Isobaric Specific Heat Capacity Research Articles

Математична модель камери згоряння газотурбінного двигуна, який працює на етанолі

Ethanol is one of the most promising alternative fuels for Ukraine. To convert existing projects of power and cogeneration plants based on gas turbine engines (GTEs) operating on petroleum products and natural gas to ethanol, as well as for their design and performance calculation, it is necessary to have a mathematical model of the working process of GTE combustor. The object of the study is the working process of the GTE combustor fueling on ethanol. The subject of the study is a mathematical model of the working process of GTE combustor fueling on ethanol. The work aims to improve a mathematical model of the working process of a GTE combustor fueling on ethanol by changing the algorithm for calculation of the fuel air ratio, considering thermal dissociation, and a correctly formulated equivalent chemical reaction path of the combustion process. To achieve the aim, the following tasks were solved: based on the use of experimental values of specific isobaric heat capacities of combustion products, which are a function of temperature and pressure, a mathematical model of the working process of the GTE combustor was improved ("simplified" mathematical model); based on the solution of the system of equations of chemical thermodynamics, a mathematical model of the working process of the GTE combustor was developed ("complex" mathematical model); the results of calculation by "simplified" mathematical model of the working process of the GTE combustor were compared with the "complex" one. The following results were obtained: the difference in the calculation of the combustion products' thermodynamic parameters between the developed mathematical models was less than 1.2% for the three modes of the General Electric CF6-80A engine. Conclusion: the "simplified" mathematical model of the working process of the GTE combustor fueling on ethanol was improved. A feature of the model is the implicit consideration of the effect of thermal dissociation and correctly formulated equivalent chemical reaction path of the combustion process by using experimental values of specific isobaric heat capacities of combustion products. This will improve the accuracy of fuel air ratio calculation and other thermodynamic parameters of GTE combustor mathematical models fueling on ethanol, without significantly complicating the model algorithm.

Isobaric Specific Heat Capacity Measurement in the Trans-Critical Temperature Regions for Kerosene RP-3 under Pressures of 6–8 MPa

Isobaric Specific Heat Capacity Measurement in the Trans-Critical Temperature Regions for Kerosene RP-3 under Pressures of 6–8 MPa

Proper orthogonal decomposition of wall-bounded high-pressure transcritical fluids

This study explores the principal modes of high-pressure transcritical channel flow from direct numerical simulation data. The four cases investigated correspond to CO2 at high-pressure conditions (P/Pc=1.5) confined between a cold/bottom wall (T/Tc=0.8−0.95) and a hot/top wall (T/Tc=1.1−1.4); Pc and Tc correspond, respectively, to the pressure and temperature of the critical point. The bulk velocity ranges between Ub=0.5−1.0 m/s with corresponding bulk Reynolds numbers of Reb≈1000−2500. The four cases considered are first characterized into laminar and turbulent regimes, followed by an analysis of energy decay using singular value decomposition. This method allows us to identify the most energetic modes of velocity, temperature, and specific isobaric heat capacity for the laminar and turbulent cases considered. The results reveal that fewer modes are needed to represent the hydrodynamics compared to the thermodynamics of the system. The findings also highlight that the pseudo-boiling region, prevalent in high-pressure transcritical systems, disrupts the coherent structures formed (especially) in the hotter region of the flow. Finally, a correlation analysis between the most energetic modes shows an interdependence between velocity and specific isobaric heat capacity modes when conditioned to focus solely on the pseudo-boiling affected regions. This correlation underscores the complex interplay between hydrodynamic and thermodynamic variables in such high-pressure transcritical environments.

Effect of alkyl chain length on the thermal properties and toxicity of n-alkyl-ammonium nitrate ionic liquids (n = 2, 3, 4, 5, 6, 8) for energy applications

AbstractThe most currently used ionic liquids (ILs) are protic ionic liquids (PILs), subject to extensive investigation regarding their physical properties. These compounds along with their mixtures with other substances such as salts and solvents, serve as electrolytes in next generation electrochemical smart devices, and emerge as viable candidates to replace conventional Heat Transfer Fluids (HTFs) in various energy applications. Despite the extensive number of studies, important information about this kind of compounds is still unknown, such as the effect of alkyl chain length on thermal and thermophysical properties, as well as toxicity. This work, extending previous studies of our group, summarizes the liquid range, heat capacity and acute toxicity level of six ammonium ILs: specifically, n-alkyl-ammonium nitrate ILs with increasing alkyl chain length (n = 2, 3, 4, 5, 6, 8). For this study, the synthesis of the three ILs with the longest alkyl chain was performed, along with DSC, TGA and toxicity measurements. It was observed that an increase in alkyl chain length resulted in a decrease in short-term thermal stability and an increase in melting temperature, indicating a reduction in the liquid range. A compensation effect between enthalpy and entropy of melting was observed for the studied chain lengths. The isobaric specific and molar heat capacities increase with temperature for all the compounds studied here, and good correlations were obtained between molar heat capacity and the number of carbon atoms in the alkyl chain for every temperature. Finally, most of the ILs are non-toxic, although toxicity increases with alkyl chain length.

The isobaric specific heat capacity and viscosity for 3,3,3-trifluoroprop-1-ene in liquid phase at temperatures from (230 to 293) K and pressures up to 8 MPa

In this paper, the 65 isobaric specific heat capacity (cp) and 9 viscosity (η) data of 3,3,3-trifluoroprop-1-ene (R1243zf) were measured at temperatures from (230 to 293) K and pressure up to 8 MPa using a flow calorimeter and a vibrating-wire viscometer. The uncertainty of temperature, pressure, isobaric specific heat capacity and viscosity were evaluated to be less than 11 mK, 0.02 MPa, 1.0 % and 2.7 %, respectively. Three saturated liquid viscosity (ηs) data were obtained based on the extrapolation of the viscosity data. Empirical correlations were established based on the cp and ηs data, the average absolute relative deviation for cp and ηs are 0.5 % and 1.3 %, respectively.

Highly Accurate Densities and Isobaric and Isochoric Heat Capacities of Compressed Liquid Water Derived from New Speed of Sound Measurements

Comprehensive and accurate measurements of the speed of sound in liquid water are reported. The measurements were carried out by a double-path-length pulse-echo technique and cover the temperature range from 273.65 K to 368.15 K with pressures up to 100 MPa. The relative expanded (k=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${ k}=2$$\\end{document}) uncertainties are 2.1 mK in temperature, 45 parts-per-million (ppm) in pressure, and between 40 ppm and 70 ppm in speed of sound. Furthermore, values for the density and specific isobaric and isochoric heat capacities were derived from the speed of sound data in the measured temperature range up to 100 MPa by the method of thermodynamic integration. Very accurate values for the derived properties were obtained by using density data of Takenaka and Masui (Metrologia 27:165–171, 1990) and isobaric heat capacity data of Osborne et al. (J Res Natl Bur Stand 23:197, 1939) at ambient pressure as initial values in combination with an accurate correlation of our speed of sound. The relative expanded (k=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${ k}=2$$\\end{document}) uncertainties of the derived properties are 2 ppm in density, 0.11% in isobaric heat capacity, and 0.12% in isochoric heat capacity. The experimental speeds of sound and derived properties are compared with experimental data of other authors from the literature, the IAPWS-95 (International Association of the Properties of Water and Steam) formulation for the thermodynamic properties of water, and a recent equation of state for supercooled water.

Characterization of the physical properties of the thermoresponsive block-copolymer PAGB2000 and numerical assessment of its potentialities in Forward Osmosis desalination

Forward Osmosis is a promising strategy for desalination processes, however some aspects have to be better characterized to make it competitive with other affirmed technologies. One of these aspects is the selection of the draw agent, i.e., a polymeric solution that has to fulfill different requirements to guarantee both high membrane performances and good regeneration process. Previous studies have identified a thermoresponsive copolymer known as PAGB2000 as potential draw agent. However, in the open literature there is no information on the thermo-physical properties required for a fully characterization of the polymer itself, hence, different experimental campaigns have been conducted to quantify: phase behavior, osmotic pressure, density, dynamic viscosity, thermal conductivity, thermal diffusivity and isobaric specific heat capacity. These properties were then used in a computational model to simulate the whole desalination process. Recovery ratio, specific electric consumption and specific thermal consumption were compared with the ones obtained in a previous work, showing that a detailed characterization of the thermo-physical properties is required to get accurate and realistic predictions of the system performance.

On isobaric heat capacity of ionanofluids with carbon nanotubes – An experimental study

Ionanofluids (INFs) are defined as ionic liquids (ILs) with therein dispersed nanoparticles. The addition of nanoparticles results in an increase in the thermal conductivity of INFs. In terms of specific isobaric heat capacity (cp) this influence is not yet clear due to contradictory results published up to date. In this work, we assessed the influence of carbon nanotubes (CNTs) on the cp of INFs by means of DSC. We selected 13 different types of ILs and two mixtures of them as the base for INFs. 9 different types of CNTs were chosen: (singlewalled carbon nanotubes) SWCNTs, helical CNTs, Nanocyl multiwalled carbon nanotubes (MWCNTs) and in-house 16h MWCNTs, MWCNTs functionalized with carboxylic groups (COOH), hydroxylic groups (OH), C18n-alkyl chain or polyethylene glycol (PEG). Functionalized MWCNTs have never been investigated in terms of the cp of INFs. A total of 43 INFs were obtained and studied. The influence of CNTs on the cp of INFs was critically analyzed with consideration to the cp of base liquid and its agreement with data available in the literature, and with consideration to measurement uncertainty. Also, the cp of some pristine CNTs (as a bulk material), namely Nanocyl MWCNTs and in-house 16h MWCNTs, was examined. In the most of systems, the addition of CNTs did not affect the cp of INFs. In the others, the effects were minor and not greater than 3.1 %. In the end, the model proposed to estimate the cp of nanofluid, including the existence of nanolayer of IL on the CNT, was critically examined.

Experimental observation of mesoscopic fluctuations to identify origin of thermodynamic anomalies of ambient liquid water

We report a new experimental approach for observing mesoscopic fluctuations underlying the thermodynamic anomalies of ambient liquid water. In this approach, two sound velocity measurements with different frequencies, namely inelastic X-ray scattering (IXS) in THz band and ultrasonic (US) in MHz band, are required to investigate the relaxation phenomenon with the characteristic frequency between the two aforementioned frequencies. We performed IXS measurements to obtain the IXS sound velocity of liquid water from the ambient conditions to the supercritical region of liquid-gas phase transition (LGT) and compared the results with the US sound velocity in the literature. We found that the ratio of the two sound velocities, Sf, which corresponds to the relaxation intensity, exhibits a simple but significant change. Two distinct rises were observed in the high-temperature and low-temperature regions, implying that two relaxation phenomena exist: in the high-temperature region, a peak was observed near the LGT critical ridge line, which was linked with changes in the density fluctuation and isochoric and isobaric specific heat capacities; in the low-temperature region, Sf increased toward the low-temperature region, which was linked with the change in the isochoric heat capacity. We concluded that these two relaxation phenomena are originated from critical fluctuations of liquid-gas phase transition (LGT) and liquid-liquid phase transition, respectively. The linkage between Sf and isochoric heat capacity in the low-temperature region proves that the relaxation is the cause of the well-known heat capacity anomaly of ambient liquid water. In this study, both LGT and LLT critical fluctuations were observed, and the relationship between thermodynamics and the critical fluctuations was comprehensively discussed.

Thermophysical characterization on water and ethylene glycol/water-based MgO and ZnO nanofluids at elevated temperatures: An experimental investigation

In the current work, the main objective is to investigate the dynamic viscosity, thermal conductivity and isobaric specific heat capacity of MgO and ZnO nanoparticles that are dispersed in water and mixtures of ethylene glycol and water (EG/W). The measurements were carried out with various volumetric fractions (0.25 to 1%) and temperatures varied from 40 to 120 °C. According to the experimental results, the viscosity and thermal conductivity of the investigated nanofluids rise uniformly with increasing the nanoparticle concentration. The maximum viscosity augmentation for 1% MgO-(50:50)EG/W nanofluid is 34.5%, while the maximum augmentation for 1% ZnO-(50:50)EG/W nanofluid is 45.1%. For MgO-EG/W nanofluids, the maximum percentage of thermal conductivity enhancement occurs at 1% nanoparticles fraction and is 33.1%; for 1% ZnO-EG/W, the maximum enhancement is 23%. Measurements revealed that the nanofluids’ isobaric specific heat decreases as the nanoparticles fraction and EG concentration ratio in the base fluid increase but augments as the temperature increases. New correlations for predicting nanofluids’ thermophysical characteristics were suggested depending on the current experimental results. A theoretical evaluation of heat transfer performance was carried out, and it was demonstrated that MgO and ZnO nanofluids have the potential to be used in heat transfer applications with laminar flow regimes. For the turbulent regime, it is preferable to utilize nanoparticles concentrations of <0.5% for ZnO nanofluids and ≤1% MgO nanofluids, respectively.

Prediction of speed of sound and specific heat capacity of ionic liquids using predictive SAFT-based equation of state

In this work, the predictive PC-SAFT EoS has been developed to predict the speed of sound, the isochoric and isobaric heat capacity of ionic liquids (ILs) over a wide range of pressures and temperatures. In this new methodology, the segment number and diameter of ILs have been estimated using the surface area and molecular volume of the UNIFAC model. The segment energy and association energy parameters have been obtained using an inverse relationship between dispersion/association energy and segment diameter. The results show that the predictive PC-SAFT model can predict the specific isochoric and isobaric heat capacity of ILs up to high pressure, accurately. In the case of the speed of sound, the model performance is acceptable by considering using no adjustable model parameters. To check the model capability, the new model results have been compared to the electrolyte PC-SAFT EoS.

A sound velocity method for determining isobaric specific heat capacity

AbstractIsobaric specific heat capacity (Cp) is an important parameter not only in physics but also for most materials. Its accurate measurement is particularly critical for performance evaluation of thermoelectric materials, but the experiments by differential scanning calorimetry (DSC) often lead to large uncertainties in the measurements, especially at elevated temperatures. In this study, we propose a simple method to determine Cp by measuring the sound velocity (υ) based on lattice vibration and expansion theory. The relative standard error of the υ is smaller than 1%, showing good accuracy and repeatability. The calculated Cp at elevated temperature (&gt;300 K) increases slightly with increasing temperature due to the lattice expansion, which is more reasonable than the Dulong–Petit value.image

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.

Heat capacity measurements of conventional aviation fuels

Isobaric specific heat capacities were measured for six conventional petroleum-derived aviation fuel samples: JP-10, JP-7, JP-4, JP-TS, TS-1, and Avgas. All measurements were made using modulated differential scanning calorimetry over the combined temperature range of (213 to 442) K. Experimental data, including an assessment of the associated expanded uncertainties, have been reported. Additionally, measurement results for the six fuels were compared with one another and with available literature data and existing surrogate mixture models.

Analytical expressions for thermophysical properties of solid and liquid beryllium relevant for fusion applications

The status of the literature is reviewed for thermophysical properties of pure polycrystalline solid and liquid beryllium which constitute input for the modeling of intense plasma–surface interaction phenomena that are important for fusion applications (thermal analysis, vapor shielding, melt motion, arcing, dust generation, dust transport). Reliable experimental data are analyzed for the latent heats, specific isobaric heat capacity, electrical resistivity, thermal conductivity, mass density, vapor pressure, work function, total hemispherical emissivity and absolute thermoelectric power from the room temperature up to the normal boiling point of beryllium as well as for the surface tension and the dynamic viscosity across the liquid state. Analytical expressions are recommended for the temperature dependence of these thermophysical properties, which involve high temperature extrapolations given the absence of extended liquid beryllium measurements.

Prediction of thermal properties of phosphorus dimer – The analytical approach

In this study, modified hyperbolical-type oscillator was used to simulate the internal vibration of a diatomic molecule. By employing the expression of partition function of the system, new analytical equations for the prediction of molar entropy, enthalpy, Gibbs free energy, and isobaric specific heat capacity were derived. The thermodynamic equations were applied to ground-state phosphorus dimer. Average absolute deviations of 0.3795, 0.8939, 0.3895, and 0.6978% were obtained. The results are in good agreement with existing data on gaseous phosphorus molecules in the literature.

Measurements of isobaric specific heat capacity (cp) for pure trans-1,3,3,3-tetrafluoropropene and (trans-1,3,3,3-Tetrafluoropropene + 1,1,1,2-tetrafluoroethane) binary mixtures at temperatures from (231.84 to 338.68) K and pressures up to 8.2 MPa

Due to the increasingly serious greenhouse effect, R134a with high global warming potential (GWP) will be phased out gradually. Pure trans-1,3,3,3-Tetrafluoropropene (R1234ze(E)) and (R1234ze(E) + 1,1,1,2-tetrafluoroethane (R134a)) mixtures have become one of the most potential alternative refrigerants owing to lower GWP. The isobaric specific heat capacity (cp) is one of the most important thermophysical properties for the design of heat exchangers and the verification of the accuracy of the equation of state (EoS). In this paper, the cp of pure R1234ze(E) and (R1234ze(E) + R134a) mixtures at temperatures from (231.84 to 338.68) K was measured by a self-design flow calorimeter, and the pressures up to 8.2 MPa. A total of 160 liquid cp data are reported, including 57 data points for pure substance and 103 data points for mixtures. Uncertainties for temperature, pressure and cp were estimated to be less than 11 mK, 0.02 MPa and 1.0 %. In addition, the experimental data were compared with the pieces of literature data and the predictions of three models (Helmholtz energy EoS, Peng-Robinson (PR) EoS and corresponding states equation (CSE)). Among the three models, the Helmholtz energy EoS gives the best description, while the prediction performance of the PR EoS is the worst, especially in the low-temperature region and the near-critical region. Then, a brief investigation was performed to understand the reasons behind these discrepancies and found that the specific volume data have a significant impact on the cp prediction for PR EoS. When using the high-precision specific volume data in the cp calculation, the prediction performance of PR EoS will be significantly improved.

Density, Viscosity, Refractive Index, Isobaric Specific Heat Capacity, Ultrasonic Velocity, Molar Volume, Isentropic Compressibility, Isothermal Compressibility, and Heat Capacity Ratio for Binary Mixtures of the Organic Liquids Ethylbenzene, Ethylcyclohexane, Pentylbenzene, and Pentylcyclohexane at 298.15 K and 0.1 MPa

Density, Viscosity, Refractive Index, Isobaric Specific Heat Capacity, Ultrasonic Velocity, Molar Volume, Isentropic Compressibility, Isothermal Compressibility, and Heat Capacity Ratio for Binary Mixtures of the Organic Liquids Ethylbenzene, Ethylcyclohexane, Pentylbenzene, and Pentylcyclohexane at 298.15 K and 0.1 MPa

Effect of Silicon Fullerenes on Changes in the Heat Capacity of Nacl Electrolytes

The paper presents the results of an experimental study of the isobaric heat capacity of solutions of electrolytes of the water and NaCl system in the temperature range 288-373K. To measure the heat capacity of electrolytes, the method of monotonous heating was used (developed by Professor M.M.Safarov). The total relative error of measuring the heat capacity of this place with a confidence probability of 95% is on average equal to 3.8%. It is established that the specific isobaric heat capacity of electrolytes decreases with increasing temperature and concentration of sodium chlorine. The addition of fullerene leads to an increase in the heat capacity of solutions of the water and sodium chlorine system. On the basis of experimental data and the law of thermodynamic similarity, approximation dependences were obtained. Using the expressions obtained, it is possible to calculate the heat capacities of electrolytes at different temperatures and concentrations of fullerene nanoparticles.

A new empirical model and neural network-based approach for evaluation of isobaric heat capacity of natural gas

Isobaric heat capacity of natural gas is of prominent thermophysical property as it is directly related to thermodynamic energy functions, thereby its trustworthy prediction can open a new window for better establishment of the basis for its theoretical and engineering studies. In the present study, a new accurate and simple empirical correlation as a function of specific gravity (γg), temperature (T), and pressure (P) was developed to rapidly estimate the isobaric specific heat capacity (Cp) of natural gas without using gas composition. Due to the limitations of proposed experimental models and relations derived from gas compressibility factor (Z-factor) equations in the literature to a certain temperature, pressure and specific gravity range, an artificial neural network (ANN) based on back-propagation method was also applied for reliable prediction of Cp of natural gas. 847 sets of data from a diverse range of T, P, and γg were used to develop the neural network architecture and topology. Moreover, Genetic algorithm (GA) and Particle swarm (PS) optimization as population-based stochastic search algorithms were also utilized to optimize the weights and biases of networks to establish the best combination of input variables leading to the minimum Cp. The ANN demonstrated an accurate and promising prediction with a correlation coefficient of 0.99691 and 0.99518 for total dataset and test data, respectively.