Experimental study of speed of sound in gaseous refrigerant R-507a

The speed of sound in gaseous refrigerants R-134a and R-507a is measured by the method of ultrasonic interferometer in a temperature interval from 293 to 373 K and pressure values from 0.01 to 0.5–2.9 MPa. The errors in measurement of the temperature, pressure, and speed of sound are ±20 mK, ±4 kPa, and ±(0.1–0.2)%, respectively. On the basis of the data obtained, the temperature dependence of the idealgas heat capacity is calculated. The results obtained are compared with calculation of speed of sound from the fundamental state equation for Helmholtz free energy.     

Thermodynamic Properties of HFC-236ea

The density of gaseous and liquid 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) and the speed of sound in liquid HFC-236ea have been studied by a γ-attenuation technique, an ultrasonic interferometer, and an isochoric piezometer method over the temperature range of 263–423 K at pressures up to 4.05 MPa. The purity of the samples used throughout the measurements is 99.68 mol%. The pressures of the saturated vapor were measured over the same temperature range. The experimental uncertainties of the temperature, pressure, density, and speed-of-sound measurements were estimated to be within ±20 mK, ±1.5 kPa, ±(0.05–0.30)%, and ±(0.05–0.10)%, respectively.     

Gas-phasePVT properties of 1,1,1,2,3,3-Hexafluoropropane

We have measured the gas-phasePVT properties of 1,1,1,2,3,3,-hexafluoro-propane (R-236ea), which is considered to be a promising candidate for the replacement of 1,2-dichlorotetrafluoroethane (R-114). The measurements have been performed with a Burnett apparatus over a temperature range of 340 390 K and at pressures of 0.10–2.11 MPa. The experimental uncertainties of the measurements were estimated to be within ±0.5 kPa in pressure. ±8 mK in temperature, and ±0.15% in density. A truncated virial equation of state was developed to represent thePVT data and the second virial coefficients were also derived. The saturated vapor densities were also calculated by extrapolating the gas-phase isotherms to the vapor pressures. The critical density estimated from the rectilinear diameter was compared with the experimental value. The purity of the R-236ea sample used in the present measurements was 99.9 mol%. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Density and speed of sound of R-406A refrigerant in the vapor phase

The speed of sound and the density of the gaseous R-406A refrigerant within the temperature range 293–373 K and at the pressures from 0.05 MPa up to 0.6–2.3 MPa were investigated by means of an ultrasound interferometer and a constant volume piezometer. The measurement errors for the temperature, the pressure, and the speed of sound were ±20 mK, ±4 kPa, and ±(0.1–0.3)%, respectively. The approximation dependences of the investigated properties of the R-406A vapor are obtained and their errors are estimated. The obtained results are compared with the calculations using the REFPROP software.     

A Thermodynamic Equation of State for Pentafluoroethane (R-125)

We developed a fundamental equation of state for pentafluoroethane (R-125, CHF₂CF₃) which is represented in terms of a non-dimensional Helmholtz free energy. The equation has been established on the basis of selected measurements of the pressure-density-temperature relation, speed of sound, heat capacities, and saturation properties. Linear and non-linear regression analysis was employed to determine the functional form and the numerical parameters. The equation represents all the thermodynamic properties of R-125 in the liquid and gaseous phases for temperatures between the triple point and 470 K, and pressures up to 35 MPa. The uncertainties are estimated to be about ±0.05% or 0.1 kPa for the vapor pressure, ± 0.05 % for the liquid and vapor densities, about ± 1 % for the isobaric and isochoric heat capacities in the liquid, and ± 0.5 % or ± 0.02 % for the speed of sound in the liquid and vapor, respectively.     

Thermal conductivity, heat capacity, and compressibility of atactic poly(propylene) under high pressure

The thermal conductivity λ and the heat capacity per unit volume of atactic poly(propylene) have been measured in the temperature range 90–420 K at pressures up to 1.5 GPa using the transient hot-wire method. The bulk modulus has been measured in the range 200–295 K and up to 0.7 GPa. These data were used to calculate the volume dependence of λ,g=−[∂λ/λ)/(∂V/V)] _T , which yielded the following values for the glassy state (T<256 K at atmospheric pressure): 3.80±0.19 at 200 K, 3.74±0.19 at 225 K, 3.90±0.20 at 250 K, 3.77±0.19 at 271 K, and 3.73±0.19 at 297 K. The resultant value forg of the liquid state was 3.61±0.15 at 297 K. Values forg which are calculated at 295 K, using theoretical models of λ(T), agree to within 12% with the experimental value for the glassy state.     

Measurement of surface tension and specific heat of Ni-18.8 at.% Si alloy melt by containerless processing

The surface tension and specific heat of superheated and undercooled Ni-18.8 at.% Si alloy melt have been measured by the oscillating drop method and the drop calorimetry technique in combination with electromagnetic levitation, respectively. The surface tension follows a linear relationship with temperature within the range of 1370–2100 K. The surface tension at the melting temperature and the temperature coefficient are determined to be 1.796 N/m and −3.858 × 10⁻⁴ N/m/K, respectively. The specific heat is determined to be 40.80 ± 1.435 J/mol/K over the temperature range 1296–2000 K. The maximum undercooling of 178 K is achieved in the experiments. Based on the measured data of surface tension and specific heat, the viscosity, solute diffusion coefficient, density and thermal diffusivity of liquid Ni-18.8 at.% Si alloy are calculated.     

Electrochemical and mechanical behavior of laser processed Ti–6Al–4V surface in Ringer’s physiological solution

Laser surface modification of Ti–6Al–4V with an existing calcium phosphate coating has been conducted to enhance the surface properties. The electrochemical and mechanical behaviors of calcium phosphate deposited on a Ti–6Al–4V surface and remelted using a Nd:YAG laser at varying laser power densities (25–50 W/mm²) have been studied and the results are presented. The electrochemical properties of the modified surfaces in Ringer’s physiological solution were evaluated by employing both potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The potentiodynamic polarizations showed an increase in the passive current density of Ti–6Al–4V after laser modification at power densities up to 35 W/mm², after which it exhibited a decrease. A reduction in the passive current density (by more than an order) was observed with an increase in the laser power density from 25 to 50 W/mm². EIS studies at the open circuit potential (OCP) and in the passive region at 1.19 V showed that the polarization resistance increased from 8.274 × 10³ to 4.38 × 10⁵ Ω cm² with increasing laser power densities. However, the magnitudes remain lower than that of the untreated Ti–6Al–4V at OCP. The average hardness and modulus of the laser treated Ti–6Al–4V, evaluated by the nanoindentation method, were determined to be 5.4–6.5 GPa (with scatter <±0.976 GPa) and 124–155 GPa (with scatter <±13 GPa) respectively. The corresponding hardness and modulus of untreated Ti–6Al–4V were ~4.1 (±0.62) and ~148 (±7) GPa respectively. Laser processing at power densities >35 W/mm² enhanced the surface properties (as passive current density is reduced) so that the materials may be suitable for the biomedical applications.     

Correlation for the Carbon Dioxide and Water Mixture Based on The Lemmon–Jacobsen Mixture Model and the Peng–Robinson Equation of State

Models representing the thermodynamic behavior of the CO₂–H₂O mixture have been developed. The single-phase model is based upon the thermodynamic property mixture model proposed by Lemmon and Jacobsen. The model represents the single-phase vapor states over the temperature range of 323–1074 K, up to a pressure of 100 MPa over the entire composition range. The experimental data used to develop these formulations include pressure–density–temperature-composition, second virial coefficients, and excess enthalpy. A nonlinear regression algorithm was used to determine the various adjustable parameters of the model. The model can be used to compute density values of the mixture to within ±0.1%. Due to a lack of single-phase liquid data for the mixture, the Peng–Robinson equation of state (PREOS) was used to predict the vapor–liquid equilibrium (VLE) properties of the mixture. Comparisons of values computed from the Peng–Robinson VLE predictions using standard binary interaction parameters to experimental data are presented to verify the accuracy of this calculation. The VLE calculation is shown to be accurate to within ±3 K in temperature over a temperature range of 323–624 K up to 20 MPa. The accuracy from 20 to 100 MPa is ±3 K up to ±30 K in temperature, being worse for higher pressures. Bubble-point mole fractions can be determined within ±0.05 for CO₂.     

Determination of thermal properties of dilute LiBr-water solutions

We are developing an absorption air cooling system which can supply 2°C chilled water for air cooling by the usage of dilute solutions of LiBr in water with an evaporating temperature of −6°C as a nonfreezing refrigerant. However, there are few published data for the thermal properties of dilute LiBr water solutions (0 to 30%) below 10°C. In this paper, the freezing temperature and the saturated vapor pressure are reported. The results clearly show the possibility of developing a new type of LiBr absorption refrigerating machine to generate evaporating temperatures below 0°C. To obtain accurate data for the design of this new type of absorption refrigerating machine, an apparatus has been developed to measure the thermal properties of dilute LiBr water solutions below 10°C. The experimental arrangement consists of a cooling bath (340×240×190 mm) filled with fluorocarbon, a glass measuring bottle (ϕ120×100 mm), and an absolute pressure gauge (0–1.3 kPa). The accuracy of the temperature, pressure, and density are within ±0.1°C, 0.01 kPa, and ±0.005%, respectively. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Experimental study of thermal conductivity of the R-407C refrigerant in the vapor phase

Thermal conductivity of the gaseous R-407C refrigerant was investigated by the coaxial cylinders method within the temperature range of 303–425 K and the pressure range of 0.7–2.1 MPa. Approximating dependence of thermal conductivity on pressure and temperature was obtained. Thermal conductivity on dew line and in ideal gas state was calculated. The comparison is performed of the data obtained with those available in the literature.     

Thermodynamic properties of the R-415A refrigerant in the vapor phase and on the condensation line

The speed of sound in the R-415A refrigerant vapor and its density and pressure on the condensation line were measured by the ultrasonic interferometer and constant-volume piezometer methods within a range of temperatures from 293 to 373 K and pressures from 0.04 to 0.5–2.45 MPa. The temperature, pressure, density and speed of sound measurement errors were ±20 mK, ±4 kPa, and ±(0.1–0.2)%, respectively. The temperature dependence of the ideal-gas heat capacity was calculated on the basis of the obtained data. The obtained results were compared with the properties calculated by the REFPROP software.     

Construction of collagen II/hyaluronate/chondroitin-6-sulfate tri-copolymer scaffold for nucleus pulposus tissue engineering and preliminary analysis of its physico-chemical properties and biocompatibility

To construct a novel scaffold for nucleus pulposus (NP) tissue engineering, The porous type II collagen (CII)/hyaluronate (HyA)–chondroitin-6-sulfate (6-CS) scaffold was prepared using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS) cross-linking system. The physico-chemical properties and biocompatibility of CII/HyA–CS scaffolds were evaluated. The results suggested CII/HyA–CS scaffolds have a highly porous structure (porosity: 94.8 ± 1.5%), high water-binding capacity (79.2 ± 2.8%) and significantly improved mechanical stability by EDC/NHS crosslinking (denaturation temperature: 74.6 ± 1.8 and 58.1 ± 2.6°C, respectively, for the crosslinked scaffolds and the non-crosslinked; collagenase degradation rate: 39.5 ± 3.4 and 63.5 ± 2.0%, respectively, for the crosslinked scaffolds and the non-crosslinked). The CII/HyA–CS scaffolds also showed satisfactory cytocompatibility and histocompatibility as well as low immunogenicity. These results indicate CII/HyA–CS scaffolds may be an alternative material for NP tissue engineering due to the similarity of its composition and physico-chemical properties to those of the extracellular matrices (ECM) of native NP.     

Measurement of thermal conductivity of cis-1,1,1,4,4,4-hexafluoro-2-butene (R-1336mzz(Z)) by the transient hot-wire method

A Hydro-Fluoro-Olefin refrigerant cis-1,1,1,4,4,4-hexafluoro-2-butene (R-1336mzz(Z)) has low global warming potentials and it is considered as a potential working fluid for high temperature heat pump and Organic Rankine Cycle. Thermophysical properties of this fluid are necessary to be used in practical system. In this work, thermal conductivity of R-1336mzz(Z) is measured using a well-known transient hot wire method. A polarization voltage of 6 V was applied to minimize the effect of polarity. The thermal conductivity of liquid and gaseous R-1336mzz(Z) is measured in the temperature which ranges from 314 K to 435 K and 321 K to 496 K, respectively at a pressure up to 4 MPa and proposed simplified correlations. Total standard uncertainties of thermal conductivity measurements in liquid and gas phase were estimated to be less than ±2.07% and ±2.26% respectively and near the critical temperature, the uncertainty increases to ±3.40%.     

Isochoric Heat Capacities of Propane + Isobutane Mixtures at Temperatures from 280 to 420 K and at Pressures to 30 MPa

The isochoric heat capacity (c_v) and pressure–volume–temperature-composition (pvTx) properties were measured for propane + isobutane mixtures in the liquid phase and in the supercritical region. The expanded uncertainty (k = 2) of temperature measurements is estimated to be ±13 mK, and that of pressure measurements is ±8 kPa. The expanded relative uncertainty for c_v is ±3.2% for the liquid phase, increasing to ±4.8% for near-critical densities. The expanded uncertainty for density is estimated to be ±0.16%. The present measurements for {xC₃H₈ +(1−x)i-C₄H₁₀} with x = 0.0, 0.498, 0.756, and 1.0, were obtained at 659 state points at temperatures from 270 to 420 K and at pressures up to 30 MPa. The experimental data were compared with a published equation of state. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Bubble-Point Pressures and Saturated- and Compressed-Liquid Densities of the Binary R-125 + R-143a System

Bubble-point pressures and saturated- and compressed-liquid densities of the binary R-125 (pentafluoroethane) + R-143a (1,1,1 -trifluoroethane) system have been measured for several compositions at temperatures from 280 to 330 K by means of a magnetic densimeter coupled with a variable-volume cell mounted with a metallic bellows. The experimental uncertainties of the temperature, pressure, density, and composition were estimated to be within ±10mK, ± 12 kPa, ±0.2%, and ±0.2mass%, respectively. The purities of the samples used throughout the measurements are 99.96 area% for R-125 and 99.94 area% for R-143a. Based on these measurements, the thermodynamic behavior of the vapor-liquid equilibria of this binary refrigerant mixture has been represented using the Peng–Robinson equation for the bubble-point pressures, a correlation for the saturated-liquid densities, and an equation of state for the compressed-liquid densities.     

Measurements of Gaseous PVTx Properties and Saturated Vapor Densities of Refrigerant Mixture R-125+R-143a

The experimental PVTx properties of a binary refrigerant mixture, R-125 (pentafluoroethane)+R-143a (1,1,1-trifluoroethane), have been measured for a composition of 50 mass% R-125 by a constant-mass method coupled with an expansion procedure in a range of temperatures from 305 to 400 K, pressures from 1.5 to 6.1 MPa, and densities from 92 to 300 kg·m^–3. The experimental uncertainties of the present measurements are estimated to be within ±7.2 mK in temperature, ±3.0 kPa in pressure, ±0.12 kg·m^–3 in density, and ±0.040 mass% in composition. The sample purities are 99.953 mass% for R-125 and 99.998% for R-143a. Seven saturated vapor densities and dew point pressures of the R-125+R-143a system were determined, on the basis of rather detailed PVTx properties measured in the vicinity of the saturation boundary as well as the thermodynamic behavior of isochores near saturation. The second and third virial coefficients for temperatures from 330 to 400 K were also determined.     

Effect of pulsed DC current on atomic diffusion of Nb–C diffusion couple

The effect of pulsed DC current on the atomic diffusion of an Nb–C system using Spark Plasma Sintering (SPS) was investigated. In all experiments, a current density of approximately 723 A/cm² was applied to the specimen and used in a temperature range of 1,673–1,973 K. From the results of X-ray diffraction analysis, the product phases formed between Nb and C were found to be Nb₂C and NbC. The growth of product layers significantly increased in the presence of current. However, the thickness of the product layer did not change in the current direction in the SPS. The activation energies for the formation of the Nb₂C and NbC layers were calculated to be 298 ± 4 kJ/mol and 282 ± 3 kJ/mol in the presence of current, which were similar values compared to the activation energies of 300 ± 5 kJ/mol and 285 ± 2 kJ/mol in the absence of current, respectively.     

Thermodynamic principles of the synthesis of CdTe,ZnTe, and CdZnTe solid solutions

Results of thermodynamic investigations of the P-T-X phase equilibria in Cd-Te, Zn-Te and Cd-Zn-Te systems carried out by measuring total vapor pressure in the 1–760 Torr (0.13–101 kPa) range at temperatures up to ∼1370 K are systematized. Concentration boundaries of the existence of intermediate phases with the compositions CdTe_1±δ, ZnTe_1±δ, and Cd_{1 − x} Zn _x Te_1±δ (x = 0.05, 0.10, 0.15) are established. Vapor compositions in crystal-vapor equilibria are determined and isopleths of partial pressures for the CdTe_1±δ and Cd_{1 − x} ZnxTe_1±δ (x = 0.05, 0.10, 0.15) systems are calculated. Being presented in an analytical form, the thermodynamic data provide a basis for targeted synthesis of the indicated compounds.     

New Fundamental Equations of State with a Common Functional Form for 2,3,3,3-Tetrafluoropropene (R-1234yf) and <Emphasis Type="Italic">trans</Emphasis>-1,3,3,3-Tetrafluoropropene (R-1234ze(E))

New fundamental equations of state explicit in the Helmholtz energy with a common functional form are presented for 2,3,3,3-tetrafluoropropene (R-1234yf) and trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)). The independent variables of the equations of state are the temperature and density. The equations of state are based on reliable experimental data for the vapor pressure, density, heat capacities, and speed of sound. The equation for R-1234yf covers temperatures between 240 K and 400 K for pressures up to 40 MPa with uncertainties of 0.1 % in liquid density, 0.3 % in vapor density, 2 % in liquid heat capacities, 0.05 % in the vapor-phase speed of sound, and 0.1 % in vapor pressure. The equation for R-1234ze(E) is valid for temperatures from 240 K to 420 K and for pressures up to 15 MPa with uncertainties of 0.1 % in liquid density, 0.2 % in vapor density, 3 % in liquid heat capacities, 0.05 % in the vapor-phase speed of sound, and 0.1 % in vapor pressure. Both equations exhibit reasonable behavior in extrapolated regions outside the range of the experimental data.