Equil

Equil is a program for the calculation of equilibrium composition. There are different methods for calculating the equilibrium composition of a reacting mixture. For a system that consists of $N$ species and $K$ elements ($N > K$), the elements are conserved, and the classical approach involves the solution of $N+K$ non-linear equations. This approach calculates the moles of different species ($N$ numbers) at equilibrium and $K$ number of Lagrangian multipliers. An alternate method solves $N-K$ non-linear equations involving equilibrium constants and $K$ equations describing component activities. The latter approach is adopted in this program.

Documentation for Equil.

Installation

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

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

General interfaces

Equil.equilibrate — Method

This function calculates equilibrium composition based on initial conditions read from an input filter

Usage

equilibrate(input_file::AbstractString, lib_dir::AbstractString)
  • input_file ; input xml file, which specifies T, p, species list, molefracs
  • lib_dir : the folder in which therm.dat file exists

Alternatively the same be calculated based on user input, wherein the species composition is passed as a Dictionary

Usage

equilibrate(T::Float64, p::Float64, species_comp::Dict{String, Float64}, thermo_obj)
  • T : Temperature in K
  • p : Pressure in Pa
  • thermoobj : Thermodynamic object created using IdealGas.createthermo
  • species_comp : Dictionary of species composition {String, Float64}

Alternatively the same be calculated based on user input where in the species list and molefractions are passed in as separate arrays

Usage

equilibrate(T, p, thermo_obj, mole_fracs, gasphase)
  • T : Temperature in K
  • p : Pressure in Pa
  • thermoobj : Thermodynamic object created using IdealGas.createthermo
  • mole_fracs : species mole fractions
  • gasphase : list of gasphase species
source

Executing the code

In order to calculate the equilibrium composition based on input file, do the following. On the Julia REPL 

julia>using Equil
julia>equilibrate("equil.xml","../lib/")

Input file

The method takes file_path as the argument. The file_path points to the input XML file. The structure of the XML input file is shown below.

<?xml version="1.0" encoding="ISO-8859-1"?>
<equil>
    <gasphase>CH4 H2 CO CO2 H2O O2 N2 </gasphase>
    <molefractions>CH4=0.6, H2O=0.1, CO2=0.2, N2=0.1</molefractions>
    <T>1073.15</T>
    <p>1e5</p>
</equil>

The meaning of different tags is specified below.

  • <equil> : The root XML tag for equilibrate
  • <gasphase> : list of gas-phase species. The species names must be separated by white spaces or tab
  • <molefractions> : Initial mole fraction 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 unity. There are no internal checks to ascertain this.
  • <T>: operating temperature in K
  • <p>: initial pressure in Pa

Output

The code generates screen output as well as a CSV file (chequil.csv). The *chequil.csv* file will be located in the same directory where the input xml file is located. An example output is shown below.

Inititial condition:

Species 	 moles 		 molefraction
       CH4 	 6.7244e+00 	 6.0000e-01 
        H2 	 0.0000e+00 	 0.0000e+00 
        CO 	 0.0000e+00 	 0.0000e+00 
       CO2 	 2.2415e+00 	 2.0000e-01 
       H2O 	 1.1207e+00 	 1.0000e-01 
        O2 	 0.0000e+00 	 0.0000e+00 
        N2 	 1.1207e+00 	 1.0000e-01

Equilibrium composition @ T= 1073.15 K and p=100000.0 Pa

Species          moles           molefraction
       CH4       3.3912e+00      1.8973e-01
       CO2       1.2649e-02      7.0766e-04
       H2O       1.6324e-02      9.1329e-04
        CO       5.5621e+00      3.1118e-01
        O2       3.2984e-23      1.8454e-24
        H2       7.7709e+00      4.3476e-01
        N2       1.1207e+00      6.2703e-02

In certain cases, you may want to calculate the equilibrum composition from within another program. For such cases Equil package provides another interface equilibrate

julia>using Equil
julia>using IdealGas
julia>gasphase = ["CH4","H2", "CO", "CO2", "H2O", "O2" ,"N2"]
julia>mole_fracs = [0.6, 0.0, 0.0, 0.2, 0.1, 0.0, 0.1]
julia>thermo_file = get_path(lib_dir, "therm.dat")
julia>thermo_obj = create_thermo(gasphase, thermo_file)        
julia>T = 1073.15
julia>p = 1e5
julia>gasphase_in, moles_all, eq_molefracs  = equilibrate(T,p, thermo_obj, mole_fracs, gasphase)

Instead of passing the species list and the mole fractions separately, you may pass a Dictionary of species names and the molefractions a described below.

julia>using IdealGas
julia>using Equil
julia>species_comp = Dict("CH4"=>0.6,"H2"=>0.0, "CO"=>0.0, "CO2"=>0.2, "H2O"=>0.1, "O2"=>0.0 ,"N2"=>0.1)        
julia>thermo_file = get_path(lib_dir, "therm.dat")
julia>thermo_obj = create_thermo(collect(keys(species_comp)), thermo_file)        
julia>T = 1073.15
julia>p = 1e5
julia>gasphase_in, moles_all, eq_molefracs  = equilibrate(T,p, thermo_obj, species_comp)

The ch_equil.csv file will not be generated for call from the REPL or for an interface call.

Input file download

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