SurfaceCoverage

SurfaceCoverage is a packge for testing a surface reaction mechanism. The code integrates the surface coverages until a steady state is reached for a given gas phase composition, temperature and pressure. i.e.,

\[\frac{d\theta_k}{dt} = \frac{\dot{s}_k \sigma_k}{\Gamma}\]

where $\theta_k$ is the surface coverage of species $k$, $t$ is the time, $\dot{s}_k$ is the molar production rate (mol/m$^2$-s) of species $k$, $\sigma_k$ is the site coordination number and $\Gamma$ is the total site density (mol/m$^2$). After successful integration, the code returns the steady-state coverages, surface flux (reaction rate) of individual surface species and the sum of surface coverages and fluxes. Ideally, the surface coverages must sum to 1, and the sum of fluxes must vanish at steady state.

Documentation for SurfaceCoverage.

Installation

To install the package, use the following commands in the julia REPL

julia> using Pkg
julia> Pkg.add("SurfaceCoverage")

General interface

SurfaceCoverage.coverage — Method

This function is to test a surface reaction mechanism. Ideally the sum of fluxes must vanish at steady state. The function also gives the surface coverages for a given gasphase concentration and T,p conditions. The program generates only a screen outout

Usage:

  • coverage(inputfile, libdir)
  • input_file: name of the input file (String)
  • lib_dir: path to the folder where the data files are present
source

Executing the code

The code is invoked by using the following method.

On the Julia REPL 

julia>using SurfaceCoverage
julia>coverage("coverage.xml","lib/")

Input file

The method takes two arguments input_file and lib_dir. The input_files specifies the input XML file (in this example it is "coverage.xml") and lib_dir speficies the path to the data files folder where therm.dat is present. The structure of the XML input file is shown below.

<?xml version="1.0" encoding="ISO-8859-1"?>
<coverage>
    <gasphase>CH4 H2O H2 CO CO2 O2 N2</gasphase>
    <molefractions>CH4=0.2,H2O=0.1,CO2=0.7</molefractions>
    <T>1073.15</T>
    <p>1e5</p>
    <mech>ch4ni.xml</mech>
</coverage>

The meaning of different XML tags is explained below.

  • <coverage> : tag specifying the model
  • <gasphase> : list of gas-phase species present in the reaction mechanism. The species names must be separated by white spaces or tab
  • <molefractions> : mole fractions of the gas-phase species. Instead of mole fractions, mass fractions may also be specified. In that case, the tag must be <massfractions>. You must ensure that the sum of mass or mole fractions specified is one. There are no internal checks to verify this.
  • <T>: Temperature in K
  • <p> : Pressure in Pa
  • <mech>: name of the mechanism input file

In addition to the XML input file, the code also requires a therm.dat file. The code expects this file in the lib_dir folder by default. You must ensure that all the species present in the XML element <gasphase> are listed in the therm.dat file.

Input file download

The xml input file and the lib directory containing other required input files may be downloaded from here

Output

The code does not generate any file output. An example of terminal output that inspect generates is shown below

Initial coverage: 
-----------------------
        (NI)     6.0000e-01 
       H(NI)     0.0000e+00 
       O(NI)     0.0000e+00 
     CH4(NI)     0.0000e+00 
     H2O(NI)     4.0000e-01 
     CO2(NI)     0.0000e+00 
      CO(NI)     0.0000e+00 
      OH(NI)     0.0000e+00 
       C(NI)     0.0000e+00 
     HCO(NI)     0.0000e+00 
      CH(NI)     0.0000e+00 
     CH3(NI)     0.0000e+00 
     CH2(NI)     0.0000e+00 

T(K):   1073.15
p(Pa):  100000.0

Final coverage and flux after [10.0](s): 

     Species     coverage        flux(mol/m2-s)
-------------------------------------------------
        (NI) 	 2.9259e-01 	 +1.0338e-14 
       H(NI) 	 3.4172e-03 	 +7.5090e-15 
       O(NI) 	 7.0353e-01 	 -3.2467e-15 
     CH4(NI) 	 4.5279e-10 	 +1.1648e-16 
     H2O(NI) 	 8.4369e-05 	 +2.1847e-15 
     CO2(NI) 	 8.5809e-06 	 -4.3368e-19 
      CO(NI) 	 1.4316e-04 	 +1.1914e-17 
      OH(NI) 	 2.2621e-04 	 -2.5742e-15 
       C(NI) 	 1.1795e-06 	 +5.4699e-19 
     HCO(NI) 	 3.0945e-16 	 +0.0000e+00 
      CH(NI) 	 1.8607e-10 	 -8.6209e-20 
     CH3(NI) 	 1.7535e-09 	 -5.8953e-19 
     CH2(NI) 	 1.2266e-09 	 +5.0271e-19 

Sum of fluxes (mol/m2-s): 1.4339057611099624e-14
Sum of coverages: 1.0000000036937517