % H 2 O, with the mass ratio of Ca 90 Fe 10 /B to 1.5, the H 2 yield is 210.50 mL/g. The H 2 yield improves by 2.39 times and the tar yield decreases by 16 % compared to without CaO. In the pine chips gasification simulation with the system's own thermal equilibrium, at 700 °C, the heat release of Ca 90 Fe 10 adsorption of CO 2 is 56.91 MJ/h for Ca 90 Fe 10 /B mass ratio of 1.5, and the required O 2 inflow is 1.9 kg/h, the molar flow of H 2 is 0.58 kmol/h. To achieve material circulation, 0.5 kg/h of CH 4 is added to the calciner for combustion to satisfy heat absorption of CaCO 3 to regenerate CaO, which consumes 2.0 kg/h of O 2. The whole cycle O 2 consumption is 3.90 kg/h, which is 1.02 kg/h less than without CaO, and the H 2 yield has increased by 1.35 times. [ABSTRACT FROM AUTHOR]

• Wavy microchannel with compound rib of porous layer and solid wall is proposed. • The thermal-hydraulic performance is related to three types of structural parameters. • Multi objective genetic algorithm method is employed to optimize MCHS performance. • The 37.61% and 16.67% decreases in R and Ω with optimal compound rib compared to solid rib. The combining rib of porous layer and solid wall is set in wavy microchannel heat sink to enlarge heat transfer area and convection with smaller increase in flow resistance, in which the consumption of pump power relates to the ratios of wave amplitude to length or to width and the thickness of porous layer due to vortices generation while coolant passing through channel. The local thermal equilibrium occurs in porous layer, and the Forchheimer-Brinkman-Darcy relations were used to describe the flow inside porous ribs. The effects of channel-to-pitch width ratio, width ratio of porous layer to pitch and microchannel height on its cooling performance are investigated, and the parameter of figure of merit (FOM) is defined to evaluate thermo-hydraulic performance in wavy microchannel. Besides, the multi objective genetic algorithm method is employed to optimize structure parameters in wavy microchannel to obtain better performances, in which the increase in thermal resistance from 0.062 K/W to 0.166 K/W together with consumption of pump power decreasing from 0.00416 W to 0.00185 W can be obtained in the Pareto front set, and it relates to the heat dissipation in convection between coolant and bottom surface or vertical side ribs. Compared to wavy microchannel with solid rib, the 37.61% and 16.67% decreases respectively in thermal resistance and consumption of pump power occur in the case with optimal combining rib of porous layer and solid wall. [ABSTRACT FROM AUTHOR]

• Whole phase transition process of droplet at supercritical conditions was analyzed. • Classical, transitional and supercritical stage form whole phase transition process. • Interface deviates from global thermal equilibrium in transitional two-phase stage. • Miscible boundary layer in supercritical stage will replace non-continuum interface. • Pseudo-boiling occurs in miscible boundary layer containing supercritical fluids. With the development of heavy-duty diesel engines, the in-cylinder ambient conditions of the diesel engine are well above critical points of the main components of the diesel fuel. Therefore, significant changes arise in the phase transition process of the liquid fuels. However, the entire phase transition process of the liquid fuels in such supercritical environments is not well understood compared with that under subcritical conditions. In this work, A high-pressure transient droplet evaporation model was presented for the theoretical analysis of phase transition processes of the heptane/dodecane/hexadecane-nitrogen binary system under supercritical conditions. Analysis of the thermodynamic pseudo-trajectories reveals that the alkane droplets will undergo a three-stage phase transition process when the ambient condition is much higher than the critical point of alkanes, including classical two-phase mode, transitional two-phase mode, and supercritical single-phase mode. The evaporation dominates the phase transition process in the classical two-phase mode, and the transition from classical two-phase modes to transitional two-phase modes occurs when gas-liquid interfaces deviate from the global thermal equilibrium. In transitional two-phase modes, a gas-liquid interface still exists and separates the liquid phase and vapor phase, but with a questionable adoption of vapor-liquid equilibrium. The transition from the transitional two-phase mode to the supercritical single-phase mode occurs when the thermodynamic state of the binary mixture in the interface reaches the critical mixing state. We distinguished the phase states for the whole phase transition process according to the thermodynamic analysis of binary systems. Analogous to the immiscible interface in classical two-phase mode, a miscible boundary layer containing supercritical fluids exits between the liquid core and gas in the initial period of the supercritical single-phase mode. The pseudo-boiling phenomenon occurs in this boundary layer. [ABSTRACT FROM AUTHOR]

Thermal postbuckling analysis is presented for shear-deformable anisotropic laminated cylindrical shell with general imperfection distribution under several typical temperature fields are analyzed, including uniform temperature, tent-like linear distribution, axial and circumferential quadratic parabolic temperature fields over the shell surface and through the shell thickness. On this basis, the general temperature distribution can be obtained based on the three-dimensional steady-state heat transfer equation. At the same time, based on the high order shear deformation theory including anisotropic coupling effect, geometrically nonlinear large deflection displacement-strain relationship, the general initial geometric imperfections obtained by measurement and analytical means are introduced, and the thermal buckling equilibrium differential equation of anisotropic shear deformable laminated cylindrical shell with initial imperfections is established. A two-step perturbation-Galerkin integral method is used to obtain explicit solutions for the path development direction of post-thermal buckling equilibrium. The results of parameter analysis show that the material properties and temperature dependence, temperature distribution, lay-up and geometric parameters such as radius-to-thickness ratio have important effects on the thermal buckling load and postbuckling equilibrium path. The present method provides an effective theoretical prediction and analysis method for the design of the carrying capacity of submarine pipelines. • A new set of explicit solutions for postbuckling behaviour of anisotropic shear deformable laminated cylindrical shells with general imperfection distribution under thermal loading is obtained. • General imperfections are introduced into the thermal buckling and postbuckling analysis of anisotropic laminated cylindrical shells. • Uniform temperature, non-uniform temperature fields over the shell surface and through the shell thickness are involved. • A boundary layer theory of shell buckling has been extended to the case of anisotropic laminated cylindrical shells with general imperfection subjected to non-uniform temperature. [ABSTRACT FROM AUTHOR]

There are strong interests in hypersonic propulsion communities in predicting the flow and heat transfer characteristics over a hypersonic vehicle. However, this is quite challenging due to the emergence of thermal and chemical out-of-equilibrium effects as prominent in a high-temperature flow. In this work, we conduct 2D numerical investigations on the hypersonic double cone flow in a surrounding of the stagnation enthalpy of 15.23 MJ/kg by solving the laminar Navier–Stokes equation systems with the vibrational non-equilibrium processes and seven species air reactions. We then conduct the sensitivities analyses on the flow and heat transfer features, as different transport models and different thermochemical models are applied. It is shown that the aerodynamic heat is more sensitive to the transport models than the flow, and the transport coefficients computed by the Gupta-Yos model are more suitable for predicting the double cone flow at the high enthalpy. On the other hand, the flow field of the high enthalpy double cone is more sensitive to the thermochemical models than the heat transfer on the wall excluding the peak position. Behind the detached shock, chemical reactions are found to enhance thermal or vibrational out-of-equilibrium effects. However, vibrational non-equilibrium effects are revealed to weaken the degree of molecule dissociation reactions. Two flow separations occur in the flow field computed by using the thermal non-equilibrium gas models, but the flows of thermal equilibrium gas models separate only once. The maximum values of wall parameters without chemical reactions are found to deviate greatly from the experimental measurements. The thermochemical out-of-equilibrium gas model can predict the separation region size closer to the experiment than the two reported numerical results. The wall static pressure and heat flux are also shown to well match the experimental results. The present work should shed lights on better understanding thermochemical non-equilibrium effects of complex flow phenomenon like the shock wave/boundary layer interaction in hypersonic propulsion with high enthalpy surroundings. [ABSTRACT FROM AUTHOR]

The porous ribs and solid ribs paved with porous layer (combining ribs for short) on sidewalls are set respectively in upper and lower channels in double-layered microchannel heat sink (MCHS) with microencapsulated phase change material (MPCM) slurry as coolant to obtain better thermal performance. In the cases, more heat transfer occurs between coolant and solid ribs with MPCM slurry as coolant due to phase change in microencapsulate, and larger specific area in porous layer. The local thermal equilibrium is considered to be in porous layer, and the Forchheimer-Brinkman-Darcy relations were used to describe the flow inside porous ribs. The effects of porous layer, its thickness in combining ribs, channel-to-pitch width ratio and channel aspect ratio on heat transfer and hydraulic properties in channel with MPCM slurry as coolant are investigated. Besides, the heat flux from heating surface released through the upper channel or lower channel to the outside can be allocated with the channel-to-pitch width ratio, width ratio of porous layer to pitch in the lower channel, and channel aspect ratio in double-layered microchannel. The parameter of figure of merit (FOM) is defined to evaluate thermo-hydraulic performance. Compared to the case with copper solid ribs in lower and upper channels as benchmark (i.e. FOM = 1), the 14% and 124.56% higher FOM value occur in the cases respectively of solid and porous ribs, and combining and porous ribs in lower and upper channels, as well as the 18.93% and 65.96% decreases respectively in thermal resistance and pumping power in case of MPCM slurry as coolant with combining and porous ribs in lower and upper channels. The appropriate width ratio of porous layer to pitch and porosity in porous layer will benefit thermal behavior. [ABSTRACT FROM AUTHOR]

In this study, the thermal performance of triplex-tube heat storage system consisting of RT55 phase change material and Cu metal foam composite was investigated to find out the most efficient configuration among 17 distinct models (M1-M17) categorized into 4 distinct classes. Under simultaneous charging and discharging conditions, the melt fraction and latent heat storage capacity were calculated and finally an enhancement parameter was formulated. Additionally, the multi-criteria decision-making methods such as Analytical Hierarchy Process (AHP) and Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) were employed to obtain preference-based optimized designs. The findings revealed that model M7 has the highest steady melt fraction of λ ss = 0.81 with 107% enhancement among the models having equal volumes of PCM and composite PCM, i.e., M3-M8. The fin-type model M13 and rhombus-type model M14 provide the larger space for enhanced convection that leads to a high steady-state melt fraction values of λ ss = 0.71 and 0.75, respectively. In addition, both AHP and TOPSIS techniques predict model M13 as the optimized choice among all models upon considering the equal weightage criteria for the steady-state melt fraction (λ ss), steady-state time (t ss), and rate of steady latent heat stored per unit cost (L ⁎ ). • Simultaneous charging/discharging of CPCM inside triplex-tube is studied. • Circular, segmented, fin-type, and rhombus-type filling of CPCM are compared. • Melt fraction, melting time, and latent heat storage at thermal equilibrium are presented. • System is optimized by multi-criteria decision making techniques (AHP and TOPSIS). [ABSTRACT FROM AUTHOR]

Pathological detonations are detonations with a propagation velocity higher than the classical Chapman–Jouguet velocity and which depends on the wave structure. Such a behavior has been experimentally observed in low-pressure hydrogen-chlorine mixtures and important discrepancies were reported between the experimental and the theoretical velocities. Using the steady planar detonation model, along with a state-of-the-art chemical mechanism this work aims at investigating two aspects potentially responsible for these discrepancies: (i) the impacts of uncertainties in chemical kinetics mechanisms, and (ii) thermal non-equilibrium effects. The uncertainties in the rate constants of reactions R2: 2Cl+M=Cl 2 +M and R3: Cl 2 +H=HCl+Cl are found to be the dominant sources of uncertainty for the steady propagation velocity and the induction length of the pathological detonations. The multi-temperature, thermal non-equilibrium model is found to provide generally higher detonation velocity than the experimental value and the eigenvalue solutions obtained under thermal equilibrium. Nevertheless, for specific values of the initial vibrational temperature of HCl, the results can be closer to the experimental values. This latter aspect provides the motivation for future work that relies on more comprehensive thermal non-equilibrium modeling. [ABSTRACT FROM AUTHOR]

Logging tools are essential for high-temperature downhole oil exploration. Passive thermal management has been widely used to ensure the normal operation of downhole electronics. A key requirement for passive thermal management is the quick on-site prediction of real-time logging tool temperature. This is challenging due to variable downhole environments, initial temperature distributions, and power dissipations of heat sources. To address this issue, a transient thermal model for predicting the real-time temperature of logging tools is proposed. This model is based on a thermal network model with a discrete thermal equilibrium equation and considers heat transfer processes inside and outside the logging tool. The proposed model considers both the accuracy and the efficiency of prediction and can be applied under different working conditions. The average relative error between the proposed model and the experiment is only 6.5 %. In addition, the computing time and resources of the proposed model are significantly reduced compared with traditional numerical simulations. The proposed prediction model shows promise for wide use in real-time logging tool operations. • A real-time temperature prediction model for downhole electronics was proposed. • The accuracy of the proposed model was verified by the experiment. • The proposed model possessed high computational efficiency. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is an ideal real-time on-line method for the detection of minor elements in alloy steel, but it needs to solve the undesired self-absorption effect in plasma. Since the plasma electron temperature (T), radiation particle number density and absorption path length (Nl) determine the degree of self-absorption and affect the corrected spectral line intensity, a new temperature iterative self-absorption correction method based on the plasma thermal equilibrium radiation model is proposed to continuously calculate and correct these two parameters. Compared with generally applied self-absorption correction methods, this method has obvious advantages of simple programming, high computational efficiency, and independence of the availability or accuracy of Stark broadening coefficients. The quantitative analysis results of Cu show that the linearity of calibration curves and the measurement accuracy of elemental content are significantly improved with the self-absorption correction. In addition, this method can directly obtain the accurate radiation particle number density and absorption path length, which benefits the plasma diagnostics and quantitative analysis. [Display omitted] • A quantitative relationship model between self-absorption and parameters of spectral line and plasma was established. • The proposed method is based on temperature iteration and does not need the Stark broadening coefficient. • The proposed method can directly obtain the accurate radiation particle number density and absorption path length. • Experimental results proved that both the linearity of the Boltzmann plot and the measurement accuracy was improved. [ABSTRACT FROM AUTHOR]

In order to study the impact of different influencing factors on the active cooling effect of electromagnetic rail. The effects of the flow velocity of cooling medium, the geometric shape of the cooling channel, the cooling water inlet temperature and the nanoparticle mass fraction on the cooling effect of rail are experimentally investigated. The results indicate that increasing the flow velocity of cooling medium can enhance the heat transfer effect. But when the flow velocity exceeds 2 m/s, further increasing the flow velocity has little effect on enhancing heat transfer, and the correlation between the Nusselt number and the Reynolds number has been obtained and expressed as Nu = 0.316 Pr 1 / 3 Re 0.530. Among the three cooling channel geometries studied in this article, square channel has the best cooling effect. The inlet temperature of cooling water has little effect on the convective heat transfer coefficient, but has a significant impact on the thermal equilibrium temperature of the rail. The mass concentration of nanoparticles has a significant impact on the cooling effect of the rail. The larger the mass fraction of nanoparticles, the greater the convective heat transfer coefficient, and the lower the rail peak temperature after reaching thermal equilibrium. However, if the concentration of nanoparticles continues to increase, the effect of enhancing heat transfer will gradually weaken. [ABSTRACT FROM AUTHOR]

Heat conduction in heterogeneous solid mixtures is a crucial problem across various engineering domains. There are two types of assumptions to build the heat conduction model for such mixtures, local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE). However, a general model works for both LTE and LTNE models for different mixture structures is still to be developed. In this research, we propose a flexible heat conduction model for two-phase solid mixtures under both LTE and local thermal non-equilibrium (LTNE) conditions. The model innovates by introducing an effective volume fraction that aligns with the heat flow direction, eschewing the need for empirical quantities. Our research demonstrates that the LTE model can be directly derived from the LTNE model when constituential temperatures are equal, ensuring methodological consistency. Four mixture structures are numerically analyzed using the finite difference method, validating the model's predictive accuracy and computational efficiency. It is shown that this general heat conduction model offers an effective approach to analyzing heat transfer behavior in different types of two-phase solid mixtures, and it can be extended to multi-phase problems. [ABSTRACT FROM AUTHOR]

Characterization of the onset of combustion reactions within organic materials, such as the tobacco in tobacco products, is very complex. Such materials are commonly used as a porous matrix and the combustion reactions, if present, are generally heterogeneous in nature and compete with drying, vaporization, endothermic and exothermic pyrolysis, as well as assisted exothermal degradation. Fundamental approaches towards the characterization of the onset of combustion reactions are not well established and therefore the literature only provides information that can be used as signatures that aim to reflect the presence or absence of a combustion reaction. These signatures many times link characteristic emissions to specific temperature bands in the organic material assuming local thermal equilibrium between solid and gas phases. This paper presents a review of the literature that reports on the characterization of ignition of heterogeneous combustion within porous combustible materials and the processes commonly associated with thermal degradation and combustion. The review covers emissions and other signatures that aim to establish the onset of heterogeneous combustion, and while the discussion remains general, this review focuses on the evidence that serves to differentiate thermal degradation from the onset of combustion of tobacco products. The literature shows consistency in that below a characteristic temperature of 400 °C, thermal degradation of the tobacco in tobacco products is net endothermic, the formation of products that can be related to oxidation is limited, yields of polycyclic aromatic hydrocarbons (PAHs) are negligible and atmospheric oxygen has very limited influence on the degradation chemistry. Furthermore, the reactions leading to the conversion of PAHs into soot do not occur until much higher temperatures. Therefore, the characteristic signatures associated to the effluent released below a characteristic temperature of 400 °C consist of gaseous compounds and liquid droplets. These liquid-based aerosols are fundamentally different from the carbonaceous soot particles that represent a characteristic signature of combustion. Moreover, an extensive review of the effluent of heated tobacco products during operation establishes that the effluent exhibits the signatures of liquid-based aerosols and does not show the characteristic signatures of combustion processes. • This paper reviews the literature that characterizes the onset of combustion reactions within organic materials, such as the tobacco in tobacco products. • Literature review on fundamental approaches towards the characterization of the onset of combustion reactions. • Information that can be used as signatures that aim to reflect the presence or absence of a combustion reaction. • Signatures that many times link characteristic emissions to specific temperature bands in the organic material are presented. • The review covers emissions and other signatures that aim to establish the onset of heterogeneous combustion, and while the discussion remains general, this review focuses on the evidence that serves to differentiate thermal degradation from the onset of combustion of tobacco products. [ABSTRACT FROM AUTHOR]

Hydrogen-enriched natural gas (HENG) is a promising low-carbon fuel in the industry. The fuel flexibility of the existing natural gas-fueled industrial combustion equipment is a crucial issue for the HENG application. This study evaluates the thermal and emission performances of a large-scale industrial steam boiler fueled with HENG. Considering different operation strategies, three boiler operation scenarios were proposed, namely, the unchanged fuel/air valve opening (Scenario 1), the maintained boiler capacity with unchanged valve control logic (Scenario 2), and the maintained boiler capacity with unchanged excess air ratio (Scenario 3). A model considering the thermal equilibrium and heat transfer inside the boiler was built to study the thermal efficiency under the three scenarios, and a chemical reaction network model was established to investigate the NOx emission characteristics. The results showed that thermal efficiency and NOx emission presented a similar variation trend. Both of them decreased in Scenarios 1 and 2 while increased in Scenario 3 as hydrogen volumetric fraction in HENG increased from 0 to 0.9. The differences in decarbonization potentials among the three scenarios were limited. This study implies that the trade-off between thermal efficiency and NOx emission should be carefully concerned when applying HENG to industrial steam boilers. • Performance of an industrial steam boiler fueled with HENG was investigated. • Three boiler operation scenarios were proposed based on the real practice. • Thermal efficiency of the boiler fueled with HENG was evaluated. • NOx emissions were assessed using the chemical reactor network method. • Trade-off between the thermal efficiency and NOx emission should be concerned. [ABSTRACT FROM AUTHOR]

As a passive cooling method without extra energy expenditure, the passive daytime radiative cooling (PDRC) technology has the potential for wide range of applications. Manufacturing PDRC materials with low-cost and high solar band reflectivity are still facing challenges for their commercialization. In the present study, we used the spectral band complementarity method to realize high reflectivity in the sunlight band and excellent cooling performance of the PDRC coating, with a simple, inexpensive, and scalable preparation process. PDRC coating with a solar reflectance of 97.6% was demonstrated by properly designed BaSO 4 , CaCO 3 , and SiO 2 particles. During the outdoor test, the average daytime temperature of PDRC coating was 8.3 °C lower than the air temperature in the cavity, and 5.5 °C lower than that of commercial white paints. Under the thermal equilibrium condition, the theoretical radiative cooling power of PDRC coating at nighttime and daytime can reach 119.3 W/m2 and 94.3 W/m2, respectively. The assessment results indicate that the PDRC coating has the potential for large-scale commercial production, with a low-cost (approximately $0.5/m2) and simple manufacturing process. This study can provide new ideas for the design and preparation of high-performance low-cost PDRC materials. • PDRC coating with a variety of mixed particles and broad particle size is prepared. • The solar reflectance of the prepared PDRC coating is 97.6%. • The average daytime temperature of PDRC coatings is 8.3 °C than that of cavity. • The prepared PDRC coating has the potential of large-scale commercial production. [ABSTRACT FROM AUTHOR]

In our previous work, a novel laser cooling method was developed using anti-Stokes fluorescence from thermal equilibrium levels of Er3+, with its efficacy proven in Er3+ doped ZBLAN glass. This study has extended the method to Er3+ doped LiYF 4 single crystal, where anti-Stokes fluorescence from 2H 11/2 is utilized by excitation at the 4S 3/2 level of Er3+ for optical in situ temperature control. The non-radiative and radiative transition probabilities among 4f levels of Er3+ were assessed, and the populations of all levels relevant to laser cooling and temperature sensing were calculated. Results demonstrate that the Er3+ doped LiYF 4 crystal achieves effective cooling within a specific temperature range, exhibiting high temperature sensitivity. [ABSTRACT FROM AUTHOR]

Self-assembly of polarization domain in relaxor-ferroelectrics Pb[(Mg 1/3 Nb 2/3) 0.722 Ti 0.278 ]O 3 is discussed based on the observation of the coherent soft X-ray laser reflection. We investigate the autocorrelation of the polarization domain at the early stage of evolution. Local order of the polarization domain become in phase and periodic over 600 μm as the temperature of the crystal cool down to 383 K keeping with almost thermal equilibrium condition. Minimum domain formation free energy is discussed qualitatively. • Self-assembly of polarization domain following the minimum sum of dipole-dipole free energy and elastic free energy. [ABSTRACT FROM AUTHOR]

• Porous tubes mimicking porous media were developed for gas temperature measurement. • Uncertainty quantification for the method was evaluated with heat transfer model. • The method is effective for the simultaneous measurement with acceptable error level. • The thermal equilibrium state was determined by the proposed method. • The homogenous/heterogenous combustion regime was determined by the proposed method. Simultaneous measurement of gas and solid temperatures in porous media is crucial for phenomenological determination of gas-solid thermal equilibrium state and homogenous/heterogenous combustion regime. Yet, it has remained an unsolved challenging issue for porous media temperature measuring techniques including thermocouple, thermal infrared photography, and X-ray computed tomography. In this work, a simple and convenient method using thermocouples and porous tubes was proposed for simultaneous measurement of gas and solid temperatures in porous media. A variety of experiments with three porous media (steel, sand and biomass), three particle sizes (5 mm, 10 mm, and 15 mm), and three air flow velocities (2.95 cm s −1, 5.90 cm s−1, and 14.88 cm s −1) were conducted to examine the effectiveness and capability of the proposed method. Uncertainty quantification for measuring gas temperature in inert porous media using porous tubes was elucidated with experiments and heat transfer models. Simultaneous measurement uncertainty due to radial deviation of gas and solid measurement locations was also evaluated. It was demonstrated that the proposed method was effective for simultaneous measurement of solid and gas temperature in porous media with acceptable error level (Normalized Root-Mean-Square Deviation, NRMSD = 0.02 – 0.09). Besides, case studies showed that the proposed method was capable to provide valuable experimental data for phenomenological determination of the thermal equilibrium state and the homogenous/heterogenous combustion regime. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new lattice Boltzmann model for thermoplastic composites with heat generation. • Phase transition and local temperature difference under LTE and LTNE are compared. • Effects of heat generation, interfacial heat exchange, matrix fraction are studied. • Dynamic heat generation in thermoplastic composite is a critical LTNE mechanism. • A high internal heat generation enhances the phase transition and LTNE effects. Under the excitation of external fields, fiber reinforced thermoplastic (FRTP) composites can be thermally processed due to the internal heat generation, in which the local thermal non-equilibrium (LTNE) can be significant during the phase transition. In this study, a representative elementary volume scale Lattice Boltzmann model was developed to simulate the phase transition process of FRTP composites with the temperature-dependent internal heat source. The results from LTNE model and local thermal equilibrium (LTE) model were compared in terms of the phase interface evolution and the local temperature difference between fibers and matrix, so that the LTNE effects on phase transition behaviors were examined with different material properties and internal heat sources. It is found that the LTNE effects cannot be ignored in FRTP composites, and the main mechanisms include the dynamic local heat generation, endothermic phase transition of matrix, and relatively high thermal conductivity of fiber. A small heat exchange between the fibers and matrix results in a large local temperature difference and a slow phase transition. A high internal heat generation enhances the phase transition and LTNE effects, but an increase in the temperature range for heat generation leads to a slow phase transition with slight change in LTNE effects. With the increase of matrix fraction, LTNE effects first increase and then decrease due to the combined results of the more internal heat generation and the increase of endothermic mass of matrix and the less heat loss through fibers. This study is significant for guiding the reliable thermal processing of FRTP composites in emerging industrial applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel instrument for thermodynamic evaluation of nanofluids has been created. • A novel characteristic regarding thermal equilibrium time is investigated for evaluation. • MWCNTs, MgO, and BN are utilised in synthesising ternary and binary nanoparticles. • MWCNTs–MgO–BN ternary nanofluids achieved the highest thermal effectiveness. • The thermophysical behind the created instrument has the potential to be a fundamental reference for nanofluid analysis. Nanofluids enhance thermal energy transfer in energy storage applications. Proper nanoparticles are crucial, especially regarding their thermophysical properties. This work fabricated a novel instrument to evaluate a mixture of distilled water-based ternary and binary nanofluids. This work prepared novel ternary and binary nanofluids by mixing multi-wall carbon nanotubes (MWCNTs), magnesium oxide (MgO), and boron nitride (BN) into distilled water at various volume concentrations. The instrument that has been fabricated measures the time taken by the nanofluids to reach a thermal equilibrium state as a new characteristic to evaluate and compare the thermal potential of nanofluids, which alleviates the dependence on other instruments that are occasionally inaccessible or costly for researchers. Thermodynamically, this instrument enables the assessment of nano-energy, manifested as the heat transferred to the nanofluid while reaching an equilibrium state. The results verified the purpose of the proposed instrument; the novel characteristic was affected perfectly by increasing the volume concentration of the nanoparticles in the base fluid. All nanofluids prepared with a concentration of 0.5 % emerged as the most effective in achieving thermal equilibrium in a shorter time than the other concentrations. The ternary hybrid nanofluid MWCNTs–MgO–BN with a volume concentration of 0.5 % had the shortest thermal equilibrium time, 157 s. MWCNTs–MgO–BN ternary hybrid nanofluids transferred 8.3, 5.8, and 11.8 % more heat than MWCNTs–MgO, MWCNTs–BN, and MgO–BN binary hybrid nanofluids. The thermophysical essence behind the result obtained by the created instrument lies in the fact that it generated a new approach to evaluating the nanofluids, thanks to which it was possible to evaluate and find out which fluid has the highest thermal conductivity. The uncertainty analysis showed error acceptability in the experimental instrument, with an average uncertainty value percentage for all presented composites of ± 0.936 %. [ABSTRACT FROM AUTHOR]

This work explores theoretically the gas phase oxidation of allyl methyl sulfide (AMS, H 2 C CHCH 2 SCH 3) initiated by •OH radicals, focusing on the H-abstraction pathway at the M06-2X-D3/aug-cc-pVTZ and MN15/aug-cc-pVTZ levels of theory ( m06Tz and mn15Tz ). The formation of a prereactive complex (PRC) is involved in H-abstraction processes with two potential directions of approach for the OH radical, denoted as "α" and "β". The PRCs, demonstrate increased reactivity, primarily due to the interaction between the sulfur atoms and the hydroxyl hydrogen. A scheme for the H-abstraction mechanism that supports the experimentally identified products and predicts the formation of some S-containing low volatility products is proposed. The comparison of the potential energy surface (PES) between the double bond addition and H-abstraction paths in the AMS molecule shows that at the m06Tz level of theory, the H-abstraction on C3 and the addition to C1 have nearly the same profile of energy, while at the mn15Tz level, the minimum energy channel is the addition to C1. The theoretical rate coefficient for each reaction channel was calculated, considering the formation of a PRC prior to reaching the transition state of each channel and assuming thermal equilibrium between reactants and the PRC. The rate constants were calculated in a multi-TS/multi-conformer way at the SVECV-f12/ m06Tz and SVECV-f12/ mn15Tz levels of theory. The SVECV-f12 method is consistent in its predictions in both systems and exhibits only minor deviations from the experimental rate constants. Despite some specific differences due to the DFT method supporting the SVECV-f12 calculations, both methodologies predict a significant H-abstraction contribution in the AMS + OH gas phase reaction, which explains the high formation yield for acrolein determined experimentally. [Display omitted] • H-abstraction pathway has a significant contribution in the AMS+OH gas-phase reaction, alongside the addition path. • The addition-abstraction branching ratio was 29 - 71 % at the SVECV-f12 level. • The SVECV-f12 method exhibits minor deviations from the experimental rate constants. • The results explain the high formation yield for acrolein determined experimentally. [ABSTRACT FROM AUTHOR]

Non-thermal plasma systems beyond the state of thermal equilibrium must have non-thermality dependent effective temperatures. These particle populations cannot have Maxwellian temperatures T ∥ , ⊥ e (M) which are typically considered at thermal equilibrium in the context of Maxwellian plasmas. Previously, in such dilute environments, numerous non-thermal distributions incorporating the concept of Maxwellian temperature T ∥ , ⊥ e (M) have been utilized, one of them is Cairns distribution (here termed as type-A). To ameliorate this inconsistency, we propose a more realistic form of Cairns distribution (type-B) with the vigorous definition of effective temperature and effective thermal velocity. Both Cairns distributions (A and B) are utilized to calculate the transverse dielectric response function (TDERF) of electromagnetic electron cyclotron (EMEC) mode. The exact numerical solution of TDERFs of EMEC instability reveals interesting and more promising repercussions in the case of Cairns-B i.e. an augmentation in the behavior of oscillatory and imaginary frequencies of the instability. • Nonthermal populations beyond thermal equilibrium have effective temperatures. • Effective temperatures update plasma betas because of nonthermality dependence. • Cairns distribution shows an appreciable agreement with the observed distribution in solar wind. • Model-B style distributions better explain plasma dynamics, waves and instabilities. • Model-B explains natural rise in temperature due to increase in nonthermality in system. [ABSTRACT FROM AUTHOR]

• A steady-state thermal conduction model for laser rock perforation is established. • The equilibrium thermal state represents the final stage of laser-induced rock breaking. • The melting properties of mineral compositions determine the thermal equilibrium state. • The equilibrium temperature is affected by the evaporation and melting points of minerals. Energy consumption during laser rock perforation is controlled by conductive losses and latent heats during the phase transitions of melting and evaporation. To understand then improve the efficiency of laser perforation, the influence of rock mineral composition on these processes is investigated, and a theoretical model of laser rock breaking under steady-state heat conduction is developed. The findings reveal that the melting properties of mineral components primarily control thermal equilibrium during laser perforation. The key minerals, namely feldspar, quartz, and clay, were used to study the melt response in both pure samples and synthetic rock composites composed of these minerals. When feldspar is dominant, the thermal equilibrium temperature remains stable after reaching the feldspar gas phase boundary. While in situations where quartz dominates, the thermal equilibrium temperature is slightly below the melting point of pure quartz. The findings highlight the relationship between laser rock perforation efficiency and melting properties of minerals. [ABSTRACT FROM AUTHOR]

• Multi-wavelength responsive PL of Dy3+ was investigated in Dy3+:CaWO 4 phosphors. • Multi-strategy ratiometric luminescent thermometry based on PL of Dy3+ was proposed. • Thermometric property of Dy3+ was proved to be independent of excitation wavelength. • Multi-strategy thermometry exhibited good sensitivity, stability, and repeatability. This paper explores the detailed photoluminescence (PL) behaviors of Dy3+ doped CaWO 4 (Dy:CaWO 4) phosphors under multi-ultraviolet wavelength excitation. Moreover, it proposes multi-strategy ratiometric thermometry based on luminescence intensity ratio (LIR) from the transitions of thermally coupled energy levels (TCLs) of Dy3+. Under excitation of multiple ultraviolet wavelengths, the Dy:CaWO 4 phosphors exhibited multi-wavelength responsive PL characteristics of Dy3+ with strong blue and yellow emissions from Dy3+ TCLs transitions. The temperature-dependent PL properties of Dy:CaWO 4 phosphors were investigated over a temperature range of 300∼650 K. Multi-strategy ratiometric luminescent thermometry was examined under various excitation wavelengths by the thermal equilibrium population of Dy3+ TCLs. The proposed six LIR schemes based on the PL emissions of Dy3+ exhibited a good quantitative relationship with temperature. They showed well-luminescent thermometric behaviors with high absolute and relative sensitivities due to the largest energy gap of TCLs and a relatively larger LIR value. The thermometry properties of the multiple LIR schemes were independent of excitation wavelength, attributed to the stable site symmetry of Dy3+ and the thermal equilibrium population of TCLs under different excitation wavelengths. The multi-strategy ratiometric thermometry of Dy3+ demonstrated the merit of high sensitivity, excellent stability , and repeatability, indicating the potential luminescent thermometric application of Dy:CaWO 4 phosphors. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the resonance frequency characteristics of the SparkJet actuator are examined through numerical investigation using modal analysis. First, an eigenvalue problem is established to compute the resonance frequencies of the SparkJet actuator, considering its configuration, boundary conditions and internal physical phenomena. To validate the eigenvalue problem, computational fluid dynamics (CFD) simulation is conducted utilizing unsteady three-dimensional Navier-Stokes equations with plasma energy source term, assuming local thermal equilibrium (LTE). Subsequently, the resonance frequencies are obtained by performing fast Fourier transform (FFT) on the thrust and average pressure data obtained from the CFD. In our investigation of the resonance frequency characteristics, eigenmode decomposition on the pressure contour obtained from the CFD is conducted utilizing the eigenfunctions obtained from the eigenvalue problem and their orthogonality. The eigenmode decomposition enables us to quantitatively evaluate the contribution of each eigenfunction to the thrust. Comparisons between the frequencies corresponding to the eigenfunctions significantly influencing on the thrust and the resonance frequencies obtained by FFT reveal a maximum error of 5.29 % and an average error of 2.35 % Moreover, when the taper angle is relatively large (approximately 45 ∘ or more), eigenfunctions significantly influencing on the thrust can be categorized into two distinct geometric patterns. These physically represent the waves that propagate and reflect in the streamwise or radial direction within the SparkJet actuator. This observation implies that the complex interactions of shock waves within the SparkJet actuator can be reduced to a few waves with simple physical interpretations. This may potentially aid in analyzing the physical phenomena within the SparkJet actuator. [ABSTRACT FROM AUTHOR]

This study aimed to determine the temperature equilibrium time of three water-equivalent phantoms (Gammex SW557 Solid Water HE, Gammex RMI457 Solid Water, and Tough water phantom WD) with room temperature using thermocouples and three-dimensional thermal analysis. The water-equivalent phantom and thermocouples were arranged in a 30 cm × 30 cm × 15 cm phantom, and temperatures were measured at five points with insertion lengths of 3–15 cm from the outside of the water-equivalent phantom. The temperature equilibrium was defined as the point at which the temperature difference between the water-equivalent phantom and room temperature reached 0.5 °C. The temperature variation of the water-equivalent phantom over time during the measurements was obtained by a compact thermo-logger. The temperature distribution in the phantom was calculated by three-dimensional thermal analysis. The time required for the three water-equivalent phantoms to reach thermal equilibrium from 32 °C to 22 °C is about 21.5 h, so it is clear that there is a waiting period before the measurement. The temperature distribution inside the water-equivalent phantom was also shown, and the temperature variation at each measurement location was clarified, providing useful data for dosimetry in quality control and other applications. The data collected from this study will provide useful information for dosimetry of the water-equivalent phantom in standard measurement methods. • The temperature equilibrium times of the three water-equivalent phantoms were determined. • The temperature equilibrium time for the three phantoms was approximately 21.5 h. • The visualization of the temperature distribution inside the phantom revealed the variation of temperature inside the phantom. [ABSTRACT FROM AUTHOR]

• Thermal modeling of porous fiber composite with compressible fluid is proposed. • Compressive effect of the fluid phase on porous fiber composite is demonstrated. • Effect of heating sources on the thermal behavior of the materials is uncovered. The study of heat transfer behavior in porous fiber composite cylinders is vital for optimizing efficient thermal management, insulation materials, and heating equipment design, with applications spanning fields like materials drying, atomization equipment, and aerospace. However, the existing research in this area faces challenges including inadequate experimental data and a lack of clarity regarding fluid-porous material interactions, particularly under the influence of compressible fluids, which demand a more nuanced investigation. This study has developed a model to depict the unsteady heat transfer behavior of porous fiber composite cylinders containing compressible fluid. Consequently, a momentum equation describing the gradual diffusion of compressible fluid within the porous medium is established based on the Darcy-Brinkman-Forchheimer equation. For the purposes of this investigation, the air is treated as a compressible fluid. Concurrently, the corresponding energy equation is formulated, assuming Local Thermal Equilibrium. Ultimately, the devised model is solved by employing the finite volume method. Additionally, a temperature measurement experiment is designed to furnish boundary conditions and verify the model's reliability. The findings indicate that omitting the influence of compressible fluid yields a maximum predicted temperature deviation of approximately 5.6 K at a heating temperature of 420 K. The temperature deviation gradually expands as the heating temperature rises. Furthermore, the parametric analysis is conducted to investigate the impact of porosity, thermal conductivity, geometric size, and the type of heat source on the non-steady heat transfer behavior of composite cylinders. This novel model contributes to a more accurate prediction of the unsteady temperature distribution within porous fiber composite structure cylinders. [ABSTRACT FROM AUTHOR]

Various geoscientific processes in the shallow subsurface experience a temperature difference between the solid and the liquid or gaseous phase. Prominent examples include the injection of cold water into a hot host rock, the fast intrusion of supercritical CO2 from the mantle into shallower regions, or the rainwater infiltration into partially frozen soil. In such an absence of local thermal equilibrium between phases, heat transfer needs to be described explicitly by Newton's law of cooling and depends on the heat transfer coefficient and the specific heat transfer area between the involved phases. Despite various works, the quantification and the dissolution of dependencies of the heat transfer coefficient remain ambiguous. The study of heat transfer is separated between porous and fractured materials due to the different geometry, the applied flow rules, and common fields of applications. Identifying scenarios in which heat transfer effects in a local thermal non-equilibrium (LTNE) situation are relevant is already a challenging task but in past years more and more scenarios with persistent differences in phase temperatures were found. In this contribution, the mathematical governing equations for heat transfer between solid rock and moving fluid are given and various approaches of parameterization are discussed. This discussion of heat transfer includes various types of heat transfer mechanisms that can occur in the subsurface. Subsequently, the state of the art for heat transfer in porous and fractured media is presented with a special emphasis on resolving dependencies on geometry (grain size, fracture aperture) and flow velocity. Possible solution strategies addressing heat transfer in heterogeneous fractured porous media are presented, and possible applications with relevant LTNE effects are discussed with an outlook on future challenges in the field of geothermal energy exploitation and storage, shallow multi-phase infiltration scenarios, CO2 sequestration, and underground H2 storage. [ABSTRACT FROM AUTHOR]

Development of the low-cost, high-efficiency, and durable non-precious metal electrocatalysts for cathodic oxygen reduction reaction (ORR) is of vital importance for fuel cells and metal-air batteries. Herein, the carbon-coated NbC nanoparticles (NbC@C NPs) were prepared using DC arc discharge plasma under a methane atmosphere. Then, the nitrogen-doping was conducted by heat treatment, resulting in nitrogen-doped carbon-coated NbC nanoparticles (NbC@C(N x) NPs). Benefiting from the merit of unique core-shell structure and best synergy between the nitrogen-doped carbon shell and the NbC core, the obtained highest nitrogen-doped NbC@C(N 1.36) NPs showed an onset potential (E onset) of 0.89 V (vs. RHE) and a half-wave potential (E 1/2) of 0.79 V, which are comparable to those of commercial Pt/C (20 wt%) (E onset = 0.90 V, E 1/2 = 0.80 V), and its diffusion-limited current density (J L) of 5.99 mA·cm−2 is even higher than that of commercial Pt/C (5.43 mA·cm−2). Moreover, it exhibited a remarkable long-term durability and impressive methanol resistance than Pt/C catalyst. In addition, the real-time optical emission spectrum (OES) analysis of arc plasma shows that the electron temperature (T e) is 7562.9 K in local thermal equilibrium (LTE) plasma. Therefore, the use of the DC arc discharge plasma method opens a fast and simple way to develop cost-effective and highly efficient non-precious metal catalysts for ORR. [Display omitted] • Prepared NbC NPs using a DC arc discharge plasma method show a core-shell structure. • N-doping induces surface electronic structure modification of the graphitic shell, creating the ORR additional active sites. • The electron transfer number of NbC@C(N x) NPs indicates that the reaction path is close to a 4-electron process. • The energy state of the working arc plasma is diagnosed by means of real-time optical emission spectroscopy. [ABSTRACT FROM AUTHOR]

In this article, we propose a numerical model for calculating the external heat transfer coefficient between the bundle region and its wall for cables in conduit conductor (CICC). With the assumption of local thermal equilibrium, one macro equation describing the steady heat transfer on the cross section of the CICC can be obtained. A key parameter, the effective transverse thermal conductivity k eff , which takes the contribution of both strands and flowing fluid into consideration, is introduced. To calculate the effective transverse thermal conductivity k eff , we first obtain the true distribution of different phases (fluid, copper and superconducting material) on a cross section of CICC with the help of the image recognition technique. Based on this, the value of the effective transverse thermal conductivity k eff can be calculated numerically. Due to the large difference among the component thermal conductivities (at 4.5 K, typical values of the thermal conductivity of liquid helium, superconducting material and copper are k He = 0.024 W m − 1 K − 1 , k N b 3 Sn = 0.04 W m − 1 K − 1 and k Cu = 708 W m − 1 K − 1 ; and the maximal ratio of thermal conductivity can be as high as about 30,000), the high-performance finite analytical method (FAM) is recommended to calculate k eff. After obtaining the effective transverse thermal conductivity k eff of the bundle region, the heat transfer coefficient can be calculated directly by solving a simple Poisson equation under proper boundary conditions. Two case studies are performed, including the JT-60 Super Advanced (JT-60SA) CICC and the dual channel International Thermonuclear Experimental Reactor, Toroidal Field Performance Sample (ITER-TFPS). The calculated values of heat transfer coefficient are consistent with the experimental results, which verifies our proposed model. [ABSTRACT FROM AUTHOR]

Langevin dynamics of a confined Brownian particle with coordinate-dependent diffusion involves multiplicative noise. Mathematically, equilibrium of such a stochastic system with multiplicative noise is an Itô-process. However, in physics literature, the process and resulting Itô-distribution are not considered to represent equilibrium because the distribution is a modified Boltzmann distribution. Itô-distribution is derived in this paper from Gibbs measure without involving any convention for stochastic integration, hence, no Itô vs Stratonovich dilemma. Then, in the light of an existing experiment reported in 1994 by Faucheux and Libchaber, we compare the Boltzmann distribution with the modified one for thermal equilibrium of Brownian particle near confining walls causing coordinate dependence of diffusion. Distribution corresponding to the Itô-process (modified Boltzmann) is shown to adequately account for the experimental results where the Boltzmann-distribution fails. • Equilibrium of confined Brownian particle with coordinate-dependent diffusion. • Itô-distribution from Gibbs measure. • Comparison of Itô-distribution with experimental results. [ABSTRACT FROM AUTHOR]

Kirkendall effect has played an important role in developing the understanding of atomic diffusion and mass transport in solids. In thin films and multilayers, in which the microstructure may be far from thermal equilibrium, behavior of a system can be very different from that of the bulk. Therefore, there is a great need to understand the peculiarities of Kirkendall shift occurring at nanometer or sub-nanometer length scale in such systems. In the present work, Kirkendall shift in thin films has been measured with sub-nanometer accuracy, by making use of x-ray planar waveguide structures. Using this technique, we report an apparently counterintuitive result of Kirkendall shift associated with self-diffusion in nanocrystalline iron. The cavity of the waveguide consists of two layers of iron having different microstructures, separated by a thin marker layer of Ag. Thermal annealing results in shift of the Ag marker towards the Fe layer having a coarser grain structure. The effect is established unambiguously by studying two samples with the order of the two Fe layers reversed, and a third sample with the two Fe layers having the same microstructure. The result can be understood in terms of the difference in the microstructure of the two Fe layers; difference in the grain size and hence different concentration of the grain boundaries in the two layers results in a net mass transfer from one region to the other. [Display omitted] [ABSTRACT FROM AUTHOR]