CONVECTIVE TRANSPORT OF AMMONIUM WITH NITRIFICATION IN SOIL

1971 ◽  
Vol 51 (3) ◽  
pp. 339-350 ◽  
Author(s):  
C. M. CHO
Keyword(s):  
Steady State ◽  
Soil Column ◽  
Reaction Rates ◽  
Convective Transport ◽  
Concentration Profiles ◽  
Nitrogen Transformations ◽  
First Order ◽  
Time Required ◽  
Solution Velocity ◽  
State Concentration

Dispersion equations with first-order reaction rates for nitrogen transformations were applied to describe the convective transport of NH4+ with nitrification and denitrification in soil. The equations describing the concentrations of NH4+, NO2− and NO3− as functions of position, time, rate constants, average solution velocity and the distribution coefficient of NH4+ between soil and soil solution were obtained. Several values of parameters were chosen to obtain the concentration profiles of NH4+, NO2− and NO3− along the soil column at several times. Steady-state concentration profiles and the time required to attain the steady state are discussed.

Theory and practical application of coupled enzyme reactions: one and two auxiliary enzymes

1984 ◽  
Vol 62 (10) ◽  
pp. 945-955 ◽  
Author(s):  
S. P. J. Brooks ◽  
T. Espinola ◽  
C. H. Suelter
Keyword(s):  
Steady State ◽  
Enzyme System ◽  
Enzyme Reaction ◽  
Mathematical Treatment ◽  
Steady State Concentration ◽  
Practical Application ◽  
Enzyme Reactions ◽  
Time Required ◽  
The Cost ◽  
State Concentration

An extended and practical set of equations which describe coupled enzyme reactions is presented. The mathematical treatment relies on two assumptions: (a) the rate of the primary enzyme reaction is constant and (b) the reverse reactions are negligible. The treatment leads to the development of new equations which relate the time required for the concentration of a reaction intermediate to reach a defined fraction of its steady-state concentration to the kinetic parameters of the enzymes when mutarotation of one of the intermediates does not occur. The new equations reduce to those previously derived when the steady-state concentration of the intermediate is small compared with its Km value. A method for minimizing the cost of the two auxiliary enzyme system is also provided.

scholarly journals Modelling of non-steady-state concentration profiles at ISFET-based coulometric sensor—actuator systems

1990 ◽  
Vol 229 ◽  
pp. 71-81 ◽  
Author(s):  
W. Olthuis ◽  
J. Luo ◽  
B.H. Van der Schoot ◽  
P. Bergveld ◽  
M. Bos ◽  
...  
Keyword(s):  
Steady State ◽  
Concentration Profiles ◽  
Steady State Concentration ◽  
Sensor Actuator ◽  
State Concentration

Concentration profiles in and around capillaries

1960 ◽  
Vol 198 (5) ◽  
pp. 991-998 ◽  
Author(s):  
Jacob J. Blum
Keyword(s):  
Constant Velocity ◽  
Zero Order ◽  
Surrounding Tissue ◽  
Concentration Profiles ◽  
Steady State Concentration ◽  
Longitudinal Diffusion ◽  
First Order ◽  
Blood Flows ◽  
First Order Kinetics ◽  
State Concentration

Capillaries, idealized as uniform cylinders through which blood flows at a constant velocity, supply substrate to the surrounding tissue, where it is consumed according to zero order or first order kinetics. Equations are developed which permit the calculation of the steady state concentration of substrate at any point inside the capillary or the tissue. The effects of finite membrane permeability and of longitudinal diffusion in the tissue are discussed. Computations are presented to show the effects of various biological parameters on the concentration profiles.

scholarly journals Gas Dispersion and Bubble-to-Emulsion Phase Mass Exchange in a Gas-Solid Bubbling Fluidized Bed: A Computational and Experimental Study

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Dhaneshwar J. Patil ◽  
Martin van Sint Annaland ◽  
J.A.M. Kuipers
Keyword(s):  
Mass Transfer ◽  
Steady State ◽  
Fluidized Bed ◽  
Mass Exchange ◽  
Concentration Profiles ◽  
Steady State Concentration ◽  
Tracer Gas ◽  
Gas Dispersion ◽  
Bubbling Fluidized Bed ◽  
State Concentration

Knowledge of gas dispersion and mass exchange between the bubble and the emulsion phases is essential for a correct prediction of the performance of fluidized beds, particularly when catalytic reactions take place. Test cases of single rising bubble and a bubbling fluidized bed operated with a jet without a chemical reaction were studied in order to obtain fundamental insights in the prevailing mass transfer phenomena. Numerical simulations were carried out to predict the dispersion of tracer gas using a two-fluid model based on Kinetic Theory of Granular Flow (KTGF). The simulations of a single-bubble rising through an incipiently fluidized bed revealed that the assumptions often made in phenomenological models in the derivation of correlations for the mass transfer coefficient, mainly that the bubble diameter remains constant and that the tracer concentration is uniform in the bubble, are not valid. The predicted bubble-to-emulsion phase mass transfer coefficient showed good agreement with the estimated values from the literature correlations assuming additive convection-diffusion transport for different bubble sizes and different particle sizes, indicating the importance of the convective distribution even for relatively small particles. Experiments were carried out to measure the steady state concentration profiles of a tracer gas in a pseudo two-dimensional bubbling fluidized bed operated with a jet. The simulated steady state concentration profiles of the tracer gas agreed well the experimental measurements. The radial convection of the gas is significantly influenced by the bubble ‘throughflow’ and therefore depends upon the particle and bubble size. The experimental comparison of theoretical results was extended to study the influence of the jet velocity and the particle diameter on the radial dispersion of the tracer gas in the bed.

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