Heat Capacity Difference Research Articles

Speed of Sound and Derivative Properties of Ethyl Laurate from Rayleigh–Brillouin Light-Scattering Spectroscopy

The experimental speeds of sound combined with Brillouin frequency shifts of ethyl laurate at temperatures from 294.97 to 572.89 K along six isobaric lines from 0.1 to 10.0 MPa were measured by Rayleigh–Brillouin light-scattering spectroscopy. The expanded relative uncertainty in the reported speeds of sound in ethyl laurate is estimated to be 1.3% (coverage factor k = 2 with a confidence level of 0.95). Within the temperature limits of 303.15–383.15 K and at pressures up to 10.0 MPa, the derived thermoacoustic properties of ethyl laurate including density, specific isobaric heat capacity, isentropic compressibility, isobaric thermal expansivity, isothermal compressibility, the difference in isobaric and isochoric heat capacity, internal pressure, and intermolecular free length were studied. Because of the heavily updated data of density and the speed of sound in the literature, a modified Jacobson’s model for biodiesels was proposed over the temperature range from 293.15 to 343.15 K, which is able to calculate the intermolecular free length of ethyl laurate with higher accuracy compared with Jacobson’s model.

Regression against Temperature of Gas–Liquid Chromatography Retention Factors. Van’t Hoff Analysis

The present work deals with the precise experimental determination of the gas–liquid chromatography (GLC) retention factors (k) in a sufficiently large temperature range to allow the calculation of the thermodynamic quantities associated with the sorption process. Once isothermal retention factors of three homologous series members of the type H-(CH2)n-Y (Y = CH3, OH, CN) were measured over a temperature range of about 110 K on a low-polar PDMS (HP-1) capillary column and checked for accuracy and precision by “arc plot” representation, the data were analyzed by applying different forms of the van’t Hoff relationship. We compared the linear versus nonlinear van’t Hoff plots representing situations characterized by ΔsolvCp° = 0, ΔsolvCp°≠ 0 = constant, and ΔsolvCp° = f(T), respectively (ΔsolvCp° represents the difference in isobaric heat capacity associated with movement of the analyte between the mobile and the stationary phase). The “logarithmic” and “quadratic” nonlinear van ‘t Hoff equations were shown to be more appropriate than the linear van‘t Hoff equation for determining enthalpy and entropy of solvation. Special attention was devoted to the fitting performance and extrapolation capability of models with nonzero ΔsolvCp°. By several metrics, the quadratic model exhibits better behavior in extrapolations yielding reasonable accuracy for retention time and/or enthalpy of solvation predictions at temperatures located below the experimental range.

The mathematical and experimental analysis on the steady-state operating temperature of bifacial photovoltaic modules

The operating temperature of bifacial photovoltaic (PV) module affects its power generation and reliability. Combined with view factor model of ground reflectivity on module backside, a thermal steady-state model is established to analyze the thermal performance of bifacial module in this paper. The module operating temperatures under three different installation conditions of roof cement ground, water surface and grassland are calculated and simulated by ANSYS software, and the experiments are designed to analyze and verify it. Based on the difference of reflectivity and heat capacity of different ground for the PV module installation, the effects of ground type and module material on bifacial module temperature and its mechanism are analyzed quantitatively. According to the simulation and experiment results, the operating temperatures of the bifacial modules installed on the roof cement ground, water surface and grassland are 44.7 °C, 41.5 °C, 43.2 °C respectively, under the setting environment condition with specific irradiance, wind speed and ambient temperature. The temperature difference of 1.7 °C–3.2 °C is caused by ground reflectivity and temperature. The operating temperature difference between glass-glass and glass-backsheet module is less than 0.4 °C under the standard condition. The conductivity and emissivity of encapsulation material does not show strong influence on module operating temperature.

Standard formation enthalpies of gas phase molecular complexes derived by taking into account the heat capacity difference of the gas phase dissociation processes: Experimental tensimetry data revisited

High temperature tensimetry data on homogeneous gas phase dissociation of donor-acceptor complexes of group 13–15 metal halides have been analyzed. Thermodynamic characteristics and heat capacities have been computed by DFT methods. Standard dissociation enthalpies and standard formation enthalpies of gaseous donor-acceptor complexes have been obtained by combination of experimental and computational data with accounting for the heat capacity change.

Modeling and simulation of heat balance and internal heat recovery targets through a combination of stream specific minimum temperature difference and polynomial temperature coefficients of specific heat capacities using pinch analysis

Existing heat balancing and energy targeting model in Pinch Analysis rely on use of interpolated values of specific heat capacities and global values of minimum temperature difference ∆Tmin, respectively. Even though this model is useful in estimation of the maximum internally recoverable heat recoverable in processing plants, it does not adequately represent the actual state properties of industrial processes. Specific heat capacities of fluids are polynomial functions of temperature of material under processing. The values of ∆Tmin also vary depending on the nature of the process stream under analysis. In this study, improvement to the heat balancing and energy targeting processes of pinch analysis was proposed. The study combined the use of stream specific values of ∆Tmin and polynomial temperature functions of specific heat capacities for heat targeting model. This was coded and executed using a PHP program. The model performance was tested using data from three thermochemical plants, Plant A, B and C, which process linear alkyl benzene sulphonic acid, dairy products and ethanol, respectively. The proposed method for heat balancing computed more heating requirements for plant A, B and C by 0.37%, 0.65% and 0.72% respectively, compared to the traditional method of heat balancing. The cooling loads for Plant A and B were less by 2.23% and 32.52% respectively, while for Plant C, they were more by 0.64%. The computed internally recoverable heat targets were more by 1.5%, 4.5% and 2.2% for Plants A, B and C. Simulations of the proposed model were carried out over a range of temperature targets, for different process streams. For gaseous process streams, heating and cooling load requirements were less. Reverse behavior was observed in liquid and steam containing streams, where the heating and cooling load requirements were more.

Thermal performances of saturated porous soil during freezing process using lattice Boltzmann method

A stochastic growth method for generating the porous soil structure is proposed, and an enthalpy-based lattice Boltzmann phase transition model is introduced. Thermal performance of phase transition in saturated porous soil during freezing is investigated. The effects of thermal diffusivity ratio of porous medium to fluid, difference in specific heat capacity between liquid and solid phase, and porosity of porous medium are investigated. The results show that higher thermal diffusivity ratio will promote the low-temperature propagation and phase interface movement while higher specific heat capacity difference and porosity will hinder the temperature propagation and phase transition from liquid to solid. The solid–liquid interface moves from 39 to 51 mm with the ratio increasing from 2 to 5; the interface position decreases from 51 to 26 mm with the difference increasing from 2000 to 26,000; the interface moves from 59 to 47 mm when the porosity increases from 0.2 to 0.8.

(p,ρ,T) data of 1-butyl-3-methylimidazolium hexafluorophosphate

Herein, experimental pressure-density-temperature (p,ρ,T) data of 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], are reported over a wide range of temperatures T = (278.15 to 413.15) K and pressures p = (0.101 to 140) MPa. These measurements were carried out using an Anton Paar DMA HPM vibrating tube densimeter. (p,ρ,T) data of [BMIM][PF6] were correlated with a designed equation of state (EoS). After a thorough analysis of the validity of the constructed EoS, various thermophysical properties such as: isothermal compressibility, isobaric thermal expansivity, differences in isobaric and isochoric heat capacities, thermal pressure coefficient, internal pressure, heat capacities at constant pressure and volume, speed of sound and isentropic exponent were then calculated. Finally, the predictive capability of various models available in the literature was then tested by using the collected (p,ρ,T) data to highlight the best approach to be used to evaluate the volumetric properties of the selected ionic liquid.

Thermodynamics of hydrothermal carbonization: Assessment of the heat release profile and process enthalpy change

A reliable and reproducible procedure for the determination of the heat release rate profile and for the enthalpy change of the hydrothermal carbonization (HTC) process is applied using High Pressure Differential Scanning Calorimetry (HP-DSC). Cellulose, wood, and digestate are used as feedstocks. The temperature program is run once to let the process complete in the first run, whereas in the second the thermal effect of products is assessed. A provisional heat release profile is obtained subtracting the two curves, with a very high reproducibility (standard deviations between 1.8 and 8.0%). To consider the heat capacity difference between reactants and products, a baseline is computed and subtracted from the heat release profile. The integral of this curve gives the enthalpy change associated to HTC, which was −0.88, −0.64, and −0.25 MJ/kg for cellulose, wood and digestate respectively. This methodology can be adopted for the development of accurate thermal-based HTC kinetics.

The role of Co/Al ratio in glass-forming GdCoAl magnetocaloric metallic glasses

In this work, a prominent improvement of glass-forming ability is achieved through the adjustment of Co/Al ratio in the ternary GdCoAl system. The critical diameter of Gd55Co17.5Al27.5 bulk metallic glass (BMG) is up to 8 mm, which is larger than that of the Gd55Co22.5Al22.5 BMG with a critical diameter of 3 mm and most ternary Gd-based BMGs. Thermodynamic investigations in terms of specific heat capacity and Gibbs free energy difference indicate that the Gd55Co17.5Al27.5 BMG possesses a lower driving force for crystallization. Kinetic analyses based on viscosity and dynamic relaxation spectrum reveal a stronger liquid behavior and more sluggish kinetics of the Gd55Co17.5Al27.5 BMG compared with the Gd55Co22.5Al22.5 BMG. Through the combination of the linear thermal expansion behavior and relaxation, the distinct difference of the contraction in supercooled liquid region of Gd55Co17.5Al27.5 and Gd55Co22.5Al22.5 BMGs is well explained. In addition, the magnetic entropy change is further enhanced by appropriate annealing treatment through the formation of more complex structures comprising short-range order, medium-range order and nano-crystallized structure.

Nanoscale thermal transport in amorphous and crystalline GeTe thin-films

We use frequency-domain thermoreflectance to determine the predominant phonon scattering mechanisms in thin films of GeTe. Thickness-dependent thermal conductivity is measured at room temperature to determine an effective mean free path for heat energy carriers in both amorphous and polycrystalline GeTe thin films and to subsequently compare intrinsic defect scattering with the magnitude of boundary scattering that occurs due to nanostructuring. Similarities in the effective mean free paths of amorphous and polycrystalline GeTe suggest that the crystalline alloy's microstructure results in a magnitude of intrinsic scattering between phonons comparable to that experienced by the amorphous phase. Variability in thermal conductivity between phases at comparable thicknesses is attributed to differences in volumetric heat capacity and phonon group velocity. These results are critical for the design of next-generation nanophotonic and optoelectronic devices that utilize nanostructured chalcogenide glasses.

The molar surface Gibbs energy and polarity of ether-functionalized ionic liquids

Ether groups are well-known for their unique contribution to low viscosity and high conductivity, hence ether-functionalized ionic liquids (EFILs) have been widely studied and successfully employed in various applications. Three EFILs 1-(2-methoxyethyl)-3-methylimidazolium chloride, 1-(2-ethoxyethyl)-3-methylimidazolium chloride and 1-(2-ethoxyethyl)-3-methylimidazolium bromide were prepared and characterized. Their surface tension, density and refractive index in the range of T = (288.15–328.15) K were measured and the molar surface Gibbs energy, gs, were calculated. Combined gs with Lorentz-Lorenz equation, an expression for predicting surface tensions of ionic liquids was obtained, and the predicted values were in good agreement with the experimental ones. According to the gs, the vaporisation enthalpies were predicted and the association enthalpies of ionic liquids were estimated. A new method for estimating the difference of heat capacities between the vapour phase and the liquid phase of ionic liquids was put forward, and the estimated values were in the same order of magnitude as the Verevkin method. Moreover, the concept of the polarity coefficient P for ionic liquids was proposed and the polarity of many ionic liquids was estimated.

Thermal Properties of Electro Insulating Paper

This paper is focused on the determination of thermal parameters (thermal conductivity, thermal diffusivity, and specific heat capacity) of electrical insulating paper from various producers. The transient step-wise method was used to determine all thermal parameters simultaneously. Evaluation was carried out using the differential method. Thermal conductivity was determined from the steady-state temperature response on thickness (corresponding to the number of paper layers), while thermal diffusivity and specific heat capacity was obtained from the dependence of derivative maximum and the corresponding temperature on thickness. Four electro insulating papers differing by composition and thickness: materials NKN (Nomex-Kapton-Nomex), DMD (Dacron-Mylar-Dacron), TFT (TufQUIN TFT 50) and TVAR (ThermaVolt AR) were studied. As a result, the highest value of thermal conductivity (0.17 W/m/K) was determined for the DMD. Remaining three materials possessed thermal conductivity about 0.12 W/m/K. However, differences in specific heat capacity and thermal diffusivity were found to be significantly higher. The lowest specific heat capacity was found for the DMD sample (1200 J/kg/K), while the highest specific heat capacity was found for TVAR sample (4000 J/kg/K).

Optical and Thermal Characterizations of PMMA Composites

Thick composite films were prepared employing hand – layup method . A definite quantity of PMMA ( 98%wt ) , fixed content ( 2% wt ) of rutile titanium dioxide TiO2 , gamma alumina ( ᵞ- Al2O3 ) and Zirconia powder ( ZrO2 ) , were added to polymer solution gradually and separately. Optical constants were obtained of the prepared samples using spectrometer (UV- VIS). The prepared composite samples were thermally characterized by differential scanning calorimeter ( DSC ). We notice increasing value of glass temperature and differential heat capacity ( ∆Cp ) for composites compared with pure PMMA .

Retention of Delta Ferrite in the Heat-Affected Zone of Grade 91 Steel Dissimilar Metal Welds

This study aimed to determine the mechanism of δ-ferrite retention in the coarse-grained HAZ (CGHAZ) of Grade 91 steel dissimilar metal welds (DMWs) with Ni-based filler metals. This phenomenon was investigated in four DMWs made with cold-wire gas tungsten arc process using Alloys 625, 617, 82, and P87 filler metals. A narrow band of δ-ferrite grains was identified in the CGHAZ in all welds. It was hypothesized that δ-ferrite retention was caused by local carbon depletion in the CGHAZ, which was validated through extensive thermodynamic and kinetic simulations and metallurgical characterization. Carbon diffusion across the fusion boundary was driven by the carbon chemical potential gradient between Grade 91 steel and the Ni-based filler metals, which was facilitated by long high-temperature dwell times resulting from a difference in heat capacity and thermal conductivity between the base and filler metals. A linear relationship was established between the amounts of retained δ ferrite and the predicted carbon depletion in the CGHAZ of each DMW. Alloy 625 filler metal generated the largest extent of carbon depletion and the most retained δ ferrite, followed by Alloys 617, 82, and P87. The carbon depletion resulted in local softening of the CGHAZ martensite.

Echo dephasing and heat capacity from constrained and unconstrained dynamics of triiodothyronine nuclear receptor protein.

The objective of this study is to observe the echo feature curves, vibrational dephasing, and heat capacity of a protein-hormone system taking thyroid hormone receptor-beta (THR-β) as an example. Constrained and unconstrained molecular dynamics simulations are performed by implementing the theory of velocity reassignments to probe the phase coherent state in terms of echo pulses. The constrained vibrations are incorporated by adjusting rigid bonds to all hydrogen atoms with an integrator parameter of 2fs/step in order to reduce the degrees of freedom whereas 1fs/step is used in the free vibrations of the atomic cluster. The nature of temperature auto-correlation functions changes so that echo feature curves also show a distinct nature in the cases of constrained and unconstrained vibrations. There is a large variation in kinetic temperature and internal potential energy in the echo time zone. The temperature rate of change of internal potential energy is the main contributor to the heat capacity of the native state protein-hormone system. The heat capacity of proteins estimated from this technique is in good agreement with the values from experiments. This study shows that triiodothyronine (T3) hormone makes some differences in heat capacity upon binding to the THR-β ligand binding domain (LBD). The physical properties of unliganded THR-β and T3-bound THR-β LBD in the cases of constrained and unconstrained dynamics are observed distinctly under the effect of anharmonicity on the phase coherent state of normal modes and the dephasing time lies in a range of 0.6-0.8ps when the systems are perturbed suddenly.

Temperature-Dependent Heat Capacity (ΔCP(T)) Modification of the Thermodynamic Framework for Thermotrp Channels Eliminates Predicted Dual Thermosensitivity

Many candidate protein domains have been proposed as the thermosensor in temperature sensitive TRP channels (thermoTRPs). In contrast, Clapham & Miller, 2011 proposed that the whole protein, rather than a localized area of the channel, could be responsible for thermosensation (C-M framework). The proposed thermosensitivity is caused by the heat capacity difference (ΔCp) between the open and closed states. This theory makes a surprising prediction that thermoTRPs should have two thermosensitive regions, responding to both hot and cold temperatures. In the original formulation, ΔCp was assumed to be temperature-independent, an assumption that could be reasonably relaxed. Using the Po vs. temperature data of Jara-Oseguera and Swartz (Jara-Oseguera et al., 2016), we used the C-M framework to backcalculate the ΔCp per degree temperature. The estimated ΔCp showed clear temperature dependence that warranted modeling. Here, we chose to use a Taylor series expansion of ΔCp as a function of temperature (ΔCp(T)). Each of the ΔCp(T) functions were then used to calculate Po over temperature and were compared to the original Po vs. temperature data. The second and the third order ΔCp(T) approximations were the best fits to the original data. Over the temperature range of −273oC to 233oC, the third order equation predicted only one thermosensitive temperature region. The modified ΔCp(T) C-M framework eliminates the necessity to experimentally determine the dual thermosensitive temperature regions in order to prove the C-M framework. As a key component of protein heat capacity is solvation, further work on the effects of solvent and lipid composition could help validate the modified ΔCp(T) C-M framework.

Influences of Structure Components on Thermal Distribution of a Cylindrical Lithium-ion Battery

Temperature is one of key influences on the lithium-ion battery performance. Difference of both specific heat capacity and thermal conductivity of elements leads to otherness of temperature distribution of a whole cell during electrochemical cycles. An 18650 lithium-ion cell is disassembled for its element measurements. The finite element thermal model of the cell is built on the multi-physics software COMSOL for its thermal characteristics simulation. Results show that cell elements such as the steel case, the electrolyte, and the relief valve have larger impacts on the internal temperature distribution than the surface temperature during charge. The shape and position of the highest temperature zone can be seriously changed when one of cell elements is either added or reduced, although the cell surface temperature varies slightly. On this basis, a method for improving the battery structure is proposed and verified by simulation. All thermal models predict the cell surface temperature with relative errors less than 5% compared to the measurement values.

The ferroelectric properties of 4-aminopyridinium perchlorate

Molecule-based ferroelectrics are a class of highly desirable intelligent materials for their highly variable physical properties, easy and environmentally friendly processing, especial light weight and mechanical flexibility. 4-Aminopyridinium Perchlorate (APP), used to be known as a pyroelectric below 243 K, is first discovered to be a new molecular ferroelectric in this work, which has a perfect electric hysteresis loops with a large spontaneous polarization of 1.0 μC/cm2 and a small coercive field of 0.67 kV/cm below 246 K. Owing to the dramatic changes of the protonated cations and order–disorder of anions, the crystal symmetry of APP transforms from P21/c to P21 in this first-order phase transition, which is revealed by other measurements, such as differential scanning calorimetry, heat capacity, dielectric anomalies and Raman spectrum.

Anthropogenic and Natural Contributions to the Lengthening of the Summer Season in the Northern Hemisphere

Observed long-term variations in summer season timing and length in the Northern Hemisphere (NH) continents and their subregions were analyzed using temperature-based indices. The climatological mean showed coastal–inland contrast; summer starts and ends earlier inland than in coastal areas because of differences in heat capacity. Observations for the past 60 years (1953–2012) show lengthening of the summer season with earlier summer onset and delayed summer withdrawal across the NH. The summer onset advance contributed more to the observed increase in summer season length in many regions than the delay of summer withdrawal. To understand anthropogenic and natural contributions to the observed change, summer season trends from phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel simulations forced with the observed external forcings [anthropogenic plus natural forcing (ALL), natural forcing only (NAT), and greenhouse gas forcing only (GHG)] were analyzed. ALL and GHG simulations were found to reproduce the overall observed global and regional lengthening trends, but NAT had negligible trends, which implies that increased greenhouse gases were the main cause of the observed changes. However, ALL runs tend to underestimate the observed trend of summer onset and overestimate that of withdrawal, the causes of which remain to be determined. Possible contributions of multidecadal variabilities, such as Pacific decadal oscillation and Atlantic multidecadal oscillation, to the observed regional trends in summer season length were also assessed. The results suggest that multidecadal variability can explain a moderate portion (about ±10%) of the observed trends in summer season length, mainly over the high latitudes.

Application of fast scanning calorimetry to the fusion thermochemistry of low-molecular-weight organic compounds: Fast-crystallizing m-terphenyl heat capacities in a deeply supercooled liquid state

Fusion enthalpy temperature dependence is related to the difference in heat capacity of the liquid and solid. Below the melting temperature, it is hard to measure the liquid heat capacity using conventional methods due to fast crystallization.Based on an indirect solution calorimetry approach, we previously concluded that the temperature dependence of heat capacities below the melting temperature is the extrapolation of the linear function above it. In this study, we employed a fast scanning calorimetry technique to test the validity of this conclusion.Three compounds were studied: two organic glass formers, benzophenone and o-terphenyl, for which the liquid and supercooled liquid heat capacities were known to be accurately described by a linear function of temperature, and m-terphenyl, which had never been studied in the supercooled liquid state. The results were in good agreement with the literature for liquid benzophenone and o-terphenyl heat capacities above and below the melting temperature. The heat capacity of the supercooled liquid and glassy m-terphenyl was obtained for the first time. The measured molar heat capacity of supercooled liquid m-terphenyl was the linear extrapolation of the temperature dependence of the heat capacity of the melt found in the literature.The molar heat capacity of the solid, the enthalpy and fusion temperature of m-terphenyl were determined by conventional DSC. Kirchhoff’s integral, calculated from the measured molar heat capacities of solid and liquid m-terphenyl, was in accordance with the fusion and solution thermochemistry data.