Calculation of Transport-Shifted CVD Phase Diagrams

1989 ◽  
Vol 168 ◽  
Author(s):  
Daniel E. Rosner ◽  
Joshua Collins
Keyword(s):  
Mass Transfer ◽  
Phase Diagrams ◽  
Chemical Species ◽  
Chemical Vapor ◽  
Multicomponent Diffusion ◽  
Chemical System ◽  
Transfer Coefficients ◽  
Fiber Deposition ◽  
Vapor Deposit ◽  
Element Segregation

AbstractA non-iterative method is presented for constructing CVD phase diagrams which include the systematic effects of chemical element segregation in mass-transfer controlled flow reactors. Element segregation is shown to substantially shift predicted deposit phase boundaries when the vapor/deposit interface equilibrium is calculated using the local element fractions instead of the feed gas elemental composition, as is usually done. The mass transfer analysis developed here accounts for both Fick and Soret multicomponent diffusion acting across a non-isothermal boundary layer. The gas phase is assumed to be chemically frozen, with local thermochemical equilibrium imposed only at the vapor/deposit interface (as in a cold wall reactor with a hot substrate). As a specific example, this model is applied to the chemical vapor deposition of titanium diboride from TiCl4(g), BC13(g) and H2(g) in an Ar(g) carrier gas for ceramic composite material applications. These calculations, which account for boron and titanium transport via 17 chemical species, are illustrated for a long cylindrical reactor with a resistively heated coaxial fiber deposition substrate and coaxial annular flow. However, the method presented here is general in that both the chemical system and CVD reactor geometry can be changed to any other system of interest, provided: i) adequate themochemical and thermophysical data are available, ii) the deposition rate is vapor transport controlled, and iii) convective-diffusion heat and mass transfer coefficients are estimable.

Modeling mass transfer and substrate utilization in the boundary layer of biofilm systems

1998 ◽  
Vol 37 (4-5) ◽  
pp. 139-147 ◽  
Author(s):  
Harald Horn ◽  
Dietmar C. Hempel
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Theory ◽  
Substrate Utilization ◽  
The Other ◽  
Concentration Profiles ◽  
Hydrodynamic Conditions ◽  
Time Axis ◽  
Transfer Coefficients

The use of microelectrodes in biofilm research allows a better understanding of intrinsic biofilm processes. Little is known about mass transfer and substrate utilization in the boundary layer of biofilm systems. One possible description of mass transfer can be obtained by mass transfer coefficients, both on the basis of the stagnant film theory or with the Sherwood number. This approach is rather formal and not quite correct when the heterogeneity of the biofilm surface structure is taken into account. It could be shown that substrate loading is a major factor in the description of the development of the density. On the other hand, the time axis is an important factor which has to be considered when concentration profiles in biofilm systems are discussed. Finally, hydrodynamic conditions become important for the development of the biofilm surface when the Reynolds number increases above the range of 3000-4000.

Henry's constants and mass transfer coefficients of halogenated organic pollutants in an air stripping packed column

1998 ◽  
Vol 38 (6) ◽  
pp. 287-294 ◽  
Author(s):  
Pen-C. Chiang ◽  
Chung-H. Hung ◽  
J. C. Mar ◽  
E. E. Chang
Keyword(s):  
Mass Transfer ◽  
Methylene Chloride ◽  
Packed Column ◽  
Transfer Coefficients ◽  
Chlorinated Organic Compounds ◽  
Air Stripping ◽  
Mass Transfer Coefficients ◽  
Equilibrium Partition ◽  
Henry's Constants ◽  
Chlorinated Organic

Both Henry's constants and volumetric mass transfer coefficients (KLa) of eight priority chlorinated organic compounds including 1,1-dichloroethene, methylene chloride, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, and 1,4-dichlorobenzene in an air stripping packed column were investigated in this study. The liquid and gas phase EPICS (Equilibrium Partition in Closed System) and direct calculating methods were applied to determine the Henry's constants of VOCs. The interference of co-solute on Henry's constants was also investigated. Experimental results indicated that decrease in Henry's constants of VOCs was observed in the presence of humic acid but no apparent effect on Henry's constants was detected when there was NaCl and surfactant in solution. Four different configurations of packing media including Intalox Saddle, Super Intalox Saddle, Telleret, and Hedgehog made of polypropylene were respectively packed in the air stripping tower and investigated in the study. The dependence of hydraulic loading, air-water ratio, and configurations of packing media on mass transfer coefficients of VOCs was discussed.

Transport of chlorinated hydrocarbons between sewage and sewer atmosphere

1996 ◽  
Vol 34 (3-4) ◽  
pp. 557-564 ◽  
Author(s):  
Bettina S. Haas ◽  
Reimer Herrmann
Keyword(s):  
Mass Transfer ◽  
Aromatic Compounds ◽  
Chlorinated Hydrocarbons ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Sewerage System ◽  
Mass Fluxes ◽  
Single Compound

Sewage containing volatile contaminants is a potential VOC-source in cities. Thus we tried to evaluate volatilization out of the sewerage system by measurements of contaminants in sewer gas and sewage. Our results from a medium sized town with little industry showed that sewer gas is mainly contaminated with alkanes, small aromatic compounds and chlorinated hydrocarbons. For three chlorinated hydrocarbons (chloroform, trichloroethene, tetrachloroethene) we determined mass transfer coefficients out of sewage and used these data to estimate mass fluxes from sewage and emissions out of the sewerage system for two sewer stretches. Considerable emission of chlorinated hydrocarbons from sewage, i.e. fluxes of some 10 to 100 g per m2·d, occurred only when the contaminant input via sewage was between some g and mg per litre for a single compound. For concentrations that were about 3 orders of magnitude less, emissions were negligible.

Mass Transfer in Liquid in an Apparatus with Mobile Packing. Application of a Dispersion Model

1993 ◽  
Vol 58 (5) ◽  
pp. 1078-1086
Author(s):  
Zdeněk Palatý
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Empirical Equation ◽  
Dispersion Model ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients

The paper deals with the mass transfer in a liquid on a plate with mobile packing. A procedure has been suggested which enables estimation of the mass transfer coefficients from experimental data considering the dispersion flow of the liquid. The results obtained from the desorption of CO2 from water are presented graphically and in the form of empirical equation.

On the convective diffusion under partial slip at wall

1989 ◽  
Vol 54 (4) ◽  
pp. 967-980 ◽  
Author(s):  
Ondřej Wein ◽  
Petr Kučera
Keyword(s):  
Mass Transfer ◽  
Numerical Solution ◽  
Analytic Solution ◽  
Convective Diffusion ◽  
Linear Velocity ◽  
Partial Slip ◽  
Accurate Calculation ◽  
Transfer Coefficients ◽  
Empirical Formulas ◽  
Mass Transfer Coefficients

Extended Leveque problem is studied for linear velocity profiles, vx(z) = u + qz. The existing analytic solution is reconsidered and shown to be inapplicable for the accurate calculation of mean mass-transfer coefficients. A numerical solution is reported and its accuracy is checked in detail. Simple but fairly accurate empirical formulas are suggested for the calculating of local and mean mass-transfer coefficients.

Sign in / Sign up

Export Citation Format

Share Document