Reference Values and Reference Correlations for the Thermal Conductivity and Viscosity of Fluids.

In this paper, reference values and reference correlations for the thermal conductivity and viscosity of pure fluids are reviewed. Reference values and correlations for the thermal conductivity and the viscosity of pure fluids provide thoroughly evaluated data or functional forms and serve to help calibrate instruments, validate or extend models, and underpin some commercial transactions or designs, among other purposes. The criteria employed for the selection of thermal conductivity and viscosity reference values are also discussed; such values, which have the lowest uncertainties currently achievable, are typically adopted and promulgated by international bodies. Similar criteria are employed in the selection of reference correlations, which cover a wide range of conditions, and are often characterized by low uncertainties in their ranges of definition.

Correlations for the Viscosity and Thermal Conductivity of Ethyl Fluoride (R161).

This paper presents new wide-ranging correlations for the viscosity and thermal conductivity of ethyl fluoride (R161) based on critically evaluated experimental data. The correlations are designed to be used with a recently published equation of state that is valid from 130 K to 450 K, at pressures up to 100 MPa. The estimated uncertainty at a 95% confidence level is 2% for the viscosity of low-density gas (pressures below 0.5 MPa), and 3% for the viscosity of the liquid over the temperature range from 243 K to 363 K at pressures up to 30 MPa. The estimated uncertainty is 3% for the thermal conductivity of the low-density gas, and 3% for the liquid over the temperature range from 234 K to 374 K at pressures up to 20 MPa. Both correlations may be used over the full range of the equation of state, but the uncertainties will be larger, especially in the critical region.

Reference Correlation of the Thermal Conductivity of Cyclohexane from the Triple Point to 640 K and up to 175 MPa.

New, wide-range reference equations for the thermal conductivity of cyclohexane as a function of temperature and density are presented. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. We estimate the uncertainty (at the 95% confidence level) for the thermal conductivity of cyclohexane from the triple point (279.86 K) to 650 K at pressures up to 175 MPa to be 4% for the compressed liquid and supercritical phases. For the low-pressure gas phase (up to 0.1 MPa) over the temperature range 280 K to 680 K, the estimated uncertainty is 2.5%. Uncertainties in the critical region are much larger, since the thermal conductivity approaches infinity at the critical point and is very sensitive to small changes in density.

Reference Correlations of the Thermal Conductivity of Ethene and Propene.

New, wide-range reference equations for the thermal conductivity of ethene and propene as a function of temperature and density are presented. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. For ethene, we estimate the uncertainty (at the 95% confidence level) for the thermal conductivity from 110 K to 520 K at pressures up to 200 MPa to be 5% for the compressed liquid and supercritical phases. For the low-pressure gas phase (to 0.1 MPa) over the temperature range 270 K to 680 K, the estimated uncertainty is 4%. The correlation is valid from 110 K to 680 K and up to 200 MPa, but it behaves in a physically reasonable manner down to the triple point and may be used at pressures up to 300 MPa, although the uncertainty will be larger in regions where experimental data were unavailable. In the case of propene, data are much more limited. We estimate the uncertainty for the thermal conductivity of propene from 180 K to 625 K at pressures up to 50 MPa to be 5% for the gas, liquid, and supercritical phases. The correlation is valid from 180 K to 625 K and up to 50 MPa, but it behaves in a physically reasonable manner down to the triple point and may be used at pressures up to 100 MPa, although the uncertainty will be larger in regions where experimental data were unavailable. For both fluids, uncertainties in the critical region are much larger, since the thermal conductivity approaches infinity at the critical point and is very sensitive to small changes in density.

Reference Correlation of the Thermal Conductivity of Carbon Dioxide from the Triple Point to 1100 K and up to 200 MPa.

This paper contains new, representative reference equations for the thermal conductivity of carbon dioxide. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. In the case of the dilute-gas thermal conductivity, we incorporated recent theoretical calculations to extend the temperature range of the experimental data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 1100 K and pressures up to 200 MPa. The overall uncertainty (at the 95% confidence level) of the proposed correlation varies depending on the state point from a low of 1% at very low pressures below 0.1 MPa between 300 K and 700 K, to 5% at the higher pressures of the range of validity.

Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System.

A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.

Thermal Conductivity of Saturated Liquid Toluene by Use of Anodized Tantalum Hot Wires at High Temperatures.

Absolute measurements of the thermal conductivity of a distilled and dried sample of toluene near saturation are reported. The transient hot-wire technique with an anodized tantalum hot wire was used. The thermal conductivities were measured at temperatures from 300 K to 550 K at different applied power levels to assess the uncertainty with which it is possible to measure liquid thermal conductivity over wide temperature ranges with an anodized tantalum wire. The wire resistance versus temperature was monitored throughout the measurements to study the stability of the wire calibration. The relative expanded uncertainty of the resulting data at the level of 2 standard deviations (coverage factor k = 2) is 0.5 % up to 480 K and 1.5 % between 480 K and 550 K, and is limited by drift in the wire calibration at temperatures above 450 K. Significant thermal-radiation effects are observed at the highest temperatures. The radiation-corrected results agree well with data from transient hot-wire measurements with bare platinum hot wires as well as with data derived from thermal diffusivities obtained using light-scattering techniques.

Methanol inhalation: site and other factors influencing absorption, and an inhalation toxicokinetic model for the rat.

PURPOSE: This investigation was conducted to identify the site and characteristics of methanol absorption and to develop an inhalation model relating methanol absorption, blood concentration, and elimination. METHODS: Rats were exposed to methanol in chambers that allowed measurement of methanol uptake, ventilation, and blood concentrations; anesthetized rats with a tracheal cannula were examined to determine tracheal concentrations. In separate experiments, methanol exposed rats received an iv methanol bolus to examine the effect of blood methanol on ventilation and absorption; ventilation also was manipulated by CO(2) or pentobarbital to assess the effect of ventilation rate on methanol absorption. These data were combined to construct a semi-physiologic model of methanol uptake. RESULTS: Only 1-3 percent of inhaled methanol reached the trachea, primarily from systemic methanol partitioning into the trachea; blood methanol did not alter methanol absorption. Manipulation of ventilation and application of the pharmacokinetic model indicated that ventilation was less significant than environmental methanol concentration in determining the fraction of inhaled methanol absorbed, although both parameters were important determinants of the total mass absorbed. CONCLUSIONS: These data indicate that methanol uptake is a complex process that depends upon several parameters. Despite these complexities, a relatively simple semi-physiologic model was capable of describing methanol uptake over a wide range of exposure concentrations in the rat.

Comparative toxicokinetics of inhaled methanol in the female CD-1 mouse and Sprague-Dawley rat.

Female CD-1 mice were exposed for 8 hr, both individually and in groups of eight to nine, to 2500, 5000, and 10,000 ppm methanol vapor in a flowthrough exposure chamber. The ventilation of individually exposed mice and the absorption of methanol from the chamber airstream were measured. The extraction of methanol from the airstream and the blood methanol concentration at various time points during and following exposure were determined for the group-exposed mice. The similarity of systemic kinetic parameters (volume of distribution; Michaelis-Menten elimination parameters, Vmax and KM) between inhalation exposure and iv and po routes of administration was verified. Total 8-hr ventilation decreased slightly with increasing exposure concentration. The fraction of inhaled methanol absorbed (0.85 +/- 0.14) did not vary statistically with exposure concentration. Measured ventilation, fractional absorption, and systemic kinetic parameters were combined in a semiphysiologic pharmacokinetic model that yielded accurate predictions of blood methanol concentrations during and after an 8-hr exposure. Model predictions for the mouse were compared to a previously developed inhalation toxicokinetic model for the rat. The comparison demonstrated that at similar methanol vapor concentrations, mice evidenced a two- to threefold higher blood methanol concentration than rats, despite the fact that the apparent Vmax for methanol elimination in the mouse is twofold larger than that in the rat. These data may have significant implications in understanding species differences in methanol-induced teratogenic effects.

Comparative toxicokinetics of methanol in the female mouse and rat.

The toxicokinetics of methanol in female CD-1 mice and Sprague-Dawley rats were examined to explore the possibility of species differences in the disposition of the compound. Mice received a single dose of 2.5 g/kg methanol either po (by gavage) or i.v. (as a 1-min infusion). Rats received a single oral dose of 2.5 g/kg methanol. As expected, the disposition of methanol was nonlinear in both species. Data obtained after i.v. administration of methanol to mice were well described by a one-compartment model with Michaelis-Menten elimination. Blood methanol concentration--time data after oral administration could be described by a one-compartment (mice) or two-compartment (rats) model with Michaelis-Menten elimination from the central compartment and biphasic absorption from the gastrointestinal tract. Kinetic parameters (Vmax for elimination, apparent volume of the central compartment [Vc], first-order rate constants for intercompartmental transfer [k12 and k21], and first-order absorption rate constants for fast [kAF] and slow [kAS] absorption processes) were compared between species. When normalized for body weight, mice evidenced a higher maximal elimination rate than rats (Vmax = 117 +/- 3 mg/hr/kg vs 60.7 +/- 1.4 mg/hr/kg for rats). The contribution of the fast absorption process to overall methanol absorption also was larger in the mouse than in the rat.

A pharmacokinetic model of inhaled methanol in humans and comparison to methanol disposition in mice and rats.

We estimated kinetic parameters associated with methanol disposition in humans from data reported in the literature. Michaelis-Menten elimination parameters (Vmax = 115 mg/L/hr; Km = 460 mg/L) were selected for input into a semi-physiologic pharmacokinetic model. We used reported literature values for blood or urine methanol concentrations in humans and nonhuman primates after methanol inhalation as input to an inhalation disposition model that evaluated the absorption of methanol, expressed as the fraction of inhaled methanol concentration that was absorbed (phi). Values of phi for nonexercising subjects typically varied between 0.64 and 0.75; 0.80 was observed to be a reasonable upper boundary for fractional absorption. Absorption efficiency in exercising subjects was lower than that in resting individuals. Incorporation of the kinetic parameters and phi into a pharmacokinetic model of human exposure to methanol, compared to a similar analysis in rodents, indicated that following an 8-hr exposure to 5000 ppm of methanol vapor, blood methanol concentrations in the mouse would be 13- to 18-fold higher than in humans exposed to the same methanol vapor concentration; blood methanol concentrations in the rat under similar conditions would be 5-fold higher than in humans. These results demonstrate the importance in the risk assessment for methanol of basing extrapolations from rodents to humans on actual blood concentrations rather than on methanol vapor exposure concentrations.

Change in lip vermilion height during orthodontic treatment.

The extent that the height of the vertical aspect of the vermilion of the lips decreases during treatment may determine the ultimate esthetic results for a particular patient. Marked decrease in vertical height of the vermilion may prove to be esthetically pleasing for the patient with excessive vermilion; whereas it may prove esthetically disastrous for the patient exhibiting relatively small vermilion heights before treatment. Frontal esthetics should equal the profile in importance when treatment planning. The objectives of this study were (1) to quantify vermilion height changes when incisors are retracted, (2) to determine whether the pretreatment vertical position of the upper lip on the maxillary central incisor is associated with vermilion height changes, and (3) to relate vermilion height changes to incisor retraction. Cephalometric films from 40 adult female orthodontic patients (20 Class I and 20 Class II, Division 1) were measured with dial calipers. Significant decrease (paired t tests, P < 0.05) of the mean vermilion heights of both lips occurred during treatment in the patients with Class I relationships (upper 0.75 mm, lower 0.95 mm) and Class II, Division 1 relationships (upper 0.75 mm, lower 0.60 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids.

A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously used as electrical heat sources and as resistance thermometers. A microcomputer controls bridge nulling, applies the power pulse, monitors the bridge response, and stores the results. Performance of the instrument was verified with measurements on liquid toluene as well as argon and nitrogen gas. In particular, new data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented. These new data can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements. Thermal conductivity data for liquid toluene, which are corrected for radiation, are reported. The precision of the thermal conductivity data is ± 0.3% and the accuracy is about ±1%. The accuracy of the thermal diffusivity data is about ± 5%. From the measured thermal conductivity and thermal diffusivity, we can calculate the specific heat, Cp , of the fluid, provided that the density is measured, or available through an equation of state.

Relation Between Wire Resistance and Fluid Pressure in the Transient Hot-Wire Method.

The resistance of metals is a function of applied pressure, and this dependence is large enough to be significant in the calibration of transient hot-wire thermal conductivity instruments. We recommend that for the highest possible accuracy, the instrument's hot wires should be calibrated in situ. If this is not possible, we recommend that a value of γ, the relative resistance change with pressure, of -2×10-5 MPa-1 be used to account for the pressure dependence of the platinum wire's resistance.