Transport properties of nonelectrolyte mixtures. IX. Viscosity coefficients for acetonitrile and for three mixtures of toluene+acetonitrile from 25 to 100°c at pressures up to 500 MPa

A two-coil self-centering falling-body viscometer has been used to measure viscosity coefficients for acetonitrile and three binary mixtures of toluene+ acetonitrile at 25, 50, 75, and 100°C and pressures up to 500 MPa. The results for acetonitrile can be interpreted by an approach based on hard-sphere theory, with a roughness factor of 1.46. The binary-mixture data are well represented by the Grunberg and Nissan equation with a mixing parameter which is pressure and temperature dependent but composition independent.     

Instrumentation, testing, and analysis of electric machine rotor steady-state heating

It is not a simple task to measure temperatures on the rotors or rotor components of large induction and synchronous machines during steady-state operation. The single greatest obstacle to obtaining these data is related to getting the data from the rotating element. Other problems are associated with instrumentation noise, sensor type, and attachment. This paper describes a number of techniques that have been used by the authors and their associates over the last 30 years. Test and calculated temperatures are presented for one machine. Also, test data from a number of machines are presented that show, for this particular population of enclosures and ventilation schemes, the steady-state temperatures at the design load can range from the value of the stator rise to greater than 70/spl deg/C higher.     

Conditioned suppression in a virtual environment

Virtual environments (VEs) provide an inexpensive way of conducting ecologically valid psychological research. The present study used a VE to demonstrate conditioned suppression, a behavioral model of anxiety, in a first-person perspective video game. During operant training, participants learned to shoot crates to find gold bars and thus score points in the game. Next, during Pavlovian conditioning, a colored light (i.e., conditioned stimulus: CS+) was followed by a white noise unconditioned stimulus (US) while a different colored light (CS−) was not paired with the US. Probe trials in a final testing phase were then used to assess suppression. We found significant suppression of accurate responding (shots hitting the designated targets) during the presence of the CS+ relative to the CS−, both in terms of total hits and hits as a proportion of total shots. Importantly, this effect emerged despite the overall level of operant responding being undiminished during the CS+. Our findings are consistent with related studies examining human behavior in real environments, and demonstrate the potential of VEs in combination with a modestly aversive CS to allow a detailed behavioral profile of anxiety to emerge.     

Correlation of high-pressure diffusion and viscosity coefficients for n-alkanes

Self-diffusion coefficient and viscosity coefficient data for liquid n-alkanes over the whole pressure range at different temperatures are satisfactorily correlated simultaneously by a method which is just an extension of that previously used to apply the smooth hard-sphere theory of transport properties to individual transport coefficients. Universal curves are developed for reduced quantities D ^* and ^* as a function of reduced volume. A consistent set of values is derived for the characteristic volume V ₀ and for parameters R _D and R , introduced to account for effects of nonspherical molecular shape and molecular roughness. On this basis, accurate calculation can be made of self-diffusion and viscosity coefficients for other members of the n-alkane series, for which data are at present limited.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Correlation and prediction of dense fluid transport coefficients. VII. Refrigerants

A recently developed scheme, based on considerations of hard-sphere theory, is used for the simultaneous correlation of the coefficients of viscosity and thermal conductivity for the refrigerants R11, R12, R22, R32. R124, R125, R134a, R141b, and R152a in excellent agreement with experiment, over extended temperature and pressure ranges. Values for the roughness factors and correlations for the characteristic volume are presented. The overall average absolute deviations of the experimental viscosity and thermal conductivity measurements from those calculated by the correlation are 2.1 and 2.3%, respectively, over a temperature range from 200 to about 10 K below the critical temperature and a pressure range from saturation to about 40 MPa. Since the proposed scheme is based on recent and accurate density values, a Tail-type equation was also employed to correlate successfully the density of the refrigerants. The overall average absolute deviation of the experimental density measurements from those calculated by the correlation is ±0.08%.Invited paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Measurements of the viscosity of toluene + mesitylene mixtures at pressures up to 55 MPa

New absolute measurements of the viscosity of mesitylene and binary mixtures of toluene + mesitylene are presented. The measurements were performed in a vibrating-wire instrument and cover a temperature range of 295–330 K and pressures up to 55 MPa. The concentrations studied were 40 and 70%, by weight, of toluene. The overall uncertainty in the reported data is estimated to be ±0.5%. A recently extended semiempirical scheme for the prediction of the viscosity of mixtures from the pure components is used to predict successfully the viscosity of these mixtures, as a function of composition, temperature, and pressure.     

Correlation and prediction of dense fluid transport coefficients. IV. A note on diffusion

Recent accurate calculations of the corrections to Enskog theory for hard-sphere diffusion have resulted in a revision of the hard-sphere based correlation for dense fluid transport coefficients. The expression previously given for. the reduced diffusion coefficient in terms of reduced volume is adjusted in line with these values. No changes are required to the characteristic volumes but the roughness factors are reduced. Of particular note is the fact that methane now corresponds to a rough hard-sphere system.     

Directional reflectance of vegetation measured by a calibrated digital camera

Obtaining directional reflectance information for vegetation canopies is often an expensive and time-consuming process. We present here a simple approach based on the use of an inexpensive digital camera equipped with a wide-angle lens. By the imaging of a large homogeneous area, a single image captures multiple views of a vegetation canopy. This gives a directional reflectance distribution fully sampled for view direction and free of variations in Sun elevation and azimuth. We determined the radiometric response of the camera sensor CCD's at the focal point and then extended this calibration to the full CCD array by using averaged images of clear blue sky. We evaluated the utility of the system by obtaining directional reflectance distributions of two vegetation targets, grass (Lolium spp) and pine forest (Pinus radiata), for red visible light. The precision of the derived biangular pattern of reflectance was +/-7%.     

Transport properties of nonelectrolyte liquid mixtures—VI. Viscosimetric study of binary mixtures of hexafluorobenzene with aromatic hydrocarbons

Viscosity coefficients for binary mixtures of hexafluorobenzene with benzene, toluene, para-xylene, and mesitylene have been measured along the saturation line at temperatures from 15 to 120°C using specially designed capillary viscometers. Densities were measured using a pyknometer and volume-change apparatus. Deviations of the viscosities from a rectilinear dependence on mole fraction are consistent with enhanced interactions between unlike species, which increase with increasing number of methyl groups on the aromatic hydrocarbon and decrease with increasing temperature. The application of the Grunberg and Nissan equation, the Hildebrand equation, and energy of activation theories to these results is examined.     

Locked-rotor and acceleration testing of large inductionmachines-methods, problems, and interpretation of the results

The measurement of locked-rotor current, torque, and power factor has been a standard test for induction machines for many years. Measurement of torque has evolved from using a brake, a dynamometer, a torque arm, and scale, through strain gauges and load cells to acceleration tests. The test must be of short duration to prevent damage to the machine and large machines present problems because of facility limitations in either kilovoltampere or torque measurement. A single test at reduced voltage when prorated to operating voltage by the square of the ratio of rated voltage to test voltage neglects the impact of saturation and results in significantly lower values of predicted torque and current. This paper discusses several methods for performing the locked-rotor and the speed-torque tests on large machines. It also discusses some of the problems associated with the test methods and shows how the tests can be performed and the results evaluated to account for saturation effects. Finally, the paper shows how to extract some machine circuit parameters from the test data