Determination Of Heat Capacity Research Articles

Взаимосвязь инновационных и классических методик профессиональной направленности обучения физике в техническом вузе

The introduction of two forms of conducting a laboratory workshop in physics for students for engineering and technology studies in the sphere of marine heat and power engineering, electrical equipment and automation means is considered to the process of studying at the Federal State Budget Educational Institution of Higher Education “Astrakhan State Technical University”. The possibility of developing students' working skills in natural conditions with industrial devices and an engineering approach taking into account the multifactorial conditions of the experiment as an independent work in the framework of the workshop of technical creativity Applied Physics organized at the Department of General Engineering Disciplines and Ground Transport is shown. The formation of the professional orientation of interdisciplinary connections of students of the specialty Thermal Power Engineering and Heat Engineering is illustrated by the example of the development of the laboratory work Determination of the specific heat capacity of metals. The advantages of virtual laboratory work and the possibility of their use on the educational portal of the “Astrakhan State Technical University”, built on the Moodle virtual learning environment, are examined. An example of creating a virtual laboratory work Studying the law of conservation of momentum is considered. It is theoretically proved that the introduction of these types of work into the educational process in physics contributes to the optimally effective formation of general professional competencies and the professional orientation of students' education. The importance of introducing these types of laboratory work into the educational process of physics at the university for the development of students' analytical abilities, creativity and innovation, which is a prerequisite for studying of modern engineers in demand in the labor market in a rapidly changing world, is shown.

Analytical determination of enthalpy, heat capacity and Gibbs free energy for nitrogen and iodine

The analytical solutions for the modified shifted Morse potential model have been obtained for some molecules. Despite the importance of this potential in molecular systems, this model hasn’t gained extensive attention. This research delves into predicting thermodynamic functions, specifically examining molar enthalpy, molar heat capacity, and molar Gibbs free energy for nitrogen and iodine molecules using this modified shifted Morse potential. The predicted result aligned with the experimental data, with iodine exhibiting a closer match.

Accurate heat capacity determination of solids and liquids using a heat conduction calorimeter

This study investigates the suitability of heat conduction calorimeters for determining the specific heat capacity of solid and liquid substances. Accurate and precise measurements were obtained for various substances, including water, ethylene glycol, the ionic liquid [EMIM][TCM], and copper, with relative standard deviations averaging less than 1%. Measurements on [EMIM][DCA] indicated a systematic deviation from the literature values. The study highlights the repeatability of the measurement method, which worked well for both temperature increases and decreases, as well as for the mean of the two. The influence of sample size on the results when it came to liquids was also investigated, revealing that large sample sizes led to underpredictions; while, small sizes yielded the opposite effect. The best results were obtained with half-filled vials; a similar filling level as was used in the electrical calibrations of the calorimeters with heaters in the vials. Additionally, no significant differences were observed among the eight calorimeters of the I-Cal Flex instrument, and different baseline calculation methods had negligible impact on the results. Overall, this study illustrates how a heat conduction calorimeter can be utilized for accurate and precise heat capacity measurements for both solid and liquid substances.

Numerical model for determining the effective heat capacity of macroencapsulated PCM for building applications

This paper presents a finite difference model of macroencapsulated PCM panels coupled with the genetic algorithm for the determination of effective heat capacity of whole panels via inverse method. This provides an accurate characterization of the thermal properties of macroencapsulated PCMs for building envelope applications. A novel definition of the effective heat capacity is proposed based on the superimposition of two Gaussian curves, applicable to any PCM whose phase transition is characterized by a single peak. Three PCMs were tested, subjected to temperature variation rates typically experienced in building envelopes: 0.5 °C/h and 1 °C/h. Surface temperature and heat flux were measured and used in the inverse method procedure. The developed model is accurate, as numerical results greatly agree with the experiments: the root mean square difference between the experimental and numerical heat fluxes ranged between 0.543 and 1.246 W/m2. Significant differences in the effective heat capacity were found between the whole macrocapsule and small quantities of PCM (specified in the datasheets). The effective heat capacity specified in the datasheets is sensibly greater than that of the whole macrocapsules determined through the inverse method: the specific heat in the solid phase was up to 107.39 % higher in the datasheet values, the specific heat in the liquid phase up to 184.04 %, and the peak effective heat capacity, between 18.28 % and 164.11 %. The same happened to the enthalpy: datasheet values were 61.24 % – 175.55 % greater than inverse method results. This proves that latent heat is overestimated if small quantities of PCM are analyzed, and not the whole panels. The scale effect was assessed by comparing two capsules with the same material, but with different quantities of PCM: 0.5 kg and 1 kg. A greater mass of PCM over the total mass of the capsule implies a different relationship between the effective heat capacity and temperature, with higher peak heat capacity. The capsule with 1 kg of PCM showed a peak effective heat capacity up to 30.65 % greater than that of the panel with 0.5 kg of PCM. Thus, adequate modeling in building applications requires characterization of whole macroencapsulated PCMs. The determination of the relationship between temperature and effective heat capacity of macroencapsulated PCMs presented in this work could easily be incorporated into other simulation software, facilitating the assessment of adaptive envelopes with PCM macrocapsules.

Simultaneous Determination of Thermal Conductivity and Heat Capacity in Thin Films with Picosecond Transient Thermoreflectance and Picosecond Laser Flash

ABSTRACT Combining the picosecond transient thermoreflectance (ps-TTR) and picosecond laser flash (ps-LF) techniques, we have developed a novel method to simultaneously measure the thermal effusivity and the thermal diffusivity of metal thin films and determine the thermal conductivity () and the heat capacity () altogether. In order to validate our approach and evaluate the uncertainties, we analyzed five different metal films (Al, Cr, Ni, Pt, and Ti) with thicknesses ranging from 297 nm to 1.2 µm. Our results on thermal transport properties and heat capacity are consistent with reference values, with the uncertainties for the thermal conductivity and the heat capacity measurements below 25% and 15%, respectively. Compared with the ps-TTR technique alone, the combined approach substantially lowers the uncertainty of the thermal conductivity measurement. Uncertainty analyses on various materials show that this combined approach is capable of measuring most of the materials with a wide range of thicknesses, including those with low thermal conductivity (e.g., mica) down to thicknesses as small as 60 nm and ultrahigh thermal conductivity materials (such as cubic BAs) down to 1400 nm. Simultaneous measurement of thermal conductivity and heat capacity enables exploration of the thermal physical behavior of materials under various thermodynamic and mechanical perturbations, with potential applications in thermal management materials, solid-state phase transitions, and beyond.

On Simultaneous Determination of Thermal Conductivity and Volume Heat Capacity of Substance

The study of nonlinear problems associated with heat transfer in substance is important for practice. Earlier, the authors proposed an efficient algorithm for determining the thermal conductivity from experimental observations of the dynamics of the temperature field in an object. In this work, we explore the possibility of extending the algorithm to the numerical solution of the problem of simultaneous identification of the temperature-dependent volume heat capacity and the thermal conductivity of the substance under study. The consideration is based on the Dirichlet boundary value problem for the one-dimensional nonstationary heat equation. The coefficient inverse problem in question is reduced to a variational problem, which is solved by applying gradient methods based on the fast automatic differentiation technique. The uniqueness of the solution to the inverse problem is analyzed.

On Simultaneous Determination of Thermal Conductivity and Volume Heat Capacity of Substance

On Simultaneous Determination of Thermal Conductivity and Volume Heat Capacity of Substance

INFLUENCE OF COMBINED DRYING OF COLLOID CAPILLARY-POROUS MATERIALS ON ENERGY EXPENDITURES

One of the berry crops that has recently gained popularity among consumers is blueberry (Vaccinium corymbosum L.). The berry is a powerful antioxidant, and besides, it contains fructose in its composition, which automatically refers it to the products of the diabetic diet. Therefore, blueberries become an interesting colloidal capillary-porous drying object. Wax on the skin of berries performs a protective function in the process of ripening, harvesting and transportation, but is a negative factor for the implementation of technological processing by artificial dehydration. The latter causes significant energy costs for the processing process. Therefore, the aim of the work is to determine the effect of combined drying of blueberry on energy consumption.
 Experimental studies of the drying kinetics of blueberry were carried out on an experimental convective stand with forced recirculation of the coolant and infrared emitters, which was developed in ІEТ of NAS of Ukraine. The effect of pre-developed hygrothermal and infrared treatment of fresh blueberries on the kinetics and change in the drying speed of berries was investigated. The use of infrared radiation made it possible to reduce the total duration of the dehydration process by 1.2 times.
 The heat of evaporation of moisture from the samples and their heat capacity were investigated using the method created in ІEТ of NAS of Ukraine installations of synchronous thermal analysis DMKI-01, which is intended for the study of colloidal capillary-porous materials. Determination of specific heat capacity was carried out according to the standardized method of step-by-step scanning DSTU ISO 11357–4:2010 in the temperature range from 30 to 95℃.
 Experimental determination of heat capacity and heat of evaporation of moisture from pre-processed blueberry showed excess energy consumption for a possible phase transition of the waxy shell of the berry during drying and a decrease in the drying efficiency of the material at moisture values Wc ≤ 20%.

Correction: Thermophysical properties evaluation for a polar fluid on the basis of the experimentally determined heat capacity and dipole moment in the ideal gas states

Correction: Thermophysical properties evaluation for a polar fluid on the basis of the experimentally determined heat capacity and dipole moment in the ideal gas states

Thermophysical properties evaluation for a polar fluid on the basis of the experimentally determined heat capacity and dipole moment in the ideal gas states

Thermophysical properties evaluation for a polar fluid on the basis of the experimentally determined heat capacity and dipole moment in the ideal gas states

Heat capacity of cytisine – the drug for smoking cessation

The characterization of cytisine (CYT) and its blends with poly(lactic acid) was performed using thermal analysis, elemental analysis, infrared spectroscopy, and powder X-ray diffractometry. The heat capacities, total enthalpy, and phase transitions of CYT were established from 1.8 to 448.15 K (−271.35 – 175 °C) by advanced thermal analysis. Data were obtained using a Quantum Design Physical Property Measurement System (PPMS) and a differential scanning calorimetry (DSC). The low-temperature heat capacity of the crystalline CYT in the range of 1.8 to 300 K (−271.35 – 26.86 °C) was measured by PPMS and fitted to a theoretical model in the low temperature region below 11 K (−262.15 °C), to orthogonal polynomials in the middle range 5 K <T < 60 K (−268.15 °C < t < −213.15 °C) and to the Debye and Einstein functions in the high range of temperature above 60 K (−213.15 °C). The liquid heat capacity was calculated based on the approximated linear regression data above the molten state of the experimental heat capacity of CYT obtained by the standard DSC measurements, and it was expressed as Cpliquid = 0.0838T + 346.78 J·K−1·mol−1. The calculated heat capacity in the solid state was extended to a higher temperature and was used, together with liquid heat capacity, as the reference baselines for the advanced thermal analysis of CYT. The PPMS and DSC/TMDSC methods are complementary methods for thermal analysis of cytisine. The PPMS method allowed determination of the equilibrium heat capacity in the solid state, which together with the equilibrium heat capacity in the liquid state allowed to analyze of the experimental apparent heat capacity of cytisine obtained based on DSC. The melting temperature and the total heat of fusion of crystalline material were established as 431.8 K (158.65 °C) and 26.5 kJ·mol−1, respectively. The solid and liquid heat capacities and transition parameters of CYT were applied to calculate total enthalpies for fully amorphous and crystalline states. Analyses of DSC and X-ray confirmed the presence of the solid-solid transition linking with not so far described a polymorphism phenomenon of CYT. Based on the thermogravimetric analysis the temperature of degradation of CYT was determined as 460.5 K (187.35 °C). Also, a preliminary thermal analysis of the blends of cytisine and poly(lactic acid) as a new candidate for drug delivery system was presented.

Liquid heat capacity of amorphous poly(vinyl methyl ether)

In this paper, the experimental heat capacity of the liquid state above the glass transition 248 K (–25 °C) was linked to the molecular motions and computed as the sum of vibrational, external (anharmonic), and conformational contributions. Most of the liquid heat capacity of poly(vinyl methyl ether) (PVME) arises from the vibrational motion calculated as the group and skeletal vibrational heat capacity contributions. The external contribution to liquid Cp was computed as a function of temperature from experimental data of the thermal expansivity and compressibility of the liquid state. The conformational heat capacity contribution to the total Cp of the amorphous poly(vinyl methyl ether) was established. It was calculated from a fit of the experimental, liquid heat capacity after subtracting the vibrational and external parts to a one-dimensional Ising-type model with two discrete states characterized by parameters linked to stiffness, cooperativity, and degeneracy. The computed and experimental data of Cp at the liquid state showed good agreement, i.e., within a few percent, close to the experimental precision at the temperature region from 250 to 360 K. The proposed approach can be used for a determination of heat capacities of more complex systems such as poly(vinyl methyl ether)-water which is widely used in medical applications.

Study of thermophysical properties of real gases by different potential models

The influence of attractive term of interaction potential on heat capacities (𝐶𝑝, 𝐶𝑣) and sound speed of real gases Ar, Kr and Xe is investigated. Two different potential models were introduced and the second virial coefficient of the potentials was analytically determined. The introduced potentials include different attractive terms. By using the two potential models, we have determined heat capacities at constant pressure and volume and speed of sound of aforementioned gases. Our obtained data have been compared with available results. The obtained data show that the potential attractive term has a key role in determining the thermodynamic functions of the gases. It is revealed that the obtained heat capacities by using both potentials are in good agreement with experimental data. But, the obtained results by potential model (1) have more agreements with experimental data. The speed of sound of Ar determined by model (1) at high pressure and temperatures are in good agreement with available data. The sound speed of Kr computed by the model (2) at high temperatures and low pressure has good agreement with experimental data. Finally, sound velocity of Xe determined by the model (2) at high temperatures and pressures gives more agreement in comparison with available data.

Експериментално определяне зависимостта на специфичния топлинен капацитет на водни разтвори на LiCl от температурата и концентрацията им

This project is focused on the experimental determination of the specific heat capacity of aqueous solutions of LiCl with different mass concentrations proposed, which is applicable for various liquids and, in contrast to calorimetry, relies on the heat transfer between two media with different temperatures and thus accounts for the heat losses of this thermodynamic system. A theoretical model based on the heat balance equation for Newtonian and Stephan-Boltzmann heat transfer has been constructed. Laboratory experiments have been carried out using aqueous solutions of LiCl with mass concentration ranging from 0 to 15% and at temperatures in the range 20-90 ℃. The data has been analysed using MATLAB and empiric equations for the temperature dependence of the specific heat capacity for fixed mass concentrations of the solute have been obtained. The results are in good agreement with the reference values.

Morse potential specific heat with applications: an integral equations theory based

The specific heat in its molar form or mass form is a significant thermal property in the study of the thermal capacity of the described system. There are two basic methods for the determination of the molar specific heat capacity, one of them is the experimental procedure and the other is the theoretical procedure. The present study deals with finding a formula of the molar specific heat capacity using the theory of the integral equations for Morse interaction which is a very important potential for the study of the general oscillations in the quantum mechanics. We use the approximation (Mean-Spherical) for finding the total energy of the compositions described by Morse interaction. We find two formulas of the heat capacity, one at a constant pressure and the other at a constant volume. We conclude that the Morse molar specific heat is temperature dependent via the inverse square low with respect to temperature. Besides, we find that the Morse molar specific heat is proportional to the square of the Morse interaction well depth. Also, we find that the Morse molar specific heat depends on the particles’ diameter, the bond distance of Morse interaction, the width parameter of Morse interaction, and the volumetric density of the system. We apply the formula of the specific heat for finding the specific heat of the vibrational part for two dimer which are the lithium and caesium dimers and for the hydrogen fluoride, hydrogen chloride, nitrogen, and hydrogen molecules.

The effect of the sample pan position on the determination of the specific heat capacity for lipid materials using heat flux DSC

Accurate measurements of specific heat capacity for lipids as a function of temperature, Cp (T), are needed for modeling their crystallization behavior. Differential Scanning Calorimetry, DSC, has been the main technique to determine Cp (T) for numerous materials, including lipids. Key experimental conditions (heating/cooling ramps, sample size, purge gas, and temperature modulation) that affect the measured heat flow, from which Cp (T) is calculated, have been extensively discussed in the literature. Usually, DSC manufacturers provide procedures of what they consider to be the best experimental conditions to measure accurate Cp (T) values with the least uncertainties. The successive nature of these procedures requires the user to perform each step separately, which means that the user needs to take out the empty pan from the DSC furnace to load either the standard material (usually sapphire) or the sample and place it back again into the furnace. Following this method will result in a different pan placement on the sensor each time the DSC furnace is opened, which consequently will influence the heat flow signals. Utilizing the Guide to the Expression of Uncertainty in Measurements (GUM),this paper is intended to quantitatively evaluate the uncertainties in Cp (T) measurements due to the pan position on a heat-flux DSC sensor. Due to this effect, relative expanded uncertainty U values were ∼1.5%, and at least 15–25% as a result of pan placement. The sapphire uncertainty values were much smaller than those from the trimyristin (MMM) sample. With the assistance of FEM simulation, the effect of the different thermal diffusivity of MMM and sapphire on the Cp (T) measurements is elucidated.

Determination of thermal conductivity, thermal diffusivity and specific heat capacity of porous silicon thin films using the 3ω method

Here the thermal transport properties of low thermal conductivity porous silicon thin films attached to high thermal conductivity silicon substrates are studied using the 3ω method implemented over the 100 Hz to 33 kHz frequency range. The thermal conductivity and thermal diffusivity of the films are extracted using temperature impedance monitoring of electrical contacts deposited on films, combined with an extended-frequency, multi-layer thermal model. From the extracted thermal conductivity and diffusivity of the films, the heat capacity could be determined. Validation of the approach is performed using the known properties of thick substrate glass and SU-8 layers spun on silicon substrates, the latter ranging in thickness from 1.35 to 12.5 µm. The technique was then applied to porous silicon films with porosities ranging from 45% to 77%. The extracted thermal properties for as-fabricated films show a reduction of thermal conductivity and diffusivity from 1.7 to 0.15 W/mK and 1.9 to 0.2 mm2/s, respectively as the porosity increases. After passivation by annealing in nitrogen and at 600 °C, the same films exhibited higher values of thermal conductivity and diffusivity ranging from 2.7 to 0.7 W/mK and 2.5 to 0.65 mm2/s. The ability to extract both thermal conductivity and thermal diffusivity for these films removes the need to make assumptions around specific heat capacity, commonly made during analysis of porous media. These results show for the first time a monotonic increase in specific heat capacity of porous silicon films as a function of porosity.

Heat capacity of dispersed rocks

Protection of automobile roads from negative cryogenic processes is a current issue to which significant attention is devoted in both scientific and engineering communities. In many cases important for practice, the the thermal factor determines the reliability and security of the use of the road in the cryolithic zone. The heat capacity of dispersed rocks is among the most important indicators of the physical properties determining the intensity of thermal processes in the road surfaces and road foundations. The precision of determination of the total heat capacity of the rocks in thawed and frozen state largely determines the precision of the forecast of the thermal regime of roads in the cryolithic zone. A complex assessment of the impact of ice content of the dispersed rocks on the value of total heat capacity was done. 2D and 3D charts which allow to assess the possible range of change in the heat capacity of the dispersed rocks in thawed and frozen state, in both a wide range and in the typical range of values, were produced. Among the main criteria determining the extent of the seasonal freezing and thawing of the soils of the active layer is the Stefan number, a dimensionless criterion. An overall assessment of the impact of ice content on the ground (rock) foundations of the roads and of the air temperature in the warm period of the year on the quantitative values of the Stefan number was done. Charts allowing to determine in both a wide and typical range the changes of values of the Stefan numbers, permitting to assess the possible range of changes of the Stefan number, were made. It was determined, in particular, that for the typical dispersed rocks of the road foundations in the cryolithic zone the range of change in the Stefan numbers is 2.1-6.5.

Thermodynamic Properties of the First-Generation Hybrid Dendrimer with "Carbosilane Core/Phenylene Shell" Structure.

The molar heat capacity of the first-generation hybrid dendrimer with a “carbosilane core/phenylene shell” structure was measured for the first time in the temperature range T = 6–600 K using a precise adiabatic vacuum calorimeter and DSC. In the above temperature interval, the glass transition of the studied compound was observed, and its thermodynamic characteristics were determined. The standard thermodynamic functions (the enthalpy, the entropy, and the Gibbs energy) of the hybrid dendrimer were calculated over the range from T = 0 to 600 K using the experimentally determined heat capacity. The standard entropy of formation of the investigated dendrimer was evaluated at T = 298.15 K. The obtained thermodynamic properties of the studied hybrid dendrimer were compared and discussed with the literature data for some of the first-generation organosilicon and pyridylphenylene dendrimers.

AN ANALYTICAL TECHNIQUE FOR EVALUATING HEAT CAPACITY OF GeS, GeSe, GeTe AND SnS SEMICONDUCTORS USING EINSTEIN-DEBYE APPROXIMATION

A new analytical method for the evaluation of heat capacities of semiconductors (GeS, GeSe, GeTe, and SnS) has been proposed using the Einstein-Debye approximation. These formulae differ from the Debye model representations and they involve a combination of the Einstein and Debye approximations. The proposed method allows developing an increasing accuracy for the determination of the temperature dependent heat capacities of semiconductors GeS, GeSe, GeTe and SnS. The approach suggested in this study for calculation of heat capacities is very well suitable to determine other thermodynamical properties of materials. The temperature dependence of heat capacities of GeS, GeSe, GeTe and SnS semiconductors has been evaluated and shows a good agreement with literature at different temperature ranges.