T2VOC Example Problem 1


This example is the first example  - One Dimensional Gas Diffusion of an Organic Chemical with Phase Partitioning - as described in the T2VOC User's Guide (Ralta, Pruess, Finsterle, and Battistelli, LBL-36400, 1995).

The geometry of the problem is given below.  A horizontal column has an initial temperature of 10 C and an initial pressure of 101325 Pa.  The left cell has a fixed thermodynamic state and acts as a source of chlorobenzene.  

The mesh uses 150 cells in the horizontal direction.

PetraSim and TOUGH2 Input File

It is recommended that the user follow the description below to create the PetraSim model and the associated TOUGH2 input file.  However, you can download the PetraSim model, T2VOC input, and results files here: T2VOC_Prob1_Files (extract the zipped files before reading into PetraSim).  These files allow you to view results even if you do not run the T2VOC analysis.

T2VOC Specification

This example uses T2VOC.  You must change PetraSim to this option by selecting File/Preferences..., set the Simulator Mode to TOUGH and the EOS to T2VOC.  Then, select File/New... to start a new model that uses T2VOC.  This selection will be remembered the next time you start PetraSim.

Model Creation

Start PetraSim by selecting Start/Programs/PetraSim.  Your display will be a blank window in which we can create the model.  In PetraSim, we first define the boundary of the model.  Select Model/Define Boundary… (or )and create the model boundary with Xmin = 0.0, Xmax = 15.0, Ymin = 0.0, Ymax = 1.0, Zmin = 0.0, and Zmax = 1.0, as shown below.

After selecting OK, the basic model will be created.  Click on the model and spin it so that it is displayed as shown below.  Hold Shift key and drag to pan; hold Alt key and drag to zoom .

To create the grid, select Model/Create Grid… (or )and specify 150 X divisions, 1 Y division, and 1 Z divisions, see below.

Select OK to close the Create Grid Data dialog.  After grid creation, the model is shown below (zoomed to show the left end).  Because this model is so long and narrow manipulating it is somewhat difficult.  One approach is to first rotate the model to the desired orientation, then pan and zoom to the left end.   

Global Properties

Global properties are those properties that apply to the entire model.  Select Properties/Global Properties…to display a tabbed dialog with Analysis, EOS, MINC, and Misc tabs.  First select the Analysis tab and edit the Name of the analysis as shown below.

The EOS (Equation of State) tab displays options for T2VOC.  In this analysis, we will perform an isothermal (no heat flow) analysis, so select the Isothermal option.  Set the Vapor-Air temperature dependence to 1.8 and the Air-Vapor diffusion to 2.13E-5. 

The coefficients used in the T2VOC manual are similar, but not exactly the same, as the default values supplied with T2VOC.  Therefore, we will create a new set of data for this analysis, but base it on the existing chlorobenzene data.  Select the Edit VOC Data button.

In this dialog, select the New button.  Then give the name of the new compound as "Chlorobenzene Example 1" and base it on the existing Chlorobenzene (STD).

Select OK to create the new compound.  There are only a few numbers we need to change.  First, select the CHEMP.4 tab and set the Reference Temperature for NAPL to 293 K, the Reference Binary Diffusivity to 8.0E-6, the Reference Temperature for Gas Diffusivity to 283.15 K, and the Chemical Diffusivity Exponent to 1.0.

Next select the CHEMP.6 tab and change the H2O Chemical Solubility Constant - SOLA to 7.996E-5.

Finally, select the CHEMP.7 tab and set the Chemical Organic Carbon to 0.15 and the Default Fraction of Organic to 0.005.

Select OK to close the Edit VOC Data dialog.

We will also turn on the gas diffusion calculation by setting the value of Air-Vapor Diffusion to 2.13E-5.

Go to the Misc tab.  Here, change gravitational acceleration to 9.806 m/s^2 (just to exactly match the example manual). 


Select OK to save the changes and return to the main window.

Material Properties

To specify the material properties, select Properties/Materials... (or .  Change the material name to DIRT1, the rock density to 2650 kg/m^3, the porosity to 0.4, the permeabilities to 1.0E-14 m^2, the conductivity to 3.1, and the specific heat to 1000 J/kg-C.  

Select the Relative Perm... button to specify additional properties. 

This example uses the Stone phase model for relative permeability function.  On the Relative Perm tab input the constants as 0.4, 0.1, 0.001, and 1.0.

To define the capillary pressure function select the Capillary Press tab.  Select the No Capillary Pressure option (note, this is not the same as the Default option).  There is no data to input for the No Capillary Pressure option.

On the Misc tab, specify the Fraction of Organic Carbon as 0.005.

Select OK to close the Additional Material Data dialog and the OK again to save material data.

Initial Conditions

To specify the default initial conditions, select Properties/Initial Conditions… (or ). Select the Two-Phase Water/Air option.  Specify a default pressure of 101,325 Pa, a temperature of 10 C, an water saturation of 0.25, and 0.0 VOC Mole Fraction in Air (the initial chlorobenzene saturation).  Since there is no initial chlorobenzene, this is a two-phase condition.

Select OK when finished.

Boundary Conditions

The cell on the left side of the model has a fixed state that is a source of chlorobenzene.  This cell has a pressure of 101,325 Pa, a temperature of 10 C, an aqueous saturation of 0.20, and a chlorobenzene saturation of 0.75.  This state will be specified for this cell in the Grid Editor.  Select Model/Edit Grid (or ) to start the Grid Editor.  Use the Box Zoom (click and drag) tool to zoom in on the left end (or use the Magnify and Drag tools, see rotate, pan, zoom for more information).  After finished zooming select the Selection tool, then click with the right mouse button to select the left cell and display a pop-up menu.

In the pop-up menu select Edit Properties... and give the Cell Name of "Left BC" and the Type as Fixed State.  This means the cell will always keep the same initial conditions.

Next select the Initial Conditions tab.  For this cell, we will over-ride the default initial conditions and define a Three-Phase initial state.  The pressure and temperature are 1.01325E5 Pa and 10 C, with a Gas Saturation of 0.75 and Water Saturation of 0.2.  This means that the initial NAPL saturation is 0.05.  

Select OK when finished.  The cell name and an "F" to indicate "Fixed" will be displayed on the cell.

Close the Grid Editor window.

Solution Controls

We next specify the information that will control the solution by selecting Analysis/Solution Controls… (or ).  The Times tab allows us to specify parameters associated with the start and ending of the analysis and the time steps used for the calculation.  In this case, we will start at 0 sec and end at 3.1558E7 sec (1 year).  The initial time step is 1 sec, with a maximum of 350 time steps.  Automatic time step adjustment is selected, with a maximum time step size of 4.32E5 sec (5 days).  For consistency with the example, we also change the Iterations to Double Time Step to 4.

The default values for all other options are satisfactory, so select OK to save the changes and close the Solution Parameters dialog.  

Output Controls

We next specify the information that will control the output by selecting Analysis/Output Controls… (or ).  Plot data is read from the TOUGH2 output file.  We will output data every 5 time steps.  We also select additional printout every iteration by clicking on the check box.

Select OK to save the changes and close the Print and Plot Options dialog.  

Write PetraSim and T2VOC Files

We have now completed the input necessary to write the T2VOC input file.  Save the PetraSim file by selecting File/Save… (or ) and save the file with the name t2voc_prob1.sim into a separate directory for the problem (the *.sim extension will be added automatically if you do not give it).

Advanced TOUGH2 Users Only - Most users will not need to explicitly save a TOUGH2 input file, since this will automatically be written when the analysis is performed using the integrated solvers.  However, some advanced users may have their own TOUGH2 versions.  These users can select File/Write TOUGH2 File... to write the standard TOUGH2 input file.  They can then edit this file and use it as input to their own executables.  When execution is complete, the results can be displayed in PetraSim.

Perform T2VOC Analysis

Now run the analysis by selecting Analysis/Run TOUGH2.. (or ).  This will display the Run Tough dialog.  The current model and output directory are used for the analysis.  During execution a dialog similar to the following will be displayed.

At the end of the analysis, the dialog will change to indicate that the analysis is finished.

Select the Close button.

If you just want to look at the results without running the analysis, please download the output files that we have already calculated.  Links to these files are given at the beginning of this example.

To view the progress of an analysis, the user can open the output file in an editor.  As each new time step is written, the user can update the view.  Similarly, in PetraSim, the user can select Results/3D Contours... to make a 3D display of the available results in the output file.  Close and reopen the 3D results window to refresh for new data.

View Results

After the analysis is complete, select Results/3D Results... (or ).  This will display a window with the boundary of the problem and iso-surfaces.  Since this a simple 1D geometry, the iso-surfaces are not very informative.  We will add a slice plane on which the contours will be displayed.  Select the Slice Planes button and define a plane normal to the Z axis at a value of 0.5 m.  


Select Close to close the Slice Planes dialog.  Now, in the 3D window select CVOCGAS as the parameter to display and select the end time.  Double click on the Scalar Legend (or select Results/Scalar Properties menu) and set the Number of Colors to 50.  This gives a smooth gradation of color contours.

After zooming, the image below shows the gradient of VOC in the column.

The same data is plotted in a spreadsheet as shown below.  These results match the results given in the User's Manual.