Question

Explain how Fick

Answer 1

1

Portable vapor diffusion coefficient meter  

Science.gov (United States)

An apparatus for measuring the effective vapor diffusioncoefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vaporthat has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transientdiffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

Ho, Clifford K. (Albuquerque, NM)

2007-06-12

2

Review of enhanced vapor diffusion in porous media  

Energy Technology Data Exchange (ETDEWEB)

Vapor diffusion in porous media in the presence of its own liquid has often been treated similar to gas diffusion. The gas diffusion rate in porous media is much lower than in free space due to the presence of the porous medium and any liquid present. However, enhanced vapor diffusion has also been postulated such that the diffusion rate may approach free-space values. Existing data and models for enhanced vapor diffusion, including those in TOUGH2, are reviewed in this paper.

Webb, S.W.; Ho, C.K.

1998-08-01

3

Review of enhanced vapor diffusion in porous media  

International Nuclear Information System (INIS)

Vapor diffusion in porous media in the presence of its own liquid has often been treated similar to gas diffusion. The gas diffusion rate in porous media is much lower than in free space due to the presence of the porous medium and any liquid present. However, enhanced vapor diffusion has also been postulated such that the diffusion rate may approach free-space values. Existing data and models for enhanced vapor diffusion, including those in TOUGH2, are reviewed in this paper

4

Water vapor permeabilities through polymers: diffusivities from experiments and simulations  

Science.gov (United States)

This study experimentally determines water vaporpermeabilities, which are subsequently correlated with thediffusivities obtained from simulations. Molecular dynamics (MD) simulations were used for determining the diffusionof water vapor in various polymeric systems such as polyethylene, polypropylene, poly (vinyl alcohol), poly (vinyl acetate), poly (vinyl butyral), poly (vinylidene chloride), poly (vinyl chloride) and poly (methyl methacrylate). Cavity ring down spectroscopy (CRDS) based methodology has been used to determine the water vapor transmission rates. These values were then used to calculate the diffusioncoefficients for water vapor through these polymers. A comparative analysis is provided for diffusivities calculated from CRDS and MD based results by correlating the free volumes.

Seethamraju, Sindhu; Chandrashekarapura Ramamurthy, Praveen; Madras, Giridhar

2014-09-01

5

Anomalous photon diffusion in atomicvapors  

CERN Document Server

The multiple scattering of photons in a hot, resonant, atomic vapor is investigated and shown to exhibit a L\\'evy Flight-like behavior. Monte Carlo simulations give insights into the frequency redistribution process that originates the long steps characteristic of this class of random walk phenomena.

Chevrollier, Martine; Guerin, William; Kaiser, Robin

2010-01-01

6

The Commercial Vapor DiffusionApparatus (CVDA) STS-95  

Science.gov (United States)

The Commercial Vapor Diffusion Apparatus will be used to perform 128 individual crystal growth investigations for commercial and science research. These experiments will grow crystals of several different proteins, including HIV-1 Protease Inhibitor, Glycogen Phosphorylase A, and NAD Synthetase. The Commercial Vapor Diffusion Apparatus supports multiple commercial investigations within a controlled environment. The goal of the Commercial Protein Crystal Growth payload on STS-95 is to grow large, high-quality crystals of several different proteins of interest to industry, and to continue to refine the technology and procedures used in microgravity for this important commercial research.

2004-01-01

7

Investigation of diffusion and biodegradation of vapor phase petroleum hydrocarbons  

International Nuclear Information System (INIS)

Petroleum released to the subsurface may be held in capillary tension above the water table for years, serving as a source of groundwater and soil gas contamination. Soil venting can be used to attack this ongoing source, sometimes in conjunction with biodegradation to permanently destroy the released hydrocarbons vapors. These processes were explored using intact soil cores from the site of an aviation gasoline release. Hydrocarbonvapor concentration profiles were analyzed by gas chromatography and interpreted using mathematical models. In the venting experiment, an intact core was subjected to a horizontal sweep flow of nitrogen. Residual petroleum in the soil volatilized and hydrocarbon vaporsdiffused upward. Soil venting significantly increased the rate of contaminant removal relative to ambient field conditions. No correlation between hydrocarbon vapor exit flux and sweep flow rate was observed, indicating that flow rates in excess of a minimum value were no more effective. A steady state model balancing volatilization and diffusionsuccessfully predicted the shape of the hydrocarbon concentration profiles. The volatilization source was construed as an LNAPL droplet surrounded by an air water aggregate surrounded by a free air pore, with the aggregate reducing the mass transfer of hydrocarbons from LNAPL to air. Source strength, estimated from adiffusive flux model, decreased with time as LNAPL droplets became smaller. The biodegradation experiment employed an The biodegradation experiment employed an intact core from mid-depth in the unsaturated zone which was subjected to a upward flow of nitrogen, oxygen, watervapor, and hydrocarbon vapors. Significant biodegradation was indicated by reductions in hydrocarbon concentration with elevation in the core. First order biodegradation rate constants were estimated by calibrating the experimental data to a simple model balancing advection and biodegradation

8

A review of porous media enhancedvapor-phase diffusion mechanisms, models, and data: Does enhanced vapor-phase diffusion exist?  

Energy Technology Data Exchange (ETDEWEB)

A review of mechanisms, models, and data relevant to the postulated phenomenon of enhanced vapor-phasediffusion in porous media is presented. Information is obtained from literature spanning two different disciplines (soil science and engineering) to gain a diverse perspective on this topic. Findings indicate that while enhanced vapor diffusion tends to correct the discrepancies observed between past theory and experiments, no direct evidence exists to support the postulated processes causing enhanced vapor diffusion. Numerical modeling analyses of experiments representative of the two disciplines are presented in this paper to assess the sensitivity of different systems to enhanced vapor diffusion. Pore-scale modeling is also performed to evaluate the relative significance of enhancedvapor diffusion mechanisms when compared to Fickiandiffusion. The results demonstrate the need for additional experiments so that more discerning analyses can be performed.

Ho, C.K.; Webb, S.W.

1996-05-01

9

Development of Nb3Sn Cavity VaporDiffusion Deposition System  

International Nuclear Information System (INIS)

Nb3Sn is a BCS superconductors with the superconducting critical temperature higher than that of niobium, so theoretically it surpasses the limitations of niobium in RF fields. The feasibility of technology has been demonstrated at 1.5 GHz with Nb3Sn vapor deposition technique at Wuppertal University. The benefit at these frequencies is more pronounced at 4.2 K, where Nb3Sn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of Nb3Sn vapor diffusiondeposition system within an R and D development program towards compact light sources. Here we present the current progress of the system development

10

Water vapor diffusion into a nanostructured iron oxyhydroxide.  

Science.gov (United States)

Water diffusion through 0.4 nm