Theoretical Gas Phase Mass Transfer Coefficients for Endogenous Gases in the Lungs

10.1114/1.145 ◽  
1999 ◽  
Vol 27 (3) ◽  
pp. 326-339 ◽  
Author(s):  
Peter Condorelli ◽  
Steven C. George
Keyword(s):  
Mass Transfer ◽  
Gas Phase ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients

Transient Numerical Modeling of Catalytic Channels

2007 ◽  
Author(s):  
P. M. Struk ◽  
D. L. Dietrich ◽  
F. J. Miller ◽  
J. S. T’ien
Keyword(s):  
Mass Transfer ◽  
Gas Phase ◽  
Heat Loss ◽  
Solid Phase ◽  
External Heat ◽  
Phase Model ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Mass Transfer Coefficients ◽  
First Case

This paper presents a transient model of catalytic combustion suitable for isolated channels and monolith reactors. The model is a “lumped” two-phase (gas and solid) model where the gas phase is quasi-steady relative to the transient solid. Axial diffusion is neglected in the gas phase; lateral diffusion, however, is accounted for using transfer coefficients. The solid phase includes axial heat conduction and external heat loss due to convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations while the solid phase reduces, after discretization, into a system of stiff ordinary differential-algebraic equations. The time evolution of the system came from alternating integrations of the quasi-steady gas and transient solid. This work outlines the numerical model and presents some sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, and external heat-loss (if applicable). The model is compared to two experiments using CO fuel: (1) steady-state conversion through an isothermal platinum (Pt) tube and (2) transient propagation of a catalytic reaction inside a small Pt tube. The model requires internal mass-transfer resistance to match the experiments at lower residence times. Under mass-transport limited conditions, the model reasonably predicted exit conversion using global mass-transfer coefficients. Near light-off, the model results did not match the experiment precisely even after adjustment of mass-transfer coefficients. Agreement improved for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increased compared to O2. The CO / O2 surface mechanism came from a sub-set of reactions in a popular CH4 / O2 mechanism. For the second case, predictions improved for lean conditions with increased external heat loss or adjustment of the kinetics as in the first case. Finally, the results show that different initial surface-species distribution leads to different steady-states under certain conditions. These results demonstrate the utility of a lumped two-phase model of a transient catalytic combustor with detailed chemistry.

scholarly journals Measurement of Gas-Phase Mass Transfer Coefficients in a Humidification Column through Random Packing

2019 ◽  
Vol 12 (3) ◽  
pp. 352-358
Author(s):  
Masoud Khorasani ◽  
Morteza Zivdar ◽  
Farshad Fashchi Tabrizi ◽  
Zahra Askari ◽  
Kaveh Ostad-Ali-Askari ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Gas Phase ◽  
Random Packing ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients

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.

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