scholarly journals EQUATIONS OF AVERAGE ISOBARIC HEAT CAPACITY OF AIR AND COMBUSTION GASES WITH INFLUENCE OF PRESSURE AND EFFECT OF THERMAL DISSOCIATION

2019 ◽  
pp. 18-29
Author(s):  
Maya Vladimirovna Ambrozhevich ◽  
Mikhail Anatol'evich Shevchenko
Keyword(s):  
Heat Capacity ◽  
Thermophysical Properties ◽  
Thermal Dissociation ◽  
Heat Capacities ◽  
Isobaric Heat Capacity ◽  
Information Storage ◽  
Working Fluid ◽  
Saturation Curve ◽  
Functional Dependencies ◽  
Temperature And Pressure

All properties of thermomechanical systems working substance are two-parameter that is determined by two parameters, the most often they are temperature and pressure which are easily measured by experiment. Representing the isobaric heat capacity as a function of temperature cp = f(T) become a thing of the past. Analytical and tabular ways are used to represent dependencies as a function of temperature and pressure. The tabular method is convenient for single calculations, but the analytical one is more convenient for a series of calculations. The advantages of an analytical description in comparison with a tabular one are obvious, namely, compactness of information storage without reference to node points, the ability to integrate and differentiate, dependencies can be embedded directly in the program body and don’t require special subroutines to access to the tables. Developers of the programs for calculating thermophysical properties, as a rule, use functional dependencies which may have a different appearance for temperature and pressure intervals of the same substance. This is explained by the fact that in the region close to the saturation curve, there is a steep change in all the thermophysical properties of substances including the isobaric heat capacity. In thermogasdynamic calculations of heat machines, the main physical parameter of the working fluid is its heat capacity, both true and average. The article presents the analytical dependencies of the average specific isobaric heat capacities of the main components of air and combustion products of hydrocarbon fuels which are united throughout the specified range of pressures and temperatures (nitrogen: p = 1 ... 200 bar, T = 150 ... 2870 K, oxygen: p = 1 ... 200 bar, T = 210 ... 2870 K, argon: p = 1 ... 200 bar, T = 190 ... 1300 K, the water vapor: p = 0,1 ... 200 bar, T = 700 ... 2600 K, carbon dioxide: p = 1 ... 200 bar, T = 390 ... 2600 K). The analytical dependencies were derived on the basis of previously obtained analytical expressions for the specific isobaric heat capacities of these gases. The average specific isobaric heat capacities of gases are also functions of temperature and pressure cp = f(T, P) and take into account the effect of thermal dissociation. Formulas for average specific isobaric heat capacities are obtained by integrating expressions for specific isobaric heat capacities. Verification of the obtained dependencies for different temperature ranges was done.

scholarly journals АНАЛИТИЧЕСКОЕ ОПРЕДЕЛЕНИЕ ИСТИННОЙ УДЕЛЬНОЙ ИЗОБАРНОЙ ТЕПЛОЁМКОСТИ КОМПОНЕНТ ВОЗДУХА И ПРОДУКТОВ СГОРАНИЯ С УЧЁТОМ ВЛИЯНИЯ ТЕМПЕРАТУРЫ И ДАВЛЕНИЯ И ЭФФЕКТА ТЕРМИЧЕСКОЙ ДИССОЦИАЦИИ

2019 ◽  
pp. 4-17
Author(s):  
Майя Владимировна Амброжевич ◽  
Михаил Анатольевич Шевченко
Keyword(s):  
Heat Capacity ◽  
Gas Turbine ◽  
Pressure Ratio ◽  
Thermal Dissociation ◽  
Combustion Products ◽  
Heat Capacities ◽  
Isobaric Heat Capacity ◽  
Working Fluid ◽  
Gas Temperature ◽  
Temperature And Pressure

The basic thermophysical parameter of the working fluid of all thermal machines without exception is isobaric heat capacity (specific heat at constant pressure). Traditionally, in engineering calculations of isobaric heat capacity are determined as a tabular value for average heat capacities, or approximated with a square parabola within a given temperature range. Isobaric heat capacity is a function of temperature only. At the current level of GTE development, when the overall compressor pressure ratio is already up to 50 and the tendency of its increase remains it is unacceptable to neglect the pressure. However, the turbine inlet gas temperature also rises that will inevitably lead to the effect of thermal dissociation in the combustion products of the gas turbine engine. The studies of the thermal dissociation effect influence on the parameters of the working process of advanced GTE show that this ignoring leads to computational errors. At the present time, there are mathematical models that allow calculating the isobaric heat capacity as a function of temperature and pressure (taking into account the effect of thermal dissociation) but they are laborious, which is not always practical when estimate calculations performing and program algorithms writing. Consequently, the authors posed the problem of obtaining of simple analytic relationships that make it possible to calculate the isobaric heat capacity as a function of temperature and pressure (taking into account the effect of thermal dissociation). Based on the tabular data for the main components of the gas turbine combustion products within a given range of pressures and temperatures (nitrogen: p = 1 ... 200 bar, T = 150 ... 2870 K, oxygen: p = 1 ... 200 bar, T = 210 ... 2870 K, argon: p = 1 ... 200 bar, T = 190 ... 1300 K, the water vapor: p = 0.1 ... 200 bar, T = 640 ... 1250 K and p = 0.1 ... 400 bar and T = 1250 ... 3200 K, carbon dioxide: p = 1 ... 200 bar, T = 390 ... 2600 K), analytical dependencies were obtained for the calculation of isobaric heat capacities as functions of temperature and pressure taking into account the effect of thermal dissociation. The results of the calculations were compared with tabulated experimental data.

Thermophysical properties of liquid and supercooled ruthenium measured by noncontact methods

2004 ◽  
Vol 19 (2) ◽  
pp. 590-594 ◽  
Author(s):  
P-F. Paradis ◽  
T. Ishikawa ◽  
S. Yoda
Keyword(s):  
Surface Tension ◽  
Heat Capacity ◽  
Temperature Interval ◽  
Expansion Coefficient ◽  
Thermophysical Properties ◽  
Volume Expansion ◽  
Isobaric Heat Capacity ◽  
Electrostatic Levitation ◽  
Entropy Of Fusion ◽  
Volume Expansion Coefficient

Several thermophysical properties of liquid and supercooled ruthenium were measured using electrostatic levitation. Over the 2225–2775 K temperature interval, the density can be expressed as ρ(T) = 10.75 × 103 – 0.56(T – Tm)(kg ⋅ m−3) with Tm = 2607 K. In addition, the surface tension can be expressed as σ(T) = 2.26 × 103 – 0.24(T – Tm)(mN ⋅ m−1) and the viscosity as η(T) = 0.60 exp[4.98 × 104/(RT)] (mPa ⋅ s) over the 2450–2725 K range. The isobaric heat capacity was estimated as CP(T) = 35.9 + 1.1 × 10−3(T – Tm)[(J/(mol K)] over the 2200–2750 K span by assuming a constant emissivity. The volume expansion coefficient, the enthalpy, and the entropy of fusion were also calculated as 5.2 × 10−5 K−1, 29.2 kJ ⋅ mol−1, and 11.2 J/(mol K).

scholarly journals 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

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5525
Author(s):  
Yuya Kano
Keyword(s):  
Heat Capacity ◽  
Dielectric Permittivity ◽  
Sound Velocity ◽  
Vapor Phase ◽  
Thermophysical Properties ◽  
Resonance Method ◽  
Ideal Gas ◽  
Working Fluid ◽  
Microwave Resonance ◽  
The Ideal

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.

scholarly journals Structural Transition in Supercritical Fluids

2011 ◽  
Vol 2011 ◽  
pp. 1-5 ◽  
Author(s):  
Boris I. Sedunov
Keyword(s):  
Supercritical Fluids ◽  
Thermophysical Properties ◽  
Structural Transition ◽  
Heat Capacities ◽  
Saturation Curve ◽  
Physical Sense ◽  
Supercritical Region

The extension of the saturation curve on the PT diagram in the supercritical region for a number of monocomponent supercritical fluids by peak values for different thermophysical properties, such as heat capacities and and compressibility has been studied. These peaks signal about some sort of fluid structural transition in the supercritical region. Different methods give similar but progressively diverging curves for this transition. The zone of temperatures and pressures near these curves can be named as the zone of the fluid structural transition. The outstanding properties of supercritical fluids in this zone help to understand the physical sense of the fluid structural transition.

Experimental Study on the Specific Heat Capacity Measurement of Water-Based Al2O3-Cu Hybrid Nanofluid by using Differential Thermal Analysis Method

2019 ◽  
Vol 15 ◽  
Author(s):  
Andaç Batur Çolak ◽  
Oğuzhan Yıldız ◽  
Mustafa Bayrak ◽  
Ali Celen ◽  
Ahmet Selim Dalkılıç ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Thermophysical Properties ◽  
Volume Concentration ◽  
Pure Water ◽  
Heat Capacity Measurement ◽  
Experimental Results ◽  
Hybrid Nanofluid ◽  
Capacity Measurement

Background: Researchers working in the field of nanofluid have done many studies on the thermophysical properties of nanofluids. Among these studies, the number of studies on specific heat are rather limited. In the study of the heat transfer performance of nanofluids, it is necessary to increase the number of specific heat studies, whose subject is one of the important thermophysical properties. Objective: The authors aimed to measure the specific heat values of Al2O3/water, Cu/water nanofluids and Al2O3-Cu/water hybrid nanofluids using the DTA method, and compare the results with those frequently used in the literature. In addition, this study focuses on the effect of temperature and volume concentration on specific heat. Method: The two-step method was used in the preparation of nanofluids. The pure water selected as the base fluid was mixed with the Al2O3 and Cu nanoparticles and Arabic Gum as the surfactant, firstly mixed in the magnetic stirrer for half an hour. It was then homogenized for 6 hours in the ultrasonic homogenizer. Results: After the experiments, the specific heat of nanofluids and hybrid nanofluid were compared and the temperature and volume concentration of specific heat were investigated. Then, the experimental results obtained for all three fluids were compared with the two frequently used correlations in the literature. Conclusion: Specific heat capacity increased with increasing temperature, and decreased with increasing volume concentration for three tested nanofluids. Cu/water has the lowest specific heat capacity among all tested fluids. Experimental specific heat capacity measurement results are compared by using the models developed by Pak and Cho and Xuan and Roetzel. According to experimental results, these correlations can predict experimental results within the range of ±1%.

Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

1988 ◽  
Vol 53 (12) ◽  
pp. 3072-3079
Author(s):  
Mojmír Skokánek ◽  
Ivo Sláma
Keyword(s):  
Heat Capacity ◽  
Phase Transformation ◽  
Phase Transformations ◽  
Dimethyl Sulfoxide ◽  
Liquidus Temperature ◽  
Molar Heat Capacity ◽  
Solid Phase ◽  
Zinc Nitrate ◽  
Heat Capacities ◽  
Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

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