In the Solver settings, parameters regarding the tracer particles are defined.

The Simulated duration defines the total amount of time that is simulated. For the typical case of simulating a full breakthrough this value needs to be set accordingly to cover the full breakthrough depending on the adsorption capacity of the system and the flow velocity.

To simulated the adsorbate distribution in the fluid, tracer particles are released into the structure in batches. The Number of batches can be set by you and influences the available number of data points for, e.g., plots in the simulation results. The duration of one batch is computed by Simulated duration/Number of batches.

With the Tracer per inflow voxel parameter the precision of the adsorption simulation can be controlled. This parameters defines how many tracer particles are used per inflow voxel in a batch. A higher number of tracers increases precision and runtime. It is recommended to use at least 5 Tracer per inflow voxel. The concentration of the adsorbing solute is not changed by this parameter, it is only distributed more finely/coarsely in the fluid.

When the Adsorption load initialization is set to Load a initial adsorption load on the adsorbent material can be provided through a volume file (*.gvf) generated by a previous adsorption simulation. This enables you to simulate desorption processes.

The number of Processes controls the parallelization option for all underlying simulations such as flow and particle tracking and should be set according to the hardware that is used.

Under the Carrier Gas settings, all parameters regarding the flow simulation are located.

The Inflow velocity needs to be defined in m/s. If the velocity is set to zero only diffusion is simulated.

Two options are available for the flow simulation. Use Navier-Stokes-Brinkman at high Reynolds numbers when inertial effects cannot be ignored. If inertial effects are negligible use the Stokes-Brinkman equation. The Brinkman term is always required since the adsorbent is required to consist of porous voxels.

Additionally, the Boundary Condition in transversal direction can be set to Symmetric or Periodic depending on the structure geometry.

The flow Boundary Condition in longitudinal direction is fixed to Symmetric and thus is not shown in the dialog.

Find more information on all parameters in the Carrier Gas panel in the FlowDict user guide.

Under the Adsorbate panel all settings regarding the solute species that adsorbs can be found.

The Inlet concentration that enters the structure with the flow is defined in Parts per Million (ppm). For pure desorption simulations set this value to zero.

Two diffusivity values need to be provided. The Diffusivity in porous sets the adsorbate diffusivity in the porous adsorbent voxel, while the Diffusivity in pore defines the adsorbate diffusivity in the free pore space. High diffusivity values can increase the runtime of the simulation. To obtain reasonable runtimes, please ensure that the Fourier number for the simulation is smaller than one. This value can be seen, e.g., in the Track Particles dialog. This ensures that the distance of diffusion is not greater than one voxel.

Set a Temperature and Ambient pressure (or gas pressure) for the simulation. Both parameters remain constant throughout the simulation and are required for the calculation of the Toth isotherm.

Under the Adsorbent panel all settings regarding the material that adsorbs the dissolved species are located.

Provide the Material ID of the adsorbing material in the structure. Make sure that the material of the adsorbent is set to a porous solid.

For this material, the properties Permeability and Density need to be defined.

In some cases the adsorbent does not consist purely of reactive material. If other components are contained, the Porosity parameter can be used. A Porosity value of zero represents pure adsorbent in the given material ID. Increase this value up to one to provide the amount of material that is no adsorbing within the porous voxels in percent.

The Mass transfer coefficient depends on the simulated adsorption reaction and controls the speed of the reaction. It is used in the computation of the adsorption rate for a linear driving force model.

For the calculation of the adsorption equilibrium three options are available:

• Toth isotherm:
  • The Toth isotherm model can be applied for monolayer adsorption and provides a temperature dependency for the adsorption. The underlying equation can be found here.
  • All default values are based on the adsorption of CO2 on a zeolite surface (see CO2/13X in table 1 in Coker and Knox, 2014).

• • In the Equilibrium calculation panel the Toth parameters , , , , and need to be provided.
    
• Langmuir isotherm:
  • The Langmuir isotherm model can be applied for monolayer adsorption without temperature dependency. The underlying equation can be found here.
  • The default values are also based on the adsorption of CO2 on a zeolite surface (calculated from the Toth isotherm in Coker and Knox, 2014).
  • In the Equilibrium calculation panel the Langmuir parameters and need to be provided.
    
• Table:
  • This option allows you to directly provide a table containing temperature, partial pressure, and adsorption loading to describe the adsorption isotherm. For example, these values can be obtained from experimental data.
    
  • The table needs to be a *.txt file. The structure of this file should be as follows:
    • The first column contains the partial pressure of the solvent in Pa.
    • The first row contains the temperature in K.
    • Then, the values for adsorbate loading in mol/kg are supplied for each of the pressure-temperature pairs.
    • See an example below: