Isochoric Specific Heat Capacity Research Articles

Measurement of Isochoric Specific Heat Capacity for Pure Alcohol with Adiabatic Twin-Cell Calorimeter

Specific heat capacity at constant volume (cv) is one of the most important thermodynamic properties to develop and evaluate reliable equation of state. With this point of view, isochoric heat capacities of methanol and ethanol have been measured with a twin-cell type adiabatic calorimeter, which was modified to measure data more precisely. Temperatures were measured with a platinum resistance thermometer on the bottom of each cell and were reported on the ITS-90. Sample pressure measurements were made with a crystal quartz transducer. Densities were calculated from the volume of the calorimeter cell and sample mass. The experimental expanded uncertainty (with a coverage factor k = 2) of temperature measurements is ±13 mK, and that of pressure measurement is ±8kPa. The expanded relative uncertainty for isochoric heat capacity is estimated to be less than ±2% for liquid phase measurements, and for density it is about ±0.16%. This study obtained 91 points for methanol and 116 points for ethanol at the temperature range from 270 to 420 K and at presures up to 30 Mpa.

An equation of state for 1,1,1-trifluoroethane (R-143a)

A fundamental equation of state has been developed for 1,1,1-trifluoroethane (R-143a) using the dimensionless Helmholtz energy. The experimental thermodynamic property data, which cover temperatures from the triple point (161 K) to 433 K and pressures up to 35 MPa, are used to develop the present equation. These data are represented by the present equation within their reported experimental uncertainties: ±0.1% in density for both vapor and liquid phase P–ρ–T data, ±1% in isochoric specific heat capacities, and ±0.02% in the vapor phase speed-of-sound data. The extended range of validity of the present model covers temperatures from 160 to 650 K and pressures up to 50 MPa as verified by the thermodynamic behavior of the isobaric heat-capacity values over the entire fluid phase.

Vapor-liquid equilibria, scaling, and crossover in aqueous solutions of sodium chloride near the critical line

We have developed a crossover scaling model for describing the thermodynamic properties of near-critical binary fluids. We have validated this model for the vapor-liquid equilibrium properties of mixtures of methane and ethane. We then apply the model to a most intriguing binary fluid, namely aqueous solutions of sodium chloride, so as to describe densities and concentrations at vapor-liquid equilibrium and isochoric specific heat capacities in the one-phase region. The description shows crossover from asymptotic Ising-like critical behavior to classical (mean-field) behavior. As the salt concentration increases, the region of Ising behavior decreases, although pure classical behavior is never attained. We suggest that processes of association/dissociation may be responsible for the failure of the model to describe compositions of the vapor phase of the solutions at very low concentrations.

Equation of state, isobaric specific heat, and thermal expansion of solids with polyatomic basis in the Einstein‐Debye approximation

AbstractA theoretical study of the thermodynamic properties in the Einstein‐Debye approximation is made for solids with polyatomic basis. Analytical expressions are derived for the equation of state, isobaric specific heat (Cp), and linear thermal expansion coefficient (αP). The temperature dependences of Cp and αp are determined by four characteristic parameters of the solid: the Debye temperature θD, the Einstein temperature θE, and the Grüneisen parameters γ and γ associated with the volume dependences of θD and θE, respectively. It is shown that the difference CP−CV between the calculated isobaric and isochoric specific heat capacities is very small at low temperatures (T ≪ θD) and increases markedly at higher temperatures. In the high‐temperature range (T ≫ θE), CP is almost independent of temperature and is determined by a simple combination of the Grüneisen parameters γ and γ. The results obtained for αP, in the low‐ and high‐temperature limits, are in accord with those found for the asymptotic behavior of CV with temperature.

Isobaric Specific Heat and Thermal Expansion of Solids in the Debye Approximation

AbstractA theoretical study in the Debye approximation is made of the isobaric specific heat (CP) and thermal expansion of solids with a Bravais lattice. Analytical expressions are obtained for the variations of CP and the linear thermal expansion coefficient (xp) with temperature. The temperature dependence of CP is determined by two characteristic parameters of the solid: the Debye temperature θand the Gruneisen parameter yc. It is shown that the difference CPCv between the calculated isobaric and isochoric specific heat capacities is very small at low temperatures (T≪θ) and increases markedly at higher temperatures. In the range T≫θ, CP is almost independent of temperature and is.determined solely by γG. This provides a technique to estimate the Gruneisen parameter γG from the measurements of isobaric specific heat at high temperatures. The results obtained for αP, in the low‐ and high‐temperature limits, are in agreement with those in literature.

N-hexane as a model for compressed simple liquids

Isobaric thermal expansivities, αp, ofn-hexane have been measured by pressure-controlled scanning calorimetry from just above the saturation vapor pressure to 40 MPa at temperatures from 303 to 453 K and to 300 MPa at 503 K. These new data are combined with literature data to obtain a correlation equation for αp valid from 240 to 503 K at pressures up to 700 MPa. Correlation equations are developed for the saturated vapor pressure, specific volume, and isobaric heat capacity of liquid n-hexane from 240 to 503 K. Calculated volumes, isobaric and isochoric specific heat capacities. isothermal compressibilities, and thermal coefficients of pressure are presented for the entire range of pressure and temperature. The pressure-temperature behavior of these quantities is discussed as a model behavior for simple liquids without strong intermolecular interactions.

Special Equations of State for Methane, Argon, and Nitrogen for the Temperature Range from 270 to 350 K at Pressures up to 30 MPa

In order to describe the thermodynamic behavior of methane, argon, and nitrogen in the so-called “natural-gas region,” namely, from 270 to 350 K at pressures up to 30 MPa as accurate as possible with equations of a very simple form, new equations of state for these three substances have been developed. These equations are in the form of a fundamental equation in the dimensionless Helmholtz energy; for calculating the pressure or the density, the corresponding equations explicit in pressure are also given. The residual parts of the Helmholtz function representing the behavior of the real gas contain 12 fitted coefficients for methane, 8 for argon, and 7 for nitrogen. The thermodynamic relations between the Helmholtz energy and the most important thermodynamic properties and the needed derivatives of the equations are explicitly given; to assist the user there is also a table with values for computer-program verification. The uncertainties when calculating the density ρ, the speed of sound w, the isobaric specific heat capacity cp, and the isochoric specific heat capacity cv are estimated as follows. For all three substances it is Δρ/ρ≤±0.02 % for p≤ 12 MPa and Δρ/ρ ≤ ±0.05% for higher pressures. For methane it is Δw/w≤±0.02% for p≤10 MPa and Δw/w≤+-0.1% for higher pressures; for argon it is Δw/w≲-0.1 % for p≤ 7 MPa, Δw/w≤±0.3 % for 7 <p≤30 MPa; and for nitrogen it is Δw/w≤±0.1% for p≤1.5 MPa and Δw/w±0.5% for higher pressures. For all three substances it is Δcp/cp≤±1 % and ΔCv/Cv≤±1 % in the entire range.

Equation of state and thermodynamic properties of propan-1-ol

A new equation of state for propan-1-ol has been developed on the basis of experimental studies of the isochoric specific heat capacity, conducted at specific volumes from 1.286 cm3·g−1 to 14.857 cm3·g−1 and temperatures between Ts(ρ) and 1.3·Ts(ρ). Here, Ts(ρ) is the temperature at the coexistence curve. By this equation, we can calculate properties in the ranges: specific volume, from 1.2 cm3·g−1 to 15 cm3·g−1; temperature, from Ts(ρ) to 660 K. This interval of the quantities of state includes the critical region and phase equilibrium.

Thermodynamic State Surface and Cycle Analysis for Refrigerant 114

An equation of state for Refrigerant 114 (CCIF2 CCIF2) was formulated based on available PVT measurements, taking the thermodynamic consistency into consideration. The developed equation of state is expressed by the reduced Helmholtz function as a function of reduced temperature and reduced density. Derived isochoric specific heat capacity, isobaric specific heat capacity, speed of sound and vapor pressure were critically examined. The developed equation is effective for a range of temperatures 200 to 550 K and of pressures up to 20 MPa, which corresponds to the density range up to 1 750 kg/m3. With the aid of the proposed equation, the cycle analysis for the heat pump, refrigeration and Rankine cycle was carried out, and it became clear that Refrigerant 114 is a suitable working fluid especially for high-temperature heat pump systems.

Thermodynamic state surface and cycle analysis for Refrigerant 22.

In order to examine thermophysical properties and cycle analysis for a nonazeotropic mixture of Refrigerant 22 (CHCIF2) +Refrigerant 114 (CCIF2CCIF2), and equation of state for Refrigerant 22 was formulated based on the available PVT measurements taking the thermodynamic consistency into consideration . The developed equation of state, whose functional form is the same as that for Refrigerant 114 reported previously, is expressed by the reduce Helmholtz function as a function of temperature and density. The derived properties of isochoric specific heat capacity, isobaric specific heat capacity, speed of sound and vapor pressure were critically examined. The developed equation is effective for a range of temperatures from 200 to 550 K, and of pressures up to 20 MPa, which corresponds to the density range up to 1500 kg/m3. With the aid of the proposed equation, the cycle analysis on the heat pump and refrigeration systems was theoretically carried out and it became clear that Refrigerant 22 is more suitable for low temperature heat pump systems than Refrigerant 114.

Thermodynamic state surface and cycle analysis for Refrigerant 114.

An equation of state for Refrigerant 114 (CClF2 CClF2) has been formulated based on available PVT measurements taking the thermodynamic consistency into consideration. The developed equation of state is expressed by the reduced Helmholtz function as a function of temperature and density. Derived isochoric specific heat capacity, isobaric specific heat capacity, speed of sound and vapor pressure have been critically examined. The devoloped equation is effective for a range of temperature 200 to 550 K and of pressures up to 20 MPa which corresponds to the density range up to 1750 kg/m3. With the aid of the proposed equation, the cycle analysis of the heat pump, refrigeration and Rankine cycle has been carried out and it becomes clear that R 114 is a suitable working fluid especially for high temperature heat pump systems.

Measurements of the isochoric specific heat capacity near the critical point and in the metastable region of CO 2 by a heat flow calorimeter : By J. Straub, Institute for Thermodynamics A, Technical University of Munich, 8 Munich 2, West Germany

Measurements of the isochoric specific heat capacity near the critical point and in the metastable region of CO 2 by a heat flow calorimeter : By J. Straub, Institute for Thermodynamics A, Technical University of Munich, 8 Munich 2, West Germany