Rotating Cylinder Apparatus for Rarefied Gas Flow Studies

A rotating cylinder type apparatus is described, suitable for determining drag in cylindrical Couette flow of rarefied gases, and for evaluating tangential momentum accommodation coefficients at gas-solid boundaries. The apparatus is equipped with a damping device using diffusion pump oil for eliminating undesirable oscillations in the system. Tangential momentum accommodation coefficients of argon on aluminum were determined with an accuracy of ± 2.5%. The results obtained indicate that the apparatus may be used over a wide pressure range, corresponding to free molecule and continuum flow conditions

A Comparison of Interpolation Methods for Sparse Data: Application to Wind and Concentration Fields

In order to produce gridded fields of pollutant concentration data and surface wind data for use in an air quality model, a number of techniques for interpolating sparse data values are compared. The techniques are compared using three data sets. One is an idealized concentration distribution to which the exact solution is known, the second is a potential flow field, while the third consists of surface ozone concentrations measured in the Los Angeles Basin on a particular day. The results of the study indicate that fitting a second-degree polynomial to each subregion (triangle) in the plane with each data point weighted according to its distance from the subregion provides a good compromise between accuracy and computational cost

Measured Spectra of the Hygroscopic Fraction of Atmospheric Aerosol Particles

The relation between dry diameter (X0) and critical supersaturation (Sc) for atmospheric submicron aerosol particles is investigated using a long term air sampling program at Rolla, Missouri. The particles are passed through an electrostatic aerosol size classifier, and then through an isothermal haze chamber. Results are reported in terms of an apparent volume fraction of soluble material, εv defined such that for particles composed only of ammonium sulfate and water insoluble compounds, εv is the actual volume fraction of soluble material. The probability distribution of εv is found to be approximately Gaussian in the εv range 0.2 to 1.3. The mean εv is 0.5, for electrostatic aerosol classifier settings of 0.2, 0.3, and 0.4 μm diameter

Intercomparison between Commercial Condensation Nucleus Counters and an Alternating Temperature Gradient Cloud Chamber

Three Commercial CNC Counters (TSI Models 3010, 3022A, and 3025A) Are Compared with an Alternating Temperature Gradient Cloud Chamber (ALGR). Electrically Size Classified Aerosols of Sodium Chloride and Silver Are Used. Diffusional Losses within the ALGR Are Much Larger Than for the TSI Instruments: Therefore the ALGR Concentrations Are Corrected for Internal Diffusional Losses, But the TSI Instruments Are Not. the Particle Size Range Tested is 4–90 Nm. for Sodium Chloride, the TSI Concentrations Agreed Fairly Well with the Corrected ALGR at Larger Sizes, and Were Below the Corrected ALGR at Smaller Sizes. the Electrical Aerosol Classifier (EAC) Setting at Which a Particular TSI Instrument Concentration is 50% of the Corrected ALGR Concentration is Denoted D 50%. for the 3010 and 3022A, the Values of D 50% Are 14.5 and 7.9 Nm, Respectively. for the 3025A the Extrapolated D 50% is 3.5 Nm. These D 50% Values Are Close to Those Reported for Comparisons between Concentrations Measured by the TSI Instruments and Concentrations Determined with an Aerosol Electrometer. However, the Count Ratio Rises to Unity Less Quickly as Size Increases for the Present Intercomparisons as Compared with Intercomparisons with Aerosol Electrometers. the ALGR Can Produce at Most a 30% Water Super-Saturation, Corresponding to a Kelvin Diameter of 8.4 Nm. Thus, Since Silver Particles Are Water Insoluble, the ALGR Detected Small Silver Particles Less Efficiently Than the TSI Model 3025A. the Data with Silver Aerosols Allowed Determination of the Relation between Size and Critical Supersaturation over the Size Range 16–30 Nm Diameter. the Silver Aerosol Exhibited Critical Supersaturations Higher, by a Factor of 1.2 to 1.8, Than Those Given by the Kelvin Equation. © 1995 American Association for Aerosol Research Published by Elsevier Science Inc

Condensation Coefficient Measurement for Water in the UMR Cloud Simulation Chamber

A systematic series of condensation coefficient measurements of water have been made using the University of Missouri-Rolla cooled-wall expansion chamber which simulates the thermodynamics of cloud. This coefficient is seen to decrease from a value near unity, at the outset of simulation, to a value in the neighborhood of 0.01 toward the end of a simulation. Final values of this coefficient are sufficiently low as to contribute significantly to the broadening of the drop-size distribution in cloud

Measurement of the Condensation Coefficient of Water in the UMR Cloud Simulation Chamber

Measurements of the condensation coefficient of water under conditions closely approximating those in natural atmospheric cloud have been made in the cooled-wall UMR cloud simulation chamber. Current measurements disclose a value of condensation coefficient near unity at the outset of the experiment, generally decreasing to lower values (~ .01) as the experiment progresses. The significance of the magnitude of condensation coefficient in atmospheric cloud is briefly discussed

Determining the Chemical Composition of Cloud Condensation Nuclei: Second Progress Report

published or submitted for publicationis peer reviewedOpe

Measurement of the Condensation Coefficient of Water in the UMR Simulation Chamber

The UMR Cloud Simulation Facility is described. The facility is designed to provide a controlled environment simulating the conditions of natural atmospheric processes. It consists of two cooled-wall expansion cloud chambers and peripheral instrumentation for generation and characterization of aerosols used for cloud formation studies. Results of initial studies of the growth of warm cloud droplets and inferred measurements of the condensation coefficient are described

Determining the Chemical Composition of Cloud Condensation Nuclei

published or submitted for publicationis peer reviewedOpe

Determining the Chemical Compostition of Cloud Condensation Nuclei: Third Progress Report

published or submitted for publicationis peer reviewedOpe