Experimental Specific Heat Data Research Articles

APPLICABILITY OF MACHINE LEARNING TECHNIQUES IN PREDICTING SPECIFIC HEAT CAPACITY OF COMPLEX NANOFLUIDS

The complexity of the interaction between base fluids and nano-sized particles makes the prediction of nanofluid thermophysical properties difficult. However, machine learning techniques can be utilized as an alternative approach due to their ability to identify complex nonlinear patterns in data and make accurate forecasts. This paper presents intuitive predictions of specific heat of various types of nanofluids using machine learning models based on experimental data obtained from 47 different studies, comprising 5009 data points. Three machine learning algorithms, namely, artificial neural network (ANN), support vector regression (SVR), and extreme gradient boosting (XGBoost), were tested to develop a universal predictor for nanofluid specific heat. To enhance the performance of the machine learning models, the best set of input variables was selected, and hyperparameter optimization was conducted to maximize the prediction accuracy. The accuracy of three selected machine learning models [i.e., MLP (a type of ANN), SVR, and XGBoost] and their unseen data prediction capability were compared with existing complicated empirical models, and the results showed that the machine learning-based predictions were more accurate. The machine learning models demonstrated excellent agreement with experimental nanofluid specific heat data. Particularly, the extreme gradient boosting method (i.e., XGBoost) showed the best nanofluid specific heat forecast results with minimal prediction error and presented broad range of applicability.

Studies on synthesis, structure and physical properties of NbMoO4

A transition metal oxide, NbMoO4, is synthesized by using a solid-state reaction method, then the morphology of the sample is characterized by the scanning electron microscopy. The X-ray diffraction refinement and transmission electron microscopy results show that the sample has a TiO2 rutile-type structure with space group P42/mnm, which is the high-temperature phase of NbO2 and MoO2. Our transport result indicates that the resistivity is as low as 0.02 Ω·cm in the temperature range from 2 to 300 K, indicating the metallicity of NbMoO4. Furthermore, the calculated density of states and experimental specific heat data from 2 to 20 K also confirm the metallic behavior. Our magnetization experiments indicate that the NbMoO4 exhibits paramagnetism. The valence states of Nb4+ and Mo4+ in NbMoO4 are revealed by the X-ray absorption spectroscopy.

High-field specific heat and entropy obtained from adiabatic temperature change

Specific heat and entropy are relevant thermodynamic properties, which may be used as macroscopic probes to microscopic properties of materials under ambient conditions and under high applied fields. However, the measurement of specific heat under intense external fields can be a challenging task, as well as to obtain the entropy in the same conditions. Here, we describe a method to obtain high-field specific heat and entropy from measurements of specific heat under ambient conditions and direct temperature change induced by adiabatic field changes. We derive straightforward thermodynamic equations to calculate the specific heat and entropy, and our results agree satisfactorily with experimental data of specific heat under magnetic field, electric field, and pressure.

Sb2Te3/graphite nanocomposite: A comprehensive study of thermal conductivity

Thermoelectric performance largely depends on the reduction of lattice thermal conductivity (κL). The study of the thermal conductivity (κ) of a Sb2Te3/graphite nanocomposite system demonstrates ∼40% reduction in κL with graphite incorporation. A plausible explanation of intrinsic low κL observed in Sb2Te3 based system is presented by modeling experimental specific heat (Cp) data. Raman spectroscopy measurement combined to X-Ray diffraction data confirms the presence of graphite as separate phase in the composite sample. It is found that phonon scattering dominates heat transport mechanism in the nanostructured Sb2Te3/graphite composite. Large reduction in κL is accomplished by intensifying scattering rate of phonons via various sources. Graphite introduces effective scattering sources, i.e., defects of different dimensionalities in synthesized nanocomposite sample. Furthermore, graphite mediates phonon-phonon coupling and enhances lattice anharmonicity, which causes an intrinsic scattering of phonons with all frequencies in the Sb2Te3/graphite nanocomposite sample. Dislocation density and phonon anharmonicity of the synthesized samples are estimated from in depth analysis of temperature dependent synchrotron powder diffraction and Raman spectroscopic data. κL value as low as 0.8 W m−1K−1 at 300 K, achieved with graphite dispersion in Sb2Te3 based composite system makes the present comprehensive study an interesting concept to be developed in thermoelectric materials.

Magnetocaloric effect as a signature of quantum level-crossing for a spin-gapped system

Recent research dealing with magnetocaloric effect (MCE) study of antiferromagnetic (AFM) low dimensional spin systems have revealed a number of fascinating ground-state crossover characteristics upon application of external magnetic field. Herein, through MCE investigation we have explored field-induced quantum level-crossing characteristics of one such spin system: (NCP), an AFM spin 1/2 dimer. Experimental magnetization and specific heat data are presented and the data have been employed to evaluate entropy, magnetic energy and magnetocaloric properties. We witness a sign change in magnetic Grüneisen parameter across the level-crossing field BC. An adiabatic cooling is observed at low temperature by tracing the isentropic curves in temperature-magnetic field plane. Energy-level crossover characteristics in NCP interpreted through MCE analysis are well consistent with the observations made from magnetization and specific heat data.

Localized Vibrations of Bi Bilayer Leading to Ultralow Lattice Thermal Conductivity and High Thermoelectric Performance in Weak Topological Insulator n-Type BiSe.

Realization of high thermoelectric performance in n-type semiconductors is of imperative need on account of the dearth of efficient n-type thermoelectric materials compared to the p-type counterpart. Moreover, development of efficient thermoelectric materials based on Te-free compounds is desirable because of the scarcity of Te in the Earth's crust. Herein, we report the intrinsic ultralow thermal conductivity and high thermoelectric performance near room temperature in n-type BiSe, a Te-free solid, which recently has emerged as a weak topological insulator. BiSe possesses a layered structure consisting of a bismuth bilayer (Bi2) sandwiched between two Bi2Se3 quintuple layers [Se-Bi-Se-Bi-Se], resembling natural heterostructure. High thermoelectric performance of BiSe is realized through the ultralow lattice thermal conductivity (κlat of ∼0.6 W/mK at 300 K), which is significantly lower than that of Bi2Se3 (κlat of ∼1.8 W/mK at 300 K), although both of them belong to the same layered homologous family (Bi2) m(Bi2Se3) n. Phonon dispersion calculated from first-principles and the experimental low-temperature specific heat data indicate that soft localized vibrations of bismuth bilayer in BiSe are responsible for its ultralow κlat. These low energy optical phonon branches couple strongly with the heat carrying acoustic phonons, and consequently suppress the phonon mean free path leading to low κlat. Further optimization of thermoelectric properties of BiSe through Sb substitution and spark plasma sintering (SPS) results in high ZT ∼ 0.8 at 425 K along the pressing direction, which is indeed remarkable among Te-free n-type thermoelectric materials near room temperature.

Investigation of thermodynamic properties of Cu(NH3)4SO4·H2O, a Heisenberg spin chain compound

Detailed experimental investigation of thermal and magnetic properties are presented for Cu(NH3)4SO4·H2O, an ideal uniform Heisenberg spin ½ chain compound. A comparison of these properties with relevant spin models is also presented. Temperature dependent magnetic susceptibility and specific heat data have been compared with the exact solution for uniform Heisenberg chain model derived by means of Bethe ansatz technique. Magnetization isotherms measured as a function of field are analyzed using the numerical results simulated by Quantum Monte Carlo technique. Specific heat as a function of magnetic field (up to 7T) and temperature (down to 2K) is reported. Subsequently, the data are compared with the corresponding theoretical curves for infinite Heisenberg spin ½ chain model with J=6K. Moreover, internal energy and entropy are calculated by analyzing the experimental specific heat data. Magnetic field and temperature dependent behavior of entropy and internal energy are in good agreement with the theoretical predictions.

Capillary effects on phase behavior of liquid and gaseous propane and dynamics of hydrate formation and dissociation in porous media

Using a precision adiabatic calorimetry method the phase behavior of liquid and gaseous propane with water in bulk as well as in dry and water saturated porous media have been studied in the temperature range from 240 to 350 K and the pressure range from 0.1 to 12 MPa. Quartz powder with a grain size from 25 to 38 mk as a porous medium was used. Water saturation of the porous medium was about 0.247 ± 0.001 of porous volume. From thermodynamic point of view such water saturation of the porous volume is sufficient to consider the pore water phase practically as a bulk phase. A composite porous medium is formed from the quartz powder grains covered by a water film. In fact, the water film is a mechanical continuation of the quartz powder grains. The water film forms a configuration (a curvature) of the porous space as well predetermines a surface wettability of the composite porous medium. We study capillary effect in composite porous media due to capillary condensation and capillary evaporation of propane, both on a lyophilic surface and on a lyophobic surface of water film. Based on the experimental data of specific heat and temperature derivative of pressure at constant volume, the phase diagrams of propane in bulk and in water saturated and dry quartz powder have been constructed (including the gas hydrate field of phase diagram).

CePdAl - a Kondo lattice with partial frustration

Magnetic frustration, which is well-defined in insulating systems with localized magnetic moments, yields exotic ground states like spin ices, spin glasses, or spin liquids. In metals magnetic frustration is less well defined because of the incipient delocalization of magnetic moments by the interaction with conduction electrons, viz., the Kondo effect. Hence, the Kondo effect and magnetic frustration are antithetic phenomena. Here we present experimental data of electrical resistivity, magnetization, specific heat and neutron diffraction on CePdAl, which is one of the rare examples of a geometrically frustrated Kondo lattice, demonstrating that the combination of Kondo effect and magnetic frustration leads to an unusual ground state.

Mean Field Theory of a Coupled Heisenberg Model and Its Application to an Organic Antiferromagnet with Magnetic Anions

We examine the mean field theory of a uniaxial coupled Heisenberg antiferromagnet with two subsystems, one of which consists of strongly interacting small spins and the other consists of weakly interacting large spins. We reanalyze the experimental data of specific heat and magnetic susceptibility obtained by previous authors for the organic compound λ-(BETS)2FeCl4 at low temperatures, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. The model parameters for this compound are evaluated, where the applicability of the theory is checked. As a result, it is found that J1 ≫ J12 ≫ J2, where J1, J2, and J12 denote the exchange coupling constant between π spins, that between 3d spins, and that between π and 3d spins, respectively. At the low-temperature limit, both sublattice magnetizations of the 3d and π spins are saturated, and the present model is reduced to the Schottky model, which successfully explains experimental observations in previous studies. As temperature increases, fluctuations of 3...

Experimental evidences of singlet to triplet transition in a spin cluster compound

Experimental realization of magnetic field induced singlet to triplet transition is reported for NH4CuPO4·H2O, a two spin cluster material with isotropic Heisenberg interaction. Experimental magnetization and specific heat data have been collected as a function of temperature and magnetic field. Experimental data have been analyzed in terms of Heisenberg dimer model. Two quantum complementary observables representing local and non-local properties of the spins are constructed using the experimental data and a clear evidence of singlet to triplet transition is observed through partial quantum information sharing when the magnetic field is swept through a particular value. Signature of this transition has also been captured when specific heat is measured as a function of magnetic field. Furthermore, using the experimental specific heat data, magnetic energy values are calculated and their variations are captured as a function of magnetic field and temperature.

Thermodynamics and fragility of Fe-based glass forming melts

Methods to determine the fragility index, m, both in thermodynamic and kinetic terms are reviewed and applied to two Fe-based glass formers, Fe40Ni40P14B6 and Fe41Co7Cr15Mo14C15B6Y2. The thermodynamic fragility is obtained from entropy curves based on experimental data of the liquid specific heat and of the enthalpy of transformation from glass or liquid to crystal phases.The thermodynamic fragility appears systematically higher than the kinetic one because of the large scatter of data and their extrapolation to obtain the Kauzmann temperature of vanishing entropy.A practical method to estimate the viscosity of glass formers in the undercooling regime was derived from the fragility index and its correlation with parameters of the VFT equation. It provides reasonable agreement with experimental data.

Signature of quantum entanglement in NH4CuPO4·H2O

Entangled solid state systems have gained a great deal of attention due to their fruitful applications in modern quantum technologies. Herein, detection of entanglement content from experimental magnetic susceptibility and specific heat data is reported for NH4CuPO4·H2O in its solid state crystalline form. NH4CuPO4·H2O is a prototype of Heisenberg spin 1/2 dimer system. Temperature dependent magnetic susceptibility and specific data are fitted to an isolated dimer model and the exchange coupling constant is determined. Field dependent magnetization isotherms taken at different temperatures are plotted in a three dimensional plot. Subsequently, entanglement is detected both from susceptibility and specific heat through two different entanglement measures; entanglement witness and entanglement of formation. The temperature evolution of entanglement is studied and the critical temperature is determined up to which entanglement exists. Temperature dependent nature of entanglement extracted from susceptibility and specific heat shows good consistency with each other. Moreover, the field dependent entanglement is also investigated.

Probing quantum discord in a Heisenberg dimer compound

A quantitative estimation of quantum discord is performed for a Heisenberg spin 1/2 dimer compound (NH4CuPO4, H2O) by means of experimental magnetic and thermal measurements. Magnetic susceptibility and specific heat data were collected for NH4CuPO4, H2O and analyzed within the framework of the Heisenberg isolated dimer model. Internal energy as a function of temperature is obtained by integrating the specific heat versus temperature data. Subsequently, quantum discord, total correlations and spin–spin correlation function are quantified from susceptibility and internal energy and plotted as a function of temperature. Violation of Bell’s inequality is also tested for NH4CuPO4, H2O via both experimental susceptibility and specific heat data signifying the presence of entanglement.

Anisotropic superconducting order parameters in the iron pnictide superconductors

The symmetry and structure of the superconducting gap in the Fe-based superconductors are the central issues for understanding these novel materials. So far the experimental data and theoretical models have been highly controversial. Some experiments favor two or more isotropic gaps, others indicate strong anisotropy and even nodes. In this paper we present the experimental data of low temperature specific heat to illustrate that the superconducting gap is anisotropic. In the case of optimally doped 122, the gap minimum may appear as point nodes or small segment of nodal lines, while in the FeTe0.55Se0.45 it may appear on the electron pockets with the gap minimum along the Γ-Z (Fe-Fe bond) direction.

Electronic structure and fermiology of superconducting LaNiGa2

We report electronic structure calculations for the layered centrosymmetric superconductor LaNiGa$_2$, which has been identified as having a possible triplet state based on evidence for time reversal symmetry breaking. The Fermi surface has several large sheets and is only moderately anisotropic, so that the material is best described as a three dimensional metal. These include sections that are open in the in-plane direction as well as a section that approaches the zone center. The density of states is high and primarily derived from Ga $p$ states, which hybridize with Ni $d$ states. Comparing with experimental specific heat data, we infer a superconducting $\lambda \le$ 0.55, which implies that this is a weak to intermediate coupling material. However, the Ni occurs in a nominal $d^{10}$ configuration in this material, which places the compound far from magnetism. Implications of these results for superconductivity are discussed.

Experimental study on optimized composition of mixed carbonate salt for sensible heat storage in solar thermal power plant

Thirty six kinds of mixed carbonate molten salts were prepared by mixing potassium carbonate, lithium carbonate, sodium carbonate in accordance with different proportions. The data of melting point, decomposition temperature, specific heat are measured by the analysis of the TGA and DSC curves of 36 kinds of salts, which show that melting points of major ternary carbonate are close at around 400 °C and decomposition temperatures of most ternary carbonate are between 800 and 850 °C. Twleve kinds of eutectic molten salts with low melting point were selected among 36 kinds of salts. The correlations of the eutectic salts between specific heat and temperature were obtained by fitting the experimental data of specific heat. The costs for sensible heat storage of 12 kinds of carbonate salts are obtained. The optimum preparation ratio is recommended for sensible heat storage.

THERMOPHYSICAL PROPERTIES OF JACKFRUIT PULP AFFECTED BY CHANGES IN MOISTURE CONTENT AND TEMPERATURE

ABSTRACT Thermophysical properties of jackfruit (Artocarpus heterophyllus L.) pulp affected by temperature and moisture content were analyzed. Density (ρ), heat capacity (cp) and thermal diffusivity (α) were experimentally determined at moisture content between 65% m/m and 95% m/m, and temperatures between 5 and 85C. Then, thermal conductivity was calculated from experimental results of thermal diffusivity, specific heat and density. The empirical models for each property as a function of moisture content and temperature were obtained (R2 ≥ 0.90). Estimated equations were fitted to the experimental data for density and specific heat, and the accuracy of those equations was checked.PRACTICAL APPLICATIONSThe design of juice concentrate plants needs thermophysical parameters. Information about tropical and exotic fruits, such as jackfruit, is insufficient, and much specific information is still unknown. The knowledge of how temperature and moisture content affect properties such as density, specific heat, thermal diffusivity and thermal conductivity will enable the development, adaptation and optimization of more efficient specific equipment for processing jackfruit.

Specific heat, internal energy, and thermodynamic Casimir force in the neighborhood of theλtransition

We discuss the relation of the specific heat, the energy density and the thermodynamic Casimir effect in the case of thin films in the three dimensional XY universality class. The finite size scaling function $\theta(x)$ of the thermodynamic Casimir force can be expressed in terms of the scaling functions h'(x) and h(x) of the excess energy density and the excess free energy density. A priori these quantities depend on the reduced temperature t and the thickness L_0 of the film. However finite size scaling theory predicts that the scaling functions depend only on the combination x=t [L_0/\xi_0]^{1/\nu}, where \nu is the critical exponent and $\xi_0$ the amplitude of the correlation length. We exploit this fact to compute \theta from Monte Carlo data for the excess energy density of the improved two-component \phi^4 model on the simple cubic lattice with free boundary conditions in the short direction. We repeat this exercise using experimental data for the excess specific heat of 4He films. The finite size scaling behaviour of the excess specific heat is governed by h''(x), which is proportional to the scaling function $f_2$ discussed in the literature. We compare our results with previous work, where the Casimir force has been computed by taking the derivative of the excess free energy with respect to the thickness of the film. As a preparative study we have also computed the scaling functions h'(x) and h(x) for finite L^3 systems with periodic boundary conditions in all directions, where L is the linear extension of the system.

Quantum Order by Disorder in Frustrated Diamond Lattice Antiferromagnets

We present a quantum theory of frustrated diamond lattice antiferromagnets. Considering quantum fluctuations as the predominant mechanism relieving spin frustration, we find a rich phase diagram comprising of six phases with coplanar spiral ordering in addition to the Néel phase. By computing the specific heat of these ordered phases, we obtain a remarkable agreement between (k, k, 0) spiral ordering and the experimental specific heat data for the diamond lattice spinel compounds MnSc2S4, Co3O4, and CoRh2O4, i.e., specific heat data is a strong evidence for (k, k, 0) spiral ordering in all of these materials. This prediction can be tested in future neutron scattering experiments on Co3O4 and CoRh2O4, and is consistent with existing neutron scattering data on MnSc2S4. Based on this agreement, we infer a monotonically increasing relationship between frustration and the strength of quantum fluctuations.