4.4.12.1. Chemistry Overview

Aria provides two ways of modeling chemical contributions to the transport equations it solves: CHEMEQ and General Chemistry. The purpose of this overview is to describe the differences between these approaches and provide guidelines for which one to select for a given application.

4.4.12.1.1. Feature Comparison

As a quick reference, a list of feature differences between the two solvers is shown in Table 4.2 below.

CHEMEQ is best suited for evaluating reactions without species transport in order to obtain a source term for the energy equation. It also links to pressurization zones to enable reduced-cost pressurization calculations. CHEMEQ stores its species concentrations in an element field and updates that element field in time while providing a source term for the energy equation.

On the other hand, General Chemistry is best suited for situations where you want to resolve species transport and reaction. General Chemistry is designed only to provide source terms, so there must be a linear system set up for each DOF (energy, species concentrations, etc…) to actually update its values in time. For cases where the species are not transported, the added cost of setting up this linear system makes CHEMEQ the more efficient choice.

Table 4.2 Feature table for CHEMEQ and General Chemistry.

Feature	CHEMEQ	General Chemistry
Reaction Blocks	Yes	Yes
Multiphase reactions	No	Yes
Coupled Solve	No	Optional
Provides Species Source	No	Yes
Reversible Reactions	No	Yes
Equilibrium Chemistry	No	Yes

4.4.12.1.2. Reaction Summary & Diagnostics

For both modeling options, additional debugging information can be provided by activating the --arialog chemistry option from the command line launch command. With this logging activated, Aria will write files containing information on the initial conditions prior to ODE failure at each evaluation point of each element on each processor. The files will be named in the following format: chemistry.E[eid]-[point].P[proc].txt for General Chemistry, and chemeq.[model].E[eid]-[point].P[proc].txt for CHEMEQ.

A summary of all the reactions parsed from the input is also printed to the log file so you can verify they are evaluating as you have intended. An example of this output is shown below. Details about these terms are described in the reaction blocks section.

+-----------------------------------------------------------------------------+
| Reaction Summary                                                            |
+-----------------------------------------------------------------------------+

 Name:                     R1
  Reaction String:         A->B
  Stoich Coeffs:           -1.00000 1.00000
  Temperature Phase:       No Material Phase
  Pressure Phase:          No Material Phase
  Heat of Reaction:        -1.00000e+06
  Multiplier Function:     Unity
  Rate Function:           Arrhenius
      Arguments:           A = 0.100000 Ea = 350.000 beta = 0.00000 R = 1.00000
  Pressure Function:       Unity
  Concentration Function:  Standard
      Arguments:           mu = 1.00000 0.00000