Joint Study of Temperature Dependences of Thermal Expansion and Heat Capacity of Solid Beryllium

This work presents the detailed joint study of temperature dependences of thermal expansion and heat capacity of solid beryllium. It is shown that, as for the earlier studied solid bodies, within the limits of experimental and statistical errors, the heat capacity C(T) and the temperature coefficient of volume expansion β(T) in the entire range of the HCP-phase of metal are in a pronounced correlation β(C) that has a typical (as earlier) “bilinear” form consisting of two smoothly conjugate linear sections with the up-fracture hitting the classical Dulong and Petit heat capacity limit 3R. The consistent values of the heat capacity obtained and the thermal expansion are tabulated and an estimate of the temperature dependence of the Grüneisen differential parameter γ′ ~ (?β/?C) is given.     

Monte Carlo Study of Magnetic and Thermal Phase Transitions of a Diluted Magnetic Nanosystem

Monte Carlo (MC) simulation method with the Metropolis algorithm is used to study the magnetic and thermal phase transition properties of a spherical nanoparticle. The system consists of two concentric spheres of rays R _C and R _S, respectively (R _c < R _s). For r < R _c, the spin is σ = ±3 /2 and ±1 /2, and for R _C < r ≤ R _S, the spin is S = ±7 /2, + 5/2, ±3 /2, and ±1 /2 with antiferromagnetic interface coupling. Between R _C and R _S, the sites are populated with the probability (p). We present a detailed discussion on the magnetic and thermal phase transition characteristics of the system under consideration. Our investigations show that this system can be used as a magnetic nanostructure possessing potential applications in magnetism.     

Calculation of thermodynamic properties of SF<Subscript>6</Subscript> including the critical region. Thermal functions and speed of sound

Specific heats C _v and C _p, entropy S, enthalpy H, and speed of sound W have been calculated using a new thermal equation of state with a small number of variable constants, which includes regular and scale contributions with a new transition function. The calculation results correspond to the accuracy level of the modern reference equations of state with a large number of determined parameters in the regular behavioral region of SF₆ properties; in the critical region, these results make it possible to supplement the existing reference data with the related tables, taking into account the scaling-theory advances. The experimental and tabular data on C _v, C _p, S, H, and W have not been used to determine the constants of the calculation equations (except for isochoric specific heat, C _v, in the ideal-gas state). These data have been applied only for comparison of the calculated values with the experimental and tabular values. To calculate the behavior of thermal properties in the critical region, universal critical indices α, β, and γ have been used according to the threedimensional Ising model. The mean error in describing thermal properties of SF₆ does not exceed the error of the existing experimental data. The calculated values coincide with the modern reference data in the regular region in the entire range of gas and liquid states. The discrepancies in the critical region are due to the application of the scale equation of state (in contrast to the regular equations used previously in this region for composing reference tables).     

Thermal performance prediction models for a pulsating heat pipe using Artificial Neural Network (ANN) and Regression/Correlation Analysis (RCA)

Pulsating heat pipe (PHP) is one of the prominent research areas in the family of heat pipes. Heat transfer and fluid flow mechanism associated with PHP are quite involved. The analytical models are simple in nature and limited in scope and applicability. The regression models and Artificial Neural Network (ANN) are also limited to a number of input parameters, their ranges and accuracy. The present paper discusses the thermal performance prediction models of a PHP based on ANN and RCA approach. Totally 1652 experimental data are collected from the literature (2003–2017). Nine major influencing input variables are considered for the first time to develop the prediction models. Feed-forward back-propagation neural network is developed and verified. Backward regression analysis is used in RCA-based regression model. Linear and power-law regression correlations are developed for input heat flux in terms of dimensionless Kutateladze (Ku) number, which is a function of Jakob number (Ja), Morton number (Mo), Bond number (Bo), Prandtl number (Pr) and geometry of a PHP. The prediction accuracy of present regression models (R²?=?0.95) is observed to be better as compared with literature-based correlations.     

Correlation between temperature dependences of thermal expansivity and heat capacity up to the melting point of tantalum

Following the course of previously published series, this work studies in detail the correlation of the volumetric thermal expansion coefficient β(T) and the heat capacity C(T) of refractory tantalum. It is demonstrated that a clear correlation β(C) takes place in the lower temperature range and remains up to the metal melting point inclusively. Significant deviation from lower temperature linear behavior of the β(C) dependence occurs when the heat capacity reaches the classical 3R Dulong–Petit limit. The temperature dependence of differential Grüneisen parameter γ' ~ (?β/?С) is estimated.     

Thermal Expansion and Isothermal Compressibility of TlGaTe<Subscript>2</Subscript>

The temperature dependences of thermal expansion and isothermal compressibility for TlGaTe₂ indicate that this compound undergoes a second-order phase transition at 98 K. The experimental data are used to evaluate the Debye characteristic temperature, rms dynamic atomic displacements, specific heat difference C _p - C _V , and Gruneisen parameter. The appreciable discrepancy between the C _p - C _V values calculated using thermodynamic relations and an empirical formula is attributed to the pronounced anisotropy of TlGaTe₂ crystals.     

Thermodynamic properties of (TeO<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(MoO<Subscript>3</Subscript>)<Subscript>1–<Emphasis Type="Italic">n</Emphasis></Subscript> glasses

The thermal behavior of (TeO₂) _n (MoO₃)_1–n (n = 0.75, 0.85, 0.90) tellurite glasses has been studied by differential scanning calorimetry in the range from T = 300 to T = 850 K and heat capacity has been measured in the temperature range. The thermodynamic characteristics of the devitrification process and glassy state have been determined. The experimental data obtained have been used to evaluate the standard thermodynamic functions of the system in glassy and supercooled liquid states: heat capacity C _p °(T), enthalpy H°(T)–H°(320), entropy S°(T)–S°(320), and Gibbs function G°(T)–G°(320) in the temperature range 320–630 K. The composition dependences of the glass transition temperature and thermodynamic functions for the glasses have been obtained. The thermal and thermodynamic properties of the tellurite glasses have been compared to those of previously studied (TeO₂) _n (WO₃)_1–n and (TeO₂) _n (ZnO)_1–n glasses.     

Effect of restricted geometry and external pressure on the phase transitions in ammonium hydrogen sulfate confined in a nanoporous glass matrix

A study of heat capacity, thermal dilatation, susceptibility to hydrostatic pressure, permittivity and polarization loops was carried out on NH₄HSO₄–porous glass nanocomposites (AHS?+?PG) as well as empty glass matrices. The formation of dendrite clusters of AHS with a size, d_cryst, exceeding the pore size was found. An insignificant anisotropy of thermal expansion of AHS?+?PG showing statistically uniform distribution of AHS with random orientations of nanocrystallites over the matrix was observed. The effect of internal and external pressures on thermal properties and permittivity was studied. At the phase transition P-1???Pc, a strongly nonlinear decrease in the entropy ΔS₂ and volume strain (ΔV/V)_T2 was observed with decreasing d_cryst. The linear change in temperatures of both phase transitions P-1???Pc???P2₁/c under hydrostatic pressure is accompanied by the expansion of the temperature range of existence of the ferroelectric phase Pc, while this interval narrows as d_cryst decreases.     

Band structure of silicon carbide nanotubes

Using the linear augmented cylindrical wave method in the muffin-tin approximation, we have calculated the band structure of (n, n) and (n, 0) silicon carbide nanotubes for n = 5–10. In the range n = 7–10, (n, n) nanotubes are semiconductors, and their band gap decreases steadily with increasing n: 0.28 eV at n = 7, 0.26 eV at n = 8, 0.19 eV at n = 9, and 0.11 eV at n = 10. Nanotubes with n = 5 and 6 are metallic. At n = 7–9, (n, 0) nanotubes are semiconductors, and their band gap increases steadily with n: 0.39 eV at n = 7, 0.46 eV at n = 8, and 0.62 eV at n = 9. Nanotubes with n = 5 and 6 have metallic conductivity according to our results.     

Measurement Uncertainty Budget of the PMV Thermal Comfort Equation

Fanger’s predicted mean vote (PMV) equation is the result of the combined quantitative effects of the air temperature, mean radiant temperature, air velocity, humidity activity level and clothing thermal resistance. PMV is a mathematical model of thermal comfort which was developed by Fanger. The uncertainty budget of the PMV equation was developed according to GUM in this study. An example is given for the uncertainty model of PMV in the exemplification section of the study. Sensitivity coefficients were derived from the PMV equation. Uncertainty budgets can be seen in the tables. A mathematical model of the sensitivity coefficients of \(T_{\mathrm{a}}\), \(h_{\mathrm{c}}\), \(T_{\mathrm{mrt}}\), \(T_{\mathrm{cl}}\), and \(P_{\mathrm{a}}\) is given in this study. And the uncertainty budgets for \(h_{\mathrm{c}}\), \(T_{\mathrm{cl}}\), and \(P_{\mathrm{a}}\) are given in this study.     

Thermal contact resistance estimation: influence of the pressure contact and the coating layer during a hot forming process

The Thermal Contact Resistance R _C Estimation constitutes an encountered problem to be resolved in any forming process. To fairly simulate a part cooling during a hot stamping process, an experimental device was designed and developed by the Laboratoire de Thermocinétique de Nantes—France in collaboration with ArcelorMittal R&;D Montataire—France. The object is to estimate the thermal contact resistance at the part/tool interface during the three stage of the hot stamping process. During hot stamping phases, different contact types occur at the part/tool interface. The forming phase is characterized by a dynamic contact due to the increasing effort applied by the punch. At the contact interfaces, thermal contact resistances R _C are estimated experimentally through a non-linear 1D inverse technique founded on sequential method of Beck. Experiments were carried out on hot stamping samples made of Usibor 1500P® and 22MnB5 galvanized steel. The range of prospected stamping pressure varies from 10 to 30?MPa. The analysis of the effort curves shows the same mechanical resistance law of the part during the forming phase, whatever the consign effort settled to reach the maximum stamping pressure. The R _C value estimated for the galvanized steel is 33% lower than the one estimated for Usibor 1500P®. It is due to a higher harmonic thermal conductivity of the coated material. Results have been established as correlation of type: R _C ?=?f(P) to be used for numerical simulation.     

Geometrical Effect on Thermal Conductivity of Unidirectional Fiber-Reinforced Polymer Composite along Different In-plane Orientations

This paper focuses on the anisotropic characteristics of the in-plane thermal conductivity of fiber-reinforced polymer composite based on experiment and simulation. Thermal conductivity along different in-plane orientations was measured by laser flash analysis (LFA) and steady-state heat flow method. Their heat transfer processes were simulated to reveal the geometrical effect on thermal conduction. The results show that the in-plane thermal conduction of unidirectional carbon-fiber-reinforced polymer composite is greatly influenced by the sample geometry at an in-plane orientation angle between 0° to 90°. By defining radius-to-thickness as a dimensionless shape factor for the LFA sample, the apparent thermal conductivity shows a dramatic change when the shape factor is close to the tangent of the orientation angle (tanθ). Based on finite element analysis, this phenomenon was revealed to correlate with the change of the heat transfer process. When the shape factor is larger than tanθ, the apparent thermal conductivity is consistent with the estimated value according to the theoretical model. For a sample with a shape factor smaller than tanθ, the apparent thermal conductivity shows a slow growth around a low value, which seriously deviates from the theory estimation. This phenomenon was revealed to correlate with the change of the heat transfer process from a continuous path to a zigzag path. These results will be helpful in optimizing the ply scheme of composite laminates for thermal management applications.     

Thermal expansion and isothermal compressibility of TlGaSe<Subscript>2(1 −<Emphasis Type="Italic">x</Emphasis>)</Subscript>S<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.1, 0.2)

The temperature dependences of the thermal expansion coefficient and isothermal compressibility for TlGaSe_{2(1 ? x)}S_2x (x = 0.1, 0.2) solid solutions show an anomaly attributable to a second-order phase transition. The thermal expansion data have been used to evaluate the Debye characteristic temperature Θ, rms atomic displacement, and specific heat difference of the solid solutions.     

Specific Heat Jump at T<Emphasis Type="Italic">c</Emphasis> of High T<Emphasis Type="Italic">c</Emphasis> Superconductors: Effect of Van Hove Singularity

In the BCS framework, exact expressions for the ratio between the jump in the specific heat at T _c and the normal phase specific heat are derived within the Van Hove singularity scenario. Analytical results are obtained for an isotropic s-wave and anisotropic d-wave pairing symmetries. Graphical solutions of the ratio as functions of ω _D /T _c and E _F /T _c , where ω _D is the cutoff energy and E _F is the Fermi energy, show significant deviations from the BCS value of 1.43.     

Convective Heat Transfer at an Annular Jet Impingement on a Flat Blockage

The experimental results on heat transfer of an annular impinging jet have been. The Reynolds numbers Re = (1.2–3.6) × 10⁴, the distance S from the nozzle to a blockage, S/d₀ = 2, 4, 6, and the circular slit height d₂/d₀ = 0.51 and 0.71, where d₀ and d₂ are the internal and external nozzle diameters, have been varied. It is shown that at the same air mass flow rate, replacement of a round nozzle with an annular one results in heat-transfer intensification (up to 70% at the stagnation point). The maximum heat transfer gain occurs at a small nozzle–wall distance (S/d₀ = 2). The heat-transfer increase is accompanied by an increase in the thermal pulsation intensity. The degree of intensification of the heat exchange depends on the height of the circular slit and the nozzle–wall distance.     

On the Interpretation of Near-Critical Gas–Liquid Heat Capacities by L. V. Woodcock,Int. J. Thermophys. (2017) 38, 139: Comments

It is shown that: (1) the expressions for the isochoric (C_V) and isobaric (C_P) heat capacities of liquid and gas, coexisting in phase equilibrium, the heat capacities at saturation of liquid and gas (C_σ) and the heat capacity C_λ used in the article “On the Interpretation of Near-Critical Gas–Liquid Heat Capacities, L. V. Woodcock, Int. J. Thermophys. (2017) 38, 139” are incorrect; (2) the conclusions of the article based on the comparison of the incorrect C_V, C_P and C_λ with experimental data are also incorrect; (3) the lever rule cannot be used to define C_V and C_P in the two-phase coexistence region; (4) a correct expression for the isochoric heat capacity describes well the experimental data; (5) there is no misinterpretation of near-critical gas–liquid heat capacity measurements in the two-phase coexistence region; (6) there are no proofs in the article that: (a) the divergence of C_V is apparent; (b) it has not been established experimentally that the thermodynamic properties of fluids satisfy scaling laws with universal critical exponents asymptotically close to a single critical point of the vapor–liquid phase transition; and (c) there is no singular critical point on Gibbs density surface. We obtained the relations connecting the isochoric heat capacity in the two-phase region with thermodynamic properties at saturation of homogeneous liquid and gas which can be used to verify the equation of state.     

Photothermal Techniques Applied to the Thermal and Optical Characterization of <Emphasis Type="Italic">Curcuma longa</Emphasis>

In recent years, has been reported an increasing interest to study vegetables and fruits in order to know their benefits to prevent different types of health problems. Curcuma longa has a great potential to prevent diseases as different types of cancer. In the present study, C. longa samples, of different trademarks, were optically and thermally characterized by using photoacoustic spectroscopy and photopyroelectric techniques, obtaining their optical absorption spectra, optical absorption length spectra, the thermal diffusivity, effusivity, conductivity and heat capacity per unit volume, observing optical absorptions corresponding to antioxidant elements, reported such as beneficial for health. These properties also could be important in the food industry for the commercialization of functional foods.     

Thermal stability and fire behavior of aluminum diethylphosphinate-epoxy resin nanocomposites

The flame retardancy of 2, 2-bis(4-glycidyloxyphenyl)propane (DGEBA)-aluminum diethylphosphinate (AlPi) nanocomposites (EP-AlPi/(P ? x), x = 1, 2, 3 %) was greatly enhanced by ultrasonic dispersion of nano-sized AlPi into epoxy resin. The UL 94 V-0 rating can be reached for EP-AlPi nanocomposites with a relatively low addition amount of AlPi (on the account of 8.4 wt% or phosphorus content of 2 wt%) as well as the LOI value over 37.2. The glass transition temperature (T _g) enhanced properties were investigated by DTA, which showed that: T _gs were about 5 °C higher than that of neat epoxy resin; T _g increased along with content increasing of AlPi. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of EP-AlPi/(P ? x) composites were studied by Kissinger’s, Ozawa’s, Flynn–Wall–Ozawa’s and Coast-Redfern’s methods, which suggested the conversion function f (α) = 1/2α ^?1 or f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 1 %); f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 2 %) and EP-AlPi/(P ? 3 %) during the investigated process. The epoxy resin nanocomposites obtained in this study are green functional polymers and will become flame retardant potential candidates in electronic fields such as printed wiring boards with high performance.     

Preparation and Thermal Expansion of Calcium Iron Zirconium Phosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> Structure

Ca_{0.5(1 + x)}Zr_2–xFe _x (PO₄)₃ phosphates have been synthesized by a sol–gel process. The individual compounds and solid solutions obtained crystallize in the NaZr₂(PO₄)₃ structure (trigonal symmetry, sp. gr. R\(\bar 3\)). Using high-temperature X-ray diffraction, we have determined their thermal expansion parameters in the temperature range from 25 to 800°C. With increasing x, the magnitudes of their linear thermal expansion coefficients and thermal expansion anisotropy decrease. Most of the synthesized phosphates can be rated as low-thermal-expansion compounds and can be regarded as materials capable of withstanding thermal “stress.”