# 1. General Model Information

### Name: Multinary gas diffusion program (STEMAX) -

### Acronym: STEMAX

**Main medium:** terrestrial, air

**Main subject:** physics biogeochemistry

**Organization level:** ecosystem

**Type of model:** not specified

**Main application:**

**Keywords:** gas diffusion,multinary gas mixtures

### Contact:

** Dr.ir. P.A. Leffelaar. **

Wageningen Agricultural University, Dept. Theoretical Production Ecology, P.O.Box 430, 6700 AK Wageningen, THE NETHERLANDS.

Phone: +31.317.483918 / 482141

Fax: +31.317.484892

email: peter.leffelaar@staff.tpe.wau.nl

### Author(s):

### Abstract:

The dynamic simulation model describes diffusion of gases in multinary gas mixtures to calculate the interdiffusion of gases in complex systems where respiration and denitrification take place. The model is based on the Stefan-Maxwell equations for concentration diffusion of isothermal, isobaric, ideal-gas mixtures and applies to an one phase system in one dimension. ** Purpose of the model:**

**Model parentage:** Program developed by P.A. Leffelaar.

**Source of the Abstract**CAMASE Register of Agro-ecosystems Models

# II. Technical Information

### II.1 Executables:

**Operating System(s):** VAX, PC

Contract necessary:

Costs: : -

Comments:

### II.2 Source-code:

**Programming Language(s):** CSMP* 2% / (standard) Microsoft FORTRAN 98%.

### II.3 Manuals:

### II.4 Data:

# III. Mathematical Information

### III.1 Mathematics

### III.2 Quantities

Rate variables: Dynamics of the rate variables mentioned in 'State variables'.
State variables: Gases in a mixture (e.g. oxygen, carbon dioxide, nitrous oxide, molecular nitrogen).

#### III.2.1 Input

Initial gas pressures, gas data to calculate binary diffusion coefficients. Input check in model: Some checks are performed.
#### III.2.2 Output

Concentration and pressure distributions of the gases in the gas layer are output of the program.

Basic spatial unit: A gas layer at the bottom of which gas production and consumption takes place is simulated.

Time interval of simulation: The maximum time step amounts to 100 seconds, but is strongly dependent on the spatial resolution and the non-linearity of the problem (for 100 seconds maximum time step the spatial co-ordinate is 2.5 millimetre).

# IV. References

** Leffelaar, P.A., 1987**. Dynamic simulation of multinary diffusion problems related to soil. Soil Science 143: 79-91

** **

# V. Further information in the World-Wide-Web

# VI. Additional remarks

Parentage: Program developed by P.A. Leffelaar.

Last review of this document by: T. Gabele: Dec 15 1997

Status of the document:

* last modified by
Joachim Benz Mon Jul 2 18:31:37 CEST 2007 *