Heat Capacity Coefficient Research Articles

Elastic mechanical thermodynamic and thermoelectric properties of pristine and titanium doped Mg2Si: a density functional theory study

Herein, we report a systematic investigation of the effect of Titanium doping on the structural, elastic, mechanical, thermodynamic, and thermoelectric (TE) dynamics of Mg2Si Compounds using first-principle investigation. The present study has been carried out using the full potential linearized augmented plane wave method as implemented inWien2kcode undermBJexchange potentials. The investigations revealed that Mg2-xTixSi compounds have structural stability with cubic phase (Fm-3msymmetry) and possess degenerate semiconducting nature. The analysis of elastic constants revealed mechanical stability of the investigated compounds following Born criteria. Thermodynamic investigations have been carried out in the temperature range of 100-1500 K at zero pressure and the quantities like heat capacity, Debye temperature, Grüneisen constant, and thermal expansion coefficient have been critically analyzed. Lastly, the TE performance of Mg2-xTixSi compounds has been predicted by estimating the thermopower (S2σ) and TE figure of merit (zT) in the temperature range of 300-1500 K. The predicted value ofzTmaxfor Mg2-xTixSi compound is 0.67 at 800 K forx= 0.25 titanium content, suggesting materials promising application for TE energy harvesting and mechanical devices.

Predicting the properties of bitumen using machine learning models trained with force field atom types and molecular dynamics simulations

This study enhances the molecular analysis of bitumen by transitioning from traditional chemical descriptors, such as SARA (Saturates, Aromatics, Resins, and Asphaltenes) fractions and elemental compositions, to specific force field atom types in Molecular Dynamics (MD) models. This shift improves the precision in predicting material properties critical for bituminous material characterization. Machine Learning Models (MLMs) were developed to use these atom types as input features, inherently reflecting fundamental chemical characteristics. Trained on data from over 1,770 LAMMPS simulations of diverse bitumen types and conditions, these MLMs enable the prediction of properties like density, heat capacity, solubility parameters, and thermal expansion coefficients without the need for additional MD simulations. The models utilize 30 chemical descriptors corresponding to specific atom types in the PCFF force field, which collectively account for over 95% of the influence on these properties. By accurately predicting fundamental, thermodynamic, and kinetic properties, the use of MLMs and force field atom types allows researchers to efficiently tweak the chemical nature of organic molecules and mixtures to achieve desired properties. With near-instantaneous prediction times, these MLMs offer valuable insights for advancing bitumen research in the construction and petroleum industries, reducing the need for more intensive simulation techniques.

Investigation on the hydrogen storage properties, electronic, elastic, and thermodynamic of Zintl Phase Hydrides XGaSiH (X = sr, ca, ba)

This study presents a comprehensive investigation of the electronic, mechanical, and thermodynamic properties of Zintl phase hydrides XGaSiH (X = Sr, Ca, Ba) using Density Functional Theory (DFT) and the FP-LAPW method within the WIEN2k package. Our analysis covers the structural stability, electronic properties, and hydrogen interaction mechanisms in these compounds. The hydrides exhibit narrow band gaps, with values ranging from 0.1 to 0.5 eV using GGA and LDA functionals, and 0.6–1.0 eV with mBJ-GGA and mBJ-LDA. The hydrogen storage capacities are determined to be 0.34 wt %, 0.47 wt %, and 0.40 wt % for SrGaSiH, CaGaSiH, and BaGaSiH, respectively, highlighting their potential for energy storage applications. Thermodynamic properties, evaluated through the quasi-harmonic Debye model, provide insights into the Grüneisen parameter, heat capacity, and thermal expansion coefficient over a range of pressures (0–50 GPa) and temperatures (up to 1000 K). Elastic constants reveal that these compounds are mechanically stable, with a notable anisotropy in the {100} plane and varying degrees of compressibility among the different hydrides. Our study further highlights the slightly ordered hexagonal Ga and Si layers, which contribute to the enhanced hydrogen storage capabilities of these materials. The compounds demonstrate high structural stability, facilitating effective hydrogen retention and release at practical temperatures, making them promising candidates for hydrogen storage applications. Additionally, the analysis of electronic band structures and density of states suggests significant conductivity potential, with band gaps ranging from 0.1 to 1.0 eV, depending on the computational method used. The unique combination of structural, electronic, thermodynamic, and mechanical properties in XGaSiH compounds positions them as valuable materials for renewable energy applications. These findings lay the groundwork for future research focused on optimizing these materials through structural modifications or doping to enhance performance metrics such as hydrogen storage capacity and electrical conductivity.

Modeling the Size Dependence of Specific Heat Capacity and Thermal Expansion Coefficient of Metallic Nanocrystals

Modeling the Size Dependence of Specific Heat Capacity and Thermal Expansion Coefficient of Metallic Nanocrystals

A DFT insight of the electronic, thermodynamic, and thermoelectric properties of RuO2

In this study, we explore the structural, electronic, thermodynamic, and thermoelectric properties of RuO2 using density functional theory. The derived equilibrium structural parameters agree with other theoretical and experimental results. The widely used modified Becke–Johnson (mBJ-GGA) potential is adopted for accurate electronic band gap estimation. To incorporate the effect of the extended orbital of the Ru atom, spin-orbit coupling has been used in combination with the mBJ potential. The investigation of electronic properties revealed an indirect semi-conducting nature with a band gap along the W-L symmetry. The calculated band gaps are 1.685 and 1.658 eV from mBJ and mBJ + SOC, respectively. The dynamical stability is tested and verified by calculating the phonon dispersion curve. We have employed the quasiharmonic approximation-based Gibbs2 package to determine the pressure and temperature-dependent thermodynamical parameters, such as cell volume, Debye temperature, heat capacity, entropy, and thermal expansion coefficient. This study uses the BoltzTraP simulation algorithm to determine the thermoelectric parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity.

Thermodynamic and thermoelastic properties of hypostoichiometric MOX fuels with molecular dynamics simulations

Employing the Cooper-Rushton-Grimes (CRG) interatomic empirical potential with new parameters for U3+ interactions in U1-y,PuyO2-x, classical Molecular Dynamics simulations were carried out for the first time to compute the enthalpy, the lattice parameter, the elastic constants and derived properties of hypostoichiometric U1-y,PuyO2-x compounds (with y in the range 0-1, x between 1.92-2.0, and from 1000 K to melting points). As hypostoichiometry results from adding oxygen vacancies to U1-y,PuyO2, this study investigates how oxygen vacancies affect the thermodynamic and thermomechanical properties of MOX compounds. The most pronounced effect appears at high temperatures, where the so-called Bredig transition occurs. We observed that the effects of this transition on the properties are softened by the presence of oxygen vacancies. The analytical law of the heat capacity for stoichiometric mixed-oxide fuels U1-y,PuyO2 developed by Bathellier et al. [9] was modified by introducing the deviation from stoichiometry as a variable. It was fitted on Molecular Dynamics data of heat capacity and linear thermal expansion coefficient and a good agreement was found. To model the thermal evolution of mechanical properties up to the melting point, a new law was developed. The laws may be used in Fuel Performance Codes.

KINETICS OF DRYING OF DISPERSED MATERIAL IN THE APPARATUS OF PERIODIC ACTION WITH FLUIDIZED BED

A theoretical method for calculating a periodically operating fluidized bed dryer is presented based on the zonal method for describing kinetics and an example of calculation is given in relation to the drying of pea grain. In the calculation, it is assumed that the solid phase in the apparatus is completely mixed, and the gas is ideally displaced, the particles have a spherical shape and are the same in size. Accounting for changes in the parameters of the drying agent in the layer is carried out on the basis of the equations of material and thermal balance for the layer with the division of the entire range of changes in the moisture content of the material into a number of concentration zones. The change in the temperature of the dried particles during the process is calculated based on the analytical solution of the linear heat conduction problem at a constant ambient temperature and the condition that moisture evaporation occurs at the surface of the particles (there is no internal evaporation). The calculation is carried out using the method of successive approximations. First, the duration of drying of the material in the concentration zone under consideration is set, then the average air parameters are determined by the height of the layer and by the drying time, and, using these data, by solving the problem of mass conductivity (moisture diffusion), the drying duration in the zone under consideration is determined and compared with the preset one. If there is a significant discrepancy, a second calculation iteration is carried out, taking the drying time found in the first calculation iteration. Calculations are carried out until an acceptable match between the previously accepted and calculated drying time. Then they move on to the second concentration zone, for which they do the same. The total drying time is equal to the sum of the times in the concentration zones. This technique was tested using the example of calculating the drying of pea grains. In the calculations, we used data previously found by the authors on the coefficient of mass conductivity (moisture diffusion), as well as literary reference data on the coefficients of thermal conductivity, thermal diffusivity and heat capacity of this material. Heat and mass transfer coefficients were calculated using criterion equations given in the literature. To select the operating air speed, the speed of the beginning of fluidization was calculated; the operating air speed was taken at a fluidization number of 1.05. The calculation of the Biothermal and mass transfer criteria showed that the thermal problem is mixed (the Biothermal number is 5.81), i.e. the heat transfer process is influenced by both internal and external heat transfer. The problem of mass transfer is purely internal (the modified mass transfer Bio number is 122.5), which was taken into account when calculating the drying time. The calculated drying curve was compared with the experimental one. A diagram of the experimental setup is given and a description of the experiment is given. Satisfactory agreement between the calculated and experimental drying curves indicates the correctness of the calculation method under consideration, which can be recommended for engineering use. For citation: Rudobashta S.P., Zueva G.A., Babicheva E.L. Kinetics of drying of dispersed material in the apparatus of periodic action with fluidized bed. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 6. P. 109-118. DOI: 10.6060/ivkkt.20246706.6968.

Transient heat conduction in multi-material topology optimization of thermoelastic structures involving dynamic constraints

This work presents a modified solid isotropic material with penalization (SIMP) for conducting dynamic-constrained multi-material topology optimization (MMTO) of thermoelastic structures subjected to transient thermal conduction. The novelty of this study is the multi-material optimization of instantaneous temperature conduction under specific frequency constraints, which has never been studied before. The proposed method has been developed for general models of multi-material interpolations such as thermal stiffness, heat capacity, and thermal stress coefficient. The temperature environment is formulated by applying prescribed mechanical and thermal loads that are exposed over a period of time. In this work, we focus on the objective of minimizing compliance in a transient heat conduction structure while simultaneously imposing constraints on the dynamics. With high temperatures, the stiffness of the optimization results decreases while stability is still guaranteed. The sensitivity of the objective function is subsequently calculated using the discretize-then-differentiate approach for the dynamic problem as well as the adjoint variable method. This study examines the impact of thermal fields and different time increments in conjunction with dynamic criteria. The outcomes of heat conduction result in notable alterations under identical dynamic constraint levels.

Measurement and comparison of transient thermal boundary layer of a Local-Heated Mini-Channel under sub- and super-critical conditions

This study is focused on experimentally measuring the transient thermal boundary layer following a sudden heat addition to turbulent flow boundary in supercritical mini-channels. Interferometric diagnostics were performed using a visualization channel to capture the time-evolution boundary layer. The measured pressure drop shows good agreement with numerical iterations according to the friction laws. Transient scenarios have been extracted from the raw interferograms to facilitate quantitative comparison of boundary conditions, such as bulk temperature and heat flux: (1) Localized heat accumulation and a slowly thermal response have been observed in subcritical state; (2) Relatively high density of 1.2 kg/m3 and low temperature changes of 0.008 K are observed in cases with relatively shorter critical distances to the critical point, attributed to the sharp increase in heat capacity and thermal expansion coefficients. (3) A relatively fast thermal convective field is established at larger heat fluxes due to the rapid density shifts of 1.2 kg/m3 and associated flow acceleration in the boundary layer.

Fire Protection of Steel Structures of Oil and Gas Facilities: Multilayer, Removable, Non-Combustible Covers

Fire protection is required to protect metal structures of oil and gas facilities from fires. Such fire protection should provide high fire resistance limits: 60, 90, 120 and more minutes. Specialists of LLC “RPC PROMIZOL ” developed a multilayer, removable type of fire protection made of superfine basalt fibre and ceramic materials for operation in Arctic conditions. Five experimental studies were carried out in standard and hydrocarbon fire regimes. The fire protection effectiveness of the products for I20 beams without load was obtained: a 50 mm thick coating provided 130 min of a standard fire regime; a 15 mm thick coating provided 60 min. The 15 mm thick coating provided 30 min of a hydrocarbon fire regime and the 50 mm thick coating provided 93 min of a hydrocarbon fire regime. The I40 beam under a load of 19.9 tf showed an R243 for the standard fire regime. The coefficients of effective thermal conductivity and specific heat capacity of fire-retardant compositions were determined by solving the inverse heat conduction problem. The problem was solved by modelling using the QuickField 7.0 software package, which implements FEM. Modelling showed that for obtaining the fire resistance limit R120 under the standard fire regime for the sample steel structure from an I40 beam, it is enough to apply fire protection with a thickness of 25 mm instead of 50 mm, which agrees with the experimental data. For the hydrocarbon regime, it is predicted that R120 can be obtained at a thickness of 45 mm instead of 50 mm.

Response of Mg2X (X = Si, Ge and Sn) compounds to extreme uniaxial compression: first-principles calculations

Abstract In this study, we perform first-principles calculations using density functional theory to examine the structural, electronic, thermodynamic, and thermoelectric properties of the Mg2X (X = Si, Ge and Sn) compounds under uniaxial compression within the generalized gradient and modified Becke–Johnson approximations. It is found that the band gap of Mg2Si, Mg2Ge and Mg2Sn decreases with applied uniaxial pressure and changes its direction from Γ-X to Γ-K. The results of phonon frequencies indicate that the studied compounds are dynamically stable at zero and higher uniaxial strains. Furthermore, the uniaxial compression and temperature dependence of the Gibbs free energy, heat capacity and thermal expansion coefficient are investigated in the frame of the quasi-harmonic approximation. The semiclassical-Boltzmann method is used to study the Seebeck coefficient, electrical conductivity, thermal conductivity and figure of merit ZT as a function of both temperature and uniaxial pressure. It is shown that the Seebeck coefficient decreases with increasing pressure whereas thermal conductivity increases, which leads to the lowering in the value of ZT and thus to a worse thermoelectric performance of the studied materials.

A simple method for obtaining heat capacity coefficients of minerals

Abstract Heat capacity data are unavailable or incomplete for many minerals at geologically relevant temperatures. Despite the availability of entropy and enthalpy values in numerous thermodynamic tables (even sometimes at elevated temperatures), there remains need for extrapolation beyond, or interpolation between, temperatures. This approach inevitably results in estimates for entropy and enthalpy values because the heat capacity coefficients required for optimal thermodynamic treatment are less frequently available. Here we propose a simple method for obtaining heat capacity coefficients of minerals. This method requires only the empirically measured temperature-specific heat capacity for calculation via a matrix algorithm. The system of equations solver is written in the Python computing language and has been made accessible in an online repository. Thermodynamically, the solution to a system of equations represents the heat capacity coefficients that satisfy the mineral-specific polynomial. Direct coefficient calculation will result in more robust thermodynamic data, which are not subject to fitting uncertainties. Using hematite as an example, this method provides results that are comparable to conventional means and is applicable to any solid material. Coefficients vary within the traditional large 950 K temperature interval, indicating that best results should instead utilize a smaller 400 K temperature interval. Examples of large-scale implications include the refinement of geothermal gradient estimation in rapidly subsiding sedimentary basins or metamorphic and hydrothermal evolution.

Heat transfer in inhomogeneous dispersed systems based on graphene oxide hydrogels

Based on the optical holography method, studies of the occurrence and development of convective flows in hydrogels of various concentrations with the addition of graphene oxide in relation to 3D-bioprinting technology have been performed. For quantitative measurement of temperature fields, the optical holography method was used in combination with the gradient thermometry method, based on the dependence of the refractive index on the properties of hydrogel systems modified with graphene oxide with different concentrations and temperatures. Under conditions of changes in the thermophysical properties of hydrogels, as well as the magnitude of the supplied heat flux, the features of heating the wall area are studied in order to determine the coefficients of thermal conductivity and heat capacity, as well as the nature of the formation of convective flows near the wall heated from below.

Analysis of the process of heat transfer in space

In work the general principles of transfer of thermal energy in limited space are theoretically considered. To simplify the task, the tasks are defined in the Cartesian coordinate system. The dependence of the transfer on the coefficients of thermal conductivity, heat capacity and eigencoefficients of differential partial differential equations of an inhomogeneous and homogeneous nature are analyzed. Modeling sets initial and boundary conditions. In solving the problem, the method of multiple separation of variables is used. In conclusion, the final form of the function of the phenomenon of heat transfer in a limited space is derived from 4 variables.

Theoretical study on the elastic and thermodynamic properties of CdS

The physical properties of CdS is calculated by using the first principles pseudopotential plane wave method based on density functional theory (DFT). The calculated lattice parameters and elastic constants agree well with other theoretical values, and the crystal is determined to be structurally stable by the Born mechanical stability condition. The Debye temperature, Grüneisen parameters, heat capacity and thermal expansion coefficient of CdS under high temperature and high pressure were studied successfully by using the quasi-harmonic Debye model. The influence of pressure on thermal expansion coefficient and Debye temperature is greater than that of temperature. The heat capacity decreases with the increase of pressure. At high temperature and high pressure, the heat capacity approaches the Dulong-Petit limit.

РАСЧЕТ ЭЛЕМЕНТОВ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ НА ОГНЕСТОЙКОСТЬ И ОГНЕСОХРАННОСТЬ В ПРОГРАММНОМ КОМПЛЕКСЕ СТАРКОН.

RCDiagra software as a part of the domestic STARKON software is presented. The software is designed to perform fire resistance and fire safety analysis of reinforced concrete beams and columns. The strength analysis is based on the nonlinear deformation theory and enables to take into account non-stationary thermal effects changing the concrete and reinforcement properties. To determine the ultimate strength, elastic modulus for concrete and reinforcement, ultimate relative deformations, a thermal analysis is performed in accordance with SP 468.1325800.2019 and MDS 21-2.2000. The thermal engineering analysis solve the problem of determining the temperature field in the beam cross-section under non-stationary thermal action, depending on the boundary conditions and thermophysical parameters of the material. It is assumed that the coefficients of thermal conductivity and specific heat capacity of concrete depend on the current temperature at the crosssection points.

Low- and high-temperature heat capacity of metallic technetium

The heat capacity of technetium metal has been measured from 2.1 K to 293 K using relaxation calorimetry and the enthalpy increment up to 1700 K using drop calorimetry. The low-temperature calorimetry measurements revealed a superconducting transition temperature of TC = (7.76 ± 0.08) K. The zero-degree Debye temperature(θE) and the electronic heat capacity coefficient (γe) of the normal state were derived as (307 ± 5) K and (4.22 ± 0.20) mJ·K−2·mol−1, respectively. The standard entropy of the superconducting standard state was derived as Sm° (298.15) = (36.8 ± 1.3) J·K−1·mol−1. The fitting of enthalpy-increment data together with high-temperature heat capacity data reported in literature yielded a heat capacity equation up to 1700 K.

Structural, mechanical and thermodynamic stability of the CaIn intermetallic compound for promising hydrogen storage: ab-initio calculations

This study was conducted to investigate the structural, elastic, dynamical, mechanical, and thermodynamic properties of the binary intermetallic compound CaIn in various crystallographic phases, utilizing density functional theory (DFT) calculations. The results reveal that the compound is chemically and mechanically stable, as indicated by the formation energy, stability in the phonon dispersion, and elastic constants calculation. The mechanical and thermodynamic properties of our studied compound are only examined in the most stable calculated phase, which is the orthorhombic phase (Pmma). By calculating Pugh’s ratio it has been determined that this compound possesses a brittle character. The quasi-harmonic Debye (QHD) model was employed to analyze various thermodynamic parameters such as Debye temperature, volume variation, isothermal bulk modulus, heat capacity, and thermal expansion coefficient. These findings are expected to encourage further theoretical and experimental studies on the CaIn intermetallic compound for potential applications as a hydrogen storage material and in various other fields.

Mechanical and thermal properties of W-20Cu alloy for packaging HgCdTe IRFPA detector at cryogenic temperatures

Tungsten-copper alloy, as an electronic packaging material with excellent comprehensive performance, is widely used in the cooled packaging dewar structure of HgCdTe infrared focal plane detector. Thermodynamic properties (Coefficient of Thermal Expansion (CET), Thermal Conductivity (TC), Specific Heat Capacity (SHC)), mechanical properties and microstructure of W-20 wt% Cu(W-20Cu) are investigated in the range of 300 K ∼ 4.2 K, respectively. The quasi-static tensile tests are carried out on an electronic universal testing machine to obtain the typical stress–strain curves and mechanical properties of W-20Cu. The yield strength (YS), ultimate tensile strength (UTS), elongation and shrinkage of the specimens are measured. Besides, the Scanning Electronic Microscopy (SEM) are applied to observe the microstructure of W-20Cu alloy. The results demonstrate that W-20Cu alloy has outstanding thermal properties of high strength and hardness, high specific heat and low heat capacity and expansion coefficient. Tensile properties of the alloy significantly improve at extremely low temperature, and compared with 300 K, the YS and UTS of W-20Cu increase by 30.68 % and 11.27 % at 77 K. At 4.2 K, the YS increase by 44.49 %, and the UTS increase by 17.20 %, while the plasticity and fracture toughness have a sharp reduction from 300 K to 4.2 K. All specimens exhibit brittle fracture characteristics. With the increase of W crystals cleavage ratio and W-W continuity, the microstructure continuity and uniformity are improved. The number of plastic dimples of Cu phase decreases and the dimples become shallow slightly.

First-principles calculations to investigate stability, mechanical and thermo-dynamic properties of AlxTMy intermetallics in aluminum alloys

The mechanical, thermal and electrical properties of 8 types of common AlxTMy (TM = Sc–Zn, Y–Cd, Hf–Hg) intermetallics in Al based alloys at various temperatures and pressures have been investigated by combining first-principles calculations with the Debye model. The results clearly show that the stability and mechanical property are closely related to the types of configurations and TM elements. The electronic structure for AlRh and AlCd alloys are used to study the characteristics of stable compounds, and it is found that more transferred electrons will make the lattice mismatch δ larger. The Cauchy pressure C12–C44 and electric local function (ELF) present underlying characteristics of bonds and physical mechanisms. Further, the Helmholtz free energies F of both Al bulk and stable AlxTMy intermetallics are decreased with increasing temperature, while the entropy S, heat capacity CV and coefficient of expansion aT show the opposite trends. And the smaller F leads to the lower aT; that is the compounds constitute of elements of IB ∼ IVB have larger F and aT, while the compounds with VB ∼ VIIB possess smaller F and aT. In short, all calculated parameters in this work show the same change with the atomic number in for three periods 3-5d, indicating that the structure of the TM valence electron layers are the main reason for the underlying mechanisms. This work is helpful for the study of high-performance of structural Al-based alloys.