Thermophysics

Photoacoustic spectroscopy (PAS) is widely used for diverse applications in different areas. These include studies in material, environmental, and life sciences. In the present work the study of pigments from pottery surfaces and volumes of Mexican (Aztec) and Poblana cultures that were developed in central Mexico from 1325 to 1521 and 1521 to 1800, respectively, is reported. The optical absorption spectra from each archeological sample was obtained using PAS. The superficial spectra were also compared with standard color pigments and archeological registers. Complementary energy dispersive spectroscopy (EDS) analysis of these archeological potteries gave us their elemental composition which agreed with other studies about their composition and technology of the pottery manufacturing.

Experimental densities at (293.15, 298.15, 303.15, 308.15, and 313.15) K and refractive indices at 298.15 K are reported for the binary liquid mixtures of ethanol with benzene and pyridine over the entire range of compositions and atmospheric pressure. From these experimental data, the excess molar volumes V E and deviations in molar refractivity Δ R were derived and fitted by the Redlich–Kister polynomial to determine the adjustable fitting parameters and the standard deviations. The number of adjustable parameters to be included in a Redlich–Kister polynomial for fitting the derived properties was optimized with the F -test. V E values are found to be negative over the entire composition range in ethanol + pyridine mixtures, without considerable changes over the temperature range studied. In the ethanol + benzene mixtures, the V E results show an S-shaped composition dependence, and the temperature contribution was found to be very important. The variation of V E with composition and temperature has been interpreted in terms of molecular interactions between the components of the mixture and structural effects. Δ R values are found to be negative for both mixtures with a minimum located between 0.45 and 0.5 volume fractions of ethanol. Furthermore, several theoretical and empirical mixing rules were applied to predict refractive indices of mixtures in order to test their validity for the present systems.

Molten salts are one of the few remaining classes of fluids for which standardquality (±1% accuracy) data on thermal conductivity have not hitherto been available. We have therefore developed a new apparatus based on the transient hot-wire technique to obtain reference-quality measurements of the thermal conductivity of molten salts at high temperatures. Liquid metal-filled quartz capillaries served as insulated hot wires in our method, and in addition, a two-wire technique was used in order to obtain absolute values of the thermal conductivity. New data for the NaNO3-KNO3 eutectic between 525 and 590 K are reported in this paper and comparisons with other recent measurements are shown.

We show how the successful empirical results of the past century for the compressibility of liquids can be obtained from a recent statistical-mechanical theory that includes dense fluids as well as low-density gases and vapors. The theory also shows to what extent the results for liquids can be extended to dense supercritical fluids and how they can be generalized to any number of dimensions. For simplicity only argon and a Lennard-Jones (12,6) fluid are examined in detail, but the results can probably be extended to real molecular fluids.

A group-contribution method has been developed to estimate the heat of sublimation (?Hsub) at the triple point for organic solids. The correlation was developed using ?Hsub values from a training set of 218 compounds, and it was tested by comparing predicted and solid vapor pressures for 87 compounds (1103 data points). The predicted solid vapor pressures were obtained from the

A vibrating-wire instrument for simultaneous measurement of the density and viscosity of liquids under conditions of high pressure is described. The instrument is capable of operation at temperatures between 298.15 and 473.15 K at pressures up to 200 MPa. Calibration was performed by means of measurements in vacuum, air, and toluene at 298.15 K. For n-dodecane measurements were made along eight

New, absolute values of the thermal conductivity of two refrigerants, R134a and R141b, in the liquid phase at saturation are reported. The measurements have been performed in transient hot-wire instruments making use of electrically insulated tantalum wires within ...

The construction, the calibration, and the use of the NIST Thermodynamic Radiation Thermometer (TRT) to measure the temperature of the gold freezing temperature blackbody and a variable-temperature blackbody from 800 to 2,700°C are described. These temperature determinations are detector-based and derived from the electrical substitution radiometer and length units. The TRT is constructed using a cooled, near-infrared enhanced silicon detector with a room-temperature-stabilized five-position filter wheel. The characteristics of the TRT, such as the size-of-source effect and preamplifier linearity, are determined. The measured temperatures are compared with those obtained using the NIST Absolute Pyrometer 1 (AP1) and the current NIST standard radiation thermometer, the Photoelectric Pyrometer (PEP). After the performance assessments, the TRT will become the standard radiation thermometer for disseminating radiance temperature scales in the United States.

The fugacity coefficients of hydrogen in binary mixtures with isobutane were measured using a physical equilibrium technique. This technique involves the use of an experimental chamber which is divided into two regions by a semipermeable membrane through which hydrogen, but not isobutane, can penetrate. Measurement of the gas pressures inside and outside the membrane allow a direct measurement of the hydrogen component fugacity at a given temperature, binary mixture mole fraction, and mixture pressure. In this paper, results are reported at 120, 140, 160, and 180°C. In each case, the total pressure of the mixture was maintained at an average value of 3.40 MPa. The general qualitative features of the data are discussed, and comparisions are made with predictions obtained from the Redlich-Kwong and the Peng-Robinson equations of state.