Heat Capacity Values Research Articles

Vaporization thermodynamics of Leuco Dyes: Measurement and prediction

Leuco Dyes are colorless reduced forms of many organic dyes used in such fields as analytical chemistry, criminalistics, and organic synthesis. Due to the low volatility of these compounds, the determination of their vaporization parameters with conventional methods is a non-trivial task. In this work, the saturated vapor pressures of three Leuco Dyes over the liquid and supercooled liquid phases were measured using fast scanning calorimetry. The respective heat capacities were obtained with DSC, and the ideal gas phase heat capacities were calculated by the methods of quantum chemistry and statistical thermodynamics. The vaporization enthalpies at 298.15 K were estimated using the “molecule-additivity” approach and adjusted to the measurement temperatures in two different ways. The first is based on an approach employing a correlation between the heat capacity change on vaporization and the vaporization enthalpy at 298.15 K, recently proposed by our group. The second way is by using the values of liquid and ideal phase heat capacities obtained in this work. The predicted, measured, and adjusted values were compared and analyzed.

Temperature-dependent elastic constants of thorium dioxide probed using time-domain Brillouin scattering

We report the adiabatic elastic constants of single-crystal thorium dioxide over a temperature range of 77–350 K. Time-domain Brillouin scattering, an all-optical, non-contact picosecond ultrasonic technique, is used to generate and detect coherent acoustic phonons that propagate in the bulk perpendicular to the surface of the crystal. These coherent acoustic lattice vibrations have been monitored in two hydrothermally grown single-crystal thorium dioxide samples along the (100) and (311) crystallographic directions. The three independent elastic constants of the cubic crystal (C11, C12, and C44) are determined from the measured bulk acoustic velocities. The longitudinal wave along the (100) orientation provided a direct measurement of C11. Measurement of C44 and C12 was achieved by enhancing the intensity of quasi-shear mode in a (311) oriented crystal by adjusting the polarization angle relative to the crystal axes. We find the magnitude of softening of the three elastic constants to be ∼2.5% over the measured temperature range. Good agreement is found between the measured elastic constants with previously reported values at room temperature, and between the measured temperature-dependent bulk modulus with calculated values. We find that semi-empirical models capturing lattice anharmonicity adequately reproduce the observed trend. We also determine the acoustic Grüneisen anharmonicity parameter from the experimentally derived temperature-dependent bulk modulus and previously reported temperature-dependent values of volumetric thermal expansion coefficient and heat capacity. This work presents measurements of the temperature-dependent elasticity in single-crystal thorium dioxide at cryogenic temperature and provides a basis for testing ab initio theoretical models and evaluating the impact of anharmonicity on thermophysical properties.

Estimation of the Standard Heat Capacity of Crystalline Alkali Metal Borates

A structure–property correlation was developed that makes it possible to choose the optimal values of the standard heat capacity of alkali metal borates, for which, according to the data of various experimental works and reference publications, wide variations are observed. This correlation enables one to estimate the standard heat capacity of unstudied alkali metal borates with sufficient validity. To ensure the reliability of the correlation, a critical analysis was made of the initial data taken from reference publications and original experimental works. Our own processing of experimental measurements of the heat capacity and the enthalpy increment was performed to verify the reliability of the literature values of the standard heat capacity of alkali metal borates.

A calorimetric and structural analysis of cooperativity in the thermal unfolding of the PDZ tandem of human Syntenin-1

Syntenin-1 is a multidomain protein containing a central tandem of two PDZ domains flanked by two unnamed domains. Previous structural and biophysical studies show that the two PDZ domains are functional both isolated and in tandem, occurring a gain in their respective binding affinities when joined through its natural short linker. To get insight into the molecular and energetic reasons of such a gain, here, the first thermodynamic characterization of the conformational equilibrium of Syntenin-1 is presented, with special focus on its PDZ domains. These studies include the thermal unfolding of the whole protein, the PDZ-tandem construct and the two isolated PDZ domains using circular dichroism, differential scanning fluorimetry and differential scanning calorimetry. The isolated PDZ domains show low stability (ΔG < 10 kJ·mol−1) and poor cooperativity compared to the PDZ-tandem, which shows higher stability (20–30 kJ·mol−1) and a fully cooperative behaviour, with energetics similar to that previously described for archetypical PDZ domains. The high-resolution structures suggest that this remarkable increase in cooperativity is associated to strong, water-mediated, interactions at the interface between the PDZ domains, associated to nine conserved hydration regions. The low Tm value (45 °C), the anomalously high unfolding enthalpy (>400 kJ·mol−1), and native heat capacity values (above 40 kJ·K−1·mol−1), indicate that these interfacial buried waters play a relevant role in Syntenin-1 folding energetics.

SEMI-EMPIRICAL METHODS FOR DETERMINING THE HEAT CAPACITY VALUES FOR SOLID INORGANIC COMPOUNDS

Modern precise experimental studies of the heat capacity values for inorganic compounds require expensive equipment. Therefore, in practice the above values are frequently estimated by using certain semi-empirical methods developed as a cheaper alternative to the experimental determinations. In particular, estimation of the isobaric heat capacity is possible, with sufficient accuracy, for many inorganic solids by using the Neumann‒Kopp, Kellogg‒Kubaschewski, and Berman‒Brown methods [1]. Sometimes, researchers employ for that purposes somewhat less precise but more universal approaches, such as the Sokolskii model [2] (applicable to a larger number of objects, including even the objects of organic nature) or crystal-energy semi-empirical calculations [3].

Improvement of Heat Release Rate Measurement from Woods Based on Their Combustion Products Temperature Rise

Heat release rate (HRR) is the principal fire characteristic of materials. There are three known methods for the measurement of HRR (based on oxygen consumption, mass loss rate, and combustion products temperature rise). The method based on oxygen consumption is considered to be the reference. However, this method is expensive and for a large part of laboratories and universities unavailable. The simplest method is based on combustion products’ temperature rise. However, this method has a fundamental problem with the temperature dependence of the heat capacity of combustion products and the thermal inertia of the measurement system. This problem has been solved by training neural networks to predict molar heat capacity and the amount of substance (chemical amount) flow rate of combustion products in the cone calorimeter exhaust duct. Data were obtained for six different wood species: birch (Betula verrucosa Ehrh.), oak (Quercus robur L.) spruce (Picea abies (L.) H. Karst.), locust (Robinia pseudoacacia L.), poplar (Populus nigra × P. maximowiczii L.), and willow (Salix alba L.) woods at heat fluxes from 25 to 50 kW m−2 have been used for neural network training. Data from three other wood species iroko (Milicia excelsa (Welw.) C.C. Berg), pine (Pinus sylvestris L.), and paulownia (Paulownia tomentosa (Thunb.) Steud.) woods have been used for testing of trained neural network. The average percentage ratio of the predicted to the true value of HRR (during the test) has been 103.8%. In addition to that, some key average fire characteristics of wood have been determined: critical heat flux 20.7 kW m−2, effective heat of combustion 14.01 MJ kg−1, and the average value of molar heat capacity of combustion products 0.045 kJ mol−1 K−1.

Preliminary Design and Numerical Investigation of a Centrifugal Compressor for Supercritical Carbon Dioxide Operating in the Vicinity of Its Critical Thermodynamic State

Waste heat recovery is one of the main practices used to reduce the carbon footprint of the industrial sector regarding environmental concern. The supercritical carbon dioxide (s-CO2) cycle is one of the most attractive heat-to-power technologies; due to the abrupt variation in CO2 properties in the vicinity of its critical point, small compression work is required and finally a high cycle efficiency is achieved. In the literature, among the various proposed layouts, the recompression s-CO2 Brayton cycle is considered to be the most efficient one. The most critical component of such a cycle is definitely the main compressor, as the related usual design procedures have been developed in the past for ideal gas as a working fluid. This study presents a methodology for the preliminary design of a centrifugal compressor with a vaned diffuser, suitable for fulfilling the desired operating requirements of a particular supercritical CO2 recompression Brayton cycle. Furthermore, it demonstrates the numerical investigation of the three-dimensional (3D) flow phenomena occurring in it, focusing on the investigation of possible condensation. To this end, a one-dimensional flow model was developed to provide information regarding the geometry of the compressor and predict its prospective performance. Commercial computational fluid dynamics (CFD) software was then employed to examine the three-dimensional flow. The effect of accuracy in the evaluation of real gas properties approaching the critical point was examined, showing that a look-up table with more points around the critical point can reduce the numerical relative error by up to 0.3% for the value of specific heat capacity. In addition, the possibility of condensation occurrence was investigated at the impeller’s inlet, where the flow is accelerated. The supersaturation pressure ratio was defined and implemented in order to identify regions where static pressure is lower than saturation pressure, possibly leading to local two-phase flow.

Studying Baikal region sand properties

The study is aimed at a more detailed determination of the thermal properties of Baikal region sands and establishment of their dependence on geological and mineralogical characteristics in order to assess the possibility of using this raw material in the food industry. The objects of the study are sands sampled on the southwestern coast of Lake Baikal. The subject of the study is the mineralogical composition of sand, its grain size composition and heat capacity. The mineral composition of sand samples and their crystal structure were studied using the method of X-ray phase analysis. A standard sieve analysis method was used for granulometric estimation of sands. The average heat capacity of sand samples was determined by the mixing method. Based on the analysis of the obtained X-ray diffraction patterns, the mineralogical composition of the studied samples was determined. It was found that quartz predominates in their composition since its percentage in samples amounts to 40–60 %. The proportion of such minerals as albite and anorthoclase is 15–30 % in different samples. Less than 5 % in each sample accounts for dickite and indialite. The presence of the mineral of anthophyllite has been found only in one sample in the amount of about 9 %. The results of granulometric composition determination show that a fraction, which accounts for 70–90 %, can be isolated in most samples. The sample from the town of Slyudyanka was the only one where the fractions of different sizes were present in approximately equal amounts. For this sample, the dependence of heat capacity on the grain size was determined. In other samples, the difference in certain heat capacity values correlated well with their mineralogical composition. The results of the conducted studies and their analysis allow to conclude that Slyudyanka and Baikalsk sands are the most attractive sands in terms of high heat capacity. The sand with the grain size from 0.125 to 0.25 mm is found to be the most suitable for the use as a thermal storage medium. This fraction is predominant in the sand of the town of Baikalsk.

An Equation of State of Corundum Based on Planck–Einstein Functions

The possibility of constructing the equation of state of a crystalline substance based on a linear combination of the Planck–Einstein functions is shown using the example of corundum α-Al2O3. Two versions of the corundum equation of state are obtained on the basis of functions F(V,T) and G(P,T) as a result of the self-consistency of the heat capacity values, the enthalpy increment, PVT data, the coefficient of thermal expansion, and the adiabatic modulus of elasticity. Both equations provide an acceptable description of the above properties in a wide range of variables (up to a pressure of 165 GPa and a temperature of 2250 K).

Assimilation of electronic, elastic, mechanical, optical, and thermal profiles in metal halide perovskite CsPbCl3, for optoelectronic applications

Potential applications for organic free Cs-based perovskite materials include optoelectronics and electronics. To examine the suitability of this material for optoelectronic devices, a thorough investigation of the mechanical, electrical, optical, and thermodynamic properties of CsPbCl3 was carried out using density functional theory with Generalized Gradient Approximation (GGA). For appropriate device applications, we estimated structural and elastic parameters to identify a better agreement of damage tolerance and electrical and optical responses. The values of Young's modulus (E), Bulk modulus (B), and Shear modulus (G) at 0–15 GPa range were found. Similarly, the values of basic mechanical parameters, Poisson's ratio (σ), Cauchy pressure (CP), and Pugh's ratio (B/G) for 0–15 GPa were also calculated. In all cases, the ductile nature of the material was found. Applied stress caused the thermodynamic properties to change. While the Debye temperature decreased as the temperature rose, the values for enthalpy and heat capacity were found to be at their highest for 15 GPa. The free energy, and entropy exhibit slightly erratic behavior. The results promise a real-world tool to tune the optical and elastic properties with applied stress in similar materials.

Group additivity values for entropy and heat capacities of C2–C8 alkanes, alkyl hydroperoxides, and their radicals

Group additivity values for the thermodynamic properties of oxygenated radicals are poorly determined due to the absence of high quality reference data. Here, a set of 58 group additive values (GAV) for the standard entropy and heat capacity of relevance to alkane oxidation is derived from fits to an extensive and accurate database of standard entropies (298.15 K) and heat capacities (300–3000 K) recently calculated with the “STAR-1D” formalism. The 192 species in this database represent the alkanes (RH), alkyl radicals (Ṙ), alkyl hydroperoxides (RO2H), alkyl-peroxy (RȮ2) and hydroperoxy-alkyl (Q˙OOH) radicals for all of the isomers of C2–C5 alkane fuels and a select number of isomers of C6–C9 species. The STAR-1D thermochemical data for this set of species was previously obtained from a coupling of scaled B2PLYPD3/cc-pVTZ vibrational analyses with scaled ωB97X-D/cc-pVTZ one-dimensional hindered rotor corrections. The 2σ uncertainties in the GAV results relative to the STAR-1D data set are 2.4 cal K–1 mol–1 for the entropies and at most 2.0 cal K–1 mol–1 for the heat capacities in the temperature range 500–800 K. The 2σ fitting uncertainties in the heat capacity gradually reduce at higher temperatures reaching a value of 0.8 cal K–1 mol–1 at 2000 K decreasing to only 0.5 cal K–1 mol–1 at 3000 K. The high degree of accuracy for the GAV representations is obtained through the introduction of various new group terms, together with the re-optimization of existing group terms. Among the full set of 58 GAV terms, 25 include non-next-nearest neighbor interactions (NNI) and β-corrections. The updated GAVs can be applied in the prediction of entropies and heat capacities for a wide range of hydrocarbons and hydroperoxide species and their radicals, which is important to the accurate prediction of fuel reactivity at low-temperatures in the range 600–1000 K.

THERMAL BEHAVIOR OF FLUIDS IN ELECTROMAGNETIC INDUCTION

In this study, the thermal behavior of different fluids in electromagnetic induction heating was investigated. Induction coil, heat exchanger and control circuit designs were made for the research. An experimental setup was created by using a temperature gauge, tachometer, DC motor and circulation pump. The thermal behavior of 650 ml of boron oil, pure water, olive oil, sunflower oil, motor oil and boron – pure water composite fluids after their circulation at 700 rpm and 92 minutes from the experimental setup was investigated. The heat exchanger surface temperature, circulation pipe temperature, beaker temperature and ambient temperature were recorded. The heat exchanger surface temperature, circulation pipe temperature, beaker temperature and ambient temperature were recorded. The specific heat capacity values of the same fluids were also calculated. At the end of the research, it was observed that the temperature of 92 minutes under the same electromagnetic induction and ambient conditions showed values between 79 °C and 95 °C. It has been determined that the most efficient fluid is the engine oil, which has a heating value of 37 °C at the 2nd minute, 85 °C at the 42nd minute and 95 °C at the 92nd minute. It was observed that boron oil, olive oil, sunflower oil, boron – pure water composite mixture and pure water followed, respectively. It has been observed that the specific heat capacity values are inversely proportional to the temperature increase of the fluids.

Design and optimization of composite phase change material for cylindrical thermal energy storage

Phase change materials store thermal energy in the form of latent heat, and are often integrated with high thermal conductivity metals to make composites that have both high power density and large energy storage capacity. In this study, we provide a theoretical framework to design and optimize cylindrical composites with three figures of merit – minimization of temperature rise, maximization of the effective volumetric heat capacity and maximization of the effective heat capacity based on mass. We validate the figures of merit experimentally by 3D printing AlSi12 alloy and using octadecane as phase change material for a heat flux of 13.3 Wcm−2 and heating time of 10 s. The metal component volume fractions in the printed structures vary from 15% to 70% for straight fin structures, 10% to 70% for the SC lattice structures, and 20% to 70% for branching fin structures. When minimizing temperature rise, the optimum volume fraction of thermally conductive material is 0.5–0.7. When maximizing the effective volumetric heat capacity, the optimum volume fraction for the high conductivity material is 0.3–0.5. Finally, when maximizing the effective heat capacity by mass in cylindrical composites, the optimum volume fraction for the high conductivity material is 0.2–0.3. Importantly, the optimum values depend on the applied thermal load, which is not captured in existing figures of merit for thermal storage systems. The volumetric and mass based heat capacity values of the optimized composites identified in this study are at least 10x higher when compared to single component PCMs that are widely used for volumetric and mass based thermal storage systems. The figures of merit developed here can assess the performance of most composite PCM systems and help to design future cylindrical composites while accounting for the thermal loads specific to the thermal storage application.

Heat capacities of different amine aqueous solutions at pressures up to 25 MPa for CO2 capture

A high-pressure flow calorimeter is used to determine isobaric heat capacities for aqueous solutions of some amines such as MEA, DEA TEA, DMAE, MDEA, PZ from T = (293.15 to 353.15) K and up to 25 MPa. The experimental device can measure heat capacities with an estimated total uncertainty better than 1% for a coverage factor k = 2. The isobaric heat capacity values are analysed in conjunction with their temperature and pressure dependencies. Furthermore, empirical equations are proposed to fit isobaric heat capacities as functions of temperature and pressure for given conditions, for this kind of mixtures, obtaining standard deviations within the uncertainty of the measurements. Finally, DMAE shows the highest value of heat capacity and TEA the lowest value, when they are compared at the same conditions of temperature, pressure and composition.

Consistency of Water Vapour Pressure and Specific Heat Capacity Values for Modelling Clay-Based Engineered Barriers

The aim of this study is to assess the consistency in the modelling of thermo-hydraulic problems in clay-based engineered barriers. This study focuses on two aspects: the modelling of vapour pressure as a function of temperature, and the specific heat capacities of liquid water and water vapour in relation to the enthalpy of vaporisation and the internal energy of liquid water and water vapour. Regarding the first aspect, several formulations of the saturated vapour pressure have been inspected, evaluating their accuracy and information provided in the temperature range from 0 to 150 °C. Regarding the second aspect, the enthalpy of vaporisation and the internal energy of water were used to assess the consistency of pairs of specific heat capacity values in the same temperature range. Values from the literature were also inspected. An accurate and simple enough expression for the saturated water vapour pressure with temperature has been identified as the optimal option for modelling. Recommendations on specific heat capacity constant values for liquid water and vapour are suggested to maximise consistency in the studied temperature range. However, the loss of accuracy in the enthalpy or internal energy of vaporisation associated with the inspected specific heat capacity pairs is limited.

Thermal Characterisation of Automotive-Sized Lithium-Ion Pouch Cells Using Thermal Impedance Spectroscopy

This study used thermal impedance spectroscopy to measure a 46 Ah high-power lithium-ion pouch cell, introducing a testing setup for automotive-sized cells to extract the relevant thermal parameters, reducing the time for thermal characterisation in the complete operational range. The results are validated by measuring the heat capacity using an easy-to-implement calorimetric measurement method. For the investigated cell at 50% state of charge and an ambient temperature of 25 °C, values for the specific heat capacity of 1.25 J/(gK) and the cross-plane thermal conductivity of 0.47 W/(mK) are obtained. For further understanding, the values were measured at different states of charge and at different ambient temperatures, showing a notable dependency only on the thermal conductivity from the temperature of −0.37%/K. Also, a comparison of the cell with a similar-sized 60 Ah high-energy cell is investigated, comparing the influence of the cell structure to the thermal behaviour of commercial cells. This observation shows about 15% higher values in heat capacity and cross-plane thermal conductivity for the high-energy cell. Consequently, the presented setup is a straightforward implementation to accurately obtain the required model parameters, which could be used prospectively for module characterisation and investigating thermal propagation through the cells.

Therapeutic Potential of B12N12-X (X = Au, Os, and Pt) Nanostructured as Effective Fluorouracil (5Fu) Drug Delivery Materials.

In view of the research-substantiated comparative efficiency of nontoxic and bioavailable nanomaterials synergic with human systems for drug delivery, this work was aimed at studying the comparative efficiency of transition metal (Au, Os, and Pt)-decorated B12N12 nanocages in the adsorption of fluorouracil (5Fu), an antimetabolite-classed anticarcinogen administered for cancers of the breast, colon, rectum, and cervix. Three different metal-decorated nanocages interacted with 5Fu drug at the oxygen (O) and fluorine (F) sites, resulting in six adsorbent-adsorbate systems whose reactivity and sensitivity were investigated using density functional theory computation at the B3LYP/def2TZVP level of theory with special emphasis on the structural geometry, electronic, and topology analysis as well as the thermodynamic properties of the systems. While the electronic studies predicted Os@F as having the lowest and most favorable Egp and Ead of 1.3306 eV and -11.9 kcal/mol, respectively, the thermodynamic evaluation showed Pt@F to have the most favorable thermal energy (E), heat capacity (Cp), and entropy (ΔS) values as well as negative ΔH and ΔG while the adsorption studies showed that the greatest degree of chemisorption with Ead magnitude of -204.5023 kcal/mol was observed in energies ranging from -12.0 to 138.4 kcal/mol with Os@F and Au@F at the lower and upper borders. The quantum theory of atoms in molecules results show that the six systems had noncovalent interactions as well as a certain degree of partial covalency but none showed covalent interaction while the noncovalent interaction analysis corroborated this by showing that the six systems had favorable interactions, though of varying degrees, with very little trace of steric hindrance or electrostatic interactions. Overall, the study showed that notwithstanding the good performance of the six adsorbent systems considered, the Pt@F and Os@F showed the most favorable potential for the delivery of 5Fu.

Interdependence of External Magnetic and Temperature Effect on Thermodynamic Properties of GaAs Two Electron Quantum Dot

The particular interest of this paper is to investigate the impact of various values of temperature exposed to weak and strong magnetic field strength. A thermodynamic property's oscillatory change as a function of magnetic field effect (B) intensifies the quantization of electron orbits in a constant magnetic field intensity and is the primary contributor to the de Haas-van Alphen effects due to cyclotron frequency and its impact on localizing electron at circular region imposed with the magnetic field that is in contrary to the result of the temperature effect. Thus the interdependent effects of external magnetic field and temperature on thermodynamic properties are studied with harmonic oscillator potentials considering material parameters of GaAs quantum dot. The finite energy state is analytically solved using Nikiforov-Uvarov mathematical formalism. Moreover, the direct impact of the external magnetic fields and temperature on thermodynamic properties of the system is analyzed, and numerically simulated using matlab R2017a version. The dominance of temperature over the external magnetic field and vice versa effect is investigated, thus the value specific heat capacity fluctuated, while the equiponderate impact of temperature and magnetic field shows similar steady values of the specific heat capacity. The study clearly shows the interdependence of magnetic field and temperature affect thermodynamic quantities: partition function, mean energy, entropy, and specific heat capacity.

Evaluation of the safe separation distances of hydrogen-blended natural gas pipelines in a jet fire scenario

The desire for sustainable development in various countries has increased the use of hydrogen energy. Considering cost and time savings, the introduction of hydrogen into existing natural gas pipelines is an excellent option, and the failure consequences of hydrogen blending in natural gas pipelines should be considered. In this study, a solid flame model is used to calculate the thermal radiation intensity of a hydrogen-blended natural gas jet fire. A method is proposed to modify the calculation of the view factor in the near field, and parameters such as the specific heat capacity and calorific value of pure gas are replaced by the parameters of the mixed gas. The data of the Thornton and modified models are compared with the experimental results, and the modified model result is found to be more accurate. Using the modified model, the variations in different hydrogen blending ratios, internal pressures, and pipe diameters with the safe separation distance of the thermal radiation intensity in a pipeline accident are investigated, and the relationships between them are analyzed.

Study of phase behavior of epoxy asphalt binders using differential scanning calorimetry

Glass transition parameters can be used to study the miscibility, or lack of it, in polymer-modified asphalt binders. In this study, the contribution of thermodynamics of mixing to glass transition was quantitatively assessed in a differential scanning calorimeter for four asphalt binders partially and fully replaced by an epoxy system. The values of heat capacity (Cp) and, subsequently the glass transition temperature (Tg) of all binders were determined to quantify the miscibility based on the entropic changes. Emphasis was also given to examining the enthalpy of mixing as a function of epoxy system composition during curing to ensure that these binders were completely crosslinked for further analyses. In all cases, the positive deviations of the measured Tg of epoxy-modified asphalt binders (Tg,mix) obtained from the ideal mixing rule led to negative values of the entropy of mixing (ΔSmixc), dictating the presence of internal repulsive forces between the asphalt and epoxy components. Softer binders were associated with binders of low deviations of Tg,mix values from the ideal mixing rule. Lastly, the partial replacement of asphalt binders by the epoxy system increased the Tg and decreased the amount of ΔSmixc, and such performance imposes the formation of immiscible products.