Ideal Gas Heat Capacity Research Articles

Vaporization enthalpies of self-associated aromatic compounds at 298.15 K: A review of existing data and the features of heat capacity correction. Part III. Polyphenols, polyanilines and aminophenols

The experimental data on the phase transition enthalpies and heat capacities of numerous polyphenols, polyanilines and aminophenols in the condensed and ideal gas state were analyzed to obtain the reliable values at 298.15 K. For this purpose, we combined experimental data on the crystal, liquid, and ideal gas heat capacities and fusion, sublimation and vaporization enthalpies. Significant part of these data, including the ideal gas heat capacities of 16 molecules, vapor pressures and vaporization enthalpies of 1,3-diaminobenzene and 1,6-dihydroxynaphthalene, were obtained in this work. A modified approach for the estimation of the temperature dependence of vaporization enthalpies of polyphenols, polyanilines and aminophenols showing performance competitive with the experimental one was proposed based on the analysis performed.

Speed of sound measurements and derived third and fourth acoustic virial coefficients of supercritical neon

We report comprehensive and accurate measurements of the speed of sound in neon. These measurements were carried out by a double-path-length pulse-echo technique and cover the temperature range between 200 K and 420 K with pressures up to 100 MPa. The standard uncertainties are 1.9 mK in temperature, 22 parts in 106 in pressure and 35 parts in 106 in speed of sound. The third and fourth acoustic virial coefficients of neon were derived from the speed of sound data in the temperature range of the measurements by fitting a fourth-order acoustic virial expansion in pressure with the second acoustic virial coefficient constrained from first-principles calculations. To support our claimed uncertainty, we determined the ratio M/γ0 between the molar mass M and the ideal-gas heat capacity ratio γ0 of the neon sample with a relative standard uncertainty of 7.7 parts in 106 by additional speed of sound measurements using a spherical resonator at 273.16 K.

Research on screening strategy of Organic Rankine Cycle working fluids based on quantum chemistry

The screening of working fluids is one of the key components in the study of power generation systems utilizing low-temperature waste heat. However, the variety of working fluids and their complex composition increase the difficulty of screening working fluids. In this study, a screening strategy for working fluids was developed from the perspective of the thermodynamic physical properties of working fluids. A comparative ideal gas heat capacity via the reduced ideal gas heat capacity factor (RCF) was proposed to characterize the dry and wet properties of working fluids, where RCF > 1 indicated a dry working fluid and RCF < 1 indicated a wet working fluid. A three-step screening strategy was developed for working fluid screening for organic Rankine cycles (ORCs). The strategy comprised basic physical property analysis of working fluids, research on dry and wet properties, and quantum chemical analysis. By comparing the RCF calculation result of 23 selected working fluid with values from the literature, the relative deviations of the data were less than 6.64% overall, indicating that the calculation result of the RCFs is reliable. The selection strategy explains the mechanism of working fluid selection in ORC systems from both micro- and macro-perspectives, laying a foundation for the study of structure-activity relationships in working fluids for ORCs.

Thermophysical Properties for Alkylphosphonate and Alkylphosphate Compounds

Organophosphorus compounds have a wide range of applications; they are commonly used as drugs or pesticides or in the production of ion batteries. However, some organophosphorus compounds, which were developed as warfare nerve agents, are neurotoxic and potentially lethal to living organisms. On the basis of the literature search, certain properties of these compounds are not well known. Knowledge of thermodynamic properties and the availability of reliable data are fundamental in the development of methods for detecting, treating, and safely analyzing decontamination. For research purposes, substitutes, called simulants, which have similar molecular structures and properties but are less toxic, are often employed. This work presents a thermodynamic study of four organophosphorus nerve agent simulants: trimethyl phosphate, triethyl phosphate, dimethyl methylphosphonate, and diethyl methylphosphonate. Differential scanning calorimeter and a Tian–Calvet type calorimeter were used to analyze their phase behavior and measure the liquid heat capacities, respectively. Vapor pressures were experimentally determined with the static method. Ideal-gas heat capacities were calculated using the R1SM approach, which combines the rigid rotor–harmonic oscillator model, the one-dimensional hindered rotor model, and the mixing model. The results obtained were compared with the data from the literature and simultaneously correlated to obtain a highly reliable thermodynamic description.Graphical

Thermodynamic Study of N-Methylformamide and N,N-Dimethyl-Formamide.

An extensive thermodynamic study of N-methylformamide (CAS RN: 123-39-7) and N,N-dimethylformamide (CAS RN: 68-12-2), is presented in this work. The liquid heat capacities of N-methylformamide were measured by Tian-Calvet calorimetry in the temperature interval (250-300) K. The vapor pressures for N-methylformamide and N,N-dimethylformamide were measured using static method in the temperature range 238 K to 308 K. The ideal-gas thermodynamic properties were calculated using a combination of the density functional theory (DFT) and statistical thermodynamics. A consistent thermodynamic description was developed using the method of simultaneous correlation, where the experimental and selected literature data for vapor pressures, vaporization enthalpies, and liquid phase heat capacities and the calculated ideal-gas heat capacities were treated together to ensure overall thermodynamic consistency of the results. The resulting vapor pressure equation is valid from the triple point to the normal boiling point temperature.

Gaseous speed of sound, ideal-gas heat capacity, and virial coefficients for cis-1,1,1,4,4,4-hexafluoro-2-butene (R1336mzz(Z)) and cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z))

The emerging low-global-warming-potential refrigerants cis-1,1,1,4,4,4-Hexafluoro-2-butene (R1336mzz(Z)) and cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z)) are showing high application potential in refrigeration and organic Rankine cycle, but the necessary thermophysical property data are too scarce to support their commercial application. Among the thermophysical properties, the speed of sound is essential for engineering design and scientific research. In this study, the speed of sound of gaseous R1336mzz(Z) and R1225ye(Z) was determined experimentally by the acoustic resonance method with the help of a fixed-path cylindrical cavity. The sound speed data of R1336mzz(Z) covers the temperature range of (323 to 363) K and pressure range of (57 to 383) kPa, and that of R1225ye(Z) covers (298 to 363) K and (40 to 1022) kPa. The relative uncertainties of these measurements are within a few parts in 10−4, allowing accurate analysis to derive the ideal-gas heat capacity and the 2nd acoustic density virial coefficients. Further, the parameters of the hard-core square-well intermolecular potentials are fitted to the acoustic data, allowing us to infer an estimate of the 2nd density virial coefficient of these substances. Quantitative calculation of uncertainties is also performed for these derived thermophysical parameters. Comparison of all these results with other data in the existing literature and the predictions of dedicated equations of state shows good agreement, supporting the claimed uncertainty of the experimental results.

Thermodynamic study of selected aromatic monoterpenoids

Thermodynamic properties of aromatic alcohols thymol, carvacrol, and cuminol were studied in this work as part of our effort to establish reliable physicochemical data for common monoterpenes. The phase behavior of the compounds was investigated by heat-flux differential scanning calorimetry (DSC) above 183 K with a special focus on the signs of polymorphic behavior. The heat capacities of the condensed phases were determined by a Tian-Calvet type calorimeter. Vapour pressure measurements were performed using two static apparatus over a wide temperature range, including environmentally important ambient temperatures. The conformational space of the compounds was examined using density functional theory (DFT) calculations, and the ideal-gas thermodynamic properties were subsequently calculated using statistical thermodynamics. A consistent thermodynamic description is presented, which was developed using the method of simultaneous correlation that processes experimental data on phase behavior, vapor pressures, and condensed phase heat capacities together with calculated ideal-gas heat capacities. The influence of the position of the hydroxyl group on the thermodynamic properties is discussed and rationalized.

Entropy, Heat Capacity, and Thermal Conductivity of trans-1,1,1,4,4,4-Hexafluoro-2-butene [R1336mzz(E)] Derived from the Gaseous Sound Speed Measurement

Thermophysical properties such as entropy, heat capacity, and thermal conductivity of trans-1,1,1,4,4,4-hexafluoro-2-butene, which is designated as R1336mzz(E) for refrigerant use, were derived from the sound speed measurement in the gaseous phase. The gaseous sound speed was measured by using an acoustic-microwave resonator with a cylindrical cavity, which enables simultaneous measurement of the gaseous relative dielectric permittivity. The ideal gas heat capacity was determined from the gaseous sound speed by analyzing the measurement data with the acoustic-virial equation, and the electric dipole moment was additionally determined from the gaseous relative permittivity measurements. In compliance with the fluid-property correlation models that involve parameters associated with the ideal gas heat capacity and the dipole moment under the corresponding states principle, entropies at saturated vapor and liquid, isobaric heat capacities at saturated liquid, and thermal conductivities at vapor and liquid phases were evaluated for R1336mzz(E).

Vapor pressures and thermophysical properties of selected monoterpenoids II

In this work, a thermodynamic study of four enantiopure terpenoids, myrtenal, myrtenol, α-terpineol, and trans-sobrerol is presented. Vapor pressures of the selected terpenoids were determined using two static apparatus in a combined temperature range from 248 to 363 K. Heat capacities of the samples were determined by Tian-Calvet calorimetry in the temperature range from 261 to 353 K. Phase behaviour (melting temperature, fusion enthalpy, crystallization temperature, and potential polymorphic transformations) were studied using heat-flux calorimetry. Using a combination of quantum-chemical calculations and statistical thermodynamics, ideal-gas heat capacities and entropies were determined. Finally, consistency of the phase behaviour, vapor pressure, and heat capacity experimental data with the theoretically calculated data was assessed using the method of simultaneous correlation.

A Multi‐Criteria Study of Optimal Working Fluids for High Temperature Heat Pumps

AbstractA bi‐objective optimization with respect to coefficient of performance (COP) and volumetric heating capacity (VHC) is performed for a high temperature heat pump. For fixed temperature levels of the heat source and sink, the values for temperature in the evaporator and condenser as well as the degree of vapor super‐heating and condensate sub‐cooling are optimized. Constraints are placed on the minimal pressure in the evaporator, the maximal pressure in the condenser and the compressor discharge temperature. Results are presented for a one‐stage and a two‐stage heat pump cycle. Cyclobutane and several butene isomers are identified as working fluids with a good compromise between COP and VHC from a CoMT‐CAMD approach based on PC‐SAFT and a realistic model for the ideal gas heat capacity.

Behavior of Isobaric Heat Capacity of trans-1,1,1,4,4,4-Hexafluoro-2-butene in the Gas Phase

The isobaric specific heat capacity cp of trans-1,1,1,4,4,4-hexafluoro-2-butene was carefully measured for temperatures T ranging from (308 to 363) K and at pressures p ranging from (0.2 to 1.0) MPa in the gaseous state. The obtained 33 cp data with a flow calorimeter were tabulated and were shown in the cp–T diagram. It is estimated that the expanded uncertainties (k = 2) of the temperature measurements U(T) and the pressure measurements U(p) are less than 37 mK and 3.6 kPa, respectively. That for cp measurements U (cp) is derived to be less than 36 J·kg–1·K–1. Based on the evaluated data, corresponding isotherms were depicted in the cp–p diagram, and the ideal-gas isobaric heat capacity and saturation in the gas phase of trans-1,1,1,4,4,4-hexafluoro-2-butene were determined.

Experimental speed of sound for cis-1,3,3,3-tetrafluoropropene (R1234ze(Z)) and hexafluoropropene (R1216) in gaseous phase

cis-1,3,3,3-Tetrafluoropropene (R1234ze(Z)) and hexafluoropropylene (R1216) are considered the alternative low-global-warming-potential working fluids due to their good performance in high-temperature heat pumps and organic Rankine cycle (ORC) systems. Thermodynamic data with high precision are required for performance analysis and industrial application, among which speed of sound data are essential for designing the system components and deriving other thermodynamic properties. In this work, we measured the speed of sound in the gaseous phase of R1234ze(Z) and R1216 using a fixed-path cylindrical acoustic resonator. The experimental temperature and pressure ranges of R1234ze(Z) are (303.15 to 363.15) K and (129 to 730) kPa, respectively; and those for R1216 are (293.15 to 363.15) K and (130 to 1001) kPa. The ideal-gas heat capacity and the virial coefficients up to 3th order were calculated from the experimental data. The uncertainties of the measured and derived properties are exhaustively analyzed and calculated. The combined expanded relative uncertainties (k=2) of the measured sound of speed are 2.8×10−4 for R1234ze(Z) and 2.4×10−4 for R1216. The combined expanded relative uncertainties (k=2) of the derived ideal-gas heat capacity are 0.018 for R1234ze(Z) and 0.010 for R1216. The combined expanded relative uncertainties (k=2) of the second density virial coefficient are 0.033 for R1234ze(Z) and 0.013 for R1216.

Experimental speed of sound for trans-1-Chloro-3,3,3-trifluoroprop-1-ene (R1233zd(E)) and trans-1,1,1,4,4,4-Hexafluorobut-2-ene (R1336mzz(E)) in gaseous phase

trans-1-Chloro-3,3,3-trifluoroprop-1-ene (R1233zd(E)) and trans-1,1,1,4,4,4-hexafluorobut-2-ene (R1336mzz(E)) have gained increasing momentum due to their low global warming potential (GWP) and good performance in heat pumps and organic Rankine cycle (ORC) systems. Accurate thermodynamic property data are required for industrial and commercial applications. Speed of sound data with high precision are vital to developing dedicated equations of state (EoS) and calculating other thermodynamic properties. In this work, we measured the speed of sound in the gas phase of R1233zd(E) and R1336mzz(E) by the fixed-path acoustic resonance method using a cylindrical resonator. The dimensions of the resonator are calibrated by Ar, Kr and He. The speeds of sound of R1233zd(E) were obtained at temperatures ranging from 313.15 to 363.15 K and pressures up to 550 kPa, and those of R1336mzz(E) were obtained in the temperature range from 298.15 to 363.15 K and the pressure up to 805 kPa. The combined expanded relative uncertainty (k = 2) of the sound of speed is 2.1 × 10−4 for R1233zd(E) and 1.5 × 10−4 for R1336mzz(E). The sound-speed data of R1233zd(E) agree with the EoS developed by Mondejar with an average relative deviation of −0.003%, which is the most accurate. The R1336mzz(E) data are the first set of published experimental sound-speed data. The ideal-gas heat capacity at constant pressure and the second acoustic virial coefficient were derived and compared to published data. The data measured and derived in this work can be used to establish the dedicated EoS of R1336mzz(E) for better prediction of thermodynamic properties.

Ideal Gas Heat Capacity and Critical Properties of HFE-Type Engineering Fluids: Ab Initio Predictions of Cpig, Modeling of Phase Behavior and Thermodynamic Properties Using Peng–Robinson and Volume-Translated Peng–Robinson Equations of State

Ideal Gas Heat Capacity and Critical Properties of HFE-Type Engineering Fluids: Ab Initio Predictions of Cpig, Modeling of Phase Behavior and Thermodynamic Properties Using Peng–Robinson and Volume-Translated Peng–Robinson Equations of State

Thermodynamic Properties of Potential Alternative Refrigerant HFO-1234ze(Z)

Cis-1,3,3,3-Tetrafluoropropene HFO-1234ze(Z) is an environmentally friendly potential alternative refrigerant for heat-pump application. In usability evaluation of this refrigerant in heat pump application, the accurate thermodynamic properties of HFO-1234ze(Z) in both single-phase and two-phase regions are needed. So, this paper aims to provide an accurate lgP-h diagram and the thermodynamic properties in both single-phase and two-phase regions. The accuracy of this published data and the lgP-h diagram was evaluated by comparing this data with available experimental data. The study shows that the average absolute deviations between our values and experimental data for vapour pressure, saturated liquid density, subcooled liquid density and gaseous pressure are 0,34%, 0,42%, 0,60%, and 0,99%, respectively. Additional evaluations for the ideal gas heat capacities and speed of sound are available in this work. The average absolute deviations between calculated values and published data for compressed liquid speed of sound, gaseous speed-of-sound data, and ideal gas heat capacity are 2.2%, 0,98%, 0,57%, respectively.

Isobaric heat capacity measurements on ternary mixtures of natural gas components methane, propane and n-heptane by differential scanning calorimetry at temperatures from 197 K to 422 K and pressures up to 32 MPa

Heat capacities for single-phase mixtures of the natural gas components methane (1), propane (2) and n-heptane (3) have been determined at temperatures (197 to 421) K and pressures up to 32 MPa using two differential scanning calorimeters with a combined standard uncertainty of (2.0 to 2.6) % (k = 1). In addition, measurements were performed at pressures (0.01 to 4.40) MPa higher than saturation conditions to estimate the heat capacities of the mixtures at their bubble points. The ternary mixture data were compared with three models: the Groupe Européen de Recherches Gazières (GERG) 2008 multi-parameter equation of state (EOS), the Peng-Robinson (PR) EOS, and the Statistical Associating Fluid Theory (SAFT)-γ Mie EOS incorporating group contributions. The relative deviations of the measured heat capacities from the values calculated by the three models show similar, systematic dependences on density, with larger deviations at cryogenic temperatures. The root mean square deviations from the measurements (with ideal gas heat capacity corrected) were 8.2%, 7.0% and 5.9% for the GERG-2008, PR and SAFT-γ Mie EOS, respectively. The presence of n-heptane increased the deviation up to 20% at the lowest temperature. The addition of methane to the binary mixture [0.500 C3H8 + 0.500 C7H16] was found to always increase the heat capacity. This work shows that the SAFT-γ Mie EOS can describe the single-phase measurements at above-ambient temperatures, while none of the models provides reliable predictions for cryogenic single-phase and near-bubble-point measurements.

Machine learning prediction of ORC performance based on properties of working fluid

In order to develop machine learning methods for performance prediction of basic ORC (BORC) and regenerative ORC (RORC), thermodynamic properties of working fluids are used to separately model thermodynamic processes including compression, expansion, evaporation and regeneration by artificial neural network (ANN), based on REFPROP calculation data of 106 working fluids. These properties include critical temperature, critical pressure, acentric factor and ideal gas heat capacity. Other cycle performances can be derived from the predictions of established ANNs. Furthermore, for RORC, considering that dry or isentropic working fluid is usually preferred, vapor slope of temperature-entropy saturation curve is modeled by ANN to determine the working fluid behavior. Meanwhile, for ensuring occurrence of heat exchange in regenerator, temperature difference between outlets of turbine and pump is modeled to judge whether temperature difference is larger than the assumed pinch point temperature difference. Based on the obtained predictions for BORC, average absolute deviations (AADs) of net work and thermal efficiency are 1.3928% and 1.5461%, respectively. As for RORC, AADs of vapor slope, temperature difference, net work and thermal efficiency are 2.3659%, 1.2020% 1.8277% and 2.1047%, respectively. Based on the above models, cycle performances of BORC and RORC can be accurately predicted from thermodynamic properties of any working fluid.

Relationship between the vaporization enthalpies of aromatic compounds and the difference between liquid and ideal gas heat capacities

Understanding connection between physicochemical parameters, molecular structure and heat capacity of liquids remains limited, especially for complex organic molecules. One of possible ways to resolve this problem is analysis of difference between the liquid and ideal gas heat capacities. This difference also defines the temperature dependence of vaporization enthalpy.This work is based on the assumption that the difference between the liquid and gas phase heat capacity is primarily related to intermolecular interactions in the liquid. As the measure of intermolecular interactions, the vaporization enthalpy at 298.15 K was considered. The relationship between the difference of liquid and gas phase heat capacities and the vaporization enthalpy was analyzed for a wide range of aromatic and heteroaromatic compounds. An excellent correlation was observed (residual standard deviation 3.7 J·K−1·mol−1, N = 99). This correlation appeared to be useful for estimation of the vaporization enthalpies of aromatic compounds at elevated temperatures solely from the value at 298.15 K. The calculated and literature vaporization enthalpies measured between 360 and 650 K of 80 compounds from 134 sources were compared. An average absolute deviation of 1.5 kJ·mol−1 was observed, being competitive with the experimental errors of vaporization enthalpy determination.

Isobaric heat capacities of a methane (1) + propane (2) mixture by differential scanning calorimetry at near-critical and supercritical conditions

Isobaric heat capacity data are needed to test and improve thermodynamic models of natural gas over wide ranges of temperature and pressure. Measurements are reported here at temperatures between (184 and 421) K and pressures between (5 and 32) MPa for supercritical mixtures of methane (1) + propane (2) at x1 = 0.950 (±0.005). Estimated relative uncertainties in the measured heat capacities range from (1.8 to 4.5) %. In addition, measurements at temperatures of (184, 190, 197, 203 and 209) K were performed at pressures (1.67 to 2.39) MPa higher than saturation conditions to estimate the heat capacity of the mixture at the bubble point. The binary mixture data were compared with the predictions of three models: the Groupe Européen de Recherches Gazières (GERG) 2008 multi-parameter equation of state (EOS), the Peng-Robinson (PR) EOS used widely by chemical engineers, and the Statistical Associating Fluid Theory (SAFT)-γ Mie EOS incorporating group contributions. Among the three models, the PR EOS was found to describe the heat capacity values best. A brief investigation indicated that the Joback and Reid method that the SAFT-γ Mie EOS is based on fails to accurately predict the ideal gas heat capacity of methane at cryogenic temperatures, while the inaccuracy of the GERG-2008 EOS stems from the residual part of the methane (1) + propane (2) mixing functions.

Thermophysical Properties of 1,1,1,3,3,3-hexafluoro-2-methoxypropane (HFE-356mmz) in the Vapor Phase Measured by Using an Acoustic-Microwave Resonance Technique

Thermophysical properties of HFE-356mmz in the vapor phase were measured by means of an acoustic-microwave resonance method. HFE-356mmz, which is 1,1,1,3,3,3-hexafluoro-2-methoxypropane in chemical name, is expected to be used as a working fluid with low global warming potential for the Organic Rankine cycle (ORC). The sound velocity and dielectric permittivity were simultaneously measured by using a cylindrical acoustic-microwave resonator. The sound velocity data were analyzed to obtain the ideal-gas heat capacity at constant pressure. The integral of the ideal-gas heat capacity as a function of temperature derives the ideal-gas enthalpy, which is a fundamental and important energy property to simulate the thermodynamic cycle. Similarly, the analysis of the dielectric permittivity data leads to information on the ideal-gas molar polarizability, dipole moment, and density. The acquired thermophysical properties of HFE-356mmz were compared to those of R-245fa and n-pentane, which are the existing working fluids for the ORC system, to prospect a feasibility of HFE-356mmz as their alternative.