3D flow modeling was used in the CFD-ACE+ program. The following figure shows the unit cell pattern used in the software, which captures the presence of the triangular obstructions within the channel.
Figure 6: Unit cell with triangular obstruction pattern
(Note: A microreactor channel would simply consist of repeating units of this cell)
Using the different values that were determined from the spreadsheet analysis, the group was able to run many different simulations. Table 2 below shows the highlights of a convergence study that was performed to ensure that the design could meet the specification of 100% conversion to biodiesel. Several different tests were run at various molar ratios with excess methanol to drive the reaction and alter the flow rates of the reactants.
Table 2: Convergence study of biodiesel conversion
As the results indicate, a molar ratio of 25:1 for methanol to soy oil produced 100% biodiesel conversion. Both the methanol and soy oil would be completely consumed and there would only be biodiesel remaining. As shown in Figure 7 below, the biodiesel concentration gradually increases as the reactants move down the channel. When the biodiesel is at the end of the channel, the hot pink color indicates that full conversion has occurred, as evidenced by the fact that it is at the maximum on the color coded scale shown below the model.
Figure 7: Biodiesel concentration with 100% conversion
When too little methanol was used in the simulations, soy oil would remain in the channel. However, if too much methanol was used, excess methanol would remain in the channel. Therefore, it was clear that a 25:1 molar ratio was needed to meet specifications. Once this number was finally determined, all the corresponding calculations were carried out using the group's Excel spreadsheet. The actual numbers yielded is discussed in the Final Design post.