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Articles you may be interested inUsing a two-capillary viscometer with preheating to measure the viscosity of dilute argon from 298.15 K to 653.15 K J.

A set of experimental measurements with a spinning rotor gauge (SRG) with 3.85, 4.00, and 4.50 mm nominal diameter steel spheres in He, Ar, and Kr is reported. The experiments covered the continuum and the slip regimes for all three gases. Theoretical results from a companion paper on the SRG, together with a calibration based on known viscosity for helium, are used to extract values of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation coefficient for each of the gases. The measured viscosities are in good agreement with existing literature values.

A selection of experimental measurements for He-Ar, He-N2, and He-Ne binary gas mixtures which were made with a spinning rotor gauge (SRG) are reported. All of the experiments were conducted in the slip regime. Theoretical results from a previous paper on the SRG are used to extract values of the viscosity and the velocity slip coefficient from the experimentally obtained data for each of the gas mixtures. The measured viscosities are in excellent agreement with existing literature values. Slip coefficients for binary gas mixtures have not previously been reported. An important issue here is whether the velocity slip coefficients for binary gas mixtures can be predicted accurately using separately measured tangential momentum accommodation coefficients. The calculation of slip coefficients from theory requires a knowledge of the accommodation coefficients of each constituent of the mixture. The dependence of these coefficients on the gas composition is not known and the simplest assumption is to regard them as being independent of the composition. The slip coefficients computed in conjunction with this work use this simple assumption in a theoretical expression for the slips. These computations led to reasonable agreement of the theoretical results with our data for the He-Ne mixture. Agreement in the cases of the He-Ar and He-N2 mixtures, however, was less than satisfactory.

[1] Carbon aerosol concentration was measured using an impactor on a 42 m tower over a wet tropical forest in northeast Costa Rica. Samples were collected at three different heights, 42, 21, and 2 m, for 2 months during the wet season in 1998. Winds originated from two directions, southeast from the Caribbean Sea and west from the continental isthmus. Concentrations were normalized by the fraction of dry sampling time during the collection. The distribution was negatively skewed for the range of aerodynamic diameter aerosols measured. The main size constituent was in the class 4.7-3.3 mm, accounting for $0.70 mg C mol À1 . No significant difference was found in the distribution of aerosol carbon with height, suggesting a well-mixed column of air, minimal resuspension, and that the source was from surrounding land use types. Functional relationships were developed to describe the loading of aerosols to the atmosphere and the removal by precipitation. Deposition was estimated using these relationships, combined with three different estimates of velocity deposition derived from (1) aerodynamic and canopy conductance, (2) aerodynamic and momentum conductance, and (3) traditional estimates of gravitational settling diffusion, impaction, and interception. Annual deposition estimates were 2.9, 5.0, and 9.6 kg ha À1 yr À1 , respectively. Concentrations of carbon aerosols reported here are as much as two orders of magnitude higher than those reported elsewhere. Annual dry deposition estimates, however, were within the range of other estimates but were likely underestimated. Potential effects on deposition caused by seasonal burns and El Niño-Southern Oscillation are discussed.